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GeoffM 05-09-2012 12:31 PM

New Framing/Foundation Plan for Existing Addition
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I have an existing sunroom off the back of my house, it's 13'8" deep by 17'6" wide. The current "foundation" runs 2/3 of the addition perimeter with one side open to access a partial dug out crawl space; which has an average of 4'6" headroom. The 2x8 joists are unevenly spaced but average 14" spacing. I'm using a trial of SmartDraw and I've attached a jpeg of the drawings.

1" = 4'
The brown is existing framing and the yellow is planned. I basically plan on cladding the rim joists with new 2x8. Creating a 20' beam with 3, 2x10's, glued and nailed. Sitting on 4 6x6 PT posts on metal saddle brackets set into my 18"x18", 6" deep square footings.

I'll also be putting another 2x10 fastened to the house wall under the existing ledger board with 6" Lags offset every 12".

Does this look good? Any comments would be appreciated.


GeoffM 05-09-2012 01:22 PM

Forgot to add, could I get away with 2 posts; one on each corner with a triple 2x10 beam or would I need a 2x12?

nealtw 05-09-2012 04:58 PM

We never get away with post footing that small, most often 30 to 36 " sq. and 10 inches deep.
Your best bet is to draw up your plans and go get your permit. You might be able to use three posts, draw your plans that way and if that isn't good enough they will let you know.

GeoffM 05-09-2012 05:30 PM

I was originally thinking of doing a 12" depth for the footings but according to code it's min 4". The post height may change depending on what's down there, the house is sitting back from a rock face and I can see a bit of limestone sticking out of the ground a few feet from the sunroom.

nealtw 05-09-2012 08:55 PM

The weight landing on it and the soil conditions do make a difference and then there is local codes. Up here the designer puts in what he thinks, if the city dosn't like it they will change it or ask for an engineer to look at, we call them geo-techs, they check the soil structure.

AndyGump 05-09-2012 09:38 PM

What is your location?

I don't mean to be harsh but that does not look like a safe addition at all.


GeoffM 05-10-2012 06:38 AM

I'm in Ontario, Canada. It's not safe, we don't use it all; the current support is much worse. But it's grandfathered and I'd never get a permit to build a new one. I can get one to fix/reno the current footprint.

It's mixed soil, sand/clay/rock mix and I might have to pin the footings to limestone.

nealtw 05-10-2012 07:11 AM

Andy; The question was, "what do you think" I'm not sure a blanket statement like unsafe, adds to the discussion. Geoff is trying to develope a plan so he can understand what the problems might be.
Geoff; A beam to support this for an 18 ft span on 2 posts would be huge and expensive.

GeoffM 05-10-2012 10:13 AM

Is a beam made from 3 20' 2x10's strong enough for that span? with 3 support posts along the front and I could put one on each side.

nealtw 05-10-2012 03:09 PM

It all depends on the room above. You will have to figure how much load you have, including snow load and how that load is tranfered to the beam, and how much weight is on each end of the structure, this the stuff engineers figure out.

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