New Building Code & Rules for Decks
May was Deck Safety Month, and this post will help you understand some of the New Requirements going into effect. If you would like an excellent document that explains how to build a deck that conforms to the 2012 IRC, download the free Prescriptive Residential Wood Deck Construction Guide, based on the 2012 International Residential Code. Anyone who inspects or builds decks should have a copy of this document, and have it available on their smartphone or tablet at all times.
Here are the two biggest deck requirements that stuck out this year:
DECK LEDGER CODE REQUIREMENTS
FOR LATERAL LOADS
New Requirements to Resist Lateral Loads
So, you own a home with a finished basement and no deck and you’d like to add a deck by attaching it to your house using a ledger board. Well, depending on where you live, your job may have just gotten significantly more difficult.
Changes to International Residential Code for projects where decks are supported by an adjacent structure (your house), now require a “Positive Attachment” to resist lateral loads. That positive attachment is a new piece of hardware called a Hold-Down Device “with an allowable stress design capacity of not less than 1,500 pounds”, which must be installed on at least two locations per deck (IRC 2012 Section R507.2.3).
These new hold-down devices must be attached to the joists of the deck, penetrate through the ledger board, the wall sheathing and band joist of the house, and then fasten to the floor framing inside the house.
The flexible chain of the GRK Deck Harness allows positive connection of house/deck joists that are not aligned.
So, if your home has finished walls, ceiling, cabinets, etc., blocking access to the home’s floor framing, then to satisfy the new code requirements you’ll need to deconstruct the interior to gain access. Naturally, this code change requires more labor, hardware and expense to building a new deck, and in some circumstances it may result in even further cost increases to the project, because the homeowner will need to repair the disturbed interior living space.
The change in code was spurred by deck failures caused by ledgers that pull away from the house structure, resulting in complete collapse. These problems are generally due to improper flashing and/or improper fastening that lead to water accumulation and rot at the ledger connection, weakening the structural integrity.
The Simpson Strong-Tie method utilizes a rigid threaded rod connected to two DTT2Z tension ties to satisfy the code requirement.
When properly protected with flashing, a bolted ledger-to-rim board connection—or a connection fastened with properly spaced and staggered wood structural screws—is a suitable connection to support the gravity load of a deck. However, the new hold-down devices are required to resist lateral loads, as required by your local building code. In such a case, the devices should be used to tie the deck joists directly to the house joists.
Whether or not the code change applies to your project depends on whether your municipality has adopted the IRC’s code change. Deck construction must always conform to local building codes and may also require a building permit. In general, building codes are developed by industry associations “to provide minimum safety standards for a home’s occupants, the environment and the public at large.”The codes are adopted and enforced by local governments and vary based on local political issues, environmental regulations, etc. Check with your local city building inspector to determine all local requirements.
If your local code requires installation of the hold-down devices, you have a couple of hardware options.
Lateral-Load Connection Device
The Lateral-Load Connection from Simpson Strong-Tie consists of two DTT2Z Deck Tension Ties—one screwed to the deck joist, the other to the house joist. Access is drilled through the ledger connection to allow passage of a rigid threaded rod that connects the two ties. This is a sturdy connection that meets the new code requirement and works well for deck joists that align with the house joists. However, deck joists don’t always line up with the house joists, and the Deck Harness from GRK Fasteners has the advantage of flexibility.
By utilizing a chain instead of a rigid rod, it’s much easier to adjust placement of the GRK anchors, enabling connection to offset joists, perpendicular joists or to wood blocking. The Deck Harness consists of a steel chain-linked assembly with a thermoplastic plug in the center that installs through the ledger connection. One end of the Deck Harness is attached to the house floor joist with a U-bolt and washer plate. The other end of the Deck Harness is attached to the deck joist with identical U-bolt and washer plate. The GRK Deck Harness is recognized in the ICC (International Code Council) Report ESR-3224.
The other advantage of GRK’s system is that the insulated plug prevents moisture and frost from building up on cold steel and causing a rot problem where the device enters the house. Rotting of the ledger is one of the problems with deck collapses, and the very reason for an additional support to hold the deck up.
In the event of deck failure and the deck separates from the house, these new lateral hold-down devices prevent it from completely collapsing.
Deck Tension Tie
This is just one type of lateral load connection device, and this specific device doesn’t need to be used. They’re just showing one example of a device that could be used. While effective, this particular device would be especially difficult to install, because it would require a lot of access to the framing inside the home, and would also require the building official to have to verify that the floor sheathing was nailed at 6″ maximum on center. How in the world is the building official supposed to do that on an existing home? Rip up the flooring? I think not.
These devices have an allowable stress design capacity of not less than 750 lbs each, so at least four of these devices would need to be installed on every deck. These aren’t specifically approved by the Minnesota State Building Code*, but if it’s good enough for the 2015 IRC, it ought to be good enough for us. More on that topic here: Installation Options for Deck Lateral Load Connections. I’ve heard a rumor that building officials throughout Minnesota are allowing these things, but it’s always wise to ask first. The Journal of Light Construction just posted a little blurb about these on their web site, along with a great cut-away photo showing one being installed: http://www.jlconline.com/framing/simpson-strong-tie-dtt1z-deck-tension-tie_s.aspx
NO MORE NONSENSE ON DECK LEDGER CONNECTIONS
Section R507.2.2 says “Girders supporting deck joists shall not be supported on deck ledgers or band joists.” The photo below shows what this means.
Also under R507.2.2, it says Deck ledgers shall not be supported on stone or masonry veneer. The deck construction guide that I referenced above has slightly different wording on that topic, but I think the intent is the same; check out their diagram on the left:
Just in case their diagram doesn’t make it clear, here are a couple of photos showing what not to do:
The fix for all of these situations shown above would be to have the deck be self-supporting. In other words, it wouldn’t rely on the house for support.
In order to obtain a building permit for a deck attached to a single family residential home, your plans must be reviewed to be in compliance with the IRC. The International Residential Code (IRC) is a comprehensive collection of the specific rules that apply to residential construction and that is administered by the International Code Council (ICC). If you are a contractor, this book is a must have. You can buy a copy online at www.iccsafe.org.
Nearly all states in the US have at some level adopted the International Residential Code as the model building code for construction of one- and two-family dwellings (duplexes), as well as townhomes. Townhomes are unique multi-family structures with an unlimited number of connected dwelling units. However, the units must be separated from the foundation vertically to the roof; no part of any one can be under or on top of another. Each unit must also be open on at least two sides. Traditional row homes are an example of townhome construction under the IRC.
In regions that have not adopted the IRC, they likely use the group R-3 exceptions contained in the International Building Code. These exceptions generally modify the commercial rules to be very similar to the IRC. Building codes are not regulated at the federal government level, and they are the authority of the state.
The building inspector’s job is to interpret and enforce the rules as they are stated in the IRC. In other words, Inspectors are not allowed to make their own rules. Because of this, building codes should be fairly consistent from City to City and State to State.