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The R eady M ixed C oncrete IndustryLE E D R eference G uide

T hird E d itio n

Copyright 2005-2010 by the RMC Research & Educat ion Foundationwww.rmc-foundation.org
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This document was underwritten by theReady Mixed Concrete (RMC) Research &Education Foundation and the PortlandCement Association (PCA). The originalversion was researched and written bySteven Winter Associates, Inc. (SWA) ,(www.swinter.com). The Third Edition wasedited and revised by Lionel Lemay, PE, SE,LEED AP, CAE and Erin Mack Ashley, PhD,LEED AP of the National Ready MixedConcrete Association (NRMCA). The projectwas managed by NRMCA.

The RMC Research & EducationFoundation is a non-profit organizationdedicated to improving the concrete industrythrough achieving its mission of promotingeducation and research projects that willstrengthen and improve an already superiorproduct in an industry committed toexcellence. PCA is an organization ofcement companies to improve and extendthe uses of portland cement and concretethrough market development, engineering,research, and public affairs work. NRMCA isa leading industry advocate working toexpand and improve the ready mixedconcrete industry through leadership,promotion, education and partnering,ensuring that ready mixed concrete is thebuilding material of choice.

SWA, RMC Research & EducationFoundation, PCA, and NRMCA would like to

express their thanks to the following peoplefor their assistance in the preparation andreview of this document: Erin Mack Ashley,David Goss, Edward R. Herbert III, BeatrixKerkoff, Jennifer LeFevre, Lionel Lemay,Jan Prusinski, David Shepherd, and MarthaVan Geem.

Abstract: Ready mixed concrete offersopportunities for designers, architects,engineers, contractors, concrete producersand others in the building industry tomaximize credits offered by the U.S. GreenBuilding Council's (USGBC) Leadership inEnergy and Environmental Design (LEED)2009 for New Construction and MajorRenovations (LEED 2009 NC). Thisdocument will guide the reader inunderstanding the LEED system and areaswhere ready mixed concrete can be appliedin a project to earn LEED points, enhancingits sustainability.

Keywords: Energy conservation,environmental factors, innovative design,LEED, ready mixed concrete, recycling,sustainability.

Reference: Steven Winter Associates,Inc., Ready Mixed Concrete Industry LEEDReference Guide, RMC Research &Education Foundation, Silver Spring,Maryland, USA, October, 2009.
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DISCLAIMER

THERE IS NO WARRANTY, ORREPRESENTATION OF ANY KINDRESPECTING THIS PUBLICATION ORANY INFORMATION CONTAINEDHEREIN; AND ANY WARRANTY,EXPRESS OR IMPLIED, IS EXCLUDEDAND DISCLAIMED, INCLUDING THEIMPLIED WARRANTIES OFMERCHANTABILITY AND FITNESS FOR APARTICULAR PURPOSE; NOR IS THEREANY THISARRANTY THATPUBLICATION OR ANY INFORMATIONCONTAINED HEREIN WILL MEET ORCOMPLY WITH THE REQUIREMENTS OFANY SAFETY OR ENVIRONMENTALCODE OF ANY STATE, MUNICIPALITY OROTHER JURISDICTION.

IT IS AGREED THAT SELLER'S LIABILITYAND PURCHASER'S SOLE REMEDY,WHETHER IN CONTRACT, UNDER ANYWARRANTY, IN TORT (INCLUDINGNEGLIGENCE), IN STRICT LIABILITY OROTHERWISE, SHALL NOT EXCEED THERETURN OF THE AMOUNT OF THEPURCHASE PRICE PAID BYPURCHASER, AND UNDER NOCIRCUMSTANCES SHALL SELLER BELIABLE FOR ANY SPECIAL, INCIDENTAL,OR CONSEQUENTIAL DAMAGES.
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T AB LE O F C ON TE NT S

Executive Summary 1Table 1 - Potential Leed Credits For Ready Mixed Concrete 2Introduction 4The LEED Certification Process 5The Ready Mixed Concrete Industry LEED Reference Guide 6

Using Ready Mixed Concrete To Achieve LEED 2009 NC Credits 8Sustainable Sites 8SS Credit 6.1: Stormwater Design - Quantity Control. 8SS Credit 6.2: Stormwater Management - Quality Control 8SS Credit 7.1: Heat Island Effect - Nonroof 17

Energy And Atmosphere 21EA Prerequisite 2: Minimum Energy Performance 21EA Credit 1: Optimize Energy Performance 21

Materials And Resources Credits 29MR Credit 2: Construction Waste Management 29MR Credit 4: Recycled Content. 35MR Credit 5: Regional Materials 48MR Credit 7: Certified Wood 50

Innovation In Design Credits 55ID Credit 1: Exemplary Performance 57ID Credit 1: Innovation In Design 60RP Credit 1: Regional Priority 63

Incidental Ready Mixed Concrete Use In Other Credits 64SS Credit 3: Brownfield Redevelopment [1] 64SS Credit 5.1: Site Development - Protect Or Restore Habitat... 64SS Credit 7.2: Heat Island Effect - Roof 65WE Credit 1: Water Efficient Landscaping 65WE Credit 2: Innovative Waste Water Technologies 65MR Credit 1.1: Building Reuse - Maintain Existing Walls, Floors And Roof 65MR Credit 6: Rapidly Renewable Materials 66IEQ Credit 4.2: Select Low-Emitting Materials - Paints And Coatings 66
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lEO Credit 4.3: Low-Emitting Materials - Floor Systems 66lEO Credit 5: Indoor Chemical And Pollutant Source Control. 67lEO Credit 7.1: Thermal Comfort - Design 67

Other Environmental Issues 68Plant Waste Water Disposal 68On-Site Wash Water Disposal 68Solid Waste 69Site Protection 69

Appendix A - Sample Letter From Ready Mixed Concrete Producer 71
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EXECUTIVE SUMMARY

Of all the green building design andconstruction evaluation programs in theUnites States, the U.S. Green BuildingCouncil's (USGBC) LEED Rating System isthe most widely adopted standard. Publicand private companies, governmentagencies, trade groups, and other entitiesthroughout the United States constructionindustry have adopted LEED as the standard

Concrete offers several opportunities for bui ldingprojects to ga in LEED points.

for determining a building's degree ofsustainability. Recognizing the importance ofLEED, NRMCA, PCA, and the RMCResearch & Education Foundationcommissioned the development of a LEEDReference Guide that could be used byarchitects, developers, clients, builders,manufacturers, suppliers, and others in theconstruction industry to determine how theuse of ready mixed concrete can contributeto green building.

The resulting document presents adetailed discussion of the LEED program,how LEED points are assigned, how materialuses and construction methods must bedocumented, and what issues must becarefully considered in using ready mixedconcrete to enhance a building'ssustainability.

Potential LEED points gained throughthe use of ready mixed concrete arediscussed in the following areas: stormwatermanagement; landscape paving; minimizingenergy use; optimizing energy performance;managing construction waste; recycledcontent; use of regional materials; use ofcertified wood; innovation in design; andreduction in the use of portland cement. Thedocument also covers plant waste waterdisposal; on-site wash water disposal; solidwaste; and site protection. In each of theseareas, the Reference Guide presentsinformation useful to the designer, thecontractor, and the ready mixed concretesupplier in achieving LEED points. Thisinformation is supplemented by extensivelists of citations, references, and otherresource documents, trade groups, andwebsites. A summary of how concretecontributes to LEED 2009 NC is provided inTable 1.

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TAB LE 1 - P otentia l LE ED C redits for R ead y M ixed C oncreteConcrete contributes to this LEED CreditIncidental concrete use in this LEED Credit

Sustainable Sites 26 Possible PointsPrerequisite 1 Construction Activity Pollution Prevention RequiredCredit 1 Site Selection 1Credit 2 Development Density and Community Connectivity 5Credit 3 Brownfield Redevelopment 1Credit 4.1 Alternative Transportation-Public Transportation Access 6Credit 4.2 Alternative Transportation-Bicycle Storage and Changing Rooms 1Credit 4.3 Alternative Transportation-Low-Emitting and Fuel-Efficient Vehicles 3Credit 4.4 Alternative Transportation-Parking Capacity 2Credit 5.1 Site Development-Protect or Restore Habitat 1Credit 5.2 Site Development-Maximize Open Space 1Credit 6.1 Stormwater Design-Quantity Control 1Credit 6.2 Stormwater Design-Quality Control 1Credit 7.1 Heat Island Effect-Nonroof 1Credit 7.2 Heat Island Effect-Roof 1Credit 8 Light Pollution Reduction 1Water Efficiency 10 Possible PointsPrerequisite 1 Water Use Reduction RequiredCredit 1 Water Efficient Landscaping 2-4Credit 2 Innovative Wastewater Technologies 2Credit 3 Water Use Reduction 2-4Energy and Atmosphere 35 Possible PointsPrerequisite 1 Fundamental Commissioning of Building Energy Systems RequiredPrerequisite 2 Minimum Energy Performance RequiredPrerequisite 3 Fundamental Refrigerant Management RequiredCredit 1 Optimize Energy Performance 1-19Credit 2 Onsite Renewable Energy 1-7Credit 3 Enhanced Commissioning 2Credit 4 Enhanced Refrigerant Management 2Credit 5 Measurement and Verification 3Credit 6 Green Power 2Materials and Resources 14 Possible PointsPrerequisite 1 Storage and Collection of Recyclables RequiredCredit 1.1 Building Reuse-Maintain Existing Walls, Floors and Roof 1-3Credit 1.2 Building Reuse-Maintain Existing Interior Nonstructural Elements 1Credit 2 Construction Waste Management 1-2Credit 3 Materials Reuse 1-2Credit 4 Recycled Content 1-2Credit 5 Regional Materials 1-2Credit 6 Rapidly Renewable Materials 1Credit 7 Certified Wood 1Indoor Environmental Quality 15 Possible PointsPrerequisite 1 Minimum Indoor Air Quality Performance RequiredPrerequisite 2 Environmental Tobacco Smoke (ETS) Control RequiredCredit 1 Outdoor Air Delivery Monitoring 1Credit 2 Increase Ventilation 1Credit 3.1 Construction Indoor Air Quality Management Plan-During Construction 1Credit 3.2 Construction Indoor Quality Management Plan-Before Occupancy 1

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INTRODUCTION

Established in 1998, the LEED GreenBuilding Rating System for New Construction(LEED NC) is a voluntary, consensus-basednational standard for designing and buildinghigh-performance, sustainable buildings.Several versions of the LEED rating systemhave been issued since its inceptionincluding LEED 2.0, 2.1, 2.2, and mostrecently, LEED 2009. LEED 2009 for NewConstruction and Major Renovations (LEED2009 NC) was approved by USGBCmembers in November 2008 and officiallyissued for public use in April 2009. June 27,2009, was the last date projects couldregister under the old LEED NC version 2.2system. All new projects registering afterJune 27, 2009 must use LEED 2009 NC.

LEED was developed by members of theUSGBC representing many segments of thebuilding industry and environmental science.LEED's mission is to: define that whichqualifies as a "green building" by establishinga common standard of measurement;promote integrated, whole-building designpractices; recognize environmentalleadership in the building industry; st imulategreen competition; consumeraiseawareness of green building benefits; andtransform the building market. While thenumber of registered LEED projects startedslowly, this number has grown dramaticallyfrom 12 registered LEED projects in 1999 to24,789 by June 2009. The number of LEEDcertified projects reached 3,111 in June 2009equating to 385 million square feet of LEEDcertified commercial space.

LEED certification can be achieved at aCertified, Silver, Gold, or Platinum levelbased on how many of the 110 LEED 2009NC Credits are awarded after a project meetseight LEED Prerequisites. The LEED 2009NC Rating System divides these credits andprerequisites into seven credit categories:Sustainable Sites, Water Efficiency, Energyand Atmosphere, Materials and Resources,Indoor Environmental Quality, Innovation inDesign, and Regional Priority. Prerequisitesand Credits are based mostly on establishedgovernmental, trade group, or laboratorystandards, such as the USEPA's"Stormwater Management for ConstructionActivities," or the standards for energyefficiency and ventilat ion effectiveness of theAmerican Society of Heating, Refrigerating,and Air Conditioning Engineers (ASH RAE}.The number of points a project earns bysatisfying the environmental performancecriteria of the various LEED creditsdetermines the level at which a project canbe certified.

While the LEED NC Rating System wasinitially designed for commercial high-riseoffice buildings, the system can be used for awide variety of projects. LEED 2009 NCincludes requirements suitable for multi-family residential high-rise projects,institutional buildings, and hotels. Existingprojects undergoing significant renovationsuch as HVAC renovation, significantenvelope modifications, and major interiorrehabilitation can also use LEED 2009 NC.USGBC created several additional ratingsystems for other project types; LEED forCommercial Interiors, LEED for Existing

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Buildings, LEED for Core and Shell, LEEDfor Schools, and LEED for Homes. Severalnew rating systems are under developmentincluding LEED for NeighborhoodDevelopment, LEED for Healthcare, LEEDfor Retail, LEED for Retail Interiors, andLEED for Existing Schools. This documentaddresses only LEED 2009 NC for NewConstruction and Major Renovations.

The LEED Certif ication Process

LEED is a voluntary rating system. Anenvironmentally conscious building owner ordeveloper may choose to design andconstruct a building to minimizeenvironmental impact using the LEED ratingsystem as a guide. LEED certificationquantifies the level of environmentalperformance for a building. Typically theowner's representative, who is usually anarchitect, is directed to design the building tomeet a certain level of LEED certification.Some building owners have committed tohaving all of their projects LEED certified andothers have committed to certifying onlyselected buildings. For example, severalpublic agencies such as city governments orfederal agencies have declared that all oftheir new buildings shall be LEED certified.Some private companies have built newheadquarters using LEED certification.

A project formally begins the LEEDcertification process by having it registeredas a LEED project on the Green BuildingCertification Institute (GBCI) website(www.gbci.org). GBCI was created byUSGBC to manage project and personnel

certification programs. Project registration isinitiated by one of the project team members.This process requires completing an onlineform that asks for information on the projectand the design team. The registration fee is$450 for USGBC members and $600 for non-members. The registration process entitlesthe project team access to LEED Online, aspecial website designed to help projectteam members navigate through the projectcertification process and Credit InterpretationRequests (CIR). CIRs are made throughLEED Online when the team members deemthat compliance with a credit's intent can bemet without meeting the letter of a givenCredit Requirement. Informally, most projectrepresentatives begin the LEED process byevaluating criteria of the various LEEDcredits and targeting those most compatiblewith the project scope, budget, andenvironmental goals. Representatives whostart this process in the early stages of thedesign process are usually more successfulbecause they can take advantage ofsynergies between LEED credits andbecause they do not need to make designchanges to meet LEED criteria.

The process of documenting compliancewith LEED criteria can begin early in thedesign, but many of the credits related toconstruction act ivit ies and building materialsrequire documentation that is not availableuntil the final stages of ConstructionAdministration, or even SubstantialCompletion. While the buildingcommissioning (the process of making finalchecks and adjustments to construction andbuilding operations) may need to continue

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beyond substantial completion for seasonalor deferred testing, projects are usually ableto assemble all the documentation needed tosubmit an application for LEED certificationto the GBCI at about the same time asSubstantial Completion.

The application for LEED certificationincludes documentation supportingcompliance for all LEED Prerequisites andtargeted LEED credits. The application isaccompanied by a certification fee that canrange from $2,250 to $22,500 for USGBCmembers ($2,750 to $27,500 for non-members) depending on the type ofcertification and size of the building in squarefeet. The application, submitted throughLEED Online, includes detailed informationon the required format for the LEEDapplication. Once the project representativehas submitted the application to GBCI, areview process begins. The GBCI will issue apreliminary review of the LEED applicationwithin 25 business days. This first formalpreliminary review will detail which creditsare accepted, which credits need additionaldocumentation. The preliminary reviewprovides descriptions of the additionaldocumentation materials required. Theproject team then has 25 business days toprovide the requested materials to the GBCI.The final review then occurs within 15business days from the date in which theGBCI receives the additional requestedmaterials. There is also an appeals process ifthe project team disagrees with GBCI reviewrulings.

If upon final review the project meetsrequirements for certification, a set of LEEDCertified, Silver, Gold, or PlatinumCertificates are issued to the design team inrecognition of the LEED Rating earned. ALEED plaque is then ordered for display onthe project.

LEED encourages and rewards anintegrated approach to design andconstruction that involves all team membersin the project, including the design andconstruction team, owners, product suppliersand manufacturers, construction managers,cost estimators, specification writers, andothers. LEED documentation is theresponsibility of several team members,although it is typically coordinated by aLEED-Accredited Professional, who alsoprepares CIRs, the final submittal, and theresponses to GBCI during the review period.

The Ready Mixed Concrete Industry LEEDReference Guide

This document presents the bestopportunities for achieving LEED creditsthrough the use of ready mixed concrete.The term "ready mixed concrete" and"concrete" are used interchangeablythroughout this publication and meant todescribe concrete that is delivered to theproject site in the plastic state in concretetrucks. The document is organized under fourcategories: "Sustainable Sites," "Energy andAtmosphere," "Materials and Resources,"and "Innovation in Design." These fourcategories are taken directly from the LEED2009 NC standard. A fifth section, "Incidental

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Ready Mixed Concrete Use in Other Credits,"offers guidance in how the material canenhance opportunities for gaining LEEDcredits in other areas.

In each section, the discussion of theLEED 2009 NC Credits relevant to readymixed concrete is separated into thoseissues primarily affecting the projectdesigners (in the section "Design Issues")and those primarily affecting the concretetrade professionals (in the section "TradeContractor and Manufacturer Issues").However, each group needs to read bothportions, as both groups are often

responsible for completing documentationrequirements. In general, "Design Issues"deals with issues that must be decidedbefore the project begins construction, while''Trade Contractor and Manufacturer Issues"is concerned with actual construction andclose-out.

A final section of the documentaddresses environmental considerations inusing ready mixed concrete with reference toplant waste water disposal, on-site washwater disposal, solid waste, and siteprotection.

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USING READY MIXED CONCRETE TOACHIEVE LEED 2009 NC CREDITS

Sustainable Sites

SS Credit 6.1: Stormwater Design - Quant ityControlIntent Tolimit disruption of natural hydrologyby reducing impervious cover, increasing on-site infiltration, reducing or eliminatingpollution from storrnwater runoff andeliminating contaminants.RequirementsCASE 1. Sites with Existing Imperviousness50% or LessOPTION 1Implement a stormwater management planthat prevents the post-development peakdischarge rate and quantity from exceedingthe pre-development peak discharge rateand quantity for the 1- and 2-year 24-hourdesign storms.OR,OPTION 2Implement a stormwater management planthat protects receiving stream channels fromexcessive erosion. The stormwatermanagement plan must include streamchannel protection and quantity controlstrategies.CASE 2. Sites with Existing ImperviousnessGreater Than 50%Implement a stormwater management planthat results in a 25% decrease in the volumeof stormwater runoff from the 2-year 24-hourdesign storm.

SS Credit 6.2: Stormwater Management -Quality ControlIntent: To limit disruption of natural waterRowsby managing storrnwater runoffRequirements

Implement a stormwater managementplan that reduces impervious cover,promotes infiltration and captures and treatsthe stormwater runoff from 90% of theaverage annual rainfall using acceptable bestmanagement practices (BMPs).

BMPs used to treat runoff must becapable of removing 80% of the averageannual post-development total suspendedsolids (TSS) load based on existingmonitoring reports. BMPs are considered tomeet these criteria if:

They are designed in accordance withstandards and specifications from a state orlocal program that has adopted theseperformance standards,OR,

There exists infield performancemonitoring data demonstrating compliancewith the criteria Data must conform toaccepted protocol (e.g., TechnologyAcceptance Reciprocity Partnership [TARP]Washington State Department of Ecology) forBMP monitoring.Summary of Concrete Applications andMaterials Relevant to the Credits

LEED includes Stormwater Managementcredits to reduce the negative effects ofrunoff created by development. Roofs,sidewalks, parking lots, driveways, streetsand other impervious surfaces prevent waterfrom naturally infiltrating soil, filtering

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pollutants and recharging aquifers. As aresult, large volumes of sheet runoff must becollected, concentrated, and directed intowaterways. These volumes of stormwatercarry sediment and other contaminants thatcompromise water quality. Expensiveinfrastructure works are necessary to controlthe erosion and flooding that occur whenstormwater is concentrated and released intowaterways.

Stormwater runoff picks up pollutantssuch as spilled oil, tire particles, detergents,pesticides, fertil izer, de-icing salt, pathogens,chemicals, sand, and many othersubstances. These pollutants are thendeposited into waterways with concentratedstormwater. Some municipalities routestormwater through sewage treatmentfacilities, and when heavy storms cause flowrates to exceed treatment plant capacity,untreated sewage is discharged intowaterways.

Concrete can be an important part ofstrategies to achieve these two credits: first,by controlling the rate and quantity ofstormwater runoff; and second by removingsome of the most important pollutants fromthe runoff.

Common and well documented uses ofconcrete for stormwater management includepiping, collection systems and wastewatertreatment. This report will concentrate onpervious pavement made from concrete, avery promising technology that is rapidlygaining popularity throughout the UnitedStates.

DESIGN ISSUESPervious Concrete Paving

Pervious paving allows water topercolate to the ground, filter contaminantsand recharge groundwater and aquifers.Pervious concrete consists of speciallyformulated mixtures of portland cement,

Pervious concrete paving example -placing pervious screed

uniform, open-graded coarse aggregate, andwater. It usually contains little or no sand. Ithas enough void space to allow rapidpercolation of liquids through the pavement.

The pervious pavement surface istypically placed over a highly permeablelayer of open-graded gravel and crushedstone. Voids in the aggregate layers act as astorage reservoir for stormwater. A filterfabric may be placed beneath the gravel andstone layers to screen out fine soil particles.The amount of storage in the stone reservoirbeneath the pavement can be varied. If thesoil has low permeability, or is highlyvulnerable to freeze-thaw cycles, perforatedpipes can be added near the top of the

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reservoir to discharge excess stormwaterafter the reservoir has been filled. Perviouspaving has many advantages in addition tomeeting LEED credit requirements. It is aconsistently improving technology withbenefits that are still being discovered by theindustry.Maintenance

The advantages of pervious pavementcan only be realized if it is designed andmaintained to prevent clogging. To ensuresuccess, employ design strategies to helpprevent clogging. Grade site areas awayfrom paving to prevent the flow of dirt anddebris into pervious paving (alternatively,"pretreatment" borders, including raingardens and bio-retention swales, can beadded to filter out particles before they flowonto the pavement).

Maintenance could include vacuumsweeping or pressure washing on a periodicbasis commensurate with the level and typeof debris that might come onto the pavementsurface. The pavement should be inspectedseveral times during the first few monthsfollowing installation and annually thereafter.Annual inspections should take place afterlarge storms, when puddles will make anyclogging obvious. The condition of adjacentpretreatment devices should also beinspected.

Provide maintenance guidelines for thebuilding owner. Consider posted signage on-site to identify pervious pavement areas.These can also serve an educational andenvironmental promotion function.

Filtering and Treating Stormwater withPervious Concrete Paving

Pervious pavement pollutant removalmechanisms include absorption, straining,and microbiological decomposition in the soil.An estimate of pervious pavement pollutantremoval efficiency is provided by two long-term monitoring studies conducted inRockville, MD, and Prince William County,VA. These studies indicate removalefficiencies of between 82% and 95% forsediment, 65% for total phosphorus, andbetween 80% and 85% of total nitrogen. TheRockville, MD, site also indicated highremoval rates for zinc, lead, and chemicaloxygen demand. There is some question ofhow closely these results reflect othersituations, but the treatment effectiveness ofproperly designed and maintained perviouspavement is not in doubt.

IPollutant Removal (%)IStudY ITSS ~ITN ICOD IMetalPrince William FFF~~2 65 80 - -County, VAR~ille,MD F F F F FTable 2. Effectiveness of porous pavementpollutant removal (Schueler, 1987)

Some key factors (other thanmaintenance) that increase pollutant removalinclude a drainage time of at least 24 hoursand the use of clean-washed aggregate.

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"Stormwater hot spots" are areas whereland use or activities generate highly

Pervious pavements allow for groundwater rechargingwhile a/so assisting with water pol lution removal.

contaminated runoff, with concentrations ofpollutants in excess of those typically foundin stormwater. Pervious pavement is aninfiltration practice, and may not beappropriate at stormwater hot spots due tothe potent ial for groundwater contamination.These areas include commercial nurseries,auto recycle facilities, fueling stations,marinas, outdoor container storage of liquids,hazardous materials generators (if containersare exposed to rainfall), vehicle service andmaintenance areas, and vehicle andequipment washing/steam cleaning facilities.Recharging Groundwater Below PerviousConcrete Paving

Pervious paving can be used either torecharge groundwater, to store stormwaterfor later reuse (and/or diversion intostormwater conveyance systems), or both.This section discusses its groundwaterrecharge function.

Some data suggest that as much as 70%to 80% of annual rainfall will go toward

groundwater recharge (Gburek and Urban,1980). These data will vary depending ondesign characteristics and underlying soils.Per the USEPA, systems that rely on soilabsorption require deep pervious soils atseparation distances of at least 4' betweenthe bottom of the structure and seasonal highgroundwater levels. In theory, pretreatmentand treatment by the pervious paving shouldreduce the depth of soil above seasonal highgroundwater levels.

Other criteria include: The pervious pavement system should

be designed such that the water stored inthe aggregate base reservoir drainsdown within 5 days after a storm. Insome cases, where infiltration rates ofthe in-situ soils are relatively low, acombination of an aggregate base,drainage pipes, rain gardens, and bio-retention swales can be used to channelthe excess water to holding ponds orunderground storage (French drain).

Generally, the bottom of the stonereservoir should be flat so that infiltratedrunoff will be able to infiltrate through theentire surface.

Consider placing pervious pavement atleast 2' above the seasonally highgroundwater table, and at least 100'away from drinking water wells.Designs may also require the inclusion of

devices to convey to the storm drain systemexcess water from storms that exceed thedesign storage capacity of the perviouspavement system. One option is to use storm

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drain inlets set slightly above the elevation ofthe pavement. This configurat ion would allowfor some ponding above the surface, butwould bypass flows that are too large to betreated by the system.Retention/Attenuation (or Tanked) Systems

The gravel underlying the paving can beused for the storage (retention) ofstormwater, substituting for expensive orland-consuming retention structureselsewhere on the property. This function ofpervious paving incorporates base and sub-base storage in conjunction with standarddrainage infrastructure to provide a delayedstormwater discharge. Retention systemscan also enable reuse of stormwater forsome domest ic purposes such as irrigation.

Two ways of modifying perviouspavement systems to function as reservoirsare (1) varying the amount of storage in thestone reservoir beneath the pavement and(2) adding perforated pipes near the top ofthe reservoir to discharge excess stormwaterafter the reservoir has been filled. Somemunicipalities have also added stormwaterreservoirs (in addition to stone reservoirs)beneath the pavement. These reservoirsshould be designed to accommodate runofffrom a design storm. For more information,see design criteria from the United StatesEnvironmental Protection Agency Office ofWater, Washington, D.C., document: EPA832-F-99-023, dated September 1999.Benefits and Costs

As with most stormwater runoff reductionmeasures, the initial incremental costs needto be compared to the costs of infrastructure

that may be required by municipal or otherauthorities for which pervious paving is anacceptable alternative (i.e. detent ion tanks).Maintenance costs, such as requiredvacuuming of pervious paving, should alsobe considered.Limitations

Several studies indicate that, with propermaintenance, porous pavement can retain itspermeability (e.g., Goforth et aI., 1983;Gburek and Urban, 1980; Hossain andScofield, 1991). Many pavement engineersand contractors lack expertise with thistechnology. Therefore, it is suggested thatspecifications require pervious concreteinstallers be NRMCA Pervious ConcreteContractor Certified, preferably at theInstaller or Craftsman level. For infiltratingsystems (the great majority of cases), theuse of pervious pavement does create risk ofgroundwater contamination, depending onsoil conditions and aquifer suscept ibility. Fuelmay leak from vehicles and toxic chemicalsmay leach from asphalt and/or bindersurface. Infiltration-type treatment systems,including pervious paving, are not designedto treat these pollutants. Likewise, nitratesand chlorides may continue to move throughthe soil profile and into the groundwater,possibly contaminating drinking watersupplies. Therefore, until more scient if ic datais available, it is not advisable to constructporous pavement near groundwater drinkingsupplies.

Special planning and expertise isnecessary for proper placement and designof pervious pavement. Retrofit may require

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redesigning and rebuilding the sub-base forproper drainage.Codes and Standards

Any paving must meet requirements formaterial quality, strength, porosity, andfreeze-thaw resistance. The NRMCApublication Freeze- Thaw Resistance ofPervious Concrete provides guidance forfreeze-thaw resistance. In areas wherecodes have not caught up with newtechnologies, requirementsgutters, stormwater piping

for curbing,and other

standard civil engineering stormwater controlmeasures may compromise the use ofpervious paving. In these cases,rat ionalization must be prepared and justifiedwith the appropriate agencies.

Regulatory agencies may require reviewand approval regarding the recharging ofunderground aquifers or the horizontalmovement of water under the paving, whenthe water may contain undesirable chemicalsor pathogens.Integration with Other LEED Credits

Pervious concrete is also known aspercolating concrete, no-fines concrete, andpervious or porous paving. Like porousasphalt pavement or porous precast concretepavers, it may be an option for theachievement of three LEED Credits inaddition to the Stormwater Managementpoints: Because concrete is much lighter in

color than asphalt, it may help satisfythe requirement for LEED SS Credit 7.1(See Heat Island Reduction Credit).

The gravel sub-base under porouspavement can be used to storestormwater for irrigation, helping tosatisfy LEED WE Credit 1. If noirrigation is required for a project, fourpoints may be earned.

TRADE CONTRACTOR ANDMANUFACTURER ISSUESSpecifications

The specifications will likely include anew section number, but otherwise, shouldbe self explanatory with regards to meetingthe LEED criteria for these credits.Installation

The equipment used to place perviousconcrete is different from that used to placestandard concrete. Deposit concrete direct lyinto f inal position since pervious concrete haslittle or no flowability. Do not pull or shovelinto final position. After the paving is struckoff and compacted, don't do any otherfinishing. Typically, compacting is completedby rolling and is different from traditionalfinishing. Personal protective equipmentused for placing pervious concrete is thesame as with placing standard concrete and

Pervious concrete f inishing uses similar equipment asfor f inishing standard concrete; technique is the key.

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includes: hardhat, safety shoes, protectiveeyewear, chemical resistant gloves, and achemical resistant knee board, if necessary.Initial set occurs quickly, in about one hour(1.5 hours with a set retarding admixture).Covering with plastic sheets is therecommended curing method.Recommended curing time is seven days.Allow traf fic after seven day curing period.

If random cracks are not desired, formcontrol (contraction) joints at 20 foot intervals(or shorter) to one-fourth the depth of thepavement.

Traditional portland cement pavementtesting procedures based on strength, aircontent and slump control are not applicableto this type of pavement material. Mostcommonly, the quality of pervious pavementsis assessed by measuring the unit weight ofboth plastic and cured concrete. Thisassessment is used to estimate the voidscontent that influences the storage capacity.See NRMCA's Pervious ConcretePavements for more information.Required LEED Documentation

Data regarding the runoff coefficient willlikely be secured by the architect orlandscape architect prior to the ConstructionDocuments.

If the concrete producer has reflectancetest results (see SS Credit 7) for the perviousconcrete mix used on the project, he maychoose to submit a letter to the contractor(and architect) indicating the results of thetests. See Appendix B for a sample letters.

REFERENCES AND INFORMATIONSOURCESResource Websiteswww.nrmca.org - The National Ready MixedConcrete Association in Silver Spring, MD,provides up-to-date information on theapplication, placing and maintenance ofpervious concrete. Of particular relevanceare the recent publications:

Pervious Concrete Pavements Freeze- Thaw Resistance of Pervious

Concrete 2006 Concrete Technology Forum

Conference Proceedingswww.rmc-foundation.org The RMCResearch & Education Foundation is a non-profit organizat ion dedicated to improving theconcrete industry through achieving itsmission of promoting educat ion and researchprojects that will strengthen and improve analready superior product in an industrycommitted to excellence.www.perviouspavement.org - This websitespecifically on pervious concrete pavementincludes details about the pavementsenvironmental benefits, applications,performance, engineering properties, mixdesign and materials, design, construction,maintenance and an FAQ sect ion.www.concreteparking.org - This websiteprovides useful information on concretepaving, parking lots and parking structures.Discusses the economic, environmental, curbappeal and fast placement benefits ofconventional concrete, Pervious Concrete,White Topping, Ultra-Thin White Topping andConcrete Paths.

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www.greenrooftops.org - Information onwaterproof concrete systems that has provenitself as a fast, smart and economical systemthat can boost the green roof industry.www.gcpa.org - Specifications for perviousconcrete paving is available on this websitefor the Georgia Concrete and ProductsAssociation.www.concreteanswers.org - Website fromNRMCA that provides a variety of concreteresources, including information about thematerials "green" characteristics, cost,durability attributes and many other topics.www.epa.gov/owow/protecting Thisdocument, "Protecting and RestoringAmerica's Watersheds," contains usefulinformation on pervious paving.http://www.epa.gov/npdes/pubs/porouspa.pdf- A 1999 USEPA document from itsMunicipal Technology Branch, Office ofWater Management. Detailedrecommendat ions for porous pavement usedfor stormwater control, including costinformation.http://www.ct.gov/dep/lib/dep/water regulatin9 and discharges/stormwater/manual/CH 11PP S-6.pdf provides a description ofpermeable pavement as a stormwater BMP.http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm - An overview and one ofa series of USEPA BMPs (Best ManagementPractice) Guides in its National PollutantDischarge Elimination System (NDPES)program.www.cwp.org - Center for WatershedProtection, 8391 Main St., Ellicott City MD

21043-4605, Phone: 410-461-8323United States Environmental ProtectionAgency, Office of Water, 1200 PennsylvaniaAvenue N.W., Washington DC 20460, Email:[email protected]

Resource Do cumen tsCenter for Watershed Protection (CWP).1998. Beiter Site Design: A Handbook forChanging Development Rules in YourCommunity. Center for WatershedProtection, Ell icott City, MD.Center for Watershed Protection (CWP).1997. Stormwater BMP Design Supplementfor Cold Climates. Prepared for: USEPAOff ice of Wetlands, Oceans and Watersheds.Washington, DC.Ferguson, Bruce, 2005, Porous Pavements,CRC Press, Boca Raton, FL.Field, R., et aI., 1982, "An Overview ofPorous Pavement Research," WaterResources Bulletin, Volume 18, No.2, pp.265-267.Galli, J. 1992. Preliminary Analysis of thePerformance and Longevity of Urban BMPsInstalled In Prince George's County,Maryland. Department of Natural Resources,Annapolis, MD.Gburek, W., and J. Urban, 1980. StormwaterDetention and Groundwater Recharge UsingPorous Asphalt-Experimental Site. InProceedings: International Symposium onUrban Storm Runoff. University of Kentucky,Lexington, KY, p. 89-97.

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Goforth, G., E. Diniz, and J. Rauhut. 1983.Stormwater Hydrological Characteristics ofPorous and Conventional Paving Systems.United States Environmental ProtectionAgency, Office of Research andDevelopment, Cincinnati, OH.Hossain, M., and L. Scofield, 1991. PorousPavement for Control of Highway Runoff.Arizona Department of Transportation,Phoenix, AZ. .Metropolitan Washington Council ofGovernments, 1987, Controlling UrbanRunoff.A Practical Manual for Planning andDesigning Urban BMPs.Metropolitan Washington Council ofGovernments, 1992, A Current Assessmentof Best Management Practices: Techniquesfor Reducing Nonpoint Source Pollution in aCoastal Zone.Portland Cement Association, 2004, PerviousConcrete Pavements, Skokie, Illinois.Schueler, T. 1987. Controlling Urban Runoff.A Practical Manual for Planning andDesigning Urban BMPs. Metropolitan

Washington Council of Governments,Washington, DC.Southeastern Wisconsin Regional PlanningCommission, 1991. Costs of Urban NonpointSource Water Pollution Control Measures,Technical Report No. 31.Stenmark, C. 1995. An Alternative RoadConstruction for Stormwater Management.Water Science and Technology32(1):79-84.USEPA, 1981, Best Management PracticesImplementation Manual.USEPA, 1992, Stormwater Management forIndustrial Activities: Developing PollutionPrevention Plans and Best ManagementPractices. EPA 833-R-92- 006.Washington State Department of Ecology,1992, Stormwater Management Manual forthe Puget Sound Basin.Watershed Management Institute (WMI),1997, Operation, Maintenance, andManagement of Stormwater ManagementSystems, prepared for the USEPA Office ofWater, Washington, DC.

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SS Credit 7.1: Heat Island Effect - NonroofIntent Reduce heat islands to minimizeimpact on microclimate and human andwildlifehabitats.

RequirementsOPTION 1

Use a combination of the followingstrategies for 50% of the site hardscape(including roads, sidewalks, courtyards andparking lots): Provide shade from the existing tree

canopy or within 5 years of landscapeinstallat ion. Landscaping (trees) must bein place at the time of occupancy.

Provide shade from structures coveredby solar panels that produce energy usedto offset some nonrenewable resourceuse.

Provide shade from architectural devicesor structures that have a solarreflectance index (SRI) of at least 29.

Use hardscape materials with an SRI ofat least 29.

Use an open-grid pavement system (atleast 50% pervious).

OR,Place a minimum of 50% of parking

spaces under cover. Any roof used to shadeor cover parking must have an SRI of at least29, be a vegetated roof or be covered bysolar panels that produce energy used tooffset some nonrenewable resource use.

Summary of Concrete Applications andMaterials Relevant to the Credit

Ready mixed concrete products can helpsignificantly in gaining not only this credit, butInnovation Credits based on exemplaryachievement of this credit (see InnovationCredits, Exemplary Performance).DESIGN ISSUESDetails

One strategy for achieving this Credit isto use concrete instead of asphalt for more

The use of l ight-colored concrete and goodlandscaping are a winning combinat ion for the

reduction of heat-island effects.

than 50% of the non-roof impervious surfacepaving on a given project or less than 50%when combined with other strategies. Solarreflectance includes not just visible light, butalso infrared heat and UV, and is measuredby the surface's "albedo." An albedo of 0.3means that 30% of all the solar energystriking a surface is reflected back into theatmosphere, while 70% is absorbed by thesurface, raising its temperature. According toresearch conducted by Lawrence BerkeleyNational Laboratory, ordinary gray cementconcrete has an initial albedo in the range of0.35 to 0.45; the more expensive white

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Conventional (thickness greater than 8") Thin (thicknesses from four to 8"), and Ultra-thin - UTW (thickness less than 4")

Ultra-Thin Whitetopping (UTW) is abonded, fiber reinforced concrete overlay. Itcan be used as a road surface course wheretraditional paving materials have failed due toshoving, rutting, or general deterioration.UTW provides an economical, durable, andlong-lasting pavement surface if theunderlying road course is sound.

The concern about the "heat islandeffect" that led to this credit is generating aninterest in light-colored paving for Greenconstruction. However, this is a relativelynew issue, and has not percolated down toeveryday pavement design and thereforewhitetopping has not experiencedwidespread use. However, as existingroadways and parking lots are beingresurfaced, whitetopping becomes a viableoption for achieving this credit.

UTW is placed as follows: the existingroadway is milled to a uniform depth andcleaned. The UTW concrete is placed directlyon the milled asphalt surface using aconvent ional vibratory screed to consolidatethe concrete and bring the concrete to finalgrade. The fresh concrete may be finishedwith a tined, broomed, or burlap draggedfinish. The UTW concrete is then jointedusing an early entry saw. Joint spacing isusually laid out in three-foot squares. Theproper joint spacing is critical to controlrandom cracking of the concrete surface.

Concrete pavement has a service life

several times greater than that of asphaltpavement. Concrete pavement is naturallylight gray in color, and can be periodicallypressure-washed to remove dirt and stainsand to help retain its reflective qualities.Benefits and Costs

UTW costs approximately $1.50 to $2.50per square foot installed excluding surfacepreparation. Conventional concrete pavingcosts $2.00 to $6.00 per square foot.Benefits derived include highly reflectivesurfaces and a high level of durability.Integrat ion with Other LEED Credits

If the concrete used is pervious and hasthe required albedo, it can help meet boththis credit and credit SS Credit 6.1. However,pervious concrete is not considered to meetthe requirements of open-grid paving since itis less than 50% pervious. The contributionof open grid paving to reducing the heatisland effect depends upon evaporation fromthe plant material within the grid, and not onits ability to transmit water. Pervious concretecan only contribute to this credit under thehigh albedo option.TRADE CONTRACTOR ANDMANUFACTURER ISSUESSpecifications

SS Credit 7.1 requires the use of "lightcolored/high albedo materials (ref lectance ofat least 0.3) for 50% of the site's non-roofimpervious surfaces," or less if combinedwith other strategies for reducing heatislands. The reflectance level of applicablematerials must be adequately documented toearn this credit. Project teams do not need to

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provide project-specific data measuring SRIvalues of new gray or white concrete.Documentation certifying that the concretemix used for a project is equivalent to apreviously used and tested mix is acceptable.Alternatively, the SRI values for typicalpaving materials provide in the USGBCLEED reference guide which lists new grayconcrete as SRI of 35.

Include reflectance documentation fromthe Concrete PavementmericanAssociation or Lawrence Berkeley NationalLaboratory, making sure to indicate theoriginal source of the research data and thereflectivity category that relates to yourconcrete mix. Alternatively, testing labs canbe found using the ASTM lab directory atwww.astm.org. Testing fees should beapproximately $200 for ASTM E 903. ASTMTest Method C 1549, "Standard Test Methodfor Determination of Solar Reflectance NearAmbient Temperature Using a Portable SolarReflectometer" is also recommended. Thelab will choose the test method and explainhow to prepare test samples. Also include asite plan showing where concrete will beused.

For the concrete portion of the site, it isacceptable to use the reflectivity rate for newconcrete for this credit, as this will meet theintent of the credit at the time of construction.Existing old concrete cannot be considered inthe square footage for high albedo materials,unless its reflectance can be measured to be0.3 or greater, and documentation isprovided showing this reflectance. Pressurewashing can be a solution for increasing thealbedo of dirty, weathered concrete. The

concrete producer may choose to haveconcrete mixes used for parking areas andplazas pre-tested to determine reflectancevalues. In such cases, the producer shouldprovide a let ter to the contractor and architectstating the mix design was tested inaccordance with ASTM E 903 or ASTM C1549 and provide the reflectivity values.REFERENCES AND INFORMATIONSOURCESResource Websiteseetd.lbl.gov/Heatisland

www.secement.org/PDFs/RT3.05.pdfAmerican Concrete Pavement Association,R&T Update #3.05, June 2002www.pavement.com/Concrete PavementlTechnical/Fundamentals/Concrete PavementResurfacing.aspwww.whitetopping.com/news.asp#iprfwww.tfhrc.gov/pubrds/02jul/09.htmhttp://www.concreteparking.org/whitetoppingResource Documentswww.secpa.org/PDFs/RT3.05.pdfEffects of Composition and Exposure on theSolar Reflectance of Portland CementConcrete, 2001, Lawrence Berkeley NationalLaboratory, Berkeley, CA.

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ENERGY AND ATMOSPHERE

EA Prerequisite 2: Minimum EnergyPerformanceIntent" To establish the minimum level ofenergy efficiency for the proposed buildingand systems to reduce environmentalimpacts associated with excessive energyuse.Requirements

In general, this prerequisite will requirethat the building team demonstrate a 10%improvement in the proposed buildingperformance rating for new buildings, or a5% improvement in the proposed buildingperformance rating for major renovations toexisting buildings, compared with thebaseline building performance rating usingANSI/ASHRAE/IESNA Standard 90.1-2007.There are other options for meeting therequirements of this credit but this is the onethat will be used in most cases.

EA Credit 1: Opt imize Energy Performancetntent: Toachieve increasing levels of energyperformance beyond the prerequisitestandard to reduce environmental andeconomic impacts associated with excessiveenergy use.Requirements

There are three options for achieving thiscredit Only Option 1 will be presented heresince this is the only option that incorporatesthe benefits of concrete in achieving thiscredit

Demonstrate a percentage improvement

in the proposed building performance ratingcompared with the baseline buildingperformance rating. Calculate the baselinebuilding performance according to AppendixG of ANSI/ASHRAE/IESNA Standard 90.1-2007 (with errata but without amendments),using a computer simulation model for thewhole building project The minimum energycost savings percentage for each pointthreshold is as follows:New Buildings Existing Building Points

Renovation12% 8% 114% 10% 216% 12% 318% 14% 420% 16% 522% 18% 624% 20% 726% 22% 828% 24% 930% 26% 1032% 28% 1134% 30% 1236% 32% 1338% 34% 1440% 36% 1542% 38% 1644% 40% 1746% 42% 1848% 44% 19Summary of RMC Applications and MaterialsRelevant to the Prerequisite and Credit

There are a number of ready mixedconcrete technologies that have an importantrole in energy saving. EA Prerequisite 2requires a 10% improvement on energy

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performance that meets ASHRAE 90.1-2007,while EA Credit 1 provides up to 19 Points forachieving better energy performance. Theprimary role of ready mixed concrete inimproving energy performance is in reducingheat loss and gain through foundation andbuilding walls and roof, using insulated walland roof technologies. The mass effect ofconcrete can also playa role in satisfying theprerequisite and in achieving points under EACredit 1, by reducing overall energyconsumption.DESIGN ISSUESDetails

Insulated wall technologies fall into threecategories: Insulating Concrete Form (ICF)systems, in which the insulation is outsidethe concrete; and sandwich construction,either tilt-up or vertically cast, in which a layerof insulation is sandwiched between twowythes of concrete, or conventionallyinsulated wall systems which consist of onelayer of concrete with a single layer ofinsulat ion on the interior or exterior, either t ilt -up or vert ically cast.

Insulating Concrete Forms: InsulatingConcrete Form (ICF) systems use formsmade of rigid insulation, or combinations ofinsulation and concrete that typically remainin place as part of the finished wall afterconcrete hardens.

The great majority of ICF systems utilizeEPS (expanded polystyrene, "beadboard") orXPS (extruded polystyrene), withpolyisocynurate (polyiso) rarely used. Thesesystems have been used extensively in thehomebuilding industry and are gaining

popularity in commercial construction. Thereare a few systems using hollow blocks madeof concrete and mineralized wood chips orfoam beads.

ICF buildings have long been knownto be particularly energy eff icient

ICF systems can be classified in twoways:By Configuration of Concrete - Flat systemsresult in a solid concrete wall of constantthickness, from four to 12" thick. Watne-Gridsystems result in a continuous concrete wallof varying thickness, as in a waffle, with atypical grid being 12" OC vertically and 16"OC horizontally. A 2" thick web and 6"-8"cores are typical. Screen-Grid systemsresemble waffle systems without theconcrete web, with the cores at 12" OC inboth direct ions (although spacing varies fromsystem to system). Post-and-Beam systemsare similar to the screen-grid systems, butwith wider spacing (up to 4' for columns andbetween 4' and 8' for beams).By Form Types - Panel systems are similar

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to standard plywood forms, ranging in sizefrom 1'-3" x 8'-9" to 4'-0" x 12'-0". Planksystems consist of long, narrow planks 8" to12" high, and 4' to 8' long. Both panelsystems and plank systems can be shippedflat. Block systems resemble large concretemasonry units (eMU's), and range in sizefrom 8" x 16" to 16" x 48". They vary in howthey interlock. Most are shipped as blocks intheir f inal conf iguration but some are shippedwith hinged ties that allow the blocks to beshipped flat.

Tilt-up Construction: Tilt -up walls are casthorizontally on-site and lifted, or tilted, intofinal vertical position once the concretereaches adequate strength, usually three tofive days after casting. Tilt-up walls, longused to build large, simple buildings such aswarehouses, are rapidly gaining in popularityfor use in a wide variety of building types.Tilt-up walls can be used in a sandwich panelconfiguration or conventional single wythe

Tilt-up construction is ottenused to save on energy costs.

configuration. For sandwich panelconfiguration: Using the floor slab as a form

bed, the outer layer of concrete is cast facedown with proprietary metal or plastic tiescast into connect the inner and outer layer ofthe sandwich panel. A layer of polystyreneinsulation specially configured to fit over theties is installed next, over which is cast theinner reinforced structural wall layer. Theresulting sandwich panel is then erected,forming an extremely durable, economical,and well-insulated wall system. For singlewythe configuration: Using the floor slab as aform bed, the outer or inner layer of concreteis cast face down. Ties and insulation areeither placed into the plastic concrete whilethe panel is in the horizontal position orattached to the hardened concrete once thepanel is erected. In many cases, tilt-up wallsare insulated using fiberglass or other battinsulat ion applied using furring strips or metalframing on the inside face of the wall.

Removable Form Systems: Removableform systems can also be used to constructsandwich panels or single wythe insulatedwalls. For residential and small commercialbuildings, the insulation is held in the centeror to one side of ordinary removable standingforms by the special metal or plasticstructural ties. Ready mixed concrete is thenplaced into the forms, creating a sandwichwall or single wythe wall in its final uprightposition. In many cases, concrete walls areinsulated using fiberglass or other battinsulat ion applied using furring str ips or metalframing on the inside face of the wall.

In both tilt-up and standing form systems,the most energy efficient systems are thosethat use plastic ties which do not create "coldbridges" because they do not readily conduct

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heat.Mass Effect of Concrete: The "thermal

mass effect" (thermal storage-and-release) ofboth interior and exterior concrete is well-documented. In principle, excess heat isabsorbed by constructed mass and releasedlater. In cold weather, excess heat suppliedby the sun or gained from internal sourcescan be released at night to warm thebuilding. In warm weather, unwanted solarheat or excess heat from internal sources istemporarily stored in massive constructionduring hours of expensive on-peak electr icityuse, and released later when it can betempered using lower cost off-peak electr icityor cool nightt ime air.

The economic benefit of thermal mass isdetermined in part by the extent to which theexterior temperature "swings" or oscillatesbetween a maximum and minimum aroundthe ideal interior temperature. Typically,passive solar buildings (or portions ofbuildings, such as a glazed south-facinggallery or atrium) are designed to undergosubstantial temperature swings, to m