how to extreme

Building a Code-Compliant Deck

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


 

 

 

 

 

Pro Tips on Building a Code-Compliant Deck

By Rob Robillard

There are approximately 40 million decks in the United States, and only half of those are code-compliant.

Deck safety is a real problem. Every year we hear about decks that collapse under the weight of people or snow load.  Improperly built decks can be dangerous.  Local codes were created to keep us safe, and many existing decks do not meet current safety codes.

If you’ve always dreamed of building your own deck but were hesitant to tackle such a large, complicated construction project, well I’m here to tell you it’s not that difficult. In this article we demonstrate the proper techniques for building a small, simple, low-to-ground deck.

Basic Design

Layout of a deck sometimes starts on that proverbial napkin drawing and needs to be transformed into reality. Whether you’re building off a napkin sketch or a detailed architectural drawing, you need to transfer the deck design onto the ground to get started.

I lay out the deck using 12-in. ground spikes at each corner of the deck. For better visualization you can join the spikes with string to show the perimeter of the deck. This is often helpful for decisions on size, spacing, etc. I sometimes leave the strings up for a few days and ask the client to walk around, place furniture, etc., to make sure they like the size or shape of the deck.

Joist Size

When planning a deck, one begins with the sizes of the framing material. This often is determined by the joist span needed. Joists typically extend from the ledger-board connected to the house. To reduce cost and material waste I always try to work within readily available pressure-treated lumber lengths, such as 8-, 10-, 12-, 14- and 16-ft. long boards. It helps to know what size material you can get; for example, I know that my lumberyard carries 20 foot boards but only in the 2×10 sizes. Any longer than that and you’re dealing with special orders or adding additional footings or beams to support joists that span the distance.

Joist Span

When choosing deck lumber based on joist span, I use the following easy-to-remember rule of thumb that works for most of the treated wood species that

I use for building. This rule is not a substitute for a proper table of spans and sizes of framing lumber, but is helpful in over-designing my joists during the early phase.

Rule of thumb for joist span: Take the “depth of the framing member” and add half that number to determine a rough footage estimate for the deck’s joist span limit. For example, on a 2×10 take 10 and add half of that (5) to equal 15. The rule of thumb says that 15 feet is your maximum allowable span for a generic 2×10 deck joist.

In my experience this rule of thumb always comes in shorter than the building codes allow—which is a good thing! This rule also assumes you are spacing your joists 16 inches on center.

Once you have determined your joist size, use this size lumber for all components of the deck frame, ledger, perimeter rim joists and blocking. For exterior use, we always use pressure-treated lumber for our framing.

The deck we build in this article is approximately 20 inches off the ground and as a result is not required by code to have a railing system on the steps or deck. The owner preferred an open, no-railing look.

If your deck is more than 30 inches off the ground it requires guardrails or handrails.

Ledger Board

I start all of my decks by determining the length of the ledger board. A ledger board is the part that attaches the deck to the house. It is the first board to be installed because it sets the base for the rest of the deck.

Most decks begin with a ledger board connected to the house rim joist.

Most decks begin with a ledger board connected to the house rim joist.

The ledger board attachment supports one end of the deck and bears about half the weight of the deck, the other half borne by the posts and footings. This means that proper attachment to the house is extremely important.

The ledger board requires continuous flashing against the house and over the ledger to prevent water intrusion. The flashing should lap up the house behind the siding.

The ledger board requires continuous flashing against the house and over the ledger to prevent water intrusion. The flashing should lap up the house behind the siding.

In my neck of the woods I always try to install my ledger board so my finished deck height is 7 inches below the house interior floor. Stepping down 7 inches onto the deck reduces snow buildup and rain splashing and getting in under the house door. It also allows for me to install ledger flashing. The ledger board must be located 4 to 7-3/4 inches below the door sill. Snap a level line for quick reference (but don’t put away the level!).

The International Residential Code requires decks supported by an adjacent house to be built with a “positive attachment” to resist lateral loads. The latest permitted lateral-load connection detail requires hardware that connects the bottom of a joist back to the wall plates, foundation, studs, or window or door headers. Check local codes for requirements in your area. (See sidebar for the latest technique to make the necessary connection.

The International Residential Code requires decks supported by an adjacent house to be built with a “positive attachment” to resist lateral loads. The latest permitted lateral-load connection detail requires hardware that connects the bottom of a joist back to the wall plates, foundation, studs, or window or door headers. Check local codes for requirements in your area. (See sidebar for the latest technique to make the necessary connection.