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Building a Code-Compliant Deck

Construction How-To, Decks, Decks, Outdoor Living July 13, 2015 Sonia


Prior to installing a ledger board you first need to remove existing house siding and trim from the house to expose the sheathing. After ensuring that the sheathing is structurally sound, we cover the area above and below the ledger board location with self-adhering rubber.

Once the ledger is attached to the house we install a rim joist on each side and a rim or beam opposite the ledger. We use scrap lumber as “legs” to hold the two rim joists level while attaching the outer joist to complete the perimeter frame. Diagonal bracing will hold the structure square while you add permanent supports and joists.

Once the ledger is attached to the house we install a rim joist on each side and a rim or beam opposite the ledger. We use scrap lumber as “legs” to hold the two rim joists level while attaching the outer joist to complete the perimeter frame. Diagonal bracing will hold the structure square while you add permanent supports and joists.

If there is space I will run rubber 10 inches up and as far down as necessary to keep water from getting into the house. Sometimes the area below an elevated deck has siding, so I install the rubber to overlap a siding course and then cover with the last siding course or trim.

I prefer to cut our ledger board 3 inches shorter than our final frame width, which allows us to nail rim joists directly to the ledger board’s end grain.

Once we locate the ledger board height, we level it and temporarily fasten it to the house with 16d galvanized nails.

After the ledger is temporarily fastened to the house, we go back and install permanent fasteners.  Check your local building code to confirm fastener spacing in your area.

If at all possible I install through-bolts through the ledger and house rim board. This requires accessing the basement rim joist area. I use 1/2-in. diameter galvanized bolts and washers for which I drill 17/32- to 9/16-in. pilot holes. Use washers at the carriage-bolt head and the bolt nut.

I also like using structural screws because they don’t require pre-drilling, are corrosion-resistant and are designed to be used with pressure-treated lumber. Follow the manufacturers’ recommendations for fastener length and placement.

Once the ledger board is level and permanently installed, we run additional rubber down the side wall and over the ledger board.

This area will later also receive a copper, galvanized or PVC ledger flashing cap.

NOTE – The latest building codes require decks supported by a house to be built with a “positive attachment” to resist lateral loads. This is accomplished using hardware connectors that tie the deck into the house to protect against lateral stresses from wind, seismic or people on the deck. Check your local codes to see if this is required in your area.

Follow the metal connector manufacturer’s recommendations for fastening any metal connector in your deck. My general rule is to use 16d galvanized nails everywhere I can.

Rim Joists

Once the ledger is attached to the house we install a rim joist on either side and one rim or beam opposite the ledger. We use scrap lumber as “legs” to hold the two rim joists level and then attach and outer rim joist (opposite the ledger board) to complete the perimeter frame.

You’re probably saying, wait what about the footings? I’m a bit unconventional with my footings. I prefer to build the outer perimeter or the “sandbox frame” as we joke on the jobsite. Once this frame is built we take diagonal measurements and use the 3-4-5 method to square the frame. Fastening two lengths of strapping from the outer rim joist’s center diagonally to the side rim joists helps to hold the deck square.

We then add additional “temporary” support legs and start digging the footings.

Footings

I like this method because it allows me to place my footings exactly where I want them and eliminates all the layout work with strings and batter boards that’s otherwise required to locate the footings.

We dig concrete footings to support all deck posts.

We dig concrete footings to support all deck posts.

A concrete “footing” helps support the weight of 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.

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The depth of the deck footings will be determined by your local frost line and building codes.

The depth of the deck footings will be determined by your local frost line and building codes.

Deck posts are supposed to rest securely and centered on these footings with a threaded anchor or J-bolt holding it down. Anchor bolts are designed to resist post movement and deck uplift from high winds.

Tube-shaped cardboard forms can be cut to length and placed in the holes to pour the concrete footings.

Tube-shaped cardboard forms can be cut to length and placed in the holes to pour the concrete footings.

Most deck footings these days are either poured in place or precast. When poured in place most folks use footing forms from Bigfoot Systems, Sonotube or an equivalent concrete form. These tube-shaped forms are simple to use, easy to install, resist settling, and prevent uplift caused by frost to result in a stronger deck foundation.

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Deck support posts should be mechanically fastened both to the footing in the ground and the deck frame or beam. Metal brackets make a strong connection while raising the wood post away from standing water.

For this reason it’s always important to install deck and porch footings below the frost line for your area as well as to make sure the installed footing is on soil that will support the footing’s load.