Deck Building 10 - Installing the Girders

Margin of Error. 1/4”

Most Common Mistakes

  1. Using badly bowed girder stock.
  2. Girder not level.

Now you are ready to install your girders or beams. You may do this in one of two ways. One is to pre-build the girders/post system, bolt or nail the entire thing together, and then move it as one large piece into place. The other way is to build it piece by piece in place. If the posts and girders are not too long and heavy, we recommend the first procedure putting it all together as one piece and then moving it into place.

There are several different girder/post variations. The girder can rest on top of the posts attached with metal fasteners or two girders can sandwich the posts and be bolted or nailed to them. As long as it passes your local code, either system will work. You may want to cost out the wood, since one system may be more cost effective than the other.

To build your girder/post system, first cut the wooden posts the proper height In our case the posts’ height is the same as the level of the bottom of the joists. Note that the bottoms of the joists rest on top of the girders and that the tops of the girders are at the same height as the tops of the posts.

To determine this post height, go back to your two outer joists and check to be sure they are still exactly level. Now move the string that is on top of the joists so that it is connected on the bottoms of the joists. The level of the bottom of the joists is the same level as the top of the posts you are about to cut. Now measure from the top of each pier block (or metal fastener) to the string, and cut posts corresponding to each of these measurements. it is that simple. But be sure you are accurate and that you make good straight cuts so the posts will sit smoothly on the pier blocks. To do this, you will need to mark around the circumference of the post, cut one side, and then rotate it and cut the sides a4jacent to it Finally make one more cut on the side opposite the first cut.

After the posts are cut, cut your pieces of girder stock the specified length. This will be the length of the ledger plus 3”. Try to use one continuous piece of girder stock for each piece, but if the deck is too long and that is not possible, be sure the two pieces meet at a post so they can both be attached there. Also be sure that all girder stock is extremely straight Pick these pieces yourself at the store. If they are bowed, the entire deck will rise or fall, since the deck joists all sit on top of them. If there is a SMALL (1/2” over 12’) bow, point it up toward the sky and it will settle down in time.

With all your pieces cut you can now assemble posts and girders into one unit. Usually this is done with bolts, nails, or metal fasteners. recommend using bolts. If you are resting the girder on top of the posts, use metal fasteners. Be sure to always use hot dipped galvanized (HDG) fasteners, boils, or nails so they will not rust If you are bolting it together, drill your holes good and straight so the bolts will go through straight. Use a bit that is 1/8“ larger than the bolt, to allow for final adjustments. Once the entire unit is assembled, move it into place under your two outer joists. If you are assembling the pieces in place, the application is pretty much the same. Before toe nailing the outer joists to the top of the girder, measure out from the wall to be sure the girder is the proper distance from the wall.

Once you have ascertained this, check once again to be sure the joists are still at right angles from the ledger and still level. Once all this is checked, nail the joists into the girders with some 10d galvanized nails to use some special L-shaped metal fasteners.