How to build a deck or call us 601 212 5433

Deck Building 10 - Installing the Girders

Intro - Prep - Tools and Materials - Ledger - Holes - Attach Ledger - Joists - Foundation - Set Pier - Girders - Layout Joists - Install Joists - Deck Boards - Cutting Ends - Facing - Railing - Waterproof
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.

Deck Building 11 - Laying Out the Joists on the Ledger

Margin of Error: 1/4"
Most Common Mistakes

1. Nailing the joist hanger on the wrong side of the mark.
2. Improper layout.

After your girder is in place, you are now ready to install your remaining joists. To do this you need to make marks, called layout marks, on the ledger and girder that show where each joist will be located. This process is called a layout.

Usually joists are located so that their centers occur exactly every 16”, 24”, or 32”. This is called their "on-center" distance. The distance between joists depends on several important factors:

1. Size of the joists
2. Spacing of the joists
3. Length of span from ledger to girder
4. Type of wood used for joists
5. Any heavy loading, such as snow

This is one of the few crucial dimensions specified in deck building. If you undersize or over space the joists, the decking can collapse or the building inspector can stop the project. Be sure you talk to a local retailer or building code office about the proper sizing for your joists and span. Joists placed 24” on center are usually adequate.

After you have determined their spacing, the layout is rather simple. Starting from a nail nailed at the center of one of the two outer joists already in- stalled, measure along the ledger, making a clear mark every 24” (or 16”). These marks indicate the center of each joist. However, it is a good idea to make a second mark 3/4” to either the left or right side of each of these first marks. This new mark locates one side of each joist rather than the middle; this makes it easier to locate the joist hangers on the ledger. Using a combination square, draw this new mark straight down across the ledger. Be sure it is a good, straight mark, since you will be nailing your joist hanger to this mark. Nail the hangers on flush with the edge of these new marks.

Do a similar layout on the girder, so that you know exactly where each joist crosses the girder. Again, draw new lines 3/4" to one side of the center line (the same as you did for the ledger) and then make an “X” so that you will know on which side of this line the joists will finally sit


After you have made all your marks, begin nailing the metal joist hangers on the ledger using the special stubby joist hanger nails provided with the hangers. Only nail on one side of the hanger, allowing the other side to float free until the joist is inserted. Nail on the one side so that the interior edge of the joist hanger is nailed along the line you drew to mark the side of the joist. Be sure as you go along that you are dear about which side of the mark the joist hanger and joist should be nailed to, to assure proper spacing. Even a seasoned professional can accidentally put the joist and joist hanger on the wrong side of the mark.

Deck Building 12 - Installing the Remaining Joists


Margin of Error: 1/4”
Most Common Mistakes

1. Not crowning joists.
2. Placing joist on wrong side of layout mark.

It is now time to install the remaining joists. Again, this is rather simple. Some builders cut the joists to length before installing. I recommend you cut the joists after almost all your decking boards are in place. The reason for this will become clear later on. Now, simply insert the joists into the joist hangers. Be sure, however, as you do this, that you crown each joist, pointing the bow skyward. Insert it in the hanger, nail the other (loose) side of the hanger tight up against the joist, and then nail hanger nails through the hanger into

the joist and ledger. Then toenail the joist (using two 10d HDG nails) through the joist into the girder. Special HDG L-shaped fasteners can be used here instead of nails. This is especially recommended in earthquake areas.

NOTE: Some builders, especially in areas of heavy rain or snow, also place galvanized metal flashing on top of each joist before the deck boards are applied. This flashing helps keep water from getting trapped between the decking and the joists, causing rot. Inquire whether this is done in your area.