Question on height of foundation with sonotubes.

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PolyBatman

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I am planning on building a very small house with a wrap around porch. By small I mean 400 square feet. I am going to make it square with a hip roof, and hopefully a 4 foot wide wrap around porch. I would like to have the house raised off the ground 7 feet. Also I would like to make the walls tall enough so that I can extend the roof joists to cover the porch. This is so I can enclose the porch with a screen. How feasible is this and what issues might I run into with the foundation? The reason I'm asking is because I would like to utilize the space under the house without actually having to enclose the space. Any insight would be appreciated, thanks!
 
I'd be using pilings set to below the frost line.
Sort of like this.
https://www.google.com/search?q=Pil...cO0A-w&biw=1366&bih=657#imgrc=QEtkvOHFuJZ8pM:
Very common to build this way in a flood zone.
Going to find out real quick a 4' porch is about useless.
Going to have to walk sideways just to get by someone sitting in a chair.
Just build the roof so it extends out beyond the outside walls of the porch.
You want that roof to extend a minimum of 12" beyond the porch walls to reduce the amount of rain getting in.
 
If the pitch of the roof is 6/12, adding four feet will bring the roof down 2 feet . A 9/12 will bring it down 3 ft.
You could add beams over the porch and extend the roof to include the porch.
 
Alright I took your suggestions into consideration and reworked some of the numbers. I decided to run with a 4/12 roof pitch and go with an 8 foot deep porch. This put the roof height at 6 feet, and should allow for the trusses to extend all the way and cover the porch. This should be perfect and I live in a hot climate so I don't have to worry about snow at all. Do you think that raising the house 7 feet off the ground is too much, or will be possible? I might drop it one foot down to 6 feet off the ground. I just find it would be nice for security purposes as well as flood purposes. The depth of the frost line is pretty shallow at 12".

Edit: Argh, I forgot to factor in the 12" extension past the porch. Let me do that real fast. Not too big of a difference, 6.33' for the roof height and 20' for the truss length. That should be perfect, with 8' walls for the house.
 
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For the foundation I would use poured concrete in sonotubes to just above grade and 8x8 pt posts on galvi stand-offs to at least 7'. Pt in the ground will always eventually rot. If you look at houses on the Outer Banks of NC you'll see huge houses that are raised even higher. Cross bracing is also needed.
 
If you want to eliminate the cross bracing go with masonry piers either brick or concrete block on a suitable footer. With wood posts you'll need X bracing in both directions which will limit the usability of the space under the house.

You might be able to eliminate cross bracing with sonotube piers. I'm not sure, I don't build for a living so I'll defer to the builders here. I can eliminate cross bracing with brick piers here in NC.
 
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If you dig a hole for the post to frost depth and enlarge the bottom of the hole for a footing. fill the hole with concrete add sono tube and fill to construction level, 3 lengths of 5/8 rebar in each all the way to the footing. The sono tube has to be supported and braced in place. run a 2x4 right beside where the tube will go and when you are ready, wrap it with shrink wrap to hold it in place.
 
Well it is going to be built in the NE of Texas. There shouldn't be much of a snow load and the frost line is right around 12". I was definitely wanting to do the piers all sonotube. I was going to get some footing attachments for the sonotube and if rebar is necessary for the structural integrity of the sonotube pier I can accomplish that pretty easily. I haven't calculated the weight of the structure but it is going to be single story. Plus I was thinking of pouring enough sonotubes to support the wrap around porch as well as the structure of the house. I'll get some more numbers run and see if I can figure out how many piers I'll need and the spacing. Also with being able to install brackets into the top of the sonotube piers it should be rather quick to install the floor joists and get the floor down fast.
 
Before you get too far ahead of yourself make sure local building codes will allow such construction and that you will easily be able to get insurance on the finished dwelling. They may not except your calculations as it is not the normal method of building in your area, and they may want to see designs and calculations from a pro. Geodesic buildings are like that around here. They will allow them but you have to jump thru some hoops first.

With a proper design for that size building I would think 4 corner piers would be enough and the decks could be cantilevered out if only 8 foot. If you are going to all the trouble to build in this manner then make it high enough so the space under it is of use I would think 8’ would be more like it. Sometimes I see them with garage space below and sometimes a small core structure below that holds the utilities.
 
Well luckily the county I'm in has no building code requirements outside of septic. So I shouldn't have a problem getting anything constructed. I will still get plans drawn up, architectural and engineering, and get everything inspected in case there is any kind of inquiry into the property in the future. Since I am going to be doing a lot of the construction myself I am almost thinking that as much as I would like it to be 8' off the ground it would increase the difficulty in working on the structure. Since of course I would be 8' off the ground, lol. I might have to build one structure and then come back and build another structure 8' off the ground in another location. For now I might make it more reasonable at around 4' or 5' so if I fall I won't necessarily hurt myself too bad.
 
When you're done, the first thing you'll say is that you wish you built it 8' rather than 5'. Especially after you bash your head a few time hunched over under it.
 
I wouldn’t call it lucky exactly not having building code, and that is coming from a guy that often finds some of the codes to be a little excessive for someone that really knows what they are doing. On the other hand many times too much is better than not enough and is really better than none at all. It’s good you will be having some plans made and if you would want to share them or photos as the house goes up I know many here would like to be part of it from afar.

I think this would have been a case if we would have known your location in general the advice may have been different. Most assume you are in the states when no location is given and we assume you have access to all the building supplies and equipment we have at our fingertips in the state.
 
So if you put in posts and you put beams, post to post to hold up floor joists and the deck. I would just use 3 rows of posts, one down the middle and one on each outer edge of the deck, use treaded floor joist as they will include the deck. above the deck I would install posts and beams, same height as the was of the house, order trusses full length over the decks and all the weight of the roof is on the beams over the deck.
Bud a cantilever is limited to 1/4 the length of the member. So a 4' cantilever is a joist that is 12 ft long, eight feet inside the building. eight ft would be out of the question.

If there are no codes, it is still best to understand best building practise, but that is why yoiu are here.;)
 
Good thing no one ever told Frank Lloyd Wright that.
I do agree but in a 16x26 building I would want the posts under the load bearing walls and down the center wouldn’t be too bad an idea. The porch if not cantilevered (somehow I thought the OP was talking 4’) but if it was 8’ then some smaller poles to support the deck. So actually 5 rows of poles.
I personally wouldn’t want to see the weight of the whole building not be supported at the load bearing walls.
 
If the roof is supported on the outside beams of the deck, the outside walls are no more than interior walls in any house. You would just double the joist for the front and back wall to sit on. I am talking 2x10 joists and 2 or 3 ply 2x10 beams and solid blocking between the joists at the side walls. Strap the the joists with 2x4 on the flat and install subfloor for the house area and build the house on that. Galvinized flashing behind the house wrap and below the decking on the oustide.
 
The OP started out wanting a 20x20 building and associated structure with 400 sq ft of living space. By adding 8’ all around and extending the structural supports out to include a 8’ wrap around the structure is now 1296 sq ft or 3 times the plan and at 3 times the cost most likely. That’s a lot of structure for just porch space.
In the southern states here they don’t have basements and just crawl spaces. It is much more cost effective to put in more support piers and shorter spans and size all the material down. I see this as kind of the same type construction.
 
Good thing no one ever told Frank Lloyd Wright that.
Click to expand...

Falling Water wasn't built of wood, it has a massive concrete foundation to support the cantilever. Neal was referring to a structure built of wood. A deck cantilevered out beyond 1/4 of the length of the joists would run the risk of tipping the whole thing over if you had a big party on the deck without a corresponding weight on the other side or in the house.

Deck building codes have gotten a lot tighter over the years because decks collapsed and hurt and/or killed people. When I look back at the builder built deck on my first townhouse I shake my head. It was one story off the ground with 4x4 posts and no cross bracing. A neighbor's deck had a shimmy in it so the builder installed a piece of steel cross bracing on the underside of the floor joists. The foundation in PA was a hollow core concrete block just below grade. If I remember correctly there wasn't any bolts holding the rim joist to the posts. It was built in 1984 and I haven't owned the house since 1988 so my memory may be a bit off. The decking was 1x6's (not 5/4 decking), nominal 1" boards used for fences. YIKES :hide:
 
I do know Falling Water is made from concrete and have been there many times. My comment was mostly tongue in cheek and maybe Frank should have talked to Neal as a few years ago the large cantilever deck was in danger of falling off and a huge project was undertaken to post stress the massive slab.

I don’t know but I haven’t seen the OP in a while so like many threads we end up talking to each other as to how we would best do what. In a situation like this where we would follow Neal’s plan and deal with the outside walls as if they were interior non load bearing walls, I was wondering if all the framing in the floor would be PT as 8’ of it will end up exposed outside as the support for the porch floor and subject to the weather?
 
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