how to estimate the cost of masonry wall

8/11/2019 How to Estimate the Cost of Masonry Wall

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A Concrete Masonr yUnit Wall

Te author is Rick Scott, CPE, President of Rick Scott Construction, Inc., a GeneralContractor based in Ponca City, Oklahoma. Rick Scott formed the company in Augustof 1996. Prior to starting Rick ScottConstruction, Inc. Rick had workedfor another General Contractor forthe previous 18 years. Prior to hiscareer in construction, Rick earnedan Associates Degree in Construction echnology at Northern Oklahoma

College in onkawa, Oklahoma. Rick acts as Chief Estimator for thecompany as well as General Manager. Te company, with a branch officein ulsa, Oklahoma, specializes incommercial construction projects suchas schools, banks, churches, museums,and athletic facilities.

Technical Paper

ESTIMATE THE COST OF

AN ESTIMATORS GUIDE TO POLICIES,PROCEDURES, AND STRATEGIES

submitted by Rick Scott, CPE

1) Introduction

Main CSI Division CSI Division Brief Description

2) Types and Methods of Measurement 3) Factors That May Affect Take-Off and Pricing

Effects of Small Project vs. Large Project Effects of Short Length of Walls vs. Long Straight Walls

4) Overview of Measurement, Labor, Equipment, andIndirect Costs

Materials Labor Equipment Indirect Costs Markup 5) Special Risk Consideration 6) Ratios and Analysis 7) Miscellaneous Pertinent Information 8) Sample Project Sketch 9) Sample Project Take Off

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10 Estimating Today July 2009

ESTIMATE THE COST OF A CONCRETE MASONRY UNIT WALL

INTRODUCTION

This paper will provide information required to estimate a ConcreteMasonry Unit (CMU) Wall. There are numerous features that can beadded to a CMU wall such as brick veneer, insulation, waterproo ng,

paint and ller that affect the costs, although this paper will focus ononly the CMU wall itself without these added items.

Main CSI Division- Division 04000 MasonrySubdivisions- Division 04050 Masonry Procedures Division 04100 Mortar Division 04150 Masonry Accessories Division 04200 Masonry Units Division 03200 Concrete Reinforcement

BRIEF DESCRIPTION

Concrete Masonry Unit Walls are an extremely useful framingsystem capable of bearing the weight of upper oors and roofs whilecreating the exterior and interior walls of the building. The CMUwalls can take the place of columns, beams, and drywall construction.While the initial costs may be more than other framing methods, theCMU wall is probably the most durable, and thus, over the lifespanof a building may be the least expensive framing method. The CMUwall is ideal for use in schools, stairways, high traf c public facilities,detention facilities, or anywhere an extremely abuse resistant or reresistant wall type of construction is required.

TYPES AND METHODS OF MEASUREMENT

Concrete masonry units are made in a variety of sizes but for the purpose of this paper I will be using CMUs that are nominally 8

thick (front to back) and have a nominal face dimension of 16 longand 8 high. Concrete masonry units should meet the requirementsof ASTM C90.

There are numerous special block shapes that can be used fordifferent applications in the construction of a CMU wall, as shownin Figure 1.0. For the purpose of this paper though we will be using

blocks 8-1 Stretchers and Corners, 8-12 Bond Beam, and 8-16Solid Bottom Bond Beam. These bond beam and solid bottom

bond beam blocks are lled with grout and rebar to create horizontal beams to reinforce the wall. Similarly, vertical cells of the stretcherand corner block can be lled with grout and rebar to reinforce thewall. The 8-12 Bond Beam blocks are typically installed on the

bottom course, top course, and 4 on center between the top and bottom. The 8-16 Solid Bottom Beam blocks are installed overeach opening, generally extending past the opening 8 on each side.The vertical beams are installed and at each corner, at 4-0 on center

plus at both sides of all openings. The speci c information describingthe horizontal and vertical beam requirements will usually be foundon the structural drawings.

CMUs are laid together using mortar. Mortar is a mixture of port -land cement, lime, aggregates, and water. Mortar proportions andmixing requirements are described in ASTM C270. The portions ofthe above materials determine the strength of the mortar.

The strengths and uses of mortar are classi ed as:

Type N used in general veneer masonry above grade Type S used in structural applications and more durable

veneer applications Type M typically used only below grade Type O very soft mortar usually only used in restoration

projects where it is critical to match the existing mortar

The required strength of the mortar will be found either in thespeci cations or notes on the structural plan pages.

I will be using Type S mortar mix which is a 75 lb. sack of a proper mix of portland cement and lime. This sack yields one cubicfoot. Approximately 2 cubic feet of sand (aggregate) is addedto this portland cement and lime mix along with approximately 5gallons of water to complete the batch. This batch of cement, lime,sand, and water mix will lay about (30) 8 x 8 x 16 block.

The grout used to reinforce the CMU can be mixed on site but in

this example, we will be ordering redi-mixed grout from a concretesupplier.

This grout will be delivered to the job site via concrete truck anddeposited either directly into the wall from the truck or through agrout pump to the higher or inaccessible areas of the wall. We willneed to calculate the volume of grout needed in measurements ofcubic yards. Again, the strength requirements of the grout will befound in the speci cations or notes on the structural drawing. Thestrength will be described in compressive strength of pounds persquare inch and for this paper I will be using 2500 PSI grout.

In the grout- lled blocks, I will need to nd the size, length, and

number of rebar pieces in each length of grout lled cell and beam.After I nd the total length of each size rebar, I will convert that totons of rebar.

In addition to the rebar reinforcing, most CMU walls are rein-forced with 9 gauge wire ladder or truss shaped reinforcing called

joint reinforcing. We must nd the vertical spacing of this joint reinforcing, which is usually required at every other course or 16 oncenter vertically.

While performing the take off, the estimator must be aware ofthe different types of walls called out in the drawings. The planswill typically include a wall schedule which identi es the variouswall types by using a lettering system. This schedule will provide adescription of the wall construction material (drywall, CMU, woodframe, etc.), wall thickness, insulation required, and sometimestop of wall elevations. The architectural and structural oor planis where the lengths of the different types of walls as indicated bythe designation from the wall schedule will be found. Either thewall schedule, elevations or wall sections will be where the wallheights are found. The Floor Plan and Elevations will also indicateopenings in the walls, such as doors and windows. The estimator isalso advised to review all drawings for items of work by others thatmay affect the construction of the CMU wall such as openings formechanical systems.


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*Openings the size of standard walk doors and smaller aresometimes not measured for the purpose of estimating the squarefootage of the wall, but for the purpose of this paper, I will measure

the smaller openings and deduct the area from the total.

1) .888 is the area in square feet for the face of a 16 x 8 block.2) 1.333 is the 8 bearing length on each side of an opening for the solid

bottom beam block.3) 1.333 represents the length in feet of a 16 block.4) 30 is the number of block one batch of mortar will lay.

All of the above measurements need to be made in feet and/ordecimals of a foot. From these measurements the following formulasare used to calculate the materials:

Area Wall = (Lw x Hw) [(Lop 1 x Hop 1) + (Lop 2 x Hop 2) +(additional openings if any)]

Total # Block = Area Wall / .888 1

# Solid Bottom Bond Beams = (Lop 1 + 1.333 2) + (Lop 2 +1.333 2) + (additional opening if any + 1.333 2) / 1.333 3

# Bond Beam Block = (Lhbb/1.333 3) - # Solid BottomBeam Block

# Stretchers/Corners = Total # block (# bond beam + # solid bottom bond beam)

Sacks of Cement = Total # block / 30 4

Yards of Sand = (Sacks of cement x 2.5 5) / 27 6

Gallons of Water = Sacks of cement x 5 7

Cubic Yards of Grout = [(Lhbb + Lvc) / 157 8

Tons of Rebar = (Lrb #1 x wt per ft) + (Lrb #2 x wt per ft) +(additional rebar x wt per ft) / 2000 9

Length Joint Reinforcement = Area wall / Sjr

Waste quantities must be added to most all materials. This wastefactor is for damaged and spoiled material. In the case of rebar I addan additional factor of 10% for overlaps. In the estimate at the end ofthis paper you will see how I account for waste.

FACTORS THAT MAY AFFECT THETAKE OFF AND PRICING

EFFECTS OF A SMALL PROJECT ASOPPOSED TO A LARGER PROJECT

If the project is relatively small, the cost per square foot of wallwill obviously go up. This is due to the cost of mobilization andequipment being spread over a smaller area of wall. For example,whether a project has 225 blocks (200 sq. ft) or 2,250 blocks (2,000sq. ft) the same equipment such as mixer, saw, lifting equipment,small tools, etc., must still be delivered to the jobsite and picked upand hauled away.

EFFECTS OF SHORT LENGTHS OF WALLS VERSUS LONG STRAIGHT WALLS

If the project is composed of numerous short runs of walls, thelabor cost per square foot will be more than a job that is made up oflong runs. This is because the beginning and end of each wall, calleda lead, is usually built by the head mason.

More time is taken to build the leads because they are laid withthe use of levels rather than string. After the leads are built a stringis stretched from one lead to the next and all blocks in between arelaid to the string line. This work in between the leads is much fasterthan the building of the leads; therefore, the more space between theleads, the lower the cost per square foot.

OVERVIEW OF MATERIAL, LABOR,EQUIPMENT, AND INDIRECT COSTS

This example will use a simple project to demonstrate some ofthe various components in a masonry wall. While there may beother components and other installation techniques required in other

projects, this paper will only focus on the components described inthe preceding chapter.

MATERIAL

The material take-off is the basis for the entire estimate. Thelabor, equipment, and other costs are largely built off of thematerial quantity so extreme care should be taken while gatheringinformation off of the plans for use in the estimate. It is advisableto highlight walls which have been taken off and, as always, doublecheck your work.

In summary, the material we will be estimating will be: Total

Number of block, Number of solid bottom bond beam block, Number of bond beam block, Number of stretch and corner block, Number of sacks of mason cement, Cubic yards of sand, Gallonsof water*, Cubic yards of grout, Tons of rebar, and Length of jointreinforcement.

*Water is usually paid for the general contractor or owner of the project. Therefore, cost of water is rarely, if ever, estimated.

The primary unit of measure that I prefer for this assembly issquare footage of wall; other estimators may use the unit of measurenumber of block. Both measures are equally effective. The reasonI prefer to look at the cost of a CMU wall per square foot ratherthan the cost per block is because the unit cost per square foot ismore interchangeable or comparable to other framing systems unitof measure.

5) 2.5 represents the cubic foot of sand required for each batch of mortar.6) 27 represents the number of cubic feet in a yard.7) 5 represents the gallons of water required for each batch of mortar.8) Linear feet of horizontal & vertical grout- lled beams per cubic yard of grout9) 2000 is the number of pounds per ton


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LABOR

Labor costs will be a function of the material quantity and in thiscase will be based only on the total number of block. The labor

positions that can be required are: Masonry Superintendent, LeadMason, Mason, Labor Foreman, and Laborer. The size of the joband the total number of masons that will be on a job determine the

need for a masonry superintendent and labor foreman. Generallyspeaking, if there will be ve or less masons on the job, there isreally no need for a masonry superintendent. On smaller jobs,the lead mason can assume the role of superintendent and still lay

block. If a job requires a superintendent, he will not be expected tolay block. The size of this small job will not require the masonrysuperintendent.

On most jobs, the mason to laborer ratio is one to one, sofor every mason, I will gure having one laborer on the job. If the

job is very small, then the ratio may go to two to one or two masonsto one laborer.

If the amount of grout ll is larger than normal or if the building is tall, it may require you to add laborers for the increasedwork caused by the additional grout and/or height of wall

On a normal job with standard grouting requirements thatare less than 20 feet tall, a mason should be able to lay an averageof 200 blocks per day. This will be used as the bases for estimatinglabor in my example.

EQUIPMENT

The basic equipment required for any masonry project will be:Mortar mixer, Block saw, Wheel barrow, Mortar tubs, Mortar stands,Mortar boards, and Masons hand tools.

As the job size increases, additional equipment required will be:Scaffolding, Skid loader with forks, High reach fork lifts, Self-climbing scaffolding.

For this estimate, I will be using the list of basic equipment, along

with standard scaffolding and a skid loader with forks.

The cost of the equipment will be calculated by taking the totalnumber of block divided by 200 (average number of block a masoncan lay per day). Then, that number divided by the number ofmasons I intend on having work on that project simultaneously. Thiswill give the number of days the equipment will be required, then

multiplying that number by the daily equipment cost for each pieceof equipment as prescribed by your company or a third party rentalcompany.

INDIRECT COSTS

Costs that may need to be considered and included inthe estimate are: Transportation costs of employees, Freight formaterials, Enclosures (cold weather work), Temporary heat (coldweather work), and PPE (personal protection equipment).

These costs need to be considered on a job-by-job basis depending

on the requirements of the job.

MARKUP

I prefer to have differing overhead markups for labor,material, and equipment, rather than one mark up for the totaldirect job costs. I prefer this method because the overhead costsand risks associated with labor are substantially higher than that ofmaterial and equipment. Therefore, it is my view that if a job is a

proportionately high labor job, my overhead expense for that job isgoing to be higher than that of a job with a lower labor cost and ahigher material cost.

For the purpose of this paper, I will be using: 15% overhead mark upfor labor, 10% overhead mark up for material, 12% overhead markup for equipment, and 5% pro t mark up on all job costs excludingoverhead.

SPECIAL RISK CONSIDERATIONS

At this time, one of the largest unforeseen variables is thecost of labor and materials. At this time (March 2009), costs have

stabilized somewhat as compared to one year ago. For the precedingthree years, the cost of cement, aggregates, and fuel were rising ona daily basis, resulting in a guessing game when bidding projectsthat would not start for six months. I think the lessons of the lastthree years have taught us that cost escalation can happen at any timeand be quite rapid. Therefore, a close eye on the global economy iswise; the rst sign of cost increases will appear when the economy isimproving.

Another large variable when bidding a masonry project is thecompetence of the general contractor and his on-site superintendent.A good contractor and his superintendent can make the job a breeze.They will have gathered and coordinated all pertinent informationfor you prior to mobilization to the site, including anchor bolts andtheir locations, wall layout and rough opening sizes. By the timeyou arrive on the job, the walls will be laid out, door jambs set, andall items you have to build into the wall will be on site. If thesethings are not done in a timely manner and the masonry crew hasto wait for these items or demobilize and remobilize, the productionwill decrease dramatically. My advice on this point is to knowyour contractor and if you dont know them, ask for references.Other subcontractors will likely be willing to share with you theirexperiences, both good and bad.

RATIOS AND ANALYSIS

As we have discussed earlier, I prefer to analyze the job as awhole on the cost per square foot. Historical job cost and labor hourinformation will be invaluable to you particularly the production rateof units laid per day. Units laid per day is the biggest variable inthe masonry estimate. The material amounts are relatively easy to

pin down regardless of production, time of year, height, etc., andthe cost of equipment is calculated by the number of days on the

job, which is directly related to the labor production. So, if youhave a good database of historical job-related costs and hours basedon a number of parameters, such as job size, height, time of year,masonry superintendent, general contractor, and general contractorsuperintendent, the nal bid amount should be accurate. These nal

bid amounts can be looked at and compared to past jobs to ensure


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they are within an acceptable range. Furthermore, in the value engineering stage of the job, the cost of the wall per square foot can easily becompared to other framing methods and materials.

MISCELLANEOUS PERTINENT INFORMATION

Be careful to review the speci cations, particularly your division of work, but also the General and Supplementary Conditions. Theremay be pertinent information in these sections that may pertain to you, including working hours, lay down yard area, parking restrictions,and so on. Pay close attention to your particular speci cation sections and related sections for material and product requirements, qualityrequirements, extra stock, etc. Also, the speci cations may require that certain items such as rebar may be provided by the general contractorand installed by the mason. So if this is the case, the inclusion of the rebar material in your bid costs will greatly reduce your chances ofsuccess in winning the bid.

Review all plans for items of work by others that may affect the nal cost of work by you. There may be mechanical and electricalitems built into your work that may adversely affect the production rates and thus, the cost of the masonry job.


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18 Estimating TodayJuly 2009


how to estimate the cost of masonry wall

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