Deck Building Basics
Components Of A Well Built Deck
Many decks are constructed with too few fasteners, weak deck to house connections or are improperly flashed and subsequently prematurely rot.
Around the country, hundreds of people are injured by failing decks and in almost every case the decks collapse because inadequate fastening allows them to pull away from buildings.
Deck building basics are discussed in this article.
DECK FASTENERS: Deck Building
It’s important that you use the right type and size connectors to install your deck ledger board to the house framing.
The connectors your choose will be required to support hundreds of pounds of shear load as well as prevent the deck from ripping away from the house.Attaching a ledger board to the house rim is the most basic and best option of all the ledger board applications.
The most common method is to install ½” lags with washers or carriage bolts with washers.A ½ x 4” lag bolt is rated to provide 180 lbs support of allowable shear load per screw.Many types of structural screws [Timber Lock and Ledger Lock] are also available from various fastener manufacturers.
To do this you need to be able to access the basement and be able to reach the inside face of the house’s rim joist.Unfortunately, due to framing configurations, mechanical equipment location and finished basement walls and ceilings; this is not always an option.
Contractors must now make sure that the fasteners they use are compatible with non-arsenic treated, CCA, pressure treated lumber that is sold today and used to prevent corrosion.
This non-arsenic pressure-treated CAA wood has chemicals that accelerate the corrosion of galvanized metal components, typically used on decks.
According to the IRC two galvanized lateral load connectors [tension ties] need to be installed to connect the deck joists to the interior house joists. I recommend using Simpson Tension Ties # DTT2Z on new decks and retrofits. these connectors tie the house and the deck together and protect against lateral loads from seismic, high winds or movement of people on the decl.
DECK HARDWARE: Deck Building
Heavy coated joist hardware specifically manufactured for the new pressure treated lumber, like Simpsons triple coated galvanized, Z-Max joist hangers must be used.Stainless steel hangers are by far the best solution but also the most expensive.
Aluminum, lead and copper flashing should have a rubberized flashing barrier between it and the pressure treated wood ledger, this helps decrease the corrosion rate that occurs between the flashing and pressure treated wood preservatives.
A second beneficial point for using the rubber flashing is that it helps prevent rot and decay as a result of water accumulation under the deck boards.
DECK FLASHING: Deck Building
The most critical concern while installing the ledger board should be how to prevent water from entering the seams into the house. Many of the deck repairs that I have fixed can be traced directly to improperly flashed ledger boards.
If the flashing fails and water penetrates into the house framing it can result in severe mold, decay, and overall serious and expensive structural damage.
All ledger flashing must extend 4” up and under the house siding before bending the material over the top of the ledger board.
I prefer to remove all the siding in the area and install a rubberized flashing membrane directly on the sheathing, this is called as “back flashing.”
The ledger board is then installed on top of the back flashing.
I then apply a second rubber flashing over the top of the ledger board and up and onto the back flashing, creating a redundancy flashing barrier and also separating the PT wood from my metal flashing. An excellent illustration of this detail can be viewed here WOOD.COM
It is important to take precautions to make sure that you overlap and seal all seams with a 6 to 10 inch overlap and that yo never allow the flashing to be punctured by nails or screws.
I also recommend flashing the entire joist with either tar paper or a rubber flashing product.
Deck Repair or Placement?
Is your deck up to code? Should you replace it or retrofit it? READ THIS!
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