Foundation & Framing - 2/3 - Bob Vila

Category: Foundation & Framing

How To: Measure Concrete

For those building a new foundation, there's an easy way to calculate the concrete needed for the job.

If you’re pouring a concrete foundation, how do you figure out how much concrete you’ll need? There’s a pretty simple formula. Take the length in feet times the width and height of the wall to figure your cubic footage. Then divide that figure by 27 to get your cubic yards (because there are 27 cubic feet in a cubic yard). Most cement trucks hold between eight and 14 cubic yards. An average house with a full foundation will take four truckloads.

For more on cement, consider:

9 Easy DIY Concrete Projects
Bob Vila Radio: DIY Concrete
Concrete and Cement: A Case of Mistaken Identities

Quick Tip: Using Metal Studs

Easy to work with and impervious to insects and rot, metal studs are superior to wood members in many ways.

If your home improvement project calls for new walls, you might want to consider metal studs. They fit together like an Erector set, and you can fasten them with miniscrews. You can even use metal brackets and plywood to stiffen the walls, which makes hanging cabinets easier. Metal studs are lightweight and fireproof. They won’t warp or split. You don’t have to worry about termites and in some places, they cost less than wooden studs.

For more on walls, consider:

Bob Vila Radio: Metal Studs
How To: Find a Wall Stud
Building a Metal Stud Wall (VIDEO)

The Excavation and the Foundation

Consider this advice before building on the foundation and embarking on the excavation.

Home Addition Foundations


Before the building of an addition can begin, site preparation may be necessary. Are there any garden plants, shrubs, or other vegetation you want to remove and set safely aside for later replanting? If there’s a tree in the way, you’ll need to arrange for its removal. Any other obstacles to the process—an old patio, say, or a stack of fire­wood—must be moved out of range before work can begin. Depending upon where the work is to be done with respect to the street, additional preparation may be required to clear a path for the equipment and materials to reach the work site.

If you’re building a large addition, the arrival of a surveyor may signal ground will soon be broken. With a smaller job, your designer or contractor will probably begin the process by marking out the extent of the new, enlarged footprint of the house.

The plot plan will guide whoever it is that does the staking out. For a large project, a transit will be used, an instrument that establishes elevations and levels and points, to help precisely locate where the new excavation is to be done. When the staking out is completed, there will probably be stakes and connecting strings that mark where the excavation is to be done. Perhaps lines of lime will criss­cross the ground, extending beyond the actual location of the foundation or cellar hole to guide the men with the earth-moving machines.

Don’t faint dead away upon seeing the plot staked out. Even large structures can seem diminutive when reduced to strings or lime lines struck across the ground and viewed under the canopy of the sky. Your new, expensive, and carefully imagined space may suddenly seem rather small. So prepare yourself.

After you’ve managed to keep your cool on first look, take a second and closer peek. It probably makes sense for you to extend your tape measure from comer to comer. Think of it as a warm-up exercise for the job to come. Your purpose is to make sure the new foundation abuts the old structure where it’s supposed to be and oth­erwise matches the plan.

Now the noise can begin. Diesel-powered earth-moving machines arrive a day or so later. Often a back hoe will be enough, though for big jobs there may be a bulldozer (call it a ‘dozer) with a wide blade. Or an excavator, a descendent of the steam shovel, with its long arm and the bucket at the end. None of these machines move quickly; they weren’t built for speed. But they’ll shift gargantuan quantities of soil and, if necessary, tree stumps and miscellaneous boulders. They will leave you with a foundation hole dug to a depth of at least six inches below the frost line.

The frost line is the depth to which the winter frost penetrates the earth. In the northern United States, that means the foundation must be at least 3 or even 4 feet below grade; in southern regions where subfieezing tempeiatures are rare, the foundation may virtually sit on the surface. The base or “footing” of a foundation must be beneath the frost line to prevent the frost from thrusting portions of your founda­tion upward and causing your house to settle unevenly (which would result in cracks in the foundation and, eventually, cracks and other damage upstairs in your home). The deeper frost lines in northern areas are one explanation for why full basements are more common there.

The potential problems during the excavation process are too many rocks (if it’s solid ledge, blasting may be required); too much water (an underground stream or spring may require special drainage); or even soil problems. Some soils simply aren’t firm enough to bear the weight of a structure without additional support, typ­ically an enlarged concrete footing (see below). In parts of the country where soil problems are common, your designer or architect will probably have suggested you test it in advance.

Speaking of soil problems, you may need to protect the soil you have. You may even be required to construct fences, stake hay bales, or employ other means to pre­vent soil erosion in the event of a heavy rain.

Once you have a hole in the ground, the foundation can be built. The first step is the footing, usually a base of cement wider than the wall to be constructed on it that will distribute the weight over a larger area to prevent settling. (For a house built on piers, foundation pads for the supporting posts to rest upon are necessary.)

The walls come next (after the concrete sets, which takes an average of three to five days). The wall may be of cement block or of concrete poured into a wooden form that is removed after the concrete has set. Setting up the forms for a poured foundation will take a portion of a day; the forms will be stripped two or three days later. Stone foundations are almost unheard of these days, though for aesthetic rea­sons some concrete foundations are built with a small shelf set into the portion of the foundation that will be above grade (i.e., not buried) onto which a veneer of brick or stone can be laid to hide the less attractive concrete.

After the concrete forms have been removed, perforated piping (called drain tile) is laid outside the wall at its base in damp climates. These pipes will be pitched to allow the water that enters them to drain off and away from the foundation.

The earthmoving equipment will then return and backfill around the cellar hole. The soil on the surface must be graded so that when there is rain the water will naturally flow away from the house rather than into its foundation. Done by a bull­dozer or other earthmoving machinery, this work is called cutting and filling, as the blade of the ‘dozer serves to cut off the tops of the high spots and fill in the low ones. If you are planning on landscaping work later, now is the time to give the yard at least an approximate shape while the heavy equipment is there filling in around the cellar hole.

The foundation won’t be completed in day; a week or two to complete the various steps is usual. But once your foundation is ready, the carpenters can begin their work.

Rough Construction



If you are simply reshaping existing space, you don’t have to worry about a big hole in your yard. You also won’t have to be concerned about the framing of the build­ing or the roofing (unless, that is, you’re adding a dormer or otherwise amending the existing roof, in which case you should be sure you read the roofing and siding sec­tion).

Yet almost every remodeling job requires some preliminary demoli­tion. Those kitchen cabinets you’ve always hated will be removed. Perhaps the cracked tiles in the old bath will be sledgehammered and shoveled into a dumpster.

Make a point of being present at the work site—or having your architect or designer be there—as demolition is about to begin. It’s essential that everyone understands exactly what goes and what stays. Sometimes the meeting of the minds you and your designer reached doesn’t get communicated clearly. Plans alone may not be enough, so you (or your designer) may want to apply spray paint or masking tape to guide the workers. Even if your general contractor understands, the laborer who actually wields the tools may not. Over the years, I’ve seen a lot of jobs where the wrecking bar removed or ruined something that was supposed to remain intact. The best renovations are those where you can’t tell where the existing structure ends and the new work begins. Don’t let a window frame or an old door you’re plan­ning to reuse get tossed into the dumpster.

Once the demolition has been completed, the process of building anew can begin. The carpenters will construct the wooden framing for any new walls, floors, or ceilings. In some municipalities, certain struc­tures are required to have walls constructed of brick, steel, concrete, or other materials speci­fied for fireproof construction. Most single- family homes, however, utilize a traditional wood-frame construction, so carpenters will handle the rough construction.

While the framing work is going on, you will probably hear some words that are not part of your usual vocabulary. A stud is a vertical wall  floor sup­port; a post is a larger vertical member, often at a corner; a beam is a large horizontal member that supports the structures above.

Framing doesn’t demand the kind of precise (and time-consuming) attention to detail that finishing work does, so inspecting the work site after the workers have been there only a day or two can be very satisfying. New spaces seem to emerge almost overnight, and you can suddenly get a sense of how the rooms will appear and relate to one another. With a small remodeling job, the demolition and rough framing may be completed in a day, but don’t jump to the conclusion that the job will get done much faster than expected. Framing is often uncomplicated and goes quickly. Most of the decisions will have been made already.

Sometimes the demolition and framing will take longer than expected. In the case of many older homes, only when the wall or ceiling surfaces are opened up in preliminary demolition are structural problems apparent. Your carpenter may uncover areas of insect damage or decay caused by dampness. That will mean the replacement of deteriorated structural elements that are required in the new design.

Structural problems may also result from poor construction many years earlier, or plumbers or other tradesmen who gutted members while retrofitting bathrooms or heating and cooling sys­tems. Shoring up structural weaknesses may be necessary. They’ll take time and probably cost you money as most esti­mates are based upon no unexpected obstacles.

Your job is not to supervise the men and women at work; the contractors and the subcon­tractors do that. Your job is to examine what’s been done, approve or disapprove, and determine when payment is due.

On the other hand, while the car­penters are constructing new walls, opening up new windows or doors, and doing other framing work, you and/or your designer or construction manager should spend some time measuring and inspecting carefully to be sure that the partitions as constructed coincide with the plans. I’d recommend, however, that you put your tape measure to use after hours. There’s no need to insult the carpenters, although they know as well as you do that, no matter how experienced they are, they’re still capa­ble of making a mistake. Walls do get built in the wrong place, openings set at the wrong height.

You may think there’s a discrepancy between what you see and the plans. You may find yourself very disappointed with something—perhaps you just hadn’t imagined the kitchen would feel so small. In either case, now is the time to raise the issue. Discuss the differences with whomever is supervising the construction. If your designer is in charge, ask him to have the hard conversation with the contractor/car­penter. But raise the issue as soon as you recognize it. Unbuilding gets more difficult with every nail, every board, every stage in the process. In a polite but firm fashion, raise the red flag, even at the risk of causing a small delay in construction.

Changes will probably cost you money, but this is your home. If there’ll be delays or added costs, ask yourself whether the problem will quickly fade—or will you be unable to forget about it and experience a pang of regret every time you walk into that room as long as you live in the house? As the old saying goes, speak now or forever hold your peace.

Speaking of old wisdom, if you believe in tradition, you may want to perform an ancient ritual at the time the ridge board is raised on your new roofline. (The ridge board is the uppermost horizontal piece of lumber to which the angled roof mem­bers, the rafters, attach at the peak of the roof.) Early colonists in North America placed an evergreen bough at the roof’s highest point. The evergreen was a symbol of permanence and an appeal for good luck.

Factory-Made Flooring and Roofing Systems


Most of the wood-frame houses built in the last hundred years have been assembled of dimensional lumber, the standardized two-by-fours, two-by-sixes, two-by-eights, and the rest that you encounter at your lumberyard. You shouldn’t be surprised to learn, given the finite number of trees to be harvested, that new products have been developed that take better advantage of the trees we have. Thus, a number of factory-made wood products have begun to appear at the construction site.

Perhaps the most common variety of prefabricated structural members are trusses. Trusses are carefully engineered arrangements of triangles that can carry large loads over broad spans. They’re most often used in home construction to form the triangular gable roof, but other roof shapes and even interior floors are being framed today using trusses.

Trusses use the inherent rigidity of the triangle. Most are assemblages of two-by-fours. At the same time that they conserve materials, they also give the designer the option of creating larger uninterrupted spaces. Trusses are fabricated elsewhere, delivered to the job site oh a flatbed truck, lifted into place by a crew or even a crane, and nailed in place much like traditional solid-wood joists or rafters. The costs are roughly comparable, especially when savings in labor are considered.

Laminated-veneer lumber
Made of thin layers (veneers, roughly Vio inch thick) of wood that have been glued together, LVL is extremely strong and stable. Unlike the veneers in traditional plywood, all the layers in LVL are glued together with the grain in parallel. This produces a very consistent and uniform product suitable for use as beams, joists, and headers.

LVL actually costs a bit more than solid lumber but there can be labor economies in its installation. The price may also come down as these products become more commonplace, but one argument for the use of LVL is the material’s uniformity (there’s less spoilage than with solid lumber, where a loose knot, check, or twist can render a piece unusable). Another is its strength—structural members made of LVL can reach across much tifoader spans. LVL can also be purchased in lengths of 60 or even 80 feet, allowing the builder to span an entire structure without overlapping joists.

LVL comes in two basic configurations. As their name suggests, I-joists are a cross between steel I- beams and traditional wooden joists. When looked at in cross section, they have the shape of the letter I The vertical portion is called the web, the horizontals the flanges. J-joists are made of LVL and can be used both as joists and rafters. Micro=Lams are structural lengths of LVL without flanges that are used for rim joists, headers, ridge beams, and other applications.

The advantage of all these members is they’re strong but light. One man can lift, and two men can position, lengths of 60 feet or more with ease. Trusses and LVLs are all very stable when kept dry in delivery and installation. Shrinkage is minimal, unlike with traditional kiln- dried lumber where shrinkage routinely separates baseboards from floors and cracks plasterboard walls when moisture content is too high. Trusses have the added advantage that their open structure makes the installation of wiring, plumbing, and HVAC systems easier.

Don’t be surprised if your designer specifies trusses or LVL in designing your addition, particularly if you are creating a broad open expanse within the house.

Advanced Framing Techniques

With the increased emphasis on saving the environment and costs, there is renewed interest in “advanced framing” construction techniques, which were proven effective more than a decade ago.

Advanced Framing


With the increased emphasis on saving the environment and costs, there is renewed interest in “advanced framing” construction techniques, which were proven effective more than a decade ago.

Advanced Framing Basics
Advanced framing is the name given to techniques designed to reduce the amount of lumber used and waste generated in a residential construction project and to improve a home’s energy efficiency.  Also known as Optimum Value Engineering, advanced framing includes such practices as building corners with two studs instead of three, which allows more insulation to be included.

The ideas have been known about for years, though the homebuilding industry has been slow to adopt them. A Natural Resources Defense Council handbook from 1998 included advanced framing among the ways to reduce waste of resources.

NRDC Senior Sustainable Building Specialist Kevin Mo says the techniques can be used as a package or separately depending on specific needs. The main objective is to use less lumber without compromising structural integrity so that more insulation can be put on the enclosure.

“The techniques are not rocket science but do take time for builders to adopt,” says Mo. techniques. “Now, more local building codes approve the techniques, and more contractors have gone through the learning curve. Builders are more familiar with the techniques and willing to apply the advanced framing techniques for energy efficiency.”

Proven in the Field
Advanced framing is one of many green methods Ferrier Builders & Ferrier Custom Homes of Fort Worth, TX, employs in both new homes and remodeling projects. “We have always specialized in extremely energy-efficient homes, with the first one back in 1982,” says Don Ferrier, chief executive officer. The company emphasized air sealing as well as reducing, reusing. and recycling long before the idea of “green builder” became popular.

The company works with the Building America research teams of the U.S. Department of Energy to employ cutting-edge and proven energy-efficiency techniques, including the advanced framing methods. Some potential subcontractors still balk at the idea of switching from standardz

techniques to advanced framing. “It’s not a difficult thing but it’s just enough different that we’ve heard people say ‘Never done that and don’t know if I want to,’ ” says Ferrier, who was named Green Building Advocate of the Year in 2007 by the National Association of Home Builders (NAHB).

“Studs 24 inches on center instead of 16, single top plate instead of double top plates, no headers on non-load-bearing walls—the differences are subtle,” but they add up, Ferrier says. For example, instead of two smaller headers, advanced framing would place one larger header that would allow for up to two inches of foam insulation that can increase R-value from 1.5 to 7.5.

Cost and Energy Savings
Kevin Morrow, NAHB program manager for green building standards, says the organization is doing all it can to increase builder education in all levels of green building. He suggests consumers look for a builder with the NAHB designation as certified green professional to ensure they are schooled in innovative techniques such as advanced framing.

According to the U.S. Department of Energy, advanced framing not only means the saving of resources, it also means savings for the homeowner. It estimates materials cost savings of $500 for a 1,200-square-foot house and $1,000 for a 2,400-square-foot house—a labor savings of three to five percent and heating and cooling costs savings up to five percent. The NRDC has estimated that using advanced framing techniques can reduce framing costs as much as $1.20 per square foot and reduce the amount of wood used for framing by 11 to 19 percent.

Here are several concepts to keep in mind when planning to use advanced framing on a project:

  1. Consider designing a home or remodeling project based on 24-inch modules. It makes the most efficient use of such building materials as framing lumber, wood sheathing, drywall, and trim that are typically stocked in two-foot dimensions.
  2. Consider how just one area, an exterior corner, can be changed with advanced framing. With advanced framing, insulation can be added in a commonly uninsulated area, an installed drywall clip can accommodate drywall and one less stud is used.
  3. Check with local codes first. Some advanced framing techniques may not be suitable for areas with high wind or seismic activity.
  4. Familiarize yourself with advanced framing and other green concepts before you start planning your home building or remodeling project. Section 2.1.2 of the NAHB’s Model Green Home Building Guidelines details some advanced framing techniques.

Pre-Cast Foundation System

An alternative to poured concrete, pre-case foundations have many benefits.

Precast Foundation


In Season Five of “Bob Vila’s Home Again,” the popular “Cabin in the Woods” project showcased a unique array of innovative building textiles and technology that saved time and money.  One product that continues to generate interest is the state-of-the-art precast wall and foundation system developed by Superior Walls of America.

The Superior Walls System consists of pre-cast, studded concrete walls. The ready-to-finish wall panels feature built-in plumbing and electrical access holes, and SWA crews can install an average system in about five hours, in almost any kind of weather.

Pre-insulated with DOW Styrofoam and sealed with Bostik Chem-Caulk, Superior Walls are manufactured to National Standards and recognized Building Codes with 5,000 psi concrete. This eliminates the need for additional waterproofing or tarring.

In the words of SWA literature, “Ten times stronger than a block foundation, the Superior Walls System is guaranteed to prevent water infiltration and moisture build-up. Because of its innovative design, Superior Walls keep homes warmer and drier than conventional foundations while adding valuable living space and increasing resale values.”

To enhance strength and durability, Superior Walls panels are manufactured with steel-reinforced concrete studs, rigid insulation, a reinforced top and bottom bond (footer) beam, and a 2-inch-thick concrete facing.

The bond beams and concrete facing are cast in one continuous pour. They connect to the studs by encapsulating vertical rebars and galvanized hooks and pins that protrude from the top, bottom, and back of each stud.

Pressure-treated furring strips are preattached to the inner face of each stud to provide a base to accommodate a variety of wall finishes. In addition 1-inch diameter holes are cast into each stud, allowing for the installation of wiring and plumbing.

The top bond beam is perforated with pre-formed 1/2-inch holes approximately every 24 inches to allow the bolting on of pressure-treated sill plates. The system is delivered to the jobsite with a built-in footer and is installed on crushed stone sub-footer.

The walls are pre-insulated with 1-inch DOW Styrofoam, with an R-5 rating. Additional insulation may be added to the 7-1/2-inch-deep wall cavity between the studs to increase the R-value up to R-26. A triple bead of Bostik Chem-Caulk provides a watertight sealant at the panel seams. Set 12 inches from the precast wall, a 4-inch perforated drain pipe assures a drier basement by collecting and channeling excess water away from the foundation.

Superior Walls are completely custom made and designed to accommodate door and window openings. Panels are normally formed in lengths up to 16 feet and standard heights of 4-foot, 4-foot 8 inches, 8-foot 2-inches, 9-foot and 10-foot, and can be cast to virtually any shape for unlimited design flexibility.

Installation Basics
Factory-trained crews can install an average foundation system in about five hours, regardless of most weather conditions. Backfilling can begin as soon as the floor is poured and the subfloor is properly attached to the top of the wall system. The panels come to the job site already cured, so construction may proceed immediately after installation.

Site Preparation and Installation Process
1. A 35 x 35-foot level area clear of overhead obstructions must be provided for the crane.

2. The basement must have an overdig of 24 inches at the bottom of the excavation.

3. The drainage system must be in place and functional.

4. Corner pins of the foundation must be clearly indicated.

5. Crushed stone must cover the entire floor area and be level to within one inch.

6. The builder must provide bracing materials for the wall system. Various lengths of 2x4s are preferred.

7. The site must be accessible for the delivery truck and crane. Check for mud, sharp turns, hills, bumps, trees, and overhead wires.

Cold-Weather Guidelines
1. Mix calcium with the stone all the way down to the virgin soil in an area of at least 30 inches wide around the footing.

2. Cover the area with plastic sheeting or other waterproof and nonporous material, extending two feet on each side of the center of the footing. Place stones or other heavy material along the edges to prevent air from getting under the plastic blanket.

3. Scatter at least 6 inches of loose straw over the blanket — more in severe freezing conditions.

These wintertime steps will keep the footing base stable and prevent weather-related delays. After the walls are placed, reapply the straw until backfilling is completed.

Radon Ventilation
Superior Walls can easily accommodate a simple and economical ventilation system to remove contaminated air and radon gas from the basement. Supplied and installed by the builder, a small in-line fan and piping system can be very effective. Special standard features of the SWA system add to the efficacy of this air exchange system.

The cast concrete panels offer a very low permeability rate, which is even further enhanced by the factory-installed DOW Styrofoam insulation. The crushed stone foundation allows for the free flow of air from all points of the excavation into the exhaust system beneath the floor.

Strengthen Your Roof with Trusses

Engineered roof truss systems even stand up to hurricanes.



After hurricanes ravaged Florida in recent years, building codes were strengthened to keep future damage to a minimum. Officials and builders have learned that keeping the lid on a house means forming a tight bond between the sail-like roof deck and the walls below. That job falls to the engineered roof truss system that holds it all together.

Trusses Surpass Traditional Framing
Carpenters used to use two-by lumber to frame into stringers and rafters. Engineers and architects now design roof trusses built of 2x4s in triangular configurations that are joined together with metal connector plates. The result is a cohesive roof truss that stands up to state, local, and national building codes. Trusses perform to such a high degree because the lumber is uniform in size, density, and quality, and metal connector plates ensure rigidity at joints.

Engineered trusses have been on the building scene for 35 years, a track record that impresses many builders and homeowners. Kirk Grundahl, executive director of the Wood Truss Council of America (WTCA), in Madison, WI, says homeowners can be assured their roof trusses are engineered to exacting design standards nationwide since manufacturers must meet the standards set by WTCA and the Truss Plate Institute (TPI).

Sean O’Connor of Robbins Engineering, in Tampa, FL — designers, plate fabricators, and truss system engineers — explains that roof trusses create a stronger roof structure because they are engineered using CAD (computer-aided design) design techniques and computer analysis for worst-case scenarios.

“Because every one of the roof trusses are engineered, it literally takes into consideration all the forces acting on the truss, from gravity loads to wind loads, seismic loads, and uplift loads,” O’Connor says.

Roof Trusses Allow Open Floor Plans
Trusses have many pluses, including their overall strength, ability to be placed quickly, and span capability. Since they’re built from shorter lengths of lumber, roof truss systems are typically less expensive to build than roofs with conventional framing.

Trusses are engineered to span larger distances than conventionally framed roofs. Since they transmit weight from the roof to the exterior walls, none of the interior walls needs to be load bearing. This opens up interior space and allows for many interior design options.

Wood, Steel, and Engineered Timbers
Roof trusses, historically composed of wood with metal connector plates, now have competition. As steel-framed homes catch on, so have all-steel roof trusses. O’Connor says that to date steel roof trusses are typically reserved for the light commercial and industrial markets, with wooden trusses still dominating home construction.

Engineered wood products such as I-joists have also made a big surge in the market. “They can be used almost like framing lumber, but unlike conventional lumber, they’ll span up to 60 feet in length,” O’Connor says.

Wood roof trusses with metal connectors can also be treated with fire retardant and have an “excellent fire rating,” according to O’Connor, “and from a budgetary and quality standpoint, are the price point winners.” When they are properly engineered and put together, the wood roof truss with low-cost connector plates will perform to engineered lumber parameters. “So they are a nice, low-cost solution to framing problems,” O’Connor says.

Coupled with hurricane straps for fastening the trusses to the walls, the roof system is typically better than any stick-built roof, according to O’Connor.

Roof Trusses Allow Open Floor Plans
Trusses have many pluses, including their overall strength, ability to be placed quickly, and span capability. Since they’re built from shorter lengths of lumber, roof truss systems are typically less expensive to build than roofs with conventional framing.

Trusses are engineered to span larger distances than conventionally framed roofs. Since they transmit weight from the roof to the exterior walls, none of the interior walls needs to be load bearing. This opens up interior space and allows for many interior design options.

Wood, Steel, and Engineered Timbers
Roof trusses, historically composed of wood with metal connector plates, now have competition. As steel-framed homes catch on, so have all-steel roof trusses. O’Connor says that to date steel roof trusses are typically reserved for the light commercial and industrial markets, with wooden trusses still dominating home construction.

Engineered wood products such as I-joists have also made a big surge in the market. “They can be used almost like framing lumber, but unlike conventional lumber, they’ll span up to 60 feet in length,” O’Connor says.

Wood roof trusses with metal connectors can also be treated with fire retardant and have an “excellent fire rating,” according to O’Connor, “and from a budgetary and quality standpoint, are the price point winners.” When they are properly engineered and put together, the wood roof truss with low-cost connector plates will perform to engineered lumber parameters. “So they are a nice, low-cost solution to framing problems,” O’Connor says.

Coupled with hurricane straps for fastening the trusses to the walls, the roof system is typically better than any stick-built roof, according to O’Connor.

Know Your Building Lot

Go over the ground and study site conditions before you plan your house.

Building Lots


In your mind you’ve got a dream house, but in reality you have a building lot. Before you get locked into a building plan, research your site, because site conditions affect your design and the cost to build it. No designer should draw house plans for you without a detailed site plan, and no builder should estimate the construction costs without knowing what’s under foot.

Gathering Information
It’s best to have complete site information before you build, but you can gather a lot of good data on your own before you hire a civil or geotechnical engineer. Ask neighbors; they’ll probably know if there’s a ledge, a high water table, or problem soils. Get a local soils map from the building department or local library. Take a good look at the site, noticing exposed rock, water plants, or new plant growth that may indicate fill.

Start with Soil
Since you may have layers of different soil types on site, your builder and designer need to know what’s there. The critical layers go from the surface down to about eight feet below the depth of your planned foundation.

Foundation codes are written for sand or gravel soils, which are the best natural soils for construction. Heavier silts and softer clays are not ideal and may require more than the minimum code requirements. Most building departments will want information on soils before they sign off on a permit; they may even require an engineer’s site report or stamp on your foundation design.

An engineering report is based on a site survey and test pit samples. If real problem soils are suspected, the engineer may do “soil borings,” but they are usually reserved for commercial projects.

Watch for Water
Quite often, the excavator discovers water when digging the foundation hole or test pit. This is not necessarily a problem, since water levels fluctuate from season to season in response to rainfall, drought, and melts. Engineers and site planners do, however, need to identify the water table (the depth where water sits year-round) and its high point. They do this by analyzing the color or “mottling” of the soil in the pit.

Foundation footings and basement slabs should sit above the water table so that groundwater will not put pressure on the foundation or cause a dampness problem. On a site with a high water table, you may prefer to build a shallow foundation, or bring in fill to raise the grade.

Drainage Is Essential
Soil drainage varies depending on the type of soil. Sands and gravels drain better than silts and clays, and this affects the project. If the native soil is sand or gravel, you can use soil from your excavation to backfill the foundation, placing it back against the foundation walls. But silts or clays, which don’t drain well, should not be used as fill because they tend to hold water against the foundation. This added pressure creates a structural load in addition to the obvious moisture concern. So if the original soil was a poorly draining silt or clay, it’s best to bring in gravel or sand for backfilling, and dispose of the original soil elsewhere.

Septic Planning
If your house needs a septic system, the water table and soil drainage are issues once again. Septic disposal or “leach” fields are usually four feet above the water table. You may need to build up with fill to meet that requirement, which is complicated and expensive since trucking clean fill is very costly.

Your septic permit will also depend on a “perc test,” which is done by filling a test pit with water and measuring the time it takes to drain. For a septic field to work, the wastewater has to seep through the “treatment zone” fast enough to dissipate easily, but slowly enough to give soil bacteria time to break down the wastes. Make sure your site will pass a perc test; otherwise, you can’t build there.

Building On Bedrock
Rock outcroppings on or near your property are a sign that there’s rock near the surface, commonly known as “ledge.” Blasting rock requires an expert, and costs far more than standard excavation—on the order of $20,000 a day. You may opt to forgo the full basement if your site has ledge, building instead on what you find.

The good news is that rock is strong. As long as the whole house rests on rock, settling is unlikely to be a concern. If you fill, put the whole house on engineered fill (preferably gravel); if you don’t fill, put the whole house right on the rock. At all costs, avoid uneven settling.

Get Down in Your Dirt

Study the soil of your lot before you build.

Testing Soil


Foundations rest on soil, soil pushes against their sides, and wet soil pushes water and humidity against them, so it’s hard to plan for a foundation without a basic understanding of soils. The average person thinks of soil as dirt. For engineers, soil is a complex material worthy of a lot of study. In fact, there are thousands of soil varieties, but the main categories are gravel, sand, silt, and clay. What separates them is basically the size of the particles. Gravel is made of big chunks; sand consists of grains as small as the width of a human hair; silt is made of still smaller particles that are nearly microscopic in size; clay has particles too small to see. Most soils are blends of these main types, with names like “clayey sand” or “sandy silt.” Soil also has air and water mixed into it, so compacting the soil with rollers, pounding or vibrating equipment densifies and strengthens it.

Getting Down to the Dirt
To be absolutely sure of your soil, you have to send a sample to a soils lab. If they find more than 12 percent clay, the clay will be analyzed for its behavior when wet. This is because clay can turn to liquid, reduce the soil’s bearing strength, and cause the soil to exert pressure on the foundation. On a large commercial project, soil “borings” are taken vertically in two-foot increments. On a residential project, builders often rely on instinct and rule of thumb, because some building departments don’t insist on a soils report. Unfortunately, it can be hard to identify a soil by eye, or to predict its behavior by guesswork. A soil that seems to have a lot of gravel or sand in it could still contain 20 to 30 percent clay. If it does, it’s going to act like clay, which can give your project poor drainage and plenty of problems.

Testing Basics
So, do some creative detective work on your site. First, walk on the soil. If you leave a boot mark, try driving a stake into the soil. Since it usually takes six or seven whacks to drive a stake into the ground, a stake that goes in with one or two solid drives probably indicates soil that lacks strength and needs to be compacted.

Next, if your site is already under excavation, take a handful of damp soil from the bottom of the excavation and ball it up in your hands. If it crumbles apart when you release it, it is a granular soil (with lots of sand or gravel). If it holds together, it’s a silt. If it stays in a ball when you drop it from two feet, it’s probably a clay. To be sure, you might also try rolling the ball of soil into a noodle or worm shape. If you can roll it into a pencil shape without having it crumble, consider it clay, and make sure your next call is to a soils engineer. If ever you suspect clay in your soil, a full workup will be in order. It’s always worth investing $1,000 or so in engineering work before you invest your life savings in a home site.

The Bottom Line On Soils
For home sites, the bottom line is pretty simple: You want soil that has good bearing capacity, exerts relatively low lateral pressure, and drains well, so that you can have a stable, dry foundation. The best natural soils for these purposes are sands and gravels. Silts and clays are fair, but the softest ones are poor. Then there are soils such as peat, expansive clay, and improperly deposited fill, which are so bad that they must usually be removed and replaced — often at considerable cost to you.