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creeky
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# Posted: 1 Aug 2014 11:18am - Edited by: creeky
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I'm starting my winter bedroom. I want it to be 10x14, give or take, and be an "ultralight" building.
But first I have to lay the foundation.
I have these screw in foundation posts/piles/piers. I have run a one year trial which was a success, esp. given this years deep freeze and high water. The screw posts, unweighted, didn't move at'll.
But I can't decide whether to run beams through the post/pier brackets and then put the frame on top. Or just use the beams as the outside frame and string my joists between.
The frame method cantilevers the walls one foot beyond the beams. Method two would be a bit harder to move should that be required.
Any comments? Light weight framing ideas for the building? think I can get away with 24" joist spacing?
here's a pic of the two ideas. note the elegant drawing style.
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bldginsp
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# Posted: 1 Aug 2014 11:49am - Edited by: bldginsp
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With method 2, if there is any movement of the piers, it must pull the floor assembly apart at the joist hangers. Method 1 allows the joists to 'float' to a certain extent, on top of the beams. Just a thought.
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toyota_mdt_tech
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# Posted: 1 Aug 2014 12:02pm - Edited by: toyota_mdt_tech
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I was going to say "door #2" but bldg insp made a good point. How about a combination of both. Maybe large beams like #1, floor laid out like #2, but on top of beams IMHO, would be stronger, allow float as bldg mentioned also.
Why the light weight? They do make 2X3's, or how about metal studs, or a 7 foot wall? Or foam core panels for walls? Just ideas on making it light. Are you planning on being able to move it???
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creeky
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# Posted: 1 Aug 2014 07:50pm
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I hadn't thought about movement at'll. so thx b. great point.
tmt: I also want to do an interior sprayed in white paint with exposed joists. but metal joists... hmmm. it would look cool and be lighter. this is something I really have to think about. my only concern is my capacity to work with it ... trim etc. wood I'm used to.
Originally the room was supposed to be on a trailer (already bought, easily allows 10x14). but after looking at a friends 10x12 ... wow. that's a lot of weight. (even on the jacks I bought) and moving it a few hundred yards with a small tractor...
i am doing a building science "perfect wall". well. creeky style. I have been collecting polyiso sheet insulation for over a year and am thinking
: balloon frame; 1/4" structural sheathing (?); breathable barrier; and exterior insulation at 3.5" walls, 5" roof and 4" floor. the floor being xps for higher psi. finish to be determined.
on the polyiso insulation: if yer patient it's quite remarkable what you can find.
so far, basically new
: 15 sheets of 2" (10 bucks ea. yowzer!)
: 7 sheets 3" for 150,
: 7 sheets 1.5 for 100 (foil faced).
gotta get started tho. fall bird migration is on and that may mean it's an early winter? ... ack plllll.
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Don_P
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# Posted: 3 Aug 2014 07:01am - Edited by: Don_P
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Foam is rated in psi, most building materials are in psf. If you have uniform bearing there's 144 si's in a sf... if you're sandwiched under and on a solid substrate like osb it usually doesn't require high psi material. I recently paid about $30/sheet for 2" xps, good shopping!
Beams under a floor system really need some method to restrain them laterally, something restraining rollover. Generally this is provided by a perimeter foundation, absent that method 2 looks stronger.
Your screw post test was only successful in showing that they didn't heave. My fenceposts have 25 years of that type of testing however that doesn't mean they are capable of supporting a structure... gotta be careful when designing a test.
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creeky
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# Posted: 3 Aug 2014 09:02am
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thx Don.
Yes, there is no weight on my test limiting it's usefulness. the mfct. says 5000 lb load. ... i did hit the posts with my tractor, but that wasn't part of the test. I could go to 4 posts per beam...?
Will joist hangers and joists be enough to restrain lateral movement? I was thinking I would use frame #2 with 2x8 construction on 24" centers (just within the "table" acceptable 10'3". The beams could be 2 16' 2x8s with a plywood center, glued and nailed.
any other ideas for stabilizing the floor?
thx for tip on sandwiching. i used polyiso under a laminate floor in the studio ... not the best solution. it'll be coming up, mostly because 1.5" isn't near enough insulation in the winter. the 4" i used in the shizzer shack is perfect tho. that got another layer of ply subfloor.
for the 15 sheets 2" I saw the post on kijiji (canada's craigslist) called the guy, caught him driving with his wife. I had to drive out to the farm, get my trailer, and drive back into town. cash in hand. you don't see deals like that often. 2 other guys had already called ... I suppose I should add 50 bucks worth of gas to the bill.
really nice couple. they built an all but passive house. 16" walls etc. they missed the perm rating by a fraction on air change, just lovely work.
i tried to convince the mrs. that I should get a better price as I was clearing out the basement ... she didn't go for it. they did sell me a home built solar water heater, a la build it solar style, for $20 bucks. great day all round.
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Don_P
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# Posted: 3 Aug 2014 07:17pm - Edited by: Don_P
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Manufacturers of posts and piers are usually careful to only give axial load numbers, the vertical weight bearing capacity. The way they typically fail is laterally, tipping. The tractor test was probably the most meaningful. If they are steel, welding X's of rebar, angle, or something between posts would help brace them.
at 140 sf x 50 psf floor load you have 7000 pounds so far, add the roof and snow load for the total. I'm guessing the vertical resistance is adequate. At 6 posts each girder will bear 1/4 of the total building load, the mid posts will take 1/4 of the vertical load each, the 4 corners will take 1/8 of total load each.
Between subfloor and joists laterally restraining the flush girders it creates a stronger floor than setting it atop loose beams, you just eliminated one hinge. You need to provide more load info (snow) to check girder dimensions. Just as a FYI, plywood counts as zero in a girder, it is just filler if you need it. Glue also counts as nothing strengthwise but does make a beam stiffer.
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