The Deck: A Place of Your Own Making: How to Build a One-Room Cabin, Studio, Shack, or Shed

Home | Wiring | Plumbing | Kitchen/Bath


So far the only materials you’ve had to buy are cement, per haps a pad of paper, and a long tape measure. But to go on and build the deck you’ll need more than the odd stick of lumber, and now you’re faced with the notion of spending more than the odd dollar on a project you may still not be entirely certain you can carry off. I could reassure you here by telling you it’s all more manageable than, in your more pessimistic assessments, it might appear. For one thing, you’ll be working on the ground, which is easy to get to. For another, you’ll be using lumber that, because of both its size and final destination (i.e., under the building where it won’t be seen), can soak up quite a few mis takes and not show many of the scars. But if you’re nagged by second thoughts, I’m not convinced it’s reassurance that’s appropriate. The better idea may be to realize that there’s risk attendant to the start of any sizeable endeavor. Yellow fever nearly kept the Panama Canal from getting past the mudhole stage. You, having just poured your footings, are at the mudhole stage. So yes, you’re about to take a plunge, but why not let the thrill of risk make the outset of the project all the more bracing?

Of course, the easiest risks to live with are calculated ones, and one way to infuse your risks with a comfortable degree of calculation is to purchase your materials wisely. If you hate shopping, a wise purchase is a fast purchase, and the fastest way to buy lumber is simply to open a charge account at a good all-purpose lumberyard. Even if you’ve done time in debtors’ prison, you shouldn’t have a problem getting a lumberyard charge account. Professional builders make up the bulk of the account holders at most lumberyards, and builders are notoriously re miss about paying their bills. Which means that lumberyards are usually more than happy to start an account for a layman. However good you think you are at ducking creditors, it’s the rare builder who couldn’t take you through a master class in the fine art of invoice management. Lumberyards know this very well, and they also know that having an account with them is going to discourage you from shopping around. Once you’re deep in mid-project you tend to be the prisoner of your own momentum: you hate to squander it by pausing to compare prices. And sometimes comparing prices is a waste of time. If there are several lumberyards around, ordinary free-market pressures will tend to keep their prices pretty much in parity.

Far more important, I think, is that you arrange to get a builder’s discount. An outbuilding’s worth of materials should be sufficient quantity to get it, and if one lumberyard doesn’t give it to you, try another. Builder’s discounts are typically structured so that you get a flat 10% or so off every bill and another 5% or so if you pay before the next month’s bill comes. And be wary of lumberyards that charge for delivery. A 16’-long pressure-treated 6x6 (heavier than not pressure-treated) isn’t conveniently transportable in the family car, and no one expects you to own a truck. For builders, delivery costs are already factored into the price. They should be factored into your price too.

One last thing: order materials on an as-needed basis. There’s little point in storing (and paying for) lumber that you won’t be using for some time to come. Your lumberyard is unlikely to reward you for taking early delivery by giving you a rebate for warehousing, and having piles of extraneous lumber on your property is bound to make for clutter and confusion. But don’t order too little at a time either. It’s jarring to run out of materials just when the fires of carpentry are burning brightest; sometimes you’re left so high on tenterhooks that you can’t do anything else until your next delivery arrives. A good rule of thumb is to have each order contain enough lumber to get you through a section. In this section we’ll go over what you’ll need to build the deck.


Here, from the ground up, is what you’ll need:

1. posts

2. girders

3. truss plates

4. nails

5. joists

6. boxing

7. Styrofoam (optional, but recommended)

8. plastic vapor barrier

9. plywood decking

10. shingle scraps for shimming

11. scrap lumber for later

Let’s take them an item at a time.

1. Posts

After all nine of your posts are resting on their footings and standing more or less straight up, their tops should eventually describe a level plane regardless of the depth of the postholes or the topography of your site. The deck of the outbuilding will rest on the tops of the posts, and you want your building to be level. You’ll start out with posts that are somewhat larger than they need to be and cut them off, but for now you want to know how much wood to buy. There are endless ways to do the reckoning, so I’ll suggest only one. If you prefer another way, use yours. Field expedience demands that you do whatever suits you best.

You’ll need a line level now (unless you’re handy with a transit), so borrow or buy one (they’re cheap). Being careful not to cave in any dirt, drive a stake into the ground just beside your highest posthole (i.e., the one on highest ground) and another, longer stake into the ground next to your lowest. Make the stakes sturdy enough and drive them in far enough so that you can connect them with twine that’s fairly taut without moving or breaking them. Tie the twine first to the higher stake at a point just above ground level. Then, before you tie anything else, imagine the twine proceeding to the other, lower stake along a level line. If you find yourself having trouble imagining a level line (some topographies defeat all attempts to guess at what a level line is, even to the point of making truly level houses appear tilted), go ahead and temporarily tie the other end of the twine to the lower stake and play with it until it’s level. Keeping the twine taut, measure off the halfway point between stakes and hang your line level from that point on the twine. It shouldn’t take more than a few tries to get the twine fairly level. Remember that the purpose of all this is to give you a feeling for where the tops of the posts will finally be. Girders will sit atop the posts, joists atop the girders, and flooring atop the joists, so the actual floor of your outbuilding will be another foot higher.

Now summoning your acutest powers of visualization, see the outbuilding at the level you’ve chosen and decide whether you like it there. Then, in your imagination, move it up or down a few inches and see if you like it any better. The tops of your posts needn’t be more than about 4” above grade (barring a deluge), especially since the floor framing will raise your floor well above that. And many people prefer small buildings to be low to the ground. On the other hand, leaving some room between the underside of the deck and the ground gives you covered storage space for firewood, screens, air conditioners (swaddled properly in plastic, of course), chain saws, axes, and spare lumber. You can always “bring down” the building visually by running lattice (the pressure-treated kind) along the bottom or planting shrubs around the base. A sloping site, if that’s what you’ve chosen, will give you the best of both worlds: storage space under the “high” side and a nice low profile along the other.

When you’ve arrived at what you feel is a good altitude for the tops of the posts, use your level length of taut twine as a benchmark and measure down from your chosen altitude to the surface of the footing in your “high” posthole, then do it again for your “low” posthole. I was careful to suggest that you mea sure from your chosen altitude rather than from the twine itself, since you may have decided that you want the tops of your posts to be a little higher or lower than the twine and didn’t feel like retying and re-leveling all that string. But regardless of the post height you’ve selected, you now have the approximate minimum length of your longest and shortest posts. As for the rest, you ought to be able to do them by eyeball. Unless your site undulates in an especially cockeyed way, create three categories of posts-to-be: those that are about as long as the longer of the two posts you’ve measured (i.e., the one destined for the hole in the lowest ground on your site), those about as long as the shorter of your two measured posts, and those that are halfway between. If your site does contain some abrupt changes of grade, you still ought to be able to estimate minimum post lengths from the two lengths that you’ve actually measured. This remains one of those areas in which too much precision is simply a waste of time. At all events, you’ll buy enough wood to give you a substantial margin of error when you cut the posts, and if worst comes to worst you can always bring down the whole building an inch or two with little risk of having its floor be below grade.

When you’re done reckoning, your posts will have come in somewhere around 4’. Now add half a foot or so to the length of every proposed post and call your lumberyard to find out in what lengths they carry pressure-treated, ground-contact-grade 6x6s. (Don’t worry about the question marking you as an ignoramus; frame it in monosyllables, chuck in a few regionalisms, and the people at the lumberyard won’t have any reason to doubt that you were born with a framing hammer in your little fist.) Common commercial lengths are 16’, 12’, 10’, 8’, and maybe 6’. Once you know what you can get, lay out your planned posts so you wind up with the least waste. And try as best you can to avoid using very long boards. They’re heavy and therefore hard to handle. If you can make do with, say, two posts per 8’ board or three per 12’ board, you’ll be happier than if you cut your posts from sixteen-footers. You won’t save any money by using longer boards, either. The stuff is sold by the running foot, regardless of board length.

Now, presumably, you know how many pressure-treated, ground-contact-grade 6x6s, possibly of mixed lengths, to order for posts. Write down the numbers you’ve arrived at.

2. Girders

For girders, order three 6x6s, each one the full length of your outbuilding. If you can’t get them that big (which could be the case if your building is longer than 16’), order six 6x6s, each one half the length of your outbuilding. When the time comes you’ll simply butt the two halves together.

Incidentally, at about this point there arises the question of where to switch over from pressure-treated lumber to lumber of the ordinary variety. Almost universally these days, decks built on posts are framed entirely with pressure-treated members, but that doesn’t mean you have to do it too. For the majority of small buildings, permanence is more a state of mind than a physical reality. All wood, pressure-treated or not, eventually rots or gets chewed by termites or carpenter ants; yet, throughout the northeastern United States, there are any number of wooden buildings dating back to the early 1600s, many of which are still inhabited and promise to go on being inhabited for centuries to come. Yes, the ones in use have probably seen greater or lesser amounts of restoration, but restoration is a perfectly normal part of building maintenance, and not just for wooden buildings either. Masonry crumbles too. Old bricks need to be repointed. Aging plaster walls need spackling and re-plastering. Foundations have a way of slowly disintegrating, regardless of what they’re made of. Apart from sealing your outbuilding in a helium capsule, there’s little you can do to make it proof against time. The best you can feasibly aspire to is to have the building be more of an asset than a headache. To that end, you probably want to make the girders pressure-treated too, although they needn’t be rated for ground contact. The same holds true for the joists and boxing. Even though they’re not in contact with the ground, the girders, joists, and boxing of a building set on posts are in contact with the elements, and to funguses or wood-munching insects they can look like so much chocolate cake. Still, to reverse myself, if you can get ordinary lumber much more cheaply than the pressure-treated kind and money is a problem, go with ordinary lumber and don’t worry unduly. You can always paint your lumber with a clear wood preservative, which will protect it some, or you can let the decades roll by, watch the ordinary lumber turn a pleasant shade of silver-gray, and very possibly luck out. If that’s what you opt for, add a roll of 8” aluminum flashing to your order (flashing is simply light-gauge sheet metal packaged as a rolled- up strip), because we’ll touch on making little termite shields for the tops of the posts. You’ll need flashing later anyway, and while debate continues to rage (all right, maybe not in your circles) as to whether termite shields do any good, making them may salve your conscience, whose soundness is vastly more important than that of the outbuilding.

3. Truss Plates

To hold the girders to the posts you’ll need truss plates, which are galvanized-steel rectangles with predrilled holes to drive nails through. The most convenient size is 4x9, but if your girders are in one piece you can go a hair smaller without any catastrophic sacrifice of structural integrity. If your girders are in two pieces you might go an increment larger to 5x10, since the truss plates will have to serve the additional function of strap ping the butted girder halves together. The reason truss plate size isn’t too crucial is that gravity does a good part of the work here anyway. Get eighteen truss plates, two for each post.

53 Girder, post, and truss plate

4. Nails

The subject of nails often provokes extensive opining among carpenters, most of which has never struck me as very interesting. Nails come in a variety of shapes, but the only kind you’ll need to frame your outbuilding are common nails. Common nails can be had uncoated, galvanized, or covered with various plastic resins. The last kind are sometimes called “sinkers” because the plastic lubricates the passage of the nail into the wood. You can use them if you want; I have no stance on them one way or the other. Galvanized nails don’t rust very readily, but the zinc coating forms a crackle finish that makes them slightly harder to drive than uncoated nails. You might want to use them where you’re concerned about avoiding those little drip lines of corrosion under exposed nailheads, but for most purposes ordinary uncoated, unplated, smooth-shafted common nails will do perfectly well.

As with other types of nails, the size of common nails is specified in pennies, that archaic designation whose abbreviation is “d.” The following table translates pennies into inches:

  • 3d 1 ¼”
  • 4d 1 ½”
  • 6d 2”
  • 7d 2¼”
  • 10d 3”
  • 16d 3½”
  • 20d 4”

You might start by getting 5 pounds each of plain 10d and 16d common nails and a couple of pounds of galvanized 6d common nails. Sixpenny nails are a good size for nailing truss plates to wood, and since the bright surfaces of the truss plates can become miniature billboards for rust they’re one place you probably want to avoid flaunting your corrosion.

5. Joists

As for joists, so long as your outbuilding is 16’ wide or less you shouldn’t have any problem finding 2x6s, pressure-treated or not, that span its entire width. Sixteen-, twelve-, and eight- footers are all widely available. You’ll need three joists for every 4’ of building length plus one extra joist to close up the last bay, so if your outbuilding is 16’ long you’d order thirteen 2x6s, pressure-treated preferred, untreated Douglas fir next choice.

If, for whatever reason, you can’t get 2x6s whose length equals the width of your building, figure on using twice as many joists, each of them half the width of the building. But also account for the need to tie the half-joists together with scabs.

Single scabs, each of them 2’ long, ought to suffice for the purpose, so, instead of simply doubling the number of joists you need and ordering that many half-building-width 2x6s, add 2’ to half of your order. That is, if you can’t find, say, thirteen 16’ 2x6s and have to make do with twenty-six 8’ 2x6s, order thirteen eight-footers and thirteen ten-footers. That way you can cut a 2’ scab off each of the ten-footers and wind up with the right number of joists and the right number of scabs. More over, since the scabs don’t have to be exactly 2’ long, you can save yourself some sawing by cutting the scabs so that the rest of the board is just the length you want. Presently we’ll get to what that length should be.

6. Boxing

For boxing, order 2x6 or 1x6 boards whose combined length equals twice the length of the outbuilding. The two joists at either end of the deck will essentially be their own boxing, so it’s really just the joist ends along the two long sides of the building that you’ll be boxing in. Obviously it’s easiest to get a pair of boards each of whose length equals the length of the building. But if that’s not practical for any reason, don’t be especially concerned. If you go with pressure-treated wood— and I mildly suggest that you do—you may discover that you have to get 2x6s. Pressure-treated lx6s are harder to come by. Generally 1x6 lumber is sold in the form of pine shelving, and if that’s what you wind up making your boxing with, I’d recommend that you eventually paint it, since pine has a way of getting murky with mildew.

7. Styrofoam

Regardless of whether you decide to insulate the walls and roof of the outbuilding, I think you’ll almost certainly want to insulate the floor (unless you plan to use the outbuilding exclusively as a storage shed). Floors can get cold even on chilly summer nights, especially when there’s no basement or crawl space to protect their undersides from wind and dampness. The best material to use is Styrofoam, which, like plywood, is sold in 4x8 sheets. Unless you’re building where winters are particularly cold, 1” Styrofoam should do the job, and if your winters do get bitter, go with 2”. The difference in cost isn’t that great. Either way, the thickness of the insulation isn’t as crucial as it's for roofs. Heat escapes upward much more readily than it does downward. What we’re mostly doing here is supplementing the insulating properties of the soles of your shoes.

Order enough 4x8 sheets to cover the entire floor of the outbuilding. Since you’ve designed the building in modules of 4’, it shouldn’t be very hard to calculate how much you’ll need.

8. Plastic Vapor Barrier

To keep exterior moisture from wafting upward into the outbuilding you’ll need some plastic vapor barrier. Hardware stores frequently have sales on 4-mil sheets 10’ wide and 25’ long. The kind of plastic isn’t all that important. Some kinds deteriorate much more rapidly than others when exposed to light, but yours won’t. Don’t go with a thickness of less than 4 mils, though. Something thinner may be just as proof against water vapor, but it’ll turn out to be unwieldy to put on. And make sure to get the kind that’s transparent. Black plastic works just as well, but after you’ve tacked on the vapor barrier you’ll want to be able to see the lumber you’ve tacked it to, or else nailing anything on top of the vapor barrier will involve rather more guesswork than is a good idea. You can also buy vapor barrier at the lumberyard, since nowadays it’s routinely called for in new construction. As for quantity, buy enough to cover the deck allowing a few square feet for waste.

9. Plywood Decking

Use ½” or 5/8” plywood for the subfloor decking. If you plan to install carpeting or vinyl tiles, you’ll have to put underlayment over the subfloor, and as underlayment chipboard or even particle board will do nicely. You can also have a perfectly presentable floor by laying plywood—the kind with one smooth side (or one “good” side, as they say in the trade)—and then painting it. For the subfloor, however, you don’t need any good sides. Whatever knotholes there are will ultimately be covered by wood flooring or underlayment or more plywood. So just get plain old construction-grade exterior plywood decking. (Ply wood is coded with letters that describe the condition of its surfaces: “A” means smooth and paintable, “B” means smooth with knotholes replaced by repair plugs, “C” means not so smooth with knotholes up to 1” in diameter, and “D” means not so smooth with knotholes up to 2½” across. Plywood that’s smooth on one side but has scattered knotholes on the other would typically be labeled “AC.” Rougher stuff might be labeled “CD.”) As a general rule, there’s nothing to be gained by using fancier materials than a particular task requires. It’s better to save the money for when you do need fancier materials.

As for how much plywood to order, know that it comes in 4x8 sheets and order enough to cover the deck. The 4’ modularity of your dimensions should make the computation a breeze. In fact, since you’ll be using as many sheets of plywood as of Styrofoam, you’ve already made it.

10. Shims

You’re going to be needing shims—thinnish sticks of wood to compensate for minor differences in the final height of the posts after you cut them. The most convenient shims you’ll find are wood shingles, most commonly of cedar. Shingles are sliced on a taper; they’re about ½” thick at one end and maybe 1” thick at the other. And since the taper is continuous, all thicknesses between ½” and 1/8” are available for shimming. You won’t need perfect shingles to use as shims (a bundle of new ones costs around $60). So ask the people at your lumberyard if they have any beat-up rejects lying around (they often do), or scavenge a few old ones at your local dump. A dozen should be more than enough.

11. Scrap Lumber

And while we’re on the subject of dumps, drop by yours to see what scrap lumber you can find. Longer boards are better than shorter, and appearance doesn’t count. You won’t need the boards for the deck, but you’ll need them later for the walls and roof—not as structural members but as temporary braces and as poles to fish overhead members into place. The more scrap lumber you collect the better, so you might as well begin now.

Materials List

If all’s gone well, you’ve just created a list of materials to take to the lumberyard. You place your order, and soon after ward you get your first big lumber delivery. The outbuilding has been mainly an idea thus far, but now that the delivery truck has come and gone and you’re confronted with a humongous pile of wood, it’s perfectly reasonable to allocate a moment or two for muttering, “Oh, my God! What have I gotten into?” Nevertheless, don’t be overawed. The 6x6 girders and posts are the most massive materials you’ll use throughout the project. The others will be matchsticks by comparison. And, as I’ve already said, massive as the 6x6s are, they’re also about the easiest boards you’ll work with in that they shrug off virtually all carpentry errors (except cutting them too short; that they don’t like). So if you feel the need to be crude and carefree (within humane limits) about carpentering your newfound trove of lumber, now’s the time.


Once you’ve cut the posts you’ll be off and running. Presumably you’ve retained the results of the post-height computations YOU made earlier. You added 6” or so to the length of each post to obtain some working latitude, and now is when YOU use it. Now is also a good time to get hold of a carpenter’s square— a graduated L-shaped piece of steel designed to provide you with all the right angles you’ll ever need.

Rough-cutting the Posts

Mark off the posts on the 6x6s they’ll be cut from, using the square to keep the lines perpendicular to the edges of the board. If you’re cutting with a 7 1/4” circular saw, you won’t be able to make a deep enough cut to lop the posts in one stroke, but that’s fine. Rotate the 6x6 and do it in two or three strokes. If you can’t cut quite to the core of the 6x6 no matter how many times you rotate it, cut the cores with a hand saw. Or, easiest of all, borrow a chain saw. Whatever you do, make sure not to frolic in the sawdust. The stuff with which the lumber has been pressure-treated is a compound of arsenic. Work outdoors, don’t lick your hands, consider using gloves and plastic goggles, and urge your pets and children not to graze on the debris.

All nine posts

Cutting True Lengths

When you’ve rough-cut the posts, plunk them into their corresponding postholes, once again being careful not to let too much caved-in dirt sully the pristine tops of your newly hardened footings. This time, using the longest boards you have around instead of twine, begin marking what will be the true tops of the posts. Temporarily tack the boards to the posts with nails (when you “tack” with nails, you don’t hammer them in all the way; you want to be able to get your nail-puller under them easily so you can pry them out), get your 4’ level, and play around until you’re absolutely sure that the path from the top mark on any post to the top mark on any of the other posts proceeds along a level line. Your lumber delivery will probably have provided you with boards long enough to let you level three post heights at a time. Don’t use for leveling purposes boards that are so bent (start saying “crowned” instead of “bent”) that they’ll throw your level off. And don’t take a whole day to do the leveling. If the top of one post winds up being ½” lower than the top of another post 16’ away, no posse of Error Troops will come to drag you away. You’ll simply have to use a shim.

Cutting off the top of a post

Now that you’ve marked the true tops of your posts and ascertained that all the marks are in a level plane, invent a labeling scheme that links each post with the hole it was marked in, label the rough-cut posts accordingly, and cut them to their true length. (Making the rough cuts has undoubtedly taught you everything you need to know about cutting posts.) Then put the posts back in their holes, but don’t backfill. That comes later.

Squaring up the posts


While you’ve got the feel of cutting 6x6s, cut your girders to their exact length. Even if your outbuilding is 16’ long and you’ve ordered 16’ 6x6s, some of them may be a little longer. So get out your tape, mark them carefully, use your square to scribe the pencil lines, and cut the girders to their precise length. If you’re making your girders in two equally long pieces, cut all the pieces now. And do it fairly carefully. If you’re sloppy with a circular saw, direct your sloppiness toward cutting off too little rather than too much. As one carpenter put it, “Dead wood don’t grow.”

Leveling and Truing the Girders

Next, lay out your girders in the position in which they’ll finally be nailed, one girder atop each triad of posts. Using the dimensions in your drawing, mark the precise points on the girders where they intersect the post tops, then set them up so that the posts meet their marks on the girders. Now look along the girders for crowning; the chances are that none of them will be completely straight. Rotate them so that the crowns are in the horizontal plane—i.e., so that they bend sideways, not up and down—and you’ll be less likely to wind up with unwanted hills or valleys in your floor. Be aware, though, that 6x6s can be crowned “both ways,” sideways and up and down. If that’s the case, rotate the girder so that (1) the bigger bend goes side ways, (2) the smaller bend goes up and down and (3) the center of the girder is slightly higher than its ends. When a girder is crowned from left to right, you can easily accommodate the bend by moving the middle post a little bit so that it falls under the center of the girder. But there’s a limit to how much you can reasonably shim a girder if its center is very high. I’d say that if you have a girder that’s crowned both ways and the peak of the lesser of the two crowns is more than 1” higher than its ends, exchange the board for a better one. Nonetheless, severe double crowning is comparatively rare and , under normal circumstances, the whole rotation procedure oughtn’t to take more than a few minutes. If you’re using half-length girders, butt the machine-cut ends together, prop them up so that the butt joint is just over the center of the middle supporting post, then strap them temporarily together by tacking short scraps of wood to their sides. (Once again, by “tacking” I mean nailing without driving the nails in all the way and using only as many nails as are absolutely necessary.)

Now, by sheerest trial and error, go around from post to post, level in hand and shingles at the ready, and do the final touch-up leveling of the girders. If any of your posts is a bit too low, split off a 5 1/2” (approximately) piece of shingle and shim the post with it. If any of the posts is too high, remove it, trim off the extra or so, put it back into its posthole, and try again. And while you’re touching up their heights you should also be manipulating the posts to keep them as plumb (vertical) as possible. If you trust your ability to determine the vertical by eye, do that. Otherwise use the plumb bubble gauges on your level (the gauges that are perpendicular to the level). If the posts keep toppling over in their postholes, brace them temporarily with sticks. And remember that leveling each of the three girders isn’t enough. They also have to be level with respect to one another. That means you have to look over your 2x6s until you find one that’s not visibly crowned, lay it crosswise atop your girders (not on its flat side), put the level on the 2x6, and then do whatever shimming of the posts you have to do to get the 2x6 level. If you’re using two-piece girders, there’s an additional heuristic dimension: you’ll want to stretch a length of twine along the entire girder to ensure that the two pieces form a straight line. And while you’re doing all that, you have to see to it that the ends of the girders form a straight line (keep checking them with an uncrowned joist), that all three girders are spaced according to your deck diagram, and that the whole array forms a true rectangle as opposed to any mere rhombus. To ascertain rectangularity, use your long tape to measure both diagonals of what you hope is a rectangle, making sure you’ve used corresponding reference points in both cases. The best reference points are the outer corners of the outer girders. If you’ve got a rectangle, the two diagonals will be equal. If you don’t, they won’t. So play around until they are.

Trapped forever in heuristic purgatory? Not at all. Setting up the girders won’t take as long as all that. The posts don’t have to be exactly centered on their concrete pads, and your shingle shims will give you ample room for fudging. If one end of the subfloor turns out to be ½” lower than the other, no one—probably not even you—will know. Discrepancies of ½” or less simply tend to vanish in a structure of this size. Yet don’t be too careless, either. Scruples observed at the deck stage will redound to your benefit when you’re framing the walls and roof. Deciding how perfectionistic you need to be comes down to balancing your intrinsic craftsmanship with your natural impatience. Both are real, and both deserve respect. So be punctilious but not lapidary. Trust your judgment.

Termite Shields

When the tops of your girders form a level, plane, rectangular surface, you’re ready to yoke the girders to the posts with the truss plates. If you’re using non-pressure-treated girders, how ever, there’s a parenthetical procedure you’ll want to attend to first: termite shields. So find the 8” flashing you ordered, and with tin snips or even heavy scissors cut nine 8” squares of aluminum and fish one in over the top of each post. Maneuver them until they’re centered on the post tops and bend their edges downward along the sides of the posts. Done! And you’ve accomplished two things here. Not only have you thwarted termites (maybe), you’ve also flashed the girders, thereby preventing the posts from wicking rot-inducing moisture into the joint they make with the girders.

Two girders in place

Truss plate connects girder to post

Yoking Girders to Posts

Now go ahead and lash the girders to the posts with truss plates, one on either side of each post. Set the plates up so that half is up against the post side and the other half is up against the girder, and use the 6d galvanized nails we talked about. Truss plates are generally drilled with a lot more nail holes than you’ll need; nail them mostly around the edges. If your girders are in two butted halves, the truss plates on the three center posts will also hold both halves together. How they do that's self-evident. Just make sure to keep the girder halves butted tightly while you nail the plates.

Cutting the Joists

At this point you have three unconnected units, each of them a girder sitting on three posts. The joists will tie the units together, so begin by taking pencil and carpenter’s square in hand and marking the joists where they’ll have to be cut off. To wind up with a deck that’s the size you want, the length of each joist has to equal the width of the building (some exact multiple of 4’) minus the combined thickness of the boxing. If you’re using 2x6 boxing, subtract 3” (the combined thickness of two 2x6s) from whatever multiple of 4’ you’ve chosen. If you’re using 1x6 boxing, subtract 1½”, since 1x6s are ¾” thick. Once you’ve marked the joists, simply cut them to length.

Installing the Joists

In your sketch of the deck you’ve indicated the precise spacing of the joists along the girders, so carefully mark the points on the girders where the joists will be nailed. You can scribe two parallel lines, 1 1/2” apart, where each joist will fall on each of the three girders it crosses, or you can take the traditional approach and draw a single line where one edge of the joist is supposed to fall and an X just beside the line such that the joist will cover the X when it’s nailed. The systems work equally well, but since the second way is used more widely it would be the better choice if you expect to quit or abscond or die before the building’s finished, in that a pro could more easily take things up where you left off.

Floor joists and boxing

After all the marks are on, use your 4’ level to check the joist spacing. In your diagram you spaced the joists so that if the outer 4’ edge of any sheet of plywood is flush with the edge of the building, its inner 4’ edge will fall over the middle of a joist, enabling you to nail two butted plywood edges to that same joist. So if you line up one end of your level with the outer edge of either of the building’s two end joists and set the level parallel to the girders, the other end of the level ought to fall more or less on the center of a joist. If it does, everything’s gone according to plan. If it doesn’t, go back to the section on drawing the drawing and correct the spacing of the joists.

“Slice” showing joist toenailed to girder


Now find your 10d nails and toenail the joists to the girders. Start by nailing the two end joists; you’ll nail the ones between after back-filling the postholes. If you’re concerned that you haven’t cut your joists so they’re all of equal length, find two that are equal and put them on the ends, taking care that their midpoints fall precisely over the center of the middle girder. And if you’re not comfortable with toenailing, now’s the time to get comfortable. Consider this something of a practice run; once the outbuilding’s built, no one will be able to see how egregiously you’ve screwed up or how much perfectly good lumber you’ve hammered into ugly, pathetic splinters. Try angling in each nail so that half of it catches the side of the joist and the other half sinks into the girder.

While you’re hammering the first nail, the joist will try to creep along the rafter, so, without putting a nail through your hand, hold it back. It will try to move anyway, but a certain amount of drift is okay, since after you put a nail in one side of the joist, you put the second nail in the opposite side, and nailing the second nail will tend to hammer the joist back to its marks. A third nail in the first side should do the job for each joist-to-girder joint. If after you’ve toenailed the third nail the joist still isn’t on its mark, bang it with the hammer until it's .

Rechecking Squareness

Pause after you’ve nailed the two end joists. The deck still isn’t very rigid, which makes this a good time to do one last test of rectangularity. Re-measure the diagonals of the deck and play around with it until they’re equal. When you’re satisfied that your deck is a level rectangle and that the posts are plumb and sitting comfortably on their footings, go ahead and backfill the postholes. That done, you can now nail the rest of the joists without being concerned that you’ll throw the deck out of kilter. You may want to run a taut length of twine between the ends of the end joists to help you line the other joists up. That way at least one lengthwise edge of the building will be straight (provided you don’t let any of the joist ends dent the twine). As for the other lengthwise edge, you can test for straightness either with twine or lengths of boxing, but wait until all the joists are nailed. If any one of them is egregiously overlong, trim it off with a saw. Too short is less of a problem. No one will ever notice.


For those of you who are using half-length joists linked with scabs, the fastest way to get done is to nail the scabs on first, thereby manufacturing full-length joists. Use 10d nails (eight per scab should do, four into one half-joist, four into the other), taking care to keep the ends of the half-joists butted tightly together and the resulting full-length joist straight. Toward the latter end, a good straight reference board is helpful. And when YOU nail the put-together joists to the girders, make sure the butt joint of each one is just over the center of the middle girder. The scabs are at best a source of auxiliary support; you want the inner ends of the half-joists to be sitting on a couple of inches of good solid wood.

The Boxing

Now nail on the boxing, cutting it first if you have to. A pair of 10d nails through the boxing and into every joist end should do the job. Make sure the upper edges of the boxing are flush with the upper edges of the joists. You’ll be nailing plywood to both, so you want a good flat surface to nail to.

That done, you should now have (at risk of belaboring the point) a sturdy level rectangle whose outer width and length are (1) multiples of 4’ (within ¼” or so) and (2) the dimensions you’ve chosen for the outbuilding. If that’s what you’ve got, proceed. If it isn’t (and often it isn’t quite), fix it. As simple as that.

Installing Rigid Foam Insulation

After doing what you’ve just done—moving heavy boards and then smashing the living daylights out of them—installing the insulation, if you choose to do so, will feel almost like white-collar work. Start by scribing lines along the sides of the joists, keeping them parallel to the tops. Draw them 1” down from the tops if you’re using 1” Styrofoam, 2” down if you’re using 2”. If you have scabs on your joists (no mean medical curiosity), draw the lines on the scabs too. Then, starting at the ends, drive 6d nails partway into the joists along the lines. Let the nails stick out about 1”, and space them a “long” foot apart.

[A comment here about “long” and “short” measurements. First, the concept isn’t one I just made up. It’s widely used by carpenters, and it’s valuable even when you’re communicating only with yourself. The concept has two somewhat different senses, each one plain from its context. What’s meant by putting in a nail every long foot is something like this: without using a ruler, guess at how long a foot is. Your mind will promptly furnish you with a multiplicity of guesses: short ones, long ones, and a slew of guesses in between. To get a long foot, simply select a guess that you’re reasonably sure is on the long side without being wildly long. The concept’s second sense usually applies to sawing boards. You take a measurement, and it’s, say, 43 minus a few hairs. You don’t want to bother with measurements in 32nds of an inch, even l6ths of an inch. Probably your saw won’t cut that precisely anyway. (We’ll tactfully decline to explore the question of whether it’s your saw or you personally that can’t cut to close tolerances.) So you call the measurement a “short” 43½” What that means in practice is that you mark the board at 43k’ and just barely saw off the pencil line. If it were a “long” 43½ you’d leave the pencil line unsawn. Of course, for an exact 43½ you’d saw off half the thickness of the pencil line and leave the other half on the edge of the board. (And, strangely enough, when you’re about halfway done with the outbuilding you’ll probably be able to do that.]

A reminder: if you’ve put a line of nails into the outer sides of either of the end joists, pull them out. Since their purpose is to hold up sheets of Styrofoam between the joists, the outer nails will tend to catch on your clothes and otherwise do little good.

Now pick a windless day (closed-cell Styrofoam is incredibly brittle; even a light breeze can tear it up) and cut the insulation into strips that just fit between the joists. A sharp kitchen knife is a good tool to use. Most of the strips will be 14½” wide, but where you’ve varied joist spacing as we’ve discussed they’ll be a little narrower. If any of the pieces do break—and they will— just fit them back together and keep going. Unbroken pieces don’t have that much more insulating value than ones with hairline cracks, and since the pieces fit snugly back together, hairline cracks are all you’ll have. Set the strips down onto the nails, but don’t push too hard. The final push will come from the plywood decking that follows.

Cutting rigid foam insulation

Fitting Styrofoam between the joists

Vapor Barrier

You’re ready now to tack your sheet-plastic vapor barrier over the top of the deck. Where the edges of the sheets fall across the deck’s surface, overlap them a few inches with the adjoining sheets. You can use staples or small nails, but staples are best. In fact, arranging that a staple gun be handy is a good idea. You’ll want it later anyway. Whichever you use, don’t put in too many. The plywood decking will ultimately hold the vapor barrier in place; the staples are mainly to keep the wind from taking it to China before you nail on the subfloor. A few scrap boards laid atop the deck should anchor it just fine. And don’t worry now about any vapor barrier that droops over the sides. It’s easiest to trim after the plywood is on.


Which brings us to the subfloor. If you’ve been assiduous about your deck drawing, you’ll already have sketched the “brickwork” pattern of plywood sheets. The objective is to use as many uncut 4x8 sheets as possible and still preserve the alternating scheme. For the 16’ by 12’ outbuilding shown herein, only one sheet needs to be cut in half. Start by laying out all the plywood on the deck before you drive any nails. Where there are errors in length or squareness, array the plywood so that you split the resulting differences between two sides. Butt ma chine-cut edges to machine-cut edges wherever possible and , using your 6d nails, nail the plywood down to all the joists, putting the nails in at intervals of about a foot. If you’re bad at estimating the paths of the joists under the plywood, keep doing it until you get better. A few nails hammered into air (actually into Styrofoam) won’t matter one way or the other. And when you cut plywood, regardless of whether you use an all-purpose cutoff blade or a plywood blade in your circular saw, adjust the depth of the cut so it’s fairly shallow. You’ll use a full-depth cut for sawing structural members, but plywood does considerably less splintering if you take the time to find the appropriate wing nut on your saw and shorten the cut. You’ll also find that when you need to draw lines on plywood your 4’ level makes a good straightedge.

The deck

As soon as the plywood is nailed down, you’ll no doubt want to walk around the deck and congratulate yourself. You’re now a carpenter—of sorts. You probably even have some inkling as to whether you’re a good one. If you are, that’s all to the good. If you’re not, in a curious way that’s even better. Except for a few details like walls and roof, you’ve built a building, and you’ve demonstrated that it doesn’t take all that much skill to do it. Besides, incipient skills are bubbling up in you, and soon enough you’ll have the chance to use them.

Also see: Making a Sketch

Wednesday, May 25, 2011 9:52 PST