Do tall foundation walls need bracing?

March 4, 2014 9:35 AM

I'm in the process of purchasing a house. In one of the many questionnaires, the seller responded "No" to the question "Are the exterior tall foundation walls braced?". Can you help me understand what this implies? and How concerned should I be? The house was built in the late 70s, in Northern California, where earthquakes are a thing.
posted by vega to Home & Garden (6 answers total)

You may want to retro-fit the house and have it braced, not cheap. When you have it inspected, be sure your inspector can address your question and give you a ball park of what you'll expect to pay to have it braced.

What is the foundation made of? If the frame is wood and the foundation is masonary, you'll want it braced.
posted by Ruthless Bunny at 9:40 AM on March 4, 2014

It is probably worth getting an opinion from a structural engineer on this, not just a home inspector. Yeah, it'll cost a few hundred bucks, but if it isn't a problem then the structural engineer is the person your insurance company will actually listen to, and if it is a problem, then the structural engineer can also help you with remediation plans.
posted by straw at 9:49 AM on March 4, 2014 [4 favorites]

How much of a concern it is depends on what "tall" means and whether the house in fact has any "tall" foundation walls at all. A basement or foundation wall acts pretty much the same as a beam or floor or roof, just resisting against soil pressure instead of gravity. It's quite likely that the walls in question are designed to adequately resist whatever forces they'll encounter - there were seismic design requirements in the 70s and the walls are likely reinforced in some way.

Exterior foundation or basement walls will generally be braced at the top just by the presence of the floor and its diaphragm, which will provide resistance against overturning. Late 70s floor diaphragms should have no trouble providing that resistance. If the wall is tall enough, there's a danger of the center of the wall blowing out, but this wouldn't be too likely.

If you're getting a structural inspection, which you should be doing anyway, you should probably bring up the point to the inspector as an area of concern.
posted by LionIndex at 9:52 AM on March 4, 2014

I'm a licensed engineer in the state of California. I've worked in structural design, including homes, for about 10 years.

The short answer is it depends on a number of things. This is exactly the sort of thing that you should hire an engineer to assess, and it will likely cost about $200-400. straw is right, the insurance company will want to have an assessment on record from a licensed engineer. The seismic design requirements have changed since the late 1970s, and it's possible the foundation isn't up to code. This is definitely a question you want answered before you decide on the house, as it could come up later and it would be expensive to fix.
posted by hootenatty at 10:31 AM on March 4, 2014 [1 favorite]

Does the house have a basement? If not (and a lot of California houses do not), this could be a question that would've better been marked "N/A". Otherwise, structural engineer is the way to go.
posted by Ham Snadwich at 11:07 AM on March 4, 2014

Another voice in the chorus. Consider a "no" in this checkbox to be shorthand for "No, I haven't had a structural engineer out to evaluate the property, so no bracing has been added and I have no idea whether or not bracing is necessary", and act accordingly by getting a structural engineer to come in and evaluate.
posted by davejay at 11:27 AM on March 4, 2014