Problems with an Exterior Deck?

Friday, 21 June 2013 00:00

When out on her deck, a customer noticed the deck moved when she moved across it.  Upon close inspection, she noticed a sagging girder.  She then called Cottage Construction Company for a building solution. 

Finding rot and/or failed, framing members that support a deck can be more difficult than it might at first appear.  Often these structural members are in hard to access places.  Even if they are not, few people remember to conduct annual inspections of their decks--particularly if their decks were built-out of Douglas Fir, a common and affordable species of wood more appropriate for interior spaces than exterior spaces.

Typically, Cottage Construction does not make any exterior wood structures from Douglas Fir. This species of wood does not resist termites, powder post beetles, or dry rot as well as other types of wood such as redwood or  cedar.  Although Douglas Fir is cheaper and dimensionally stronger than some of the other soft woods, it can be relied upon to have a long, structural life if kept relatively dry (below a 14% moisture content).

On the north coast of California, exterior decks do not qualify as dry installation locations; however, Douglas Fir also comes as a "pressure treated" product.  Under this process, the dimensionally-sized Douglas Fir boards and girders are subjected to a copper solution, usually alkaline copper quaternary.  This solution has a high copper content and high corrosive properties, so when pressure-treated fir is used for exterior projects, special hardware considerations are necessary.

Also during installation of structural members for decks, special considerations must also be taken with every exposed cut from pressure treated Douglas fir since the copper solution does not penetrate 100% into the wood.   If these precautions are taken--with other building pratices to reduce chances of rot and infestation to increase the lifespan, decks can last more than 50 years.

The deck we serviced in this picture was built in the late 1980's.  Although the deck has been well-maintained well and was painted routinely, places exist on any deck which will eventually fail before any other due to the inconsistent nature of wood, use, and installation.  Where the deck boards weight against the structural joist network, these sites commonly give way before any other.  By taking a sharp object of any kind, such as a knife, and poking the joist directly below the deck board connection, you can make a simple test of your deck's integrity at that point.  If your pointed object sinks easily into the joist, there are probably other areas on your deck which may be failing as well.

This particular deck, in the adjoining photograph, had some life left to it; thus, we desided on balance, we could make minor repairs for safety, but put-off demolition for some years--sparing the customer an immediate large cash outlay and giving the presently used resourses a little more life.



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