With the header board in place (as discussed on Page 3), support has now been provided for the deck at the house-end. At the opposite end, support will derive from a pier of some sort, sunk into the ground. Deck builders use a variety of techniques to accomplish this, but I will present one that I believe to be easiest for do-it-yourself deck building.
These deck piers do not have to be located at the very edge of the deck. In fact, many deck builders prefer the look of having the piers hidden from view, a few feet back from the edge. Likewise for the two sides. The number of piers and pier spacing is determined by local residential building codes.
Before digging, it will be helpful to nail the two outermost joists (extreme left and extreme right, as you face the house) to the header board. At the opposite end, use temporary braces to prop them up. These joists can serve as a reference point when working on the pier holes. More importantly, make sure that these 2 joists are level with each other (at both ends). And each joist should be set to slope 1/8 inch per foot away from the house (for drainage). Don’t be afraid to fuss over this now, even if it takes quite a bit of time to get it just right. You’ll spare yourself a plethora of problems later. You'll be calculating the height of your ground supports based on the level of these joists.
Nor are these your only concerns. For you really want your rectangle to start taking shape as soon as possible, so that you can begin squaring up your angles. For the joists must form right angles with the header board; use a carpenter’s square to make sure you begin building your rectangular frame at perfect right angles. Remembering a little high school geometry here certainly doesn’t hurt your chances. You can make use of the fact that, in a right triangle with a base of 3’, the side perpendicular to the base will be 4’, and the diagonal side 5’. If your angle is off, now is the time to adjust it – not after everything is secured!
After installing these outermost joists, run a tape measure down from the header along each joist, stopping at the distance where you’ve determined the piers should be. Mark it. Now run a string tightly between these two marks, from joist to joist, spanning the whole width of the deck. This string will be your guide as to where to locate the piers. Run a plumb bob down from this string to the ground, and mark that spot. You are now ready to begin digging.
Pier holes should extend below the frost line to avoid heaving during freeze and thaw cycles. Dig each hole the same depth, again using the plumb bob as a guide. At the bottom apply a layer of crushed stone. Mix concrete and build a small form for a square concrete footing, according to local residential building codes. Let the concrete cure. You are now ready to do more concrete work, this time for the pier itself.
Hardware stores carry a waxed cardboard tube used as a circular concrete form. Just set this form on the cured footing, plumb it, and mix and pour more concrete. Etching marks on the forms to serve as guides, make each pier the same height. Reinforce the concrete with rebar. You’ll want the top of your concrete piers to be about 2’ above ground level. Before the concrete cures, place a post base onto the top of each pier. These post bases will allow you to unite the wooden posts you’re using with the concrete piers. Allow the concrete to cure again.
One of the biggest challenges in deck building will be encountered at this point in the project: making the house-end and the opposite end of the deck the same height. More than at any other step, this is the place to apply the do-it-yourself carpenter’s golden rule: play around with it first as much as possible to get the right alignment, before cutting anything or securing anything. Otherwise, you only have one chance to get it right – in which case, I don’t like my chances!
On Page 5 we’ll tackle this challenge -- the last difficult step in building a deck.