Category Habitat for Humanity International

Unless you arc building on a slab, yoiTlI prob­ably need to provide midspan support for the floor joists. Without additional support some­where between the sills, the joists can be over­spanned, resulting in a finished floor that sags

or feels bouncv. A friend once :ook me

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through his 18th-century home in rural Connecticut. The beautiful, hand-hewn floor joists in the basement were fascinating—dry, free from rot and termites—but far over­spanned. Upstairs, it felt like walking on ocean waves. Clearly, what was needed was some support to keep the joists from sagging and bouncing in the middle.

Codes req u і re a m і n і m u m оf 18 in. between the earth and the joists in a crawl space. These days, two systems. ire commonly used to provide midspan support for the joists: crib walls (also called pony walls) and post-and-girder systems. A crib wall is just a shortened version of a regular stud wall and is supported along a continuous concrete fool­ing. With a post-and-girder system, a solid or built-up girder (also called a beam) is sup­
ported by posts every 6 ft. or so, depending on code. The girder usually fits into a recess or pocket where it meets the foundation wall, loined to the girder by metal connectors or plywood gussets, the posts bear on concrete piers (see the illustration on p. 44).

In both these systems, the joists rest on and are nailed to the top support member. The width of the joists and the length of the span determine how much support is needed. With 2×6 joists, for example, posts and girders are often placed every 6 ft. With 2x12s or engi­neered 1-joists, only one support in the center may be needed.

Crib wall construction

lust in case a moisture or termite problem develops in the future, I like to build crib walls with pressure-treated wood. To determine the length of the crib walls s. uds, first bolt the walls bottom plate to the footing. Then tightly stretch a string above the crib walls bottom plate and across the mudsills installed on the stem walls. Set two pieces of top plate stock on the bottom plate. The distance between the top plate stock and the string is the length of the crib wall’s studs (see the lop left photo on p. 60).

BUILD A CRIB WALL. Also referred to as a pony wall, a crib wall—a short, stud-framed wall—is one way to provide midspan support for joists that extend over a crawl space. After bolting the wall’s bottom plate to the footing, stretch a line over the sills to measure the length of the crib
wall’s studs (see the left photo above). Place two pieces of top plate stock on the wall’s bottom plate and measure up to the line. Toenail the studs to the bottom plate, spacing them 16 in. O. C. (see the right photo above). [Photos Memo Jasso.]

FINISHING THE WALL. After nailing both top plates, fasten plywood or OSB sheathing to one side to give the wall shear strength. Hold the bottom edge of sheathing panels V? in. off the Concrete. [Photo Memo Jasso.]

Toenail the studs to the bottom plate, spac­ing them 24 in. o. c. but leaving a 30-in.-wide opening somewhere in the wall so that plumbers, electricians, and others can got from one side of the crawl space to the other. When toenailing the studs to the crib wall’s bottom plate, you can drive either four 8d toe­nails or three 16d nails per stud. If you’re using a pneumatic nailer, make sure von fol­low the safety guidelines explained on p. 63.

Once the crib wall’s studs are in place, nail on the two top plates. Drive a pair of 16d nails through the first plate into the top of each stud. Secure the double top plate with a single 16d nail at each stud location, and toenail the plate’s ends to the sill on the foundation wall at each end of the house. 1 like to sheathe one side of a crib wall with pressure-treated ply­wood (my first choice) or OSB to provide
good lateral bracing (see the bottom photo on the facing page). Be sure not to sheathe over the opening you framed in the wall. As an alternative to sheathing a crib wall, you can stiffen it with 2x diagonal braces nailed to the top and the bottom plates and across at least one stud.

Build a post-and-girder system

If you’re using pressure-treated posts to con­struct a post-and-girder system, the base of the post can be anchored directly to the top of its concrete pier. Most piers these days are precast units that come with metal straps to anchor wood posts or pads to the lop. Secure a 11 in.-thick pressure-treated pad to the lop of the pier if the posts will be cut from untreated lumber. You can measure for the post’s length just as you measured for the crib

Select an 18-in. by іУг-іп. by Vs-in. metal plate strap.

Cut a notch in one end of the strap so that it will fit around a Уг-іп. or 5/s-in. bolt. From the center of the notch, measure back 3!/г in. for a 2×4 plate and 5V2 in. for a 2×6 plate. Drill holes at those points and insert 3/i6-in. by 3/Vin. stove bolts. Put a bend in the plate strap to make it easier to use.

A bolt-hole marker makes it easy to transfer the bolt location to the sill in preparation for drilling a hole.

Install sill seal and termite shields

Sweep the foundation clean of debris, then put down a layer of sill seal insulation where the sills will he located (see the photo on the facing page). Sill seal does just what its name says. As an alternative, you can run two heavy beads of silicone caulk between the sill plates and the foundation. This also prevents cold air leaks between the foundation and the sill. In areas where termite infestation is a possibility, you’ll also need to lay down a termite shield over the foundation bolts and under the sill. As shown in the illustrations on p. 46, the shield edges must extend beyond the founda­tion (including the foundation insulation) and the sill.

Place the sills over the bolts, put on the washers and nuts, and tighten the nuts with a crescent wrench, taking care to keep the inside edge of the sill on its layout. Note: When working on a slab, drill holes n the plates but leave them unbolted until after the wall is raised (see chapter 4 for details).

If the measuring work you did at the beginning of this step told you that parts of the foundation were out of level, you can expect the sills to be that way, too. To correct slight discrepancies (up to A in. or so), you can insert pressure-treated shims underneath the sills. For larger errors, it s best to call in a concrete contractor.

But here’s some good news: If von know how far off it is, yon can usually make the appro­priate corrections when installing the sills (see the sidebar on the facing page). It’s worth it to make the sills as straight, parallel, square, and level as possible. Otherwise, the mistakes made at this preliminary stage tend to become even more troublesome further down the line. Here’s how to check the foundation:

STRAIGHT. Check the walls for straightness bv stretching a dry line (string) from comer to corner. At this point, you just need to know­how straight the top outside edge of the foun­dation is, because you’ll be measuring in from this edge to locate the sill.

PARALLEL. Measure across the walls at both ends and in the middle. All three measure­ments should be the same. 1 use ‘/ in. over 20 ft. as the tolerance limit for parallel.

SQUARE. Plus or minus lA in. over 20 ft. is the tolerance that I use for square walls. You can check any rectangular foundation for square simply by comparing the diagonal measure­ments, which should be equal. When that isn’t possible, use the 6-8-10 rule to check for square corners. Measure 6 ft. in from a corner on one side and 8 ft. on the other side (see the photo above). Then measure between those two points. If the corner is square, the

POSITIONING SILLS ON THE FOUNDATION

ABC

Sill plates can be set flush with the edge of the foundation (A) and the siding nailed directly to the walls. When sheathing the house frame with OSB or plywood, though, hold in the sill plates l/z in. (B). When using rigid foam to insulate a basement or a crawl space (C), position the plates so that the outside face of the sheathing is in plane with the outside face of the foam.

hypotenuse of the triangle should be 10 ft. For smaller buildings, 3 ft. on one side and 4 ft. on the other should yield a 5-ft. hypotenuse. On a large building, use measurements of 12 ft.,

16 ft., and 20 ft.

LEVEL. 1 like to check a foundation for level with a builders level (especially one with a laser beam) set on a tripod. If you don’t have one of these available, an inexpensive water level will work fine (see the illustration on p. 33). The walls should be level to within Vi in. over 20 ft.

Determine the sill’s position

Depending on what you find after measuring the foundation as described above, you mav

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need to adjust the sills position using some of the techniques explained in the sidebar on
p. 34. The sill plates are often bolted flush to the outside of the foundation, but there are variations vou may want to consider (see the illustration above). For example, when the walls will he sheathed with З-in. plywood or OSB, it’s best to hold the plates V: in. inside the foundation. This puts the sheathing (lush with the foundation and allows the siding to lap down over the concrete.

The sills must be installed along snapped layout lines on lop of the foundation walls. (If you’re building on a slab, the layout lines will be on top of the slab.) The lines identify where the inside edge of the sill will fit.

Taking the width of the sill lumber into account (3V: in. for a 2×4 sill, 3/ in. for a 2×6), snap chalklines around the perimeter to indi­cate the inside edge of the sill (see the photo on p. 34). Make slight adjustment in the posi­
tions of the chalklines, if necessary, so that the sill is straight, square, and parallel.

Locate and drill bolt holes

Anchor holts sometimes come out of the foundation at odd angles. You can straighten bent bolts with a length of pipe, as shown in the photo at right. Then set long, straight, pressure-treated sill hoards in place for mark­ing and drilling. You can use a square and a tape measure to lay out the bolt hole locations on the sills, but it’s a lot faster to mark the hole locations with a boll marker (see the photo below). You can make a bolt marker or buy a ready-made version (see the illustration on p. 58 and Resources on p. 278). To use this layout tool, place each plate directly on the inside of the chalkline.

Once the bolt locations are marked, set the sill plates on blocks of wood or sawhorses and drill the holes. Use a T-in. bit to make holes for Tin. bolts. For X-in. bolts, use a /Tin. bit.

A LONG PIPE STRAIGHTENS A SHORT BOLT. A length of l-in.-dia. pipe straightens any bolts that may have been bent during (or since) the foundation pour. [Photo Roger Turk.]

A BOLT MARKER COMES IN HANDY. Use a bolt marker to transfer the bolt locations to the sills so you can drill the bolt holes accurately. [Photo by Roe A. Osborn, courtesy Fine Homebuilding magazine. The Tciinton Press, Inc.]

Some important carpentry work is about to begin. Whether you are building on a concrete slab, over a crawl space, or over a full base­ment, the first wooden member that is laid down is called a sill, mudsill, or sole plate.

T his sill is commonly a pressure-treated 2×4 or 2×6 attached directly to the foundation with anchor bolts embedded in the concrete. Occasionally, it is attached with hardened concrete nails or steel pins shot through the sill and into the concrete by a powder – actuated nailer.

Most codes require that anchor bolts be located I ft. from each corner of the founda­tion, 1 ft. from the ends of each sill plate, and a maximum of 6 ft. o. c. everywhere else. These are minimum requirements. Builders living in earthquake or high-wind areas often use %-in.-dia. anchor holts rather than /Tin. bolts and reduce the spacing to 4 ft. o. c. or less. As mentioned in chapter l, its important to check with the local building inspector to ensure that the house you’re building meets or exceeds code.

Check the foundation first

Unfortunately, you can’t assume that your foun­dation is straight, parallel, square, and level.

Foundation insulation isn’t used in mild cli­mates. But in areas with frigid winter months, il uni improve interior comfort and save on heating costs. Even though it’s not required by code in many areas, it’s definitely worth installing wherever prolonged freezing tem­peratures are expected. You can install insula­tion on the inside or outside of a crawl space or basement wall. Exterior insulation, in the form of rigid foam boards, is glued to the foundation walls before backfilling. Where they’re exposed above the finished grade on the exterior, insulation boards must be pro­tected with siding material or stucco. It’s important to remember that ary type of foun­dation insulation can provide a hidden pas­sageway for termites and other insects to enter the house. Make sure you cut off this passage­way bv installing a termite shield beneath the sill. As shown in the illustrations on pp. 46-47, the shield should be installed between the top of the foundation and the sill.

Drainage around the foundation

After you’ve taken care of the details men-

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tionedabove, you can begin backfilling around the foundation. Along the looting, install perforated drainpipes in a bed of gravel several inches thick. Cover the pipe with at least several more inches of gravel. To prevent
the drainage channel from silting up, cover the top layer of gravel with filter fabric before backfilling it with soil.

WHEN I WAS STUDYING at UCLA in the early 1950s, I lived in a small house that was held together by stucco on the outside and plaster on the inside. The wall framing had long been devoured by families of termites. Today, a number of defen­sive strategies are used to deter termites. Check with the building inspector and with builders in your area to find out which of the following strate­gies are used locally and how they work with differ­ent types of foundations.

Keeping wood dry. Termites like wet wood. Scrap wood buried at a job site can attract an infes­tation. And once they’re finished with that Lumber, they’ll look for other wet wood, such as wood siding in contact with the ground or moisture-laden floor joists in a damp crawl space. Eliminate the supply of wet wood and termites will be motivated to look elsewhere.

Pressure-treated wood. Today, most houses are required to have at least some wood that ter­mites don’t eat. Pressure-treated wood qualifies, but on most houses it’s used only as the mudsill atop the foundation. A more extensive use of pressure-treated wood (in the joists over a crawl space, for example) provides good protection in termite-prone areas.

Pesticide treatment. A licensed pest-control contractor can apply termiticide (termite-targeting pesticide) around footings and foundations before backfilling to create a barrier that deters insects.

Termite shields. This metal flashing is installed between the top of the foundation and the mudsill. The shield makes it more difficult for termites to build their earth-tone access tubes between the ground and the floor framing. The shield also makes the tubes easier to spot curing an inspection.

be applied. Asphalt-type coalings are popular because they are inexpensive and have been used for manv years. More effective and more expensive coatings are also available and should be considered when you’re building in soil that stays wet for extended periods of time. No matter how good a waterproof coat­ing is supposed to he, it shouldn’t be your only line of defense against under-house moisture (see the sidebar on p. 48).

INSULATED CONCRETE FORMS (known as ICFs) offer builders an easy way to build insulated con­crete walls for crawl space and basement founda­tions. Made from polystyrene or another rigid foam, these forms are designed to stay in place; they aren’t stripped off like standard forms.

It doesn’t take a lot of building skill to stack these blocks properly. On a recent job in Oregon, we snapped chalklines on the concrete footing to mark where the first course of form blocks would fit. We then started from the corners and laid two courses of blocks to form the crawl space walls.

With four of us working, it took less than two hours to lay the blocks.

Polystyrene blocks interlock, so very little extra bracing is needed to hold them in place as concrete is poured into them. A horizontal 2×4 screwed to the outside or inside of the wall helps hold the forms straight. Drive a stake in the ground every 4 ft. or so, and run a brace between the stake and the horizontal 2×4. This will keep the walls straight

throughout the pour. To strengthen the wall and prevent the forms from floating up and away, tie together a network of horizontal and vertical rebar, as shown in the photo above.

There are some concerns with ICF walls. The foam can offer a hidden pathway for subterranean termites. To avoid this, install a metal termite shield under the sill plate. Also, the foam surface is rather soft and can be easily dented and gouged. To prevent this, cover the outside walls with 2-ft. by 8-ft. fiber-cement panels.

lion project, and there’s nothing wrong with that choice. The important thing is to begin building on a base that’s level, square, and guaranteed to remain solid and stable for manv vears to come.

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STEP1 Form and Pour the Footings

Thick, solid, and strong, footings evenly spread the weight of the house (and every­thing inside it) over a wide area, ensuring that the finished house does not settle. With some slab foundations, it’s possible to pour the foot­ings and the slab at the same time. In other cases, the footings and the slab must be formed and poured separately. In many areas, a footing inspection by the building depart­
ment is required; this must be done before the foundation walls are buil:.

l ootings must be set on solid, undisturbed

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earth, not on fill dirt. Local soil conditions determine the depth and design of footings.

In areas of the country where the ground freezes solid in the winter, footings must extend below the frost line, which can be 4 ft. or deeper in northern regions. This prevents the freeze-thaw cycle from moving the foun­dation, cracking it, and causing damage throughout the entire house. The building department in your area will know the fooling depth that is required. They’ll also know about local soil conditions that may require a larger size footing or the use of rebar (steel reinforcing rod) in the footing.

Forms for footings

Footings are typically pouted in temporary forms constructed from plywood or 2x lum­ber. Wood stakes and braces hold the forms in position. The top edges of the footing forms must be level, and the footings must be set to the dimensions specified on the plans. A ready-mix truck is called in to fill the footings with concrete. If the site conditions make it difficult or impossible for the truck to gel close to the forms, a mobile concrete pumper can he brought in to pump the concrete from the truck to the forms. Check with your build­ing department about code requirements for footings. It also mav be necessary to embed vertical rebar in the footings so that the upper part of the reinforcing rods can extend into the foundation wall.

Pads are poured

It’s common practice to pour any pads required in the plans at the same time the footings are poured. In a crawl space founda­tion that includes a posl-and-girder frame­work, poured concrete pads provide a base for concrete piers and wood posts (see the illus­tration on p. 44). A common si/e for these pads is I b in. square by 8 in. deep. If you’re building a basement foundation, pads are also required to support each post or Lallv™ col­umn. ‘These pads are poured below the level of the basement floor and will be covered when
the slab floor is poured. If a wall will provide midspan support for joists, a continuous foot­ing is poured instead of separate pads.

STEP 2 Build the Foundation Walls

The Charlotte house has concrete block walls. With a crew of helpers to move blocks and mix mortar, an experienced block mason can erect a simple crawl space foundation wall in just a couple of days. However, in many parts of the country, poured concrete walls have surpassed concrete block walls in popularity.

Subco n tractors—specia I isls wh() have the equipment and experience to do the job quickly and, hopefully, with a high degree of accuracy—often form and pour concrete walls, if a foundation contractor arrives in the morning with a truckload of wall forms and rebar, he or she will probably have everything erected before the end of the day. Don’t forget to have the forms inspected before the ready – mix truck arrives to fill them with concrete.

Forms are usually stripped a day or two alter the pour. It takes about a week for con­crete to get its first hard set, but you can begin to lay out and install the sills as soon as the forms come off. Even though you may not be forming and pouring the walls yourself, it’s useful to know about some aspects of the process. This applies whether you’re building

Without a floor on top, there’s just a big empty space inside the foundation walls. Getting all the joists in place seems like a huge job. . .

The masonry walls look square and level, but we have to check them anyway. . .

We use pressure-treated 2x6s for the sill plates. . .

FASTENING MUDSILLS WITH METAL STRAPS

the foundation walls with concrete block or with insulated concrete forms.

Anchor bolts and tie-downs

Regardless of the type of foundation, anchor bolts are required around the perimeter to hold the sill plates and the walls securely in place. In earthquake and hurricane zones, the building code may call for additional hold – downs, such as metal straps that are embed­ded in the concrete and extended to the sills, rim joists, and wall framing (see the illustra­tion at right). Most codes require that a long piece of rebar be planted in the concrete near the planned location of the main electrical panel so that it can be used as a ground for the electrical system.

Beam pockets

Beams or girders that tie into the foundation usually do so by means of pockets built into the foundation walls (see the illustration on p. 44). If a post-and-girder system is planned fora basement or a crawl space foundation, the beam pockets are located in the end walls, inline with the concrete piers whore the posts will be installed. Its critical for the pockets to be correctly sized and located as the founda- tion walls are built. To hold a 4×6 girder, the pocket should be A1/’ in. wide and 5Vi in. deep. This provides clearance between the girder and the concrete so that moisture in the con-
crelc doesn’t seep into the wood, potentially damaging it. The 5!Tin. depth also allows a pressure-treated 2×4 shim to be installed beneath the girder, bringing its top edge flush with the sill.

Pockets are cast into poured concrete walls by fastening pocket-sized wood or rigid foam blocking inside the forms. In a concrete block or IСI wall, pockets are created as the walls are laid up.

Once they’re installed, we begin with all the joists. . . There’s a rhythm to rolling the joists up onto their layout lines ond then anchoring them in place by driving noils through the rim joists. . .

Before long, it’s time to start installing the floor sheathing. We’re already looking forward to wall framing.

STEP 3 Backfill around the Foundation

The foundation is ready for the floor framing work to begin. Bui the job site isn’t. Back­filling against the walls restores at least some of the sites original contour, making it safer and easier to move around. II you’re building a house with a full basement, the backfilling process is usually delayed until after the first floor is framed and sheathed. Because they

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are taller, basement walls need the extra rigid ity provided by the floor framing to ensure that backfilling doesn’t damage the founda­tion. This isn’t a major concern with crawl space walls, so it’s good to backfill now. But first, it’s important to take care ol the follow­ing details.

Termite protection

In areas where termite infestation is possible, some builders elect to call in a licensed pest – control contractor to apply pesticide around the base of the foundation before backfilling against the walls. However, if you don’t like

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the idea of putting chemicals in the soil, there arc other termite control options to consider (see the sidebar below).

Foundation coatings

It’s important to keep moisture out of the basement or crawl space area, as well as out of the masonry wall itself. Foundation coatings help accomplish this. Concrete block walls are often parged-covered with a layer of mortar that conceals and protects the joints between the blocks. A waterproof coating should also

WE NEED WATER. We just don’t need it in our base­ments or under our floors, causing dampness, mold, and rot. We may not be able to hold back the Mis­sissippi when it floods, but we can control most of the rainwater that falls around our homes. Follow the guidelines below and you’ll stand a good chance of keeping water on the outside of your foundation.

1. Don’t build on the lowest part of the lot.

2. Seal all holes around the pipes that go through the concrete.

3. Install perforated drainpipes at the bottom of the concrete footings around the outside of the founda­tion (see the photo at left).

4. Coat the foundation walls with a suitable damp-proofing or water­proofing treatment. Check with builders in your area or the local building department to find out which foundation coatings are rec­

ommended. Tar coatings are inexpensive but not as effective as more recently developed waterproofing treatments.

5. Compact loose fill as you backfill around the foundation, but be careful, because excessive com­paction can damage masonry walls. Make sure that the finished grade (ground level) slopes away from the foundation. But remember that loose fill can settle. A finished grade that slopes away from the house may later slope toward the house shojld set­tling occur.

6. Use gutters and downspouts to manage high roof water runoff. Make sure you keep gutters unclogged and install downspouts to direct water away from the house.

7. Get advice from your building department. The time to protect your house from water infiltration is while you are building. Fixing a leaky basement or a damp crawl space after the house has been built can be very expensive.

benefit of extra room below the main living area. Of course* basement foundations are more expensive than other types, and the living space they provide can be damp and lacking in natural light. To overcome these dis­advantages, some basements incorpo­rate window wells—windows located just below grade level—surrounded by a metal or concrete retaining wall on the outside of the foundation. When a basement will he used as a living space, the foundation walls must be waterproofed on the outside, insulated on the outside or on the inside, and finished on the inside. Today, many basement foundations are built with poured concrete walls. Other builders construct basement foundations with concrete block.

Concrete Block vs. Poured Concrete Walls

If you have a large crew, like we do on most Habitat projects, it makes sense to build foundation walls with con­crete block. All you need are a couple of experienced masons and enough volunteers to keep them supplied with blocks and mortar as they work their way around and up, course by course. A crawl-space foundation can be com­pleted in just a couple of days. When building walls with concrete block, it’s
easy to form beam pockets and open­ings for vents, doors, and windows. And by switching to a smaller block just below the planned grade level, you can create a ledge for brick veneer.

If you want a full basement and you don’t have a Habitat-size crew, poured concrete is the way to go. Most basement foundations are built with poured concrete walls that are formed and poured by foundation contractors.

This can exert tremendous pressure on a foundation. I have seen how this expansive action moves footings, cracks slabs, and causes extensive damage to a house. When builders are aware of the potential problems with day soil, they can take precautions to avoid dam­aging effects. (See the drainage guidelines dis­cussed in the sidebar below.) I have worked on sites where several feet of clav soil were removed and replaced with nonexpansive soil, which was then compacted before the footings were poured.

Foam forms are worth considering

If vou haven’t done so already, take a look at the possibilities offered by insulated concrete forms (ICFs). These lightweight foam forms are easv to handle and assemble, and they stay in place to provide wall insulation after the foundation wall is poured (see the sidebar on the facing page). With an ICT system, lay­ing up foundation walls doesn’t demand back-breaking labor. Even so, many home­builders still prefer to hire a foundation con­tractor to take on this phase of the construe-