Building a Deck - Framing

Rough Layout

You will actually have to lay out your deck twice. The first time is a "practice run" for digging out the footing holes. You want this preliminary layout to be accurate enough to place the corners of the deck within a couple inches of their final location. Mark the location of each post so you can dig the holes for the footings.

There are a variety of methods for performing this task: string and stakes and 2x4's are the most common. Each one has its pros and cons. With either method, the first activity is to locate where the ledger board will attach to your house. This will be the starting point from which you measure distances and angles to lay out the deck.

String and Stakes
With this method, you know that your lines will be straight (shortest distance between two points...) and you can start digging right away once the corners have been located. The major downsides are that distance and angles are harder to measure. First attach a string at one corner of the future ledger board. Stretch it out about two feet past the outside corner of the deck (at a right angle) and tie it to a stake. Do the same for the opposite corner. Stake out the outside edge of the deck in the same manner, overshooting each corner by about two feet. Overshooting the corners and using multiple lines will allow you to make finer adjustments to create right angles and even sides because you can pull up and relocate stakes individually. If your layout is square, the distance between opposite corners will be equal - check the opposite corners and each side to make sure they all match up as they should.

2x4 Layout
Using actual lumber to lay out the deck will be accurate because you can cut it to length and tack it together to create a pretty good approximation of the future deck. The downsides are that the lumber may not be perfectly straight (but it should be close enough at this point) and it doesn't work on uneven ground. With this method, if the pieces are cut to the correct lengths, your distances are already set so all you have to do is make sure that the layout is square using the methods above.

Footings

A "footing" helps support the deck by spreading out the loads created by each post over a wider area. The wider base also helps prevent frost heave from lifting the deck. A "pier" connects the footing and the post. Often in a deck, the footing and pier can be poured together - there are products that will form both at the same time. You can also pour them in two stages - first the footing and then the pier. If you pour them separately, you will need to add steel rebar to tie the two together.

Different decks have different footing requirements. If you are unsure whether your footings are sized correctly, consult a professional. Having incorrectly sized footings can be dangerous and can cause your deck to shift over time.

The next step is to dig the holes for the footings. In Des Moines, footings are required to be 42" below grade in order to get below the frost line. Dig your footing holes about six to eight inches wider than your pier. This will give you some "wiggle room" later if your measurements are off. Note that the pier may not be centered directly under the outside corner of the deck - consult your drawings to determine where the footing should be centered.

Once you have completed the holes for the footings, you may need to call your building inspector for a "hole inspection". The inspector verifies that the holes are deep enough to meet code.

However careful you were with your measurements, it is almost impossible to place the footings in the precisely correct location just yet. That's why you dug your holes extra wide. Before you start pouring concrete into the holes, the next step is to build the outside framing of your deck. Yes, you build the deck before you have anything to support it on! Keep reading to find out how and why.

Start by attaching the ledger board to your house. This will provide the starting point for the rest of the deck. If the ledger board attaches to a brick house, you will likely either epoxy threaded rod into the masonry wall (shown here) or bolt completely through the brick. Note how the ledger board is pieced around the sill at the door.

Ledger boards that attach to frame houses usually utilize lag screws or through bolts. Never attach a ledger board on top of siding of any kind. Doing so may put unsafe stress (shear and moment if you are interested) on the anchor bolts. A proper installation will usually require removing a portion of the siding before installing the ledger board. You will then install flashing under the siding and over the ledger to prevent water from getting into the house.

Once the ledger is installed, carefully measure and construct the rest of the outside beams, supporting them on 2x4's (leave plenty of room at the corners). You may also want to tack temporary cross bracing across the corners to make sure the frame doesn't shift. Once this frame is constructed, you will be able to place the footings and piers in their exact positions relative to the deck.

In these photos, observe that the footing and pier were poured in two stages. First the concrete was poured in the hole (without a form) to a depth of about eight inches. Since the hole was about eight inches wider than the pier, the footing will provide a stable foundation on which the pier can sit. Two rebar were formed into the footing to connect the footing and the pier.

Along the left edge, of the above photo, you can see the temporary support. This is simply a 2x sitting on the ground and screwed to the edge beam. This temporary support will remain until the posts are set later in the process. Also note the method for centering the concrete piers. The post base is set on the framing directly above its eventual location. A weight is hung from the center of the post base. This is the center of the pier below. An anchor bolt is set in the concrete at the center of the pier.

Mixing the concrete for the pier and the footing is easy, but strenuous work. Figure one and a half sacks for each footing and one and a half to two sacks for each pier. The easiest way to form the piers is to purchase cardboard tubes. The tubes are simply cut to length (8" above grade), set in place, and filled with concrete. When the concrete has cured, the cardboard can be stripped off to expose the concrete pier. It is absolutely critical to place the piers correctly as outlined above. You don't want to end up in a situation later on where the posts do not line up with the piers - your only choices at that point would be to demo the pier and repour, demo the framing and rebuild, or some combination of the two. In order to be structurally sound, the post should be centered on the pier.

An 8" carriage bolt is inserted at the center of the wet concrete. The galvanized post base is secured to this bolt. (Wood, even treated wood, should not be in contact with concrete). I also used a steel trowel to ease the edge of the piers by holding it at an angle and running it around the inside of the form.

Before you backfill the footings, you must call for the concrete inspection. As before, the inspector verifies that the footings and piers meet code and are installed per drawings.

Posts

The next stage is to place the posts that sit on the piers and support the deck. Once the posts are placed, you can remove the temporary supports and complete the floor structure and rail. Typically outside beam sits in notches that are cut into the posts and the whole structure is bolted together with hex bolts. My deck has a trellis over the "dining" area. Accordingly, the posts continue up 8' beyond the deck floor to support the trellis structure.

Notching the posts is a demanding and nerve-wracking procedure. It is critical that your measurements be checked and double checked - in my case, the 12' posts were $35 each, so I didn't want to make any mistakes! Notching the posts requires a high degree of comfort with a circular saw and good 3-d visualization. The process for each post is as follows (don't assume that any two posts are the same). First, measure the distance from the top of the post base to the bottom of the beam and transfer this line to your post. It may help with accuracy to have the post set on sawhorses so it lines up with its eventual position. Next draw a line for the top of the beam plus 1/4".

Since you will have to jockey the post into position, it is beneficial to have a little extra room at the top. To cut the notch, set your circular saw for the exact depth you want and make a series of close cuts between the top and bottom lines. Put in a new blade, make the top and bottom cuts first, and wear ear protection. Then go in with a hammer and knock out the "tabs" that are left and clean up the notch with a chisel.

Once the cuts are made, you are ready to stand the posts. I needed the help of several friends to lift and steady the 6"x6"x11' posts. Four or five foot posts may be more manageable by a single person. You will likely need to use a sledgehammer to coax the posts into place if your cuts are accurate - set the notch onto the beam and lift the assembly slightly to allow you to slide the post onto the post base. Once it is set, nail the base to the post and drill the holes for the hex bolts. You will need an 8" long bit.

There are many design ideas that can add a special element to your deck. Here are a couple of the ideas I implemented. Before drilling the hole for the through bolt, I drilled a 1/2" deep hole with a wide bit in order to countersink the visible head of the bolt from the outside. Other people choose to add a 1x board around the edge of the deck to hide the bolts completely. I also mitered the corners of the outside beam boards so that the ends aren't visible.

Framing and Decking

Once the posts are set and the temporary supports removed, you can install the joists and lay the decking. Typical joists are 2x8 or 2x10 depending on the span, and are installed at 16" on center using galvanized joist hangers. To install joist hangers, first measure out all the locations and mark the vertical lines with a speed square. Line up one side of the joist hanger with a measured line and the bottom of the beam and hammer in the tab. Do the same with the other side. Then nail the hanger to the beam filling each nail hole - never leave an empty hole. When all joist hangers are installed, cut and place the joists. Again, nail the joists in using all available holes and using the appropriate nails.

Decking is usually 5/4" (1" actual depth) or 2x6. The 5/4" decking is preferable because the edges are typically rounded over. Either way get a higher quality, number 1 grade, wood to prevent splinters and show fewer knots. In order to create a more finished look, install a "border" of decking, cutting around the posts and mitering the corners, so that the ends of the boards are not visible. Screw the decking to each joist with two screws. If the boards are dry, leave a small gap between them to allow for expansion. If they are wet (mine had been in the rain for the previous few days), install them tight to allow for contraction.