Seismic safety of houses on stilts?

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babyblue65bird
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Seismic safety of houses on stilts?

Postby babyblue65bird » Fri Aug 08, 2008 10:06 am

Hello all -

I spent most of yesterday driving around Mt. Washington and Eagle Rock, and have found a few interesting MCM houses, but they are all hanging off the side of the hill supported by stilts underneath. The stilts are basically wood framing, and the underneath kind of looks like the structure of an old wood rollercoaster.

It just looks shaky, but I presume that there are/were building codes for that type of construction that took seismic stability into account; does anyone know if these are really just waiting to tumble down the hill in the next strong breeze?
Where are we going & what are we doing in this handbasket?

daybreaker
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Postby daybreaker » Fri Aug 08, 2008 4:38 pm

Hi there. Maybe I can answer your question. I live over in NE LA and there are many homes up on stilts over in this part of LA. If the supports are steel and the footings are cement, you are probably fine as the footings are typically driven deep into the soil to the bedrock. The house will move with any earthquakes, and although it can be a bizarre experience, that's exactly what these mid century homes were designed to do. After the Northridge earthquake, LA city building codes were changed with something called Division 94. With Division 94, new hillside construction had to use an exterior skirt around the stilts. This is why you'll see the long box like stuctures surrounding newer hillside houses lower portions. You'll see this a lot on the eastern side of Mt. Washington.

Even John Lautner designed homes up on stilts, see his Garcia house:
http://www.you-are-here.com/architect/garcia.html

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Tony
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Postby Tony » Fri Aug 08, 2008 6:30 pm

I think those exterior skirts on stilt houses is more for fire protection then for earthquake reasons. Fires burn uphill really fast and can go up the slope and ignite the underside of the house.

If considering buying a "stilt house" it is always best to consult with a structural engineer first.

Tony
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modfan
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hmmm

Postby modfan » Sat Aug 09, 2008 8:38 am

That's why those homes off of Coldwater Canyon look so different now.
Compare Miss Thantatogenis' house in 'The Loved One' filmed there with what's there now, nearly all the houses have 'enclosed' their stilts, and a lot seem to have added living space there as well as adding more stories above.

daybreaker
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Postby daybreaker » Sat Aug 09, 2008 4:09 pm

I'm fairly certain the skirts are for Division 94 compliance reasons. I've read the city code and there's no mention of fire precaution.

Modfan: Yes, looks like many people decide to add on additional living space under the house. It's a natural place to add on. If you're interested in learing more, send me a pm and I can fill you in on what I know without boring the board.


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