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Most professions have their long-held truths, and one in the building trades is that no house is ever really finished. As a house goes up, its owner typically keeps getting new ideas, and the builder, after calling most of them impractical or too ex pensive, selectively incorporates a few. Finally, when the house is more or less habitable and whatever shared enthusiasm there’s been between client and builder has degenerated into animosity, the builder tires of the project and stops showing up, the owner relaxes his standards and decides to make do, and the absence of momentum comes to be interpreted, willy-nilly, as completion.
The process of designing a building is seldom really finished either. It’s apt to begin as a surge of wishes and fantasies that precede even the first crude drawing, and , long after the building is up, it tends to tail off as a series of melancholy afterthoughts riddled with phrases like "If only I’d ..." and "Maybe I could still ...." and "What would it take to...?" Somewhere in the middle of all that comes the creation of a working sketch, but it’s virtually essential to do some constructive daydreaming first. Wishes and fantasies are fine, but while you’re having them you might also make yourself comfortable with the principles of house construction, give some thought to site selection, and explore with your building department whether putting up an outbuilding on your property is even legal.
You may also want to do some realistic deliberation about allocating time and money—let’s say, very very arbitrarily, a dozen or more weekends and a couple of thousand dollars. And, yes, there are all sorts of ways you can shave money off the construction budget; as with most things, time and money have their usual inverse relationship. If, for instance, there’s a dump nearby, you may be able to scavenge some perfectly usable building materials. I met someone not long ago who made it a point of honor to build an outbuilding entirely from materials he found at the local sanitary landfill. Of course that kind of scavenging took time and patience, and I need hardly say that the materials didn’t turn up in the sequence they were needed.
By and large, decisions about time, money, the size and look of the building, where on your property it will wind up, and how to please your building inspector are ones you’ll have to make yourself. But decisions can be wise or foolish, and a certain amount of preparation can steer most of them toward being good ones. So if you already know how a frame house is put together and what its basic parts are called, you can either skip the next section or read it just to make sure we’re talking about the same thing.
SOME ESSENTIALS OF FRAME DESIGN
Basically, a frame house is one that’s supported by its walls. The walls, that's , do more than just enclose the house; they also hold it up. This contrasts with, say, post-and-beam construction, in which most of the weight of the building sits not on its walls but on horizontal beams supported by vertical posts inside the building. You commonly see post-and-beam design in barns, where the exterior walls are often too tall and flimsy to be relied on for support and where, because of the large spaces a barn has to enclose, there aren’t enough interior walls to support the lofts and large roofs that barns generally have.
Sometimes residential buildings combine frame design with post-and-beam, especially if they have a very large downstairs space—the living room, let’s say. The rest of the downstairs, composed of smaller rooms, would be crisscrossed with enough walls to support the upstairs (which is why those walls would be called “bearing walls”; they bear the weight of the story above). But the big living room, being an expanse uninterrupted by such walls, might have to be spanned overhead by a number of beams supported here and there by posts.
The outbuilding we’ll be putting up, however, relies solely on its walls for support, so it’s of pure frame design. Frame construction is probably the easiest kind for the beginner be cause structural members are comparatively light and easy to join together. It also requires only a minimum of engineering, and its basic principles can be mastered—make that “comprehended,” since mastery is somewhat beyond the scope of this guide—fairly swiftly.
We’ll start from the bottom and work our way upward.
The lowermost—and normally the most massive—horizontal members of a standard frame structure are the girders. They usually run the length of the house, and in full-sized houses they’re ordinarily doubled or tripled 2x12s. If the house has a concrete basement or crawl space, their ends often sit in depressions molded into the concrete called “girder pockets.” And if they span any appreciable distance they’re usually supported at regular intervals by cylindrical steel posts called “Lally columns.” (The post-and-beam principle intruding once again.)
The boards laid horizontally along the tops of the foundation walls are called “sills” or “house sills.” They’re usually bolted to the foundation, and because they transfer their load directly to the foundation they’re generally thinner than the girders. The top surfaces of the sills are level with the top surfaces of the girders, and for all practical purposes they function just as girders do.
Now, set at right angles across the tops of the sills and girders, come the floor joists. They’ll most likely be 2x10s or 2x8s or even 2x6s, depending on how much distance they have to span. If construction is conventional, the joists will be spaced at 16” intervals. Since they’re sitting on their short side (the 2” side rather than, say, the 10” side), there’s the chance they could twist, so if they span any appreciable distance between girders or between girder and sill, the joists will have either wooden or metal “bridging” nailed between them. The simplest bridging consists of sections of the same size boards as the joists them selves. An alternative method is called “cross-bridging,” in which wood or metal struts are nailed crosswise between the joists.
Probably the ends of the joists will be boxed in. That is, if the joists are, say, 2x8s, there’ll probably be lengths of 1x8 lumber (2x8 if the builder’s been generous) nailed to their ends. The top surfaces of the joists, together with the top surfaces of the boxing, form a level plane, and nailed down onto it are sheets of plywood, usually “ or thicker, that constitute the house’s subfloor. Taken together, the sills, Lally columns, girders, floor joists, boxing, and subfloor constitute what’s called the “deck.” During the building of a frame house, the completion of the deck is a milestone. Everything from here on in (except for any brick or masonry chimneys) will rest on, and therefore be supported by, the deck.
Next the walls are laid out on the subfloor. In most conventional construction—and for simplicity’s sake we’ll be conventional—the walls are framed with 2x4s, so 2x4s are placed on their flat side (i.e., the 4” side) around the perimeter of the deck where the outside walls will stand. More 2x4s are laid where the interior walls will stand. Gaps are left for the interior doors, and when all these 2x4s are in place they become an actual-size floor plan for the first story of the house. These bottom members of the walls are called “sills” too, but they’re wall sills as op posed to the house sills we spoke of earlier. (They’re also called “soleplates.”)
Next, the vertical members of the walls, also 2x4s, are erected on the sills. These vertical members are called “studs,” and they’re cut to give the desired ceiling height, normally around 8’. Like floor joists, they’re spaced 16” apart, and wherever possible they’re placed directly above a joist. This procedure— keeping the studs over joists and not between them—is called “stacking,” and it ensures that the upstairs floor, if there is one, will have a minimum of bounce.
Nailed horizontally across the tops of the wall studs is a double row of 2x4s called “plates” (sometimes called “top plates” or “wall plates” as distinct from “soleplates”). Sometimes, be cause of the doubling of the 2x4s, they’re called “double plates.” The plates are configured pretty much like the sills, and often what carpenters do before nailing up the studs is lay out the plates directly atop the sills to make sure they match. Then, wall by wall, they lift the plates off the sills and nail the studs up between them.
If the house has an upstairs floor, a second set of floor joists is nailed across the downstairs wall plates. The joists are sup ported at their ends by the exterior walls and along their lengths by whatever interior walls they cross. If they happen not to cross any interior walls and still need support along their lengths, the house may have additional floor girders to hold them up. A second subfloor is then nailed onto the upstairs joists, and now there’s an upstairs deck on which to erect the second-story walls. Those walls, in turn, culminate in the upstairs plates, so, whether there’s one floor or two, we still end up with a set of plates on which we have to build a roof.
The basic structural members of a frame house roof are called “rafters,” and their purpose is to span the distance between the top plates of the exterior walls and what’s called the “ridge- pole.” The ridgepole—actually a board and not a pole—is the horizontal member that goes along the peak of the roof, and the upper ends of the rafters are cut at an angle so that they butt the sides of the ridgepole cleanly. The rafters of an ordinary house are likely to be 2x6s, 2x8s, 2x10s, or even 2x12s, de pending on what the distance between the plates and the ridge- pole is. For several reasons, building codes permit a 2x8 rafter to span a greater distance than a 2x8 floor joist. Not being a floor, the roof of a frame house doesn’t have to support pianos, washing machines, refrigerators, or bathtubs full of water. (Yes, it does have to support snow and the occasional roofer, but on a load-per-square-inch basis, both are feather-light compared to a full cast-iron bathtub.) Also, even if there’s a heavy snow load, the slope of the roof—and starting now, let’s get serious and refer to a roof’s slope as its “pitch”—the pitch of the roof will aim some of the load downward onto the walls. Exceptions to this are flat roofs, which don’t have any pitch, but, questions of structure aside, flat roofs are notoriously leaky, so for now we won’t even consider them as possibilities.
Let’s stay with rafters for a moment, because of all the structural members of a frame house they’re the most complex. Since their upper ends are cut off at an angle other than 900, the length of the cut is greater than the width of the board. If we’re speaking of a 2x6 rafter, the end cut might be around 8” long. Consequently, the ridgepole into which the rafters butt would be a 2x8, not another 2x6. That way the ridgepole is butted by the rafters along the entire length of their end cuts, which gives a result that’s more pleasing both structurally and aesthetically.
Unlike their upper ends, however, the lower ends of the rafters seldom butt directly into the plates. If they did, the roof would have no overhang at all, and rainwater would drip down along the outside walls and windows. Instead, each rafter usually has a notch cut into its underside about a foot or so from its lower end. The notch is called a “bird’s-mouth,” and the two sides of the notch correspond to the width and thickness of the wall plates. When the roof goes up, the rafters are arrayed so that their bird’s-mouths sit flush onto the plates of the outside walls. (If you crave more terminology, the side of the bird’s-mouth that seats horizontally onto the plate is called the “seat cut,” and the side that’s vertically flush with the outside of the plate is called the “heel cut.”) The distance between the bird’s-mouths and the true ends of the rafters is the amount of overhang. Like most other framing members, the rafters are spaced 16” apart, and when they go onto the plates they’re stacked directly above their corresponding studs.
The lower ends of the rafters are usually sawn off with two cuts, which makes them appear to come to a point in the manner of the pickets on a picket fence. The cuts are angled so that when the rafters are put up, one cut is perfectly horizontal and the other perfectly vertical. That makes it possible to nail a board along the vertical cuts of all the rafter ends and another board along the horizontal cuts, thereby sealing up the lower edges of the roof. The boards nailed along the vertical cuts at the lower ends of the rafters are called the “fascia,” and the boards nailed up into the horizontal cuts are called the “soffits.” So, if you didn’t already, now you know what soffits are.
In most houses, sheets of “ plywood are nailed down onto the rafters to become the roof decking. Then roofing felt—a paper-like substance saturated with tar—is usually nailed over the decking, and the final roofing material, generally shingles, is nailed over the felt. Needless to say, these procedures come with any number of exceptions. Although it’s feasible to nail cedar roof shingles to an ordinary roof deck, it’s preferable to dispense with plywood and instead to put up lath—narrow parallel boards with a few inches of space between them. Wooden shingles last longer if they can “breathe,” and using lath instead of decking makes for better air circulation around the shingles. And regardless of what they’re made of, shingles aren’t the only kind of roofing. We’ll discuss some labor-saving alternatives in due course.
We’ve arrived at the top of the house by now, but before going on, let’s take one more look under the roof to observe a final structural detail. Since, as we’ve said, the roof is pitched, the rafters bear down angularly on the exterior walls that sup port them. Not only does their weight try to push the walls vertically downward, it also tries to push them horizontally apart. Something, therefore, had better counteract that outward thrust by pulling the tops of the walls together. If the house has an attic, the problem’s solved. The attic floor joists, being nailed down into the plates and also into the sides of the rafters, are more than sufficient to counteract the outward thrust of the rafters. But if there’s no attic—I’m bringing this up because our outbuilding won’t have an attic—and the ceiling under the roof is flush with the bottoms of the rafters, something else has to hold the tops of the exterior walls together. Ergo tie beams! Tie beams are beams whose sole function is to counter a roof’s outspreading thrust, and , since it takes tremendous force to grab both ends of a board and pull it apart, it’s a rare roof for which generously spaced 2x4 tie beams aren’t sufficient.
We’ve framed out our house now, but we still have to close it in. The first step is to nail sheathing onto the outsides of the exterior walls. Normally just 1/2” plywood, the sheathing is the basic envelope of the house, but it does a lot more than seal out weather. It also has structural importance. Geometrically speaking, a triangle is a very stable form. Unless you twist it out of the plane in which it lies, you can’t easily change its shape. A rectangle, on the other hand, is inherently unstable; even within the plane it lies in, it can easily sway to either side and become a mere parallelogram. It can also collapse entirely, as any number of framing carpenters who’ve been lazy about nailing temporary diagonal braces to their unfinished structures have been rediscovering since the dawn of time. And because our frame house is composed just about entirely of rectangles, it needs something to keep the angles of its rectangles at an honest 90-degree. So, by rigidly holding the studs to the vertical, the sheathing braces the entire house. (Which is why, in actual practice, the walls of a house are usually sheathed before the roof members are installed; unsheathed walls are often too un stable to support a whole roof.)
Once the house is sheathed, all we need do is tack some builder’s felt to the outside of the sheathing, nail whatever siding we choose over the felt (it can be clapboards, shingles, tongue- and -groove cedar, even vinyl or aluminum), stuff some insulation along the inside of the sheathing between the studs, put some more insulation either between the attic floor joists or under the roof decking between the rafters, run some pipes and wires through the walls and under the floors (drilling holes in studs and joists as we need to), nail some Sheetrock onto the insides of the studs and the undersides of the joists, tape and spackle and then paint the Sheetrock, nail some flooring to the subfloors (except for the bathrooms, where we observe the nice ties and glue tile to the subfloors), nail some baseboards and other assorted trim around the rooms, and -- voilà! --we have a house!
It’s true we’ve omitted the odd detail here and there, like what to do about doors and windows and ventilating the roof and making stairs and banisters and closets and counters, but nonetheless we’ve just clicked through a fair number of the essentials of frame construction. It’s simple, it works, it’s ac cumulated an admirable track record, it’s architecturally compatible with all but the strangest environments, and it’s also what we’ll use to build the outbuilding.
MATERIALS AND MODULARITY
Things aren’t always what the nomenclature says they are. A 2x4 isn’t 2 thick or 4 wide; it s only 1.5" thick and 3.5" wide. Early in its evolution, when it was first rough-cut timber, it might have been a 2x4 that measured 2” by 4”. But the board surrendered moisture through evaporation and consequently shrank, and then it was milled to smooth its surfaces and bevel its edges, and along the way it lost ½-inch in each dimension.
This is something that all professional carpenters know at least as well as their own names, and it qualifies them to patronize people who don’t know it. When a carpenter’s marriage fails and he indignantly recites his wife’s offenses to a divorce lawyer, the lawyer may take on a superior smile and say, “C’mon, now. You don’t expect to get anything like justice in court, do you?” For the moment the carpenter may feel put in his place, but later, when they’re talking about construction (and they will; it’s inevitable), the carpenter may create the chance to say, “Hey, you didn’t think a 2x4 is really 2” thick and 4” wide, did you?” Now it’s the lawyer who’s been put in his place. Parity has been achieved, the carpenter and lawyer are on something like an equal footing, and the social order has accordingly become more stable.
However, unlike the shifty 2x4, a standard 4x8 sheet of ply wood is actually 4’ wide and 8’ long, a fact that has important implications for our outbuilding. We talked about studs and joists being spaced 16” apart. Putting that into terminology, we’ll say that the joists and studs are “on 16” centers,” i.e., that the distance between imaginary parallel lines drawn through the centers of the 2” sides of the joists or studs would be 16”. Well, imagine a rectangle whose sides are two adjacent wall studs, whose bottom is the sill on which the studs are standing, and whose top is the plate across the tops of the studs. That rectangle is called a “bay.” Its height is around 8’ (we’ll be specific in due course) and its width is 14.5”. (It would be 16” if studs had a thickness of zero, but since they’re 1 thick there’s that much wood to account for.) A stud wall is made up of a series of such bays, and it won’t take you long to realize that if you nail a 4x8 sheet of plywood to a stud wall, you can do it so both its long edges fall on the centers of studs. You’d have “on each of the outer studs (half their 1.5" thickness) to nail the edges of the plywood to, and you’d be left with another ¾-inch on each stud to nail adjoining sheets to the left and to the right. The sheet of plywood would cover exactly three bays.
Now, when you build the outbuilding you want to minimize both cost and labor. Once you’ve bought plywood floor decking or roof decking or siding or Sheetrock, you want to use whole sheets wherever you can. Besides reducing waste, using whole sheets lets you take advantage of their smooth, machine-cut edges.
Consider the deck of a small one-story building. Let’s say the building is 16’ long and 12’ wide, and it’s time to nail down the plywood subfloor. In subfloors, the plywood sheets are generally laid so that their long edges are perpendicular to the joists, and they’re always set down in the same alternating pattern in which bricks are usually laid. Just as with a brick wall, alternating the elements breaks up the seams and gives you more strength. Yet, even holding to the alternating-pattern rule, in stalling a 16’ by 12’ subfloor requires only a single cut in a single sheet of plywood. If you divide the floor into three 16’ strips, each one 4’ wide, two whole 4x8 sheets set longitudinally cover the first and third strips, and one whole sheet and two half sheets cover the middle strip. Moreover, if you let the edges of the half sheets that you’ve cut yourself face the outside of the building (where, maybe thankfully, they’ll eventually be covered by siding), all the edges of all the plywood inside the subfloor will be machine-cut, which means they’ll all butt against other machine-cut edges and give you nice smooth seams. And since, as we’ve already seen, the 16” spacing of the joists enables the 4’ edges of every whole sheet of plywood to fall on the center of a joist, you can nail those edges down to the joists just as good practice dictates. The resulting subfloor will look astonishingly professional.
Benefits like these practically mandate that our outbuilding be dimensioned in 4’ modules. In fact, the outbuilding whose construction we’ll follow in forthcoming sections is 16’ long and 12’ wide. We’ll talk about varying those dimensions, but all the variations we discuss will be in units of 4’. Even within those constraints, you’ll more than satisfy whatever cravings you have for measuring, sawing, and calculating. Outside those constraints you risk the possibility of massive overdose.
SITING AND RED TAPE
Sometimes, despite the everyday profusion of hard and painful lessons, ease begets ease. In this case, making the outbuilding easy to build spins off the ancillary benefit of making it easy to choose a site.
Aesthetics aside, the rules of thumb that govern site selection for an ordinary house are largely aimed at keeping its basement dry. Hence the usual injunction to stick to high ground. The traditional bugbear of basements is runoff—rainwater that flows downhill until it encounters your foundation walls and eventually seeps in. You’re therefore commonly enjoined to site your house so that water flows away from it, not toward it.
But concrete foundations are expensive to buy. You can make one yourself, but the work is tedious and difficult, and in the end they’re still expensive. Which is why I’m recommending that you build the outbuilding on pressure-treated wooden posts. Not high ones, mind you: the house sills won’t be any higher than if they were set on a poured-concrete or concrete-block crawl space. But setting the building on posts gives you immensely more latitude in choosing a site. If you have some favored hillside that flows with sheets of water during down- pours, use it anyway. Water will pass freely under the outbuilding and leave it high and dry. The only really relevant consideration is mud, and even then it applies more to you than to the building. Unless you’re building a gazebo for your hippopotamus or an aviary for mosquitoes, pick a place that you can walk to without needing frequent recourse to your local quicksand rescue squad.
Another factor worth considering is light. If you like it, site the building in open terrain and have one of its long sides face southward toward the sun—being long, it can accommodate more windows. If you don’t care for light, choose the north slope of a densely forested hill.
Moving from the realm of the obvious, though, it’s important to discover what your legal setbacks are. Different local governments, usually villages or townships, often have zoning ordinances that regulate how close to the boundaries of your land you’re allowed to build. Sometimes there’s a setback formula that takes into account the height and nature of the building and even the slope of the site. The most cogent thing I can say about investigating what zoning restrictions govern your in tended outbuilding is that early is probably better than late. It’s dispiriting to put up a whole building only to be told that you have to move it or tear it down.
And while you’re visiting your building department, you might also find out if you need a building permit. Most local governments will let you erect an outbuilding fairly readily; what worries them is that you’ll put up a whole other house. So prepare to be forbidden to install any plumbing. To building departments it’s generally kitchens and bathrooms that define a dwelling, and if your outbuilding is classified as a residential structure you’ll either be told to forget it or you’ll have to hew to a much more stringent set of building-code requirements than would apply to a structure that’s not residential. A lot of this depends on how rural your property is. As a general rule, the closer you are to civilization the larger the presence of the building inspector looms. In the bona fide boondocks he’s barely a presence at all; in the suburbs he’s a snoop and a stool pigeon. The great value of calling your intended structure a shed or an outbuilding is that your building department is likely to be even more casual about it than they’d be about a garage. However posh their insides are, outbuildings are normally considered to be commodious tool-sheds, and getting your building department to see it that way will be all to the good.
One final caveat. In line with Buber’s notion of imagining the real, spend some time imagining how your building materials will get to the site. If the lumberyard’s delivery truck can’t come in nearby, you’ll have to move some dauntingly unwieldy sheets and boards. I won’t recommend that you site the building near an accessible roadway, because your heart’s desire may be to have a studio that’s inaccessible. But if you put the outbuilding on, say, a steep, remote hillside, prepare to know in your bones what it was like to build the pyramids. Or at least prepare to buy, borrow, or otherwise enlist one of those giant plywood garden carts or a power winch or a squadron of sturdy friends or some combination thereof. In the end it’s better to site the outbuilding where you want it and not where it’s easiest to build. But privacy will have its price. If it’s any help, try to remember that there were epochs in which exercise was practiced not on Nautilus machines but on materials that had to be moved from one place to another.
Also see: Do-it-Yourself Log Home / Cabin
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Sunday, November 14, 2010 19:06 PST