Some firms prosper by specializing almost entirely in the residential market. According to PCA data, residential construction has accounted for about 24% of cement consumption over the past 3 years—the largest single category except for pavements.
To be successful placing residential footings, foundations, and slabs you need to work efficiently and accurately so it’s easier for the other trades to follow through with construction. A range of sophisticated equipment is available to help you lay out a building site (see “Surveying and Layout WorkSurveying and Layout Work,” from CC, February 2010), but such traditional tools as tape measures, stringlines, and transits (or builder’s levels) work fine for most residential projects.
Check the survey
Start with a site plan that indicates where the house should be placed on the lot. Rob Shirley, operations manager for FraserCon, a residential concrete contractor based in Carrollton, Texas, says it’s important to confirm that the information on the site plan is correct: “First we look at the site on paper, and then we go out and see what it’s really like. We want to make sure that the surveyor’s property pins are in place, and if something doesn’t seem right, we’ll contact the builder to verify the corners before we go ahead. We try to make sure that the location of the house takes any utility easements into account and conforms to local setback requirements. We also check for any trees we’ll need to work around during construction.”
After verifying that the lot boundaries are staked correctly, the property pins provide the necessary reference information, and the site plan drawing reflects the actual site conditions, the next step is to take measurements from the property lines to stake out the footprint of the house. Some contractors, like FraserCon, use a builder’s level or laser level and a long tape measure to take these measurements themselves, then set stakes and stringlines. Shirley says his crews call in a certified land surveyor to verify the placement once they’ve dug the foundation and set forms, but before pouring concrete.
Other contractors, such as North Star Foundations, Frederick, Md., take a different tack. North Star president Nick Cockerham says his crews come in after a surveyor has already placed offset stakes. “The surveyor sets hubs [stakes] a designated distance, usually 10 to 15 feet, off the building corner points. The offsets give the excavator space to dig the foundation. We pull stringlines between the nails in the hubs to make sure the distances match the plans, then we pull points to the actual building footprint. We also pull diagonals, to make sure the corners are square. If the design of the house is complicated, we’ll measure and do stringlines for all points along the perimeter.”
“Pulling diagonals” refers to measuring across the diagonal corners as well as between adjacent corners. If the corners are laid out square, both diagonal measurements will be equal.
Setting the level
As critical as it is to get the dimensions right and the corners square, it’s just as important in layout work to set the foundation and sill properly level. A level foundation is key for all the construction that comes after. The traditional tool to achieve a level foundation is the builder’s level.
The land survey should include an elevation reference point for the site, which is often but may not be the elevation at the top of the slab as indicated on the builder’s site plan. Set up the builder’s level by pushing the ends of its tripod base firmly into the ground at a location within sight of the reference point and near a corner of the planned foundation. Screw the level onto the tripod, aligning the telescopic sight with an opposite pair of leveling screws. Turn the leveling screws until the bubble on top of the level is centered, and then rotate the sight to align with the other pair of screws and center the bubble again by adjusting those screws. Once the bubble is centered, the horizontal crosshair in the level sight represents a level plane as the level rotates. The sight magnification is enough that you can read a measuring tape or rod accurately at 100 feet or more.
Aim the level sight toward the surveyor’s reference point, where a partner is stationed with a leveling rod or measuring tape, and measure its distance from the level plane. Then rotate the level sight toward the building corner location and station the measuring partner there. If the specified slab elevation is above or below the reference point, figure out by how much and determine where that point should be in relation to the level plane. Find that point on the leveling rod or tape, and have your partner mark it on the corner stake. Repeat the process at each corner, and then use the marks to set your stringlines.
Why work manually?
Given the proliferation of sophisticated layout equipment available, why do many contractors doing residential work continue to use more traditional methods, including some companies that own and use total stations to lay out larger projects?
“Technology is good, but this is still construction. On smaller jobs, it’s sometimes best just to roll up your sleeves and get started. The traditional methods end up taking less time, and we’d probably still use them to double-check a layout derived from a total station,” Cockerham says. CC
Kenneth A. Hooker is a freelance writer based in Oak Park, Ill.
Layout: What’s today’s simple? Concrete Foundations Association (CFA) members respond:
Jim Baty at CFA asked members for their thoughts on laying out foundations using string and surveyor’s level—whether this is still considered “simple” or now, with the aid of robotic layout equipment, the old becomes “complex” and the new is the new “simple.”
Scott Smith, Modern Poured Walls, Cleveland, Ohio
Since we have used robotic instruments for a long time our men in the field generally do not have the practiced skill of laying out foundations the old-fashioned way. So in that sense it is more difficult for us to layout by hand than by machine. However, we have found it faster to have some of our layouts done manually by a crew when they arrive rather than send a separate layout person every time. So we do a blend of the two.
Bruce Neale, Modern Foundations, Baltimore, Md.
All simple jobs are done the manual way and even some more difficult ones because we only have one person trained with the total station. I think it’s good to keep doing some manually. All complicated jobs we do with the total station and our reputation for square foundations remains very good.
Mark Latorre, Latorre Concrete Construction, Columbus, Ohio
I bet if I ask some of our workers what a plumb bob was I would get a blank stare. It’s amazing how easily one forgets the basics. We rely totally on our robotic instrument although there is one old fellow (myself) that could possibly still layout by hand. We have also found that the excavators do not make much of an effort to save the offset hubs since they know we only need two to do the layout.
Matt Menke, Menke Brothers Construction, Lima, Ohio
We do everything the “old way” with the exception of the grossly complicated layouts. We want to encourage an understanding of the process. We feel that this gives us more educated eyeballs reviewing the work and ensuring accuracy. The old simple way is simple because it involves basic tools but is more complex because more brain power is needed.
