Mar 12, 2008

Be Wary When Buying a Home With a Deck

pr-post-crawl-0406.jpgGetting It Done. Paul A. Rude, retired General Contractor and member of the American Society of Home Inspectors, answers your questions on remodeling, dealing with contractors, and home maintenance.

Oh, boy, here we go again. A house I inspected for prospective buyers a few days ago had one of the "red flags" that give ASHI inspectors the willies: a big tiled deck with a view of the San Francisco Bay. This would surely be an asset, yes? Well yes, if it's properly designed and built. The problem is that a very large percentage -- 90% or more in my experience -- are not done properly, so they leak into whatever is below them. If your master bedroom is underneath, you're not going to be happy with an installation that's less than perfect.

Decks with a hard surface such as concrete, tile, or stone are often called "plaza decks" or "paved decks" by architects. The problem is that contractors and designers too often assume that such surfaces are waterproof. But concrete, mortar, tile grout, and similar materials absorb water. Once moisture gets past the surface, it will find its way into the structure if the waterproofing system is inadequate. When I see one of these, whether new or old, I tell my clients to ask for a warranty against leaks.

These decks are a nightmare for inspectors because it can be hard to explain how something can go wrong with a brand new, stunning, and very expensive architectural feature. In my recent inspection, the sellers, who had installed the deck and were "flipping" the house, got more than a little testy when I questioned their work. My client's agent made a note not to call me for inspections again, either. But defects in a deck can be extremely expensive to fix, so my responsibility to the client is my overriding concern.

Most of the critical details in a paved deck are concealed by the time a home inspector gets there, so we can only judge by the few visible clues. Below are some of the key things we look for.

Missing or improper flashings between the deck and adjacent walls. Flashings are transition pieces, usually of metal, that protect intersections in a roof. Oh yeah, by the way: If the deck is over a space that needs protection from the weather, it is a roof. It's easy to forget that when you're counting all the big bucks you're going to make from your flip.

Adjacent walls with improper waterproofing. One very common mistake is to bring the adjacent wall surface - stucco, shingles, or other siding - right down onto the deck. This is a great recipe for trapping water. We see this most often with stucco because builders -- and even some architects! -- still think it's waterproof. We want to see a separation of about 2 inches between the horizontal and vertical surface, with flashings visible between them.

Conspicuously absent flashings. Builders often figure that they don't need no stinking flashings because they are installing a "bulletproof" waterproofing membrane below the paved surface. They turn this membrane up the wall, cover the top edge with siding, and call it good. Problem is, most of these membranes deteriorate under ultraviolet light (that would be sunlight). Someone who took the time to read the manufacturer's specs would know that, but who reads? Even with materials approved for exposed installation, it can be tricky getting them to fit around corners and obstacles without creating bad seams.

Poor flashing at thresholds leading onto the deck. In better installations, a "pan flashing" is installed below a threshold; it normally extends to the interior side of the threshold and several inches up behind the jambs. Off-the-shelf pan flashings are sold in lumber yards, but a good one has to be made to specification in a shop. This is not terribly expensive -- it might add $150 or so to the cost of a $5,000 door -- but it requires actual thinking, a commodity all too rare in remodeling, as the flashing must be installed before the door goes in.

Absent drainage. We always look for a way for water to escape, both from the deck surface and from below it. The surface should slope to drains or gutters; just letting water flow over the edge and down the wall is certain to cause leaks. Drainage is also needed between the waterproofing membrane and the finished surface. This can be a corrugated plastic sheet, fine gravel, or other permeable material. It has to slope to a drain or gutter, which means that the supporting structure itself needs a slope. Although building codes have long required a minimum of ¼ inch per foot of slope for roofs, this is often ignored because building it flat is easier.

Waterproofing not accounted for in design plan. Maybe the biggest red flag of all is a designer who fails to specify the waterproofing details in the plans for a paved deck. Last summer, I looked at a $500,000 remodel in San Francisco that included a large tiled deck over a new media room. Flashings were missing and the waterproofing membrane appeared to be a roofing material turned up under the siding. The designer, an experienced architect, was on the job with a crew to take photos -- the project had won a prestigious design award. When I asked him what kind of waterproofing was used in the deck, he gave me a blank look and muttered something about "roofing." I got the call in January, about six months later -- the deck leaks and will have to be torn out and done over.


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Stacey Derbinshire