ESTIMATING CONCRETE WORK - II
E stim a ting Fou Fou nda tion Wa lls B Y EDWARD G. L E JEINE*
In this, this, the sec ond in my s eries eries on es timating timating c oncrete wo rk, rk, w e’ll e’ll examine examine founda tion tion w alls alls bea ring ring o n footings and directly directly on c ompa cted earth. We’l We’lll also discus s underunderpi pinni nning ng a n existing existing foundation wa ll and ho w to es tima tima te the form form a rea a nd c oncrete for piers piers below g rade a nd for buil building slab s on fill. fill. Readers should refer back to the Outline for Concrete Estimating which appe ared on pa ge 210 of the J une, 1967, 1967, IsIssue of C ONC RETE C ONS TRU C TION
Foundat oundat ion w alls
On foundation walls I take off the quantities for form s (in 4-foot heights), 2 by 4 keys, slab seat bearing and concret rete. After the word “fo “forms” rms” I place the words “in 4-foot heights” in brac brackets. I separate my forms every every 4 feet by height for pricing and I use one price for material and labor for walls up to 4 feet high. From 4 feet to 8 feet, I use higher pric prices. From 8 feet to 12 feet, 12 feet to 16 feet and over I use increasingly higher unit prices per square foot of wall forms. forms. I do this because be cause more bracing is req required red for higher walls and the additional cost is in both labor and material. A lot of contractors don’t believe in brea breaking up the ir f oundation wall takeoffs into d ifferent heights but b ut actually act ually it makes a tremendous di fference. For example, if a 4-foot-high wall form is on a footing, I
Foundation Walls on Footings
Des Description
Num Number
Dimensions
3A. Foundation Walls on Foo Fo otings W x H x L Line A 1’-0 x3’-6 x 78’ Line B 1’-2 1/2x7’-10x 40’ Bsmt: (at Brick Ledge) 1’-0 x9’-6 x156’ Bsmt: (for Brick Ledge) 0’-4 x3’-0 x156’ Bsmt: Seat Bea Bearin ring 0’-4 0’-4 x0’-6 x0’-6 x156’ x156’ Bsmt: Door BoxBox-Out 1’-0 x7’-0 x 4’ 18 Bsmt: Win Window BoxBox-Outs 6 x 0’-8 x3’-0 x 4’
Lineal Fee Feet Squ Square Feet Slab Seat Cubic Feet Forms Bea Bearing Con Concrete 2HxL 546 627 2964 468 156 60 -3 4680X
Estimated Quantity
Uni Unit
L WxHxL 2 73 3 80 1 482 - ( - 156 )=Fo rm 1 side ( - 26 ) ( - 28 ) -
( - 48 )
18 1 877 X = Con Concrete = 70 Cubic Yards Ya rds √ 27 4”x6” Slab Seat Bea Bearing = 156 Lineal Feet √ 0’ to 4’ H. Forms Fo rms = 1070 Squ Square Feet √ 4’ to 8’ H. Forms Fo rms = 650 Squ Square Feet √ 8’ to 12’ H. Forms Forms = 2960 Squ Square Feet √ 468 Squ Square Feet x 1/2’/Squ 1/2’/Sq uare Feet + 10% = DoveDove -Tail Slots Slots for for Brick Brick Ledge Ledge = 260 260 Lin Lineal eal Feet Feet √ 156X
The ab ove w a lls represent represent typica l co nditions nditions . Line Line A is a typica l w all below fros fros t li line. Line Line B s how s tha t a w a ll is me a sured to the fraction of an inch for width and to the closes t inch inch for height. height. The The ba sement w alls alls s how that w here here a brick brick ledg ledg e exists, the w a ll must b e figured figured the full height of 9 feet 6 inche inche s. Then Then a dd in ad ditiona ditiona l forms for the brick brick ledge area a nd subtract the concrete. Slab sea t bea ring ring is figur figured ed in li lineal feet and then you must subtrac t for the concrete. Door and window box-outs have the ad ditional ditional forms forms a dded and ag ain you must subtract for the conc rete openings. openings. The The deduc tions tions for the conc rete are in in pa renthes is to ca ll a ttention to the subtra ction. The The slab se a t bea ring ring is listed listed in lineal lineal feet feet for eas e in pricing pricing a nd is not ad ded into “ strippi stripping ng a nd c leaning” of forms. Al All walls walls are listed listed in the sa me ta keoff and s eparated into 4-foot 4-foot va riations riations in height height in the las las t co lumn for eas e in pri pricing w hen they a re extended to the reca reca p s heet. Dove-tail slots for nailing to forms (for brick anchorage) are also easily picked up at this time. If the foundation walls have pi pillas ters on them, a dd in the a dditiona dditiona l formwork formwork and c oncrete for the pilas pilas ters and mark that sec tion tion of w all (for (for example) —”0-foot to 4-foot-high forms w ith pil pilaa sters .” The The co st w il illl be figured higher higher for this this s ec tion tion o f wa ll both for mate rial rial and labor.
figure a carpenter will erect about 300 square feet a day If the wall form runs between 4 feet and 8 feet high, a carpenter can erect about 250 square feet a day; from 8 feet to 12 feet, a carpenter can erect about 160 square feet a day. This will give you some idea of the difference between a 4-foot-high and 12-foot-high wall, a s far as e rection lab or alon e is concerned. Of course, the amount of bracing material required increases with the height of the wall. These figures are for erection labor only. They do not include removing the form s. I figure form stripping separately because I always f igure laborer time only for stripping. This isn’t always possible, because theoretically the carpenters are supposed to do
the stripping if the form work is going to be reused on the job. But most of the time laborers do it. For erection of forms, however, I figure a ratio of one carpenter to one-half of a laborer’s time. My cost per day for a carpenter always includes one-half a day’s time for a labore r. If a carpenter i s to set up 300 sq uare feet of forms per day then on that job he needs one-half of a day of labore r’s time to help him. The time might be spent handling forms and lumber, unloading trucks, or other ways of helping the carpenter. The figuring of production per carpenter per day, the cost of a carpenter and laborer ratio and how to apply them will be discussed fully later. At present, I will confine the discussion to getting the quantity takeoff properly accomplished. Now, should you take off wall columns separately or should you take them off as part of the wall? It depends on how big the column is and how much extra work it causes. If it’s a lot of work, take it off separately and call it a column to put it into the correct price bracket. If it is only about 4 inches wider than the wall by about 1 foot long, call it a pilaster and include the forms and concrete with the wall. If a wall has pilasters every 20 feet apart they are not a large enough cost item to take off separatel y. Figure the wall forms straight through the pilasters and then take off the pilasters separately and let the form work double up. This simplifies the takeoff, and the extra forms will pay the differential of your pilaster cost. When I pri ce wall forms with pilasters I also deduct 10 percent from
Grade Beam Walls
Description
Number
3B. Grade Beam Walls: Line A Line B Line C Line D -
2 feet Minimum Width Hand Excvation Area— Square Feet Cubic Feet Dimensions Square Feet Forms Concrete WxHxL 1’ x3’ x 50’ 0’-8 x6’ x150’ 1’-4 1/2x7’-l1x 83’ 1’-6 x8’-6 x154’
(W+1’)xL 100 300 197 385 -2 980 X
2HxL 300 1800 1 314 2618 -2 6030X
Estimated Quantity
Unit
WxHxL 150 6 00 901 1964 3615X = Concrete 134 Cubic Yards √ 27 Hand Excavation Area = 980 Square Feet √ 0’ to 4’ H. Forms = 300 Square Feet √ 4 ‘ to 8 ‘ H. Forms = 3110 Square Feet √ 8’ to 12’ H. Forms = 2620 Square Feet √
All wa lls that be a r directly on earth belong under this g roup. They a re sepa rated from found a tion w a lls on footings b eca use of the need for hand exc ava tion a nd a lso bec aus e a 2 by 6 leveling plate is usually needed on the ground before the forms a re se t. The co st o f this leveling plate is mos t ea sily put in the w a ll forming unit price s. Line A sho w s a typica l grade bea m on c aisso ns; line B s hows a wa ll less than 12 inches. Line C is show n to illustrate that the width is c arried to the closest fraction of an inch, the height to the closes t inch a nd the length to the closes t foot. Line D show s a wa ll over 8 feet high.
UInderpinning
Description
Number
Dimensions
Cubic Feet Hand Square Feet Square Feet Excavation Forms Concrete
Cubic Feet Estimated Quantity Unit
D 3C. Underpinning: WxHxL Hand Excavation 4’ x 4’ x24’ – From 45° Line 2 Wall – 1’-6 x 4’ x 24’ Footing – 2’-0 x 1’-6 x 24’ Footing Excavation - 3’-0 x 1’-6 x 24’
}
WxHxL 192
HxL –
WxHxL –
144 108 444√
96 36 -2 130√
144 72 – 216 X 27
= Concrete 8 Cubic Yards√ Forms = 130 Square Feet√ 444 27 = Hand Excavation = 17 Cubic Yards√ 2 x 4 Keys = 24 Lineal Feet√ To unde rpin an e xisting found ation w all the w ork is us ually do ne in alterna te 4-foot-long se ctions as sho wn o n elevation “AA.” All sections ma rked 1 are co mpleted b efore the sec tions marked 2 a re s tarted. If the a rchitect show s every third sec tion to be done at one time for add itional sa fety, it merely makes three sepa rate operations o f underpinning. The hand exca vation must be figured from an es tima ted ma chine excava tion line usually a t a 45 degree ang le from the b ottom o f the existing w a ll. This is s low wo rk bec a use the s ec tion of the wa ll is o nly 4 feet long a nd it is impo rtant not to d isturb the ground bey ond the inside of the existing wa ll. Forms are figured for one s ide o f the wa ll a nd foo ting. The co ncrete footing is usua lly regular c oncrete and the wa ll is s pecified to be a dry-pac k conc rete. Some times the wa ll is regular c oncrete stopped ab out 4 inches below the existing w all and allow ed to set up a nd ta ke its initial shrinkag e. The top 4 inches under the existing wa ll is then pa cked w ith a d ry-pac k grout which ha s little or no s hrinkag e upon d rying. The q uantities a re ca lculate d a s if the underpinning w ould all be d one a t one time. All of these q uantities must be clearly ma rked for “ underpinning” on the reca p s heet so that the pricing es timato r can make an a llow anc e for the slow w ork in his labo r units bec ause only 4 foot lengths o f wa ll and footing c an b e done a t eac h plac e.
the erection time used in figuring a straight wall without pilasters. Grade beams—foundation walls without a concrete footing under them—must be treated separatel y. I take them off separatel y, because I include the cost of a mud sill in the square feet of wall area. I do this by figuring 10 percent more in the material cost and 10 percent less in the square feet erected per day. For simplicity in pricing, take off a seat bearing on a wall for slabs by total lineal feet. These usually run about 4 inches by 6 inches. If they are not too high, brick ledges in walls should also be taken off for pricing by the lineal foot. If brick ledges run 2 feet or more in height, it will most likely be necessary to
place one form inside another. In other words, you’ll have to double-form the wall. The best way to account for this in takeoff is to double the form area. Be sure to deduct the concrete volume for this area. Once again, we are trying to be most accurate on the concrete volume because concrete makes up a high percent of the total cost of the estimate. I take off a retaining wall with a battered face as follows: I start first with the s traight side of the retaining wall. This falls in the regular price for wall forming work. Then take off t he battered face separatel y. This is a distinct problem. You can erect the stra ight wall and brace the other end off of it, but still that battered face is a special problem as far as getting the labor
into your cost. When figuring your labor to erect the battered face, reduce the production output per day on it by about 20 percent from what you would figure on a straight wall of the same height. In wall forming takeoff w ork, it is ve ry important for the t akeoff estimator to ha ve notations as to the type of work that must be priced. This is needed whether he prices it himself, or more importantl y, if the work will be priced by another estimator. The form area for walls is twice the height times the length. The concrete volume in cubic feet is the height times the length times the thickness, all in feet, of course. No deduction for reinforcing steel should ever be made from the concrete volume. In listing walls on the takeoff sheet the length should be given to the closest foot, the height to the closest inch and the thickness to the fra ction of an inch. A wall that is 1 1/2 inches thick should be figured as a decimal of 1.04 feet thick. These are necessary to get the correct concrete quantities. These same rules apply, in general, for all concrete takeoff work.
Piers below grade Estimating form area and concrete for piers below
grade is relatively simple. Piers below grade are piers that will have earth backfill around them. These piers can be formed with rough lumber and this is why they are kept s e parately from columns. The formw ork is twice the width plus t wice the length times the height, or once again, the contact area. The concrete volume is the width times the length times the height.
Building slabs on fill Under this category I include sand fill, edge forms, expansion joints, finish area and concrete. The sand fill is the area of the slab times the thickness of the sand bed. However, you must add 25 percent to the actual volume you’ve figured for sand fill, or crushed stone. This is for compaction and loss in handling and is very important. Edge forms are listed by the height in total lineal feet. Expansion joints are listed by the thickness and height in total lineal feet. The finish area is the total area of the slab. The concrete is the area of the slab times the thickness in a decimal of a foot, i.e., 5 inches is .42 feet. When f iguring concrete for a sl ab on fill add 3 percent for waste. You should also be sure to consider vapor barrier s, screed material and curing and protectio n items.
Piers Below Grade Description 4. PiersBelowGrade: F1 F2 F3 F4
Number
6 3 2 2 13
Dimensions
Square Foot Cubic Foot Forms Concrete
WxLxH (2 W+2L).H x 1’ x 1’ x2’-6 60 x 1’ x 1’ x3’-0 36 x 1 ‘-0 x1 ‘-4x5’-9 54 x 0’-10x1’-6x5’-9 54 -4 200X
Estimated Quantity
Unit
WxLxH 15 9 16 16
56X 27 (13) Forms At Slab: 1/2”x5” Expansion Joint
= Concrete 3 Cubic Yards √ 200 56
Square Feet √ Lineal Feet √
The form ma teria l for piers below g rad e is usua lly 1-inch dimension lumbe r and not expens ive b ut the lab or of forming piers is high b eca use o f the sma ll area of forms p er pier. Therefore, they mus t be ta ken off as a sepa rate item. The labor of c as ting piers is high beca use of the sma ll amount of c oncre t e per pier. Marking the number of piers to be fo rmed (13) is important. It tells the pricing estimator the avera ge s qua re feet of forms pe r pier (15 sq uare feet). If the pricing es tima tor allow s one hour ca rpenter time per pier then he can figure (8 hours times 15 sq uare feet) or 120 sq ua re feet o f pier e rec tion per d a y. In fac t the number of piers to be e rected se ts the allow anc e for forming lab or in sq uare feet per da y. The 1/2-inch b y 5-inch expa nsion joint a round the piers a t the slab is most eas ily taken off under this item.
Building Slabs on Fill Description
Square Feet Cubic Feet Area Concrete
Number Dimensions
5. Bldg. Slabs on Fill: E. Wing Center W. Wing Boiler Room Entries
– – – – 2
WxLxD 40’ x 63’ x 0’-5 44’ x 36’ x 0’-5 40’x63’ x 0’-5 2 21’ x 21’ x 0’-8 x 6’ x 8’-6 x 0’-6
WxL 2520 1584 520 441 102 3 7170 X
Estimated Quantity Unit
WxLxD 1059 666 1059 296 51
3131 X 27 = Concrete 116 Hand Grade Earth Under Fill = 7170 7170 Square Feet x 6” = 3585 Cubic Feet = 133 Cubic Yards + 25% Compaction = 6” Sand Fill = 166 (10% Added for Lap) = .006 Pol yethylene Vapor Barrier = 7900 Finish Slabs = 717 6” H. Edge Forms = 42 1/2” x 5” H. Expansion Joints = 672 1/2” X 8” H. Expansion Joints = 8
Cubic Yards √ Square Feet √ Cubic Yards √ Square Feet √ Square Feet √ Lineal Fee √ Lineal Feet √ Lineal Feet √
Building slabs at d ifferent elevations such a s b as ement floors a nd s lab s a t ground floor level should b e kept separate b eca use of the different lab or cos t per cubic ya rd for plac ing these s lab s. If all slabs are of the s ame thickness, only the q uantity for the areas s hould be extended , and the co ncrete q uantity may be o btained by multiplying the tota l area by the slab thickness. An estimator should alwa ys look ahead for any time-saving step that he can use. The ha nd g rading o f earth under fill is only needed whe n the ground is exca vated to provide for the slab. If the slab is to be placed on fill material furnished under the excavation specifications, then the work required of the concrete contractor would be the final hand grading of the fill material under the slab. Whenever a fill is specified such as a 6-inch sa nd bed under the slab, this should be figured in cubic ya rds to w hich s hould be ad ded 25 percent to c over compa ction and loss in delivery. The polyethylene vapo r barrier should have 10 percent a dd ed to the a rea required, to ta ke ca re of laps and wa ste. The neces sa ry edge forming is ea sily taken off from the d rawings a t this time and listed to the c lose st lineal foot. Expansion joints a re ob tained by referring to both d rawings a nd s pecs , and should be listed to the c los est lineal foot.
Figure a vapor barrier under the slab by taking the total area plus 10 percent for lap and waste. Screed materi al and curing and protection items are priced by the square feet of slabs. Membrane curing is the exact slab area, but if paper or polyethylene materials are used add 10 percent for lap and waste. Most of these items are included under the last part of recapping, miscellaneous items. They can generally be picked out from the takeoff sheet without referring to the dra wings. However, any items that you can pick off the drawings as you go along
should be done. This is one more times aver on yo ur takeoff time.
* The author, a civil engineering graduate from the University of Notre Dame, has been estimating concrete work for the past 17 years. For eight of these years, Mr. Le J eune was president of his own estimating service. The author presently is associated with the W.E. O’Neil Construction Company, Chicago, Illinois.
PUBLICATION #C670249 Copyright © 1967, The Aberdeen Group All rights reserved
