This month's issue of Family Handyman has some tips on beefing up an old deck. During home inspections, I focus lots of attention on the deck, mainly because so many are amateur-built. Mistakes abound, and some of them can be dangerous. I know that some of you are going to take a crack at deck-building this summer, and I'm hoping you can avoid some of the more common mistakes.
One frequent problem involves how the deck is fastened to the house. Lots of people use nails, some as small as 10d (not very big) common nails. Well, this can work for a while. When the deck is new, its header board is flat and straight, so all the weight falls on the nails as sheer load (force at a direct right angle to the length of the nail). Nails are very strong in sheer, and may hold the deck up for quite a while. These builders forget that the wood changes size and shape from age and weathering. The nails get pulled partly out, and because the header is no longer flat against the house, the deck weight now shows up as bending load on the nail. Nails are not at all strong that way, and they can pull out the rest of the way very easily.
The usual scenario for disaster involves a deck several feet above ground, maybe at 2nd story level. It seems fine, because the 2 or 3 people who use it daily don't produce much structural stress. Then comes the bbq/shower/rehearsal/birthday/graduation party. Now there are 10 people on the deck, and the nails just can't do it any more. Down will come baby, deck, nails, guests, barbecue and all. The lawsuits may start before the dust settles.
The deck should be bolted to the structure of the house. If this is not possible, use lag screws (big screws with hexagonal heads). The length of the screw should be 4" plus the thickness of any siding, flashing or trim that is in the way. Bolts and lag screws have way more resistance to pulling out than do nails, and way more strength against a bending load.
An even better way is to build the deck to be completly self-supporting, with no fastening to the house at all. This eliminates the whole bolt issue, and the potential for water seeping into the house along those bolts.
Handrails are another problem. Sometimes, there just aren't any. A stairway that has 3 or more risers should have a handrail. Studies have shown (yes, someone has actually done studies on this!) that people don't reach for a handrail until they feel themselves losing their balance. Then the hand shoots out for something to grab. If the rail is too big to get a hand around, it may not be of any use. In other words, a 2 x 4 is not a handrail! Newer, professionally built decks have 1 1/2" round rails mounted above the 2 x 4's, and this is very effective. Handrails should be 34-38 inches above the stairs, measured vertically from the front edge of the treads.
Guardrails, which run around the perimeter of the deck, are another issue. The current standards call for a guardrail on any deck, porch or platform that is 30 inches or more above the ground, and the rail should be at least 36 inches high. It should be strong enough to withstand the weight of an adult falling against it. Another way to describe this is that the rail must withstand a sustained 200-lb. load from any direction. I find older decks with very low railings, and a lot of decks in general where the rail is not strong enough to be anything more than decoration. This is basic life safety stuff, so you should follow the standards even if the local code people don't inspect it. (Most cities require permits and inspections on decks. Protect yourself by following the rules!)
The vertical elements of the railings are important, too. Space them closely, so that a 4-inch sphere can't pass between them. This is to keep little kids from wiggling out through the railing, or getting their heads stuck. You can tell that some of these standards are written by fire fighters; they get tired of doing the same old rescues.
One more item for home deck builders. That pressure-treated lumber everyone is so fond of is rot-resistant because it's treated with Chromated Copper Arsenate. Yes, that's exactly as poisonous as it sounds. Wear gloves when you handle it, wear a mask to protect yourself from the sawdust, and don't burn the scraps in your fireplace. Think about how much contact should take place between arsenic-treated wood and your bare skin. And your kids' bare skin. If you are interested in building a deck with less toxic materials, let me know and I'll do an article on it later in the year.
No monthly nag this time, just a semi-annual one! Clock-change time is coming up in 2 weeks or so, and I have a short do-list for you:
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Copyright 2001, Matthew J. Bezanson
This newsletter is a 2-way street. If you have any questions or concerns, please use this e-mail link to let us know.
Presented by Sherlock Homes Inspection, Ltd.
http://www.inspectmichigan.com
copyright 2000 Matthew J. Bezanson