"Is my deck safe?"
Column #866 10/01/11
On The Level
Q. We moved into our 15 year old house last winter and we really havenít gotten a lot of use of the rear deck. Iím wondering if all this rain has had any affect on it. Is there a way I can tell if my deck is safe? I was told in one of your past articles that you had a home-made recipe for deck cleaning. I understand that a power washer is not the way to go since it can damage the wood. Could you please give me the recipe for the cleaner? Also, do you have any suggestions to clean light colored carpeting that is along the wall that has gotten black?
A. A great many of the decks that hang off the backs of houses in this country were added after the house was built and after the local building inspector had been and gone for the last time. Either the homeowners decided to build the decks themselves of they hired someone to do it but the bottom line is that the whole project went ahead without any third party supervision. The safety and structural integrity of those decks was a pure roll of the dice and depended completely upon the skill and experience of whomever did the work. As you can imagine, this is a recipe for disaster. The worst that I recall was out in Chicago some years ago where a 3 storey deck built without a City permit collapsed with loss of life plus serious injury. That is unnecessary to the point of criminal. Prof. Frank Woeste of Virginia Tech, a nationally known engineer specializing in wood construction, told me at a conference that during summer there is at least one catastrophic deck failure somewhere in this country every day. That got my attention.
The weak point of old or under-built deck construction is in its attachment to the house and lateral stability. In the old days, the deck framers used to just nail the house side band-board-- the board into the which the deck joists perpendicular to the house will be attached-- into the rim-joist-- the corresponding framing member of the house. The ability of this arrangement to work depended upon the size of the nails and the number used and at best wasnít a dependable connection should the deck ever become ďloadedĒ to design loads. Design floor load of a house is forty pounds per square foot of area and a 12í x 10í deckís design load is 4,800 pounds or the curb weight of a old Cadillac sedan. Now itís true that most floor systems donít get loaded to design load regularly and with a poorly connected deck nails gradually start to pull out until that crucial moment arrives and down it goes. A lot of rain can soak the wood and weaken the nail grip.
Building codes in the 1970ís began requiring bolting the decks to the house at ever closer intervals until the whole notion of relying on the strength and redundancy of those bolts was wisely deemed too unreliable. Now if you were to construct a deck using current requirements the deck would be a freestanding structure with bearing down to the ground at least at all four corners and more as the size increases. Properly constructed decks are now so strong that the house could fall down and the deck would still be standing there and the Cadillac could still sit on it. If you donít know the pedigree and history of your deck youíd be wise to check it out. Crawl under the deck and look for bolts holding the deck to the house. if you donít at least see that then call a private inspector or deck contractor out and make the appropriate changes as needed to keep your deck where it is.
The black band you see at the carpet edges is called filtration soiling and is caused by air movement under the bottom plate of the wall up to which the carpet is laid. The only known cure for this, beyond installing dark carpet to mask it, is to take up the carpet and the edge tack-trip and use an elastomeric caulk such as an acrylic-latex. Caulk sealing tight the junction of wall and subfloor. Then re-install the carpet.
The deck washing recipe is simple. I pass it along a couple of times a year in this column. Wash the deck with a mixture of 1-cup laundry bleach plus 1/4 cup TSP (tri-sodium phosphate) to a gallon of hot water. I used to recommend automatic dishwashing detergent but manufacturers have been required to remove phosphates from it nationally and it doesnít work as well anymore. Scrub on with a plastic bristle brush. Scrub well. Wait until itís almost dry then hose off. Wait a dry week then seal. Works on roofs and siding as well. You can buy deck washes at hardware stores and they work too but my recipe is cheaper. After all this rain any algae growth will be flourishing so now is a good time to get after it.
Iíll be starting my Basic Home Repair class at the Edgewater Senior Center Tuesday October 4 at 10 AM. It goes for 90 minutes on six consecutive Tuesdays. Itís fun so join us if you can.
Keep the mail coming. If you've got a question, tip, or comment let me know. Write "On The Level," c/o The Capital, P.O. Box 3407, Annapolis, MD 21403 or e-mail me at firstname.lastname@example.org or email@example.com.