The Bridgewater Deck That Was Built Into the Foundation

I was under a deck in Bridgewater last week, looking at how it was held up. That is where I go on every deck I inspect. The surface tells you how a deck has been maintained. The underside tells you how it was built.

This one was not built the way decks are usually built. The deck is carried by a beam that is secured into the home's concrete foundation. I have not run across many like it.

Here is what I could actually see. The beam bears at the foundation wall, and there is a metal connector at the point where the two meet. The framing above it looked sound in the areas I could view. Elsewhere on the deck there was localized rot in the planking, the frame and the railing. I did not see the attachment moving. I did not see anything failing while I was under there. What I saw was an uncommon detail in reasonable visible condition, and rot on the deck itself that has nothing to do with how it is attached.

Deck framing from underneath, looking along the carrying beam toward the lattice skirting.

Most decks are attached to the house with a ledger board, and that connection is where deck problems concentrate. The North American Deck and Railing Association puts the share of deck collapses that trace back to the ledger connection at about 90 percent. That number is useful because the ledger is a known detail. It has been built, inspected and studied for decades, so there is a body of experience behind it. A beam set into a concrete foundation is not that. I do not have a set of cases to tell me how this arrangement ages, how it behaves under load over years, or what it looks like in the early stages of going wrong. That is not a criticism of whoever built it. It is a statement about what is knowable from the outside.

Carrying beam bolted directly to foundation.

So this is what I told the buyer to do. Get a deck contractor in to price the rot. Localized rot on a deck usually means the deck is at or past its safe and useful life, which makes this a repair or rebuild decision rather than a patch. Then treat the point where the beam meets the foundation as something you look at on purpose. Once a year. After a hard winter. After anything heavy happens out there.

My opinion is that people read concrete as permanent. A deck tied into a foundation looks stronger than a deck hung off the side of a house, and I understand why it reads that way. But solid and understood are two different things. I am not telling anyone this deck is unsafe, because nothing I saw says that. I am saying that when a house is put together in a way I do not see often, nobody can hand you its track record, and the right response to that is to keep an eye on it rather than assume it is fine because it looks strong.

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