Upgrading Below Grade Spaces: Challenges & Opportunities

Pat Huelman

NorthernSTAR Building America Partnership University of Minnesota

Upgrading Below Grade Spaces: Challenges and Opportunities

• A context for why upgrading below grade spaces is challenging.

• A discussion of current practices.

• An overview of a new approach that we are researching.

• Focus is to reduce energy use by 50% in new houses and 30% in existing residential buildings.

• Promote building science using a systems engineering and integrated design approach.

• “Do no harm” => we must ensure that safety, health, and durability are maintained or improved.

• Accelerate the adoption of high-performance technologies.

Introduction to Building America

4. Infrastructure Development

3. Effective

Guidance and Tools

3. Effective

Guidance and Tools

2. House-as-a-

System Business Case

1. Advanced

Technologies & Practices

1. Advanced

Technologies & Practices

Building America Innovations

This research is paving the way for key innovations: • 1. Building Science Solutions / Assured Health & Safety

• Evaluating current methods for insulating basements • Searching for alternative approaches & materials

• 3. High Performance Home Solutions • Providing guidance and best practices

5

NorthernSTAR’s Builder Resources

• This presentation is aimed at basement foundations in heating-dominated climates.

• Most of these issues/requirements are beyond code. • It includes several detailed drawings. • Examples of how things can go wrong below grade. • Key technical references:

– Excavationless Exterior Foundation Insulation Retrofit – BSC: Hybrid Foundation Insulation Retrofits – Link to DOE resources: www.buildingamerica.gov

So What is the Problem?

• Should we insulate basement walls of existing homes? – Energy => absolutely – Moisture => probably – Indoor Air Quality => with care

• How should we insulate basement walls? – It is a system. – It depends!

Upgrading Below Grade Spaces

• Basement Remodeling: It Doesn’t Get Any Riskier! – Combustion safety – Foundation moisture – Radon (& other soil gases) – Biologicals (mold, dust mites, etc.) – Garage gases (if attached)

• And front and center are uncontrolled… – negative pressures in basements – below grade moisture transport

• Carpet on the slab • Insulating the walls (from the interior) • Egress windows • Furnace change-out • Ductwork changes

– drywalling the ceiling – rim (or extended) joists to the garage

• Adding a hot tub or sauna

Big, Bad, Boogie Men in the Basement

Basement Moisture Challenge

• Foundations get wet from four sides by all four moisture transport mechanisms. – bulk water, capillarity, diffusion, and air flow

• Foundations can only dry to the inside. – generally by diffusion only

• That means you must keep it dry from all four sides – or come up with an approach that promotes

inward drying better than outward wetting.

The Problem Isn’t New

“Changes and new developments in building construction during the past few decades have brought about an increasing need for control of moisture which often migrates upward from the ground.”

William A. Russell, Chief of Technical Standards

Housing and Home Finance Agency, 1954

Challenges of Basement Insulation

• Arguably the most challenging component of the building enclosure! – The physics is simple, but demanding

• It starts out damp and cold and goes downhill from there, especially with interior insulation.

– A road less traveled • There is a serious lack of good and useful below-grade

hygrothermal models and experimental data is limited. – Occupancy and expectations have changed

• Basement use and finishing has increased dramatically.

Basement Insulation: Benefits

Source: Oak Ridge National Laboratory

Basement Insulation: Opportunities

• Foundation heat loss can be significant in existing buildings.

• While below grade temperature differences might be smaller, – the surface area can be fairly large – the above grade portion is quite

significant, especially in older homes.

• There are a lot of uninsulated foundations in cold climates.

Basement Insulation: Challenges

• Most existing foundations do not have waterproofing and capillary break at the footing. – defined as liquid water active

• When you insulate the interior – the top of the wall is extremely

cold in the winter and – the bottom can be below the

dew point in the summer. • The foundation wall must dry inward; therefore interior

insulation generally limits the drying potential.

Basement Insulation: Background

• Below grade heat loss is always out – winter heat loss is highest at the top and

gets progressively less as depth increases. – summer heat loss is higher at the bottom.

• colder soil conditions & footing connection

• However, the above grade portion has similar issues to other above grade construction. – But not identical, due to vertical coupling.

Source: Oak Ridge National Laboratory

Basement Insulation: Background

• Below grade vapor flow is almost always inward

• However, the above grade portion has similar issues to other above grade construction. – vertical coupling is huge, especially

with concrete masonry

Source: Oak Ridge National Laboratory

Basement Insulation: Background

• Condensation Potential – Without insulation

• condensation is limited.

– With exterior insulation • condensation is virtually nil.

– With interior insulation … • condensation can occur at the top in the winter and • condensation can occur at the bottom in the summer.

Basement Insulation: Background

• Drying Potential – Without insulation

• heat and moisture move freely.

– With exterior insulation • drying to the inside is strong.

– With interior insulation • outward warming is slowed and interior drying is

severely limited.

A Reality Check

A Reality Check

A Reality Check

Foundation Insulation for Existing Homes

• Exterior insulation is almost always preferable • If interior insulation is used

– must have a very dry foundation • quality dampproofing in very dry, free-draining soils • waterproofing in moderate soils • waterproofing and drainage in tight, wet soils

– must have a capillary break – must have an interior air barrier – must use basement dehumidification

Foundation Insulation for Existing Homes

• Challenges of adding interior insulation on existing foundation walls. – Existing material properties and boundary

conditions are highly variable and unknown, so we need to focus on … • development of an water separation plane • balancing R-value and vapor diffusion characteristics • evaluate safe moisture storage.

Foundation Insulation (very low risk)

• Alternatives for Existing Basements – Dig to the footings, – Install proper perimeter drainage, – Add exterior waterproofing, – Install thermal insulation, – Backfill with free draining material with

impermeable cap.

Foundation Insulation (very low risk)

Source: Oak Ridge National Laboratory

Foundation Insulation (very low risk)

• Alternatives for Existing Basements – Interior finish w/o insulation/carpet

• empty stud wall, paperless drywall, latex paint • aggressive interior humidity control

Foundation Insulation (very low to low risk)

• Alternatives for Existing Basements – Barrier system w/ interior finishes

• sealed interior liner with concealed drainage – and possibly active drying

• use semi-permeable continuous insulation and appropriate interior finishes

Foundation Insulation (very low to low risk)

Source: Building Science Corporation

Foundation Insulation (very low to low risk)

Source: Building Science Corporation

Foundation Insulation (low to moderate risk)

• Alternatives for Existing Basements – Semi-vapor permeable, air impermeable

insulation with permeable finish • low R-value, semi-permeable, airtight foam • aggressive interior humidity control

Foundation Insulation (low to moderate risk)

Source: Oak Ridge National Laboratory

Foundation Insulation (low to moderate risk)

Source: Building Science Corporation

Foundation Insulation (high risk)

• Alternatives for Existing Basements – Frame wall with batt insulation system

• Vapor retarder needed on both sides • Air barrier is critical • Very limited drying potential • Moisture accumulation on foundation wall is likely

Foundation Insulation for Existing Homes

• Final Cautionary Note: If a Basement Floods … – Floor coverings must be removed to facilitate

clean-up and improve drying. – Interior insulation systems must be fully removed

because they are contaminated and retard drying. – From limited field experience, exterior insulation

systems appear to recover with little deterioration in performance.

Building America: 2011-12 Projects

• Exploration of methods to insulate the exterior of existing homes. – Identify approaches that could be used – Investigate means and methods – Determine how many homes would be conducive

to each approach

Building America: 2011-12 Projects

• A significant fraction of household space conditioning energy use, particularly in heating climates, can be attributed to lack of insulation on the basement wall and rim joist.

• Most existing houses have uninsulated foundations.

• There are two potential locations for basement and rim insulation upgrades: – Inside – Outside

The Ins and Outs of the Inside Approach

• Many (most?) existing foundations lack moisture control at the foundation face, and lack a capillary break at the sill.

• Interior insulation makes the wall colder, thus wetter. Interior insulation materials have low permeability, so walls stay wet.

• Rim and sill are particularly vulnerable to moisture accumulation and decay.

• Most insulation materials require an ignition barrier, adding to costs.

• Interior approaches that solve the hygrothermal issues (e.g. BSC Hybrid method) are likely expensive.

• But if you don’t go that far, it’s relatively cheap (but perhaps dangerous)!

The Ins and Outs of the Outside Approach

• Exterior foundation insulation confers multiple hygrothermal benefits, and missing moisture control materials can be added, or their importance to the hygrothermal regime diminished because the wall is warm, and can dry readily to the interior.

• Typical exterior approaches are costly, destructive to the landscape, and disruptive to homeowners.

• A cost-competitive, minimally-invasive technique is needed!

Technical Approach • It begins with the concept of an “excavationless” exterior foundation

insulation upgrade that is cost-competitive with current methods and involves little impact to existing landscape and site features. – Literature review to establish the building science case for the

advantages of exterior foundation insulation vs. interior insulation. – Presentation and analysis of two exterior, full-excavation exterior

insulation upgrades to establish a base case for costs. – Survey of five typical twin-cities neighborhoods to categorize and

quantify typical obstructions. – Web-based search to identify available materials and technologies that

have promise in this type of application. – Interviews with industry representatives from down selected products

and technologies to establish their suitability for this application, along with cost.

– BEOpt analysis to establish energy savings potential.

Recommended Guidance • Cut a narrow slot trench using air-vac / hydro-vac

technology. • Backfill with one of three potential material

candidates: – 4” pourable polyurethane (R-26) – 6” cellular concrete (R-9 to R-11) – 6” perlite aggregate concrete (R-9 to R-11)

• Above-grade foundation and rim techniques are under consideration. Rigid insulation application is one possibility.

• That could be it. There is the potential to drape waterproofing membranes into the trench prior to backfill if necessary. For the cementitious materials, admixtures that create a hygrophobic concrete can be added to include to make those materials more truly waterproof.

Cost Comparison Table *

* Cost does not include landscaping remediation, which will likely be higher for “traditional” methods

Market Readiness • Foundation insulation can have a significant influence on space

conditioning energy use. • Exterior insulation confers many hygrothermal benefits vs. typical

interior approaches. • Homeowners who understand these benefits currently choose

exterior insulation upgrades, despite the inconvenience, cost, and landscape damage.

• All technologies recommended here as a potential solution are in current use, though in market sectors other than residential foundation insulation upgrades.

• Preliminary cost estimates indicate this method is at least cost-competitive with current exterior insulation upgrade methods. Note that replacement of landscape features is not included in the analysis, so actual costs of traditional methods will be higher.

“Excavationless” Pros • Exterior insulation tends to be forgiving of existing defects. • Vacuum excavation methods greatly reduce landscape impact. • Many landscape features (walks, stoops, decks, etc.) that

would be removed for traditional excavation can remain with vacuum excavation.

• Process is quick, estimated at 2 to 3 days for a simple home. • Pourable insulation materials may be relatively waterproof,

potentially reducing bulk water intrusion. • Cost competitive with, and likely cheaper than, current

methods of exterior insulation upgrades.

“Excavationless” Cons • Method does not address moisture loading from sources

such as capillarity from the footing or through the slab • More expensive than typical interior insulation methods

(most of which increase risk of moisture problems) • Long-term thermal properties are not known; potential

for moisture accumulation within pore spaces may cause thermal degradation

• Large obstructions (patio slabs, sidewalks that abut the foundation) will need to be sawcut to the trench width, or removed and replaced

• Extent of waterproofing ability, and durability of that solution, are not well-characterized

References • Bomberg, Mark T. (1980) Some Performance Aspects of Glass Fiber Insulation on the Outside of Basement Walls. Philadelphia, PA:

American Society for Testing and Materials Special Technical Publication 718. pp. 77-91. Accessed from the National Research Council of Canada: http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=shwart&index=an&req=5210876&lang=en Feb 20, 2012

• Cellular Concrete Solutions, Inc. Technical Bulleting TB502: Cellular Concrete Strength / Density Chart. Accessed from http://www.cellularconcretesolutions.com/resources/technical-documents/, Feb 15, 2012.

• Collet, P.F. (March 2009). External thermal and moisture insulation of outer basement wall.” Danish Technological Institute; Taastrup, Denmark: prepared for Rockwool International.

• Crandell, Jay H. (2010). Below-Ground Performance of Rigid Polystyrene Foam Insulation: Review of Effective Thermal Resistivity Values Used in ASCE Standard 32-01—Design and Construction of Frost-Protected Shallow Foundations. Journal of Cold Regions Engineering, June 2010 p. 35.

• Edvardsen, Knut I. (1970). New Method of Drainage of Basement Walls. Byggmesteren, 44(18); pp.24-27. Accessed from the National Research Council of Canada: http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=shwart&index=an&req=5212536&lang=en Feb 20, 2012

• Fugler, Don (March/April 2002). Dry Notes from the Underground. Home Energy; Berkeley, CA: Energy Auditor and Retrofitter, Inc. • Horvath, John S. (1999). Lessons Learned from Failures Involving Geofoam in Roads and Embankments. Manhattan College

Research Report No. CE/GE-99-1. Bronx, New York; Manhattan College School of Engineering. • Lstiburek, Joseph and Yost, Nathan (2002). Basement Insulation Systems. Building Science Corporation; Westford, MA. • Natural Resources Canada: Basement Insulation. Accessed from http://oee.nrcan.gc.ca/residential/home-

improvement/choosing/insulation-sealing/basement/12735 , Feb. 12, 2012. • NCFI Polyurethanes: NCFI Low Density Pour System 23-004, and NCFI Trench Break Foam System 24-023. Sent directly from Mike

Larsen, Midwest sales manager, NFCI Polyurethanes. Feb 21, 2012. • Perlite Institute, Inc.: Perlite Aggregate for Lightweight Insulating Concrete. Accessed from

http://www.perlite.org/product_guides/12%20lightweight%20insulating%20concrete.pdf Feb 15, 2012. • Swinton, M.C., Bomberg, M.T., Kumaran, M.K., Normandin, N, and Maref, W. (December 1999). Performance of Thermal

Insulation on the Exterior of Basement Walls. National Research Council of Canada, Construction Technology Update No. 36; National Institute for Research in Construction: Ottawa, Canada

• Ueno, Kohta (May 2011). Residential Exterior Wall Superinsulation Retrofit Details and Analysis. Building Science Corporation, Research Report 1012; Westford, MA.

Upgrading Below Grade Spaces: Technical Gaps & Barriers

• Below grade heat transfer models are both crude and cumbersome – especially for deep basements.

• The are currently no validated and user-friendly below grade hygrothermal models in the U.S.

• Boundary conditions are not well characterized, especially for existing homes.

Upgrading Below Grade Spaces: Market Gaps & Barriers

• Most homeowners and many contractors don’t recognize the risks associated with interior insulation.

• Is uncontrolled dampness and mold growth behind interior insulation – a building materials liability? – a building performance liability? – an indoor air quality liability?

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Upgrading Below Grade Spaces: Challenges and Opportunities

• Questions?

• Contact Information – Patrick H. Huelman – 203 Kaufert Lab; 2004 Folwell Ave. – St. Paul, MN 55108 – 612-624-1286 – phuelman@umn.edu