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Small Cabin Forum / Cabin Construction / Framing on top of floor joists or flooring?
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Usa89gt
Member
# Posted: 19 Nov 2013 13:07
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Hi there,

Still getting my ideas straight before starting. I want to install 1x6 random length pine T&G flooring but don't want to do so and have them get wrecked by rain/snow while building. Can we frame directly over the joists and then install floor when enclosed? I wanted to install pine floor directly over joists without any subfloor. I will also insulate between the joists. Thx for the help

MtnDon
Member
# Posted: 19 Nov 2013 13:24
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You can but you shouldn't.

Using something like plywood or osb sheets gives the floor diaphragm lots of rigidity; helps keep it square. Before sheet goods like osb/plywood builders would lay boards on a diagonal across the joists, build the walls and the roof and then lay the hardwood strip flooring on top of the board sub floor. Anyway you do it the subfloor does have a purpose. Strip flooring laid at right angles across the joists adds very little rigidity to keep the floor diaphragm square.

Usa89gt
Member
# Posted: 19 Nov 2013 13:31
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Can I put down 7/16 OSB plywood and then the 1x6" on top? Just trying to find a cost effective solution. Thx

Salty Craig
Member
# Posted: 19 Nov 2013 14:11
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I would put a subfloor of some type first. If you use 7/16 osb, just be carefull that you don't fall thru!! Your finish floor with t&g will be beautifull. Good luck

Salty Craig

MtnDon
Member
# Posted: 19 Nov 2013 14:26
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Quoting: Usa89gt
Can I put down 7/16 OSB plywood and then the 1x6" on top?


Let's take a step back for a sec. What is the spacing on the floor joists? And have you ever walked on a roof sheathed with 7/16 osb? Roofs with 7/16 feel bouncy to me even with joists 16" OC.

Add to that, 1x6 pine is not very stiff when laid flat like for a floor. T&G helps the stiffness a very small amount.

Maybe, and that is a big maybe,... maybe the floor stiffness would be satisfactory if the joists were 12" OC, then the 7/16 osb and then 1x6 T&G. But that is a gamble. Personally I would not want to take the chance. I would also not want to place anything heavy like a iron stove on such a floor.

Note: 2 thinner layers nailed to joists is never as stiff as one thicker layer. Never. More joists would help, but there goes some of the savings.

Quoting: MtnDon
You can but you shouldn't.

I stand by that. Figure that if 7/16 osb was okay for subflooring then builders of cheap tract homes would be doing it.

MtnDon
Member
# Posted: 19 Nov 2013 14:35
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Maybe 5/8 would be an adequate compromise ???

PatrickH
Member
# Posted: 19 Nov 2013 15:33
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one house we lived in had an addition with 1/2 plywood subfloor over 16" o.c. joists terrible floor.

toyota_mdt_tech
Member
# Posted: 19 Nov 2013 15:52
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You need to sheet the floor with a thicker material, I'd say 3/4" then install walls, then its all dried in, install your pine board flooring.

I do not use OSB for anything,b ut thats just me.

Usa89gt
Member
# Posted: 19 Nov 2013 15:53
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Thx guys.... What would u suggest for a sub floor?

Salty Craig
Member
# Posted: 19 Nov 2013 16:03
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Advantech. It's the best

MtnDon
Member
# Posted: 19 Nov 2013 18:31 - Edited by: MtnDon
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Advantech is an OSB product, but with superior adhesives and water resistance. It is great! It is a T&G product. Or of that is not available then a T&G OSB. Last I would choose T&G plywood. Do not beat the T&G joint together with a big hammer. It is meant to have a slight surface gap. That has to do with spacing for expansion.

Use construction adhesive if you worry about squeaks. Use ring shank nails if possible. Or screws. 12 inch spacing on edges, 6 inch in the field. Lay them long dimension across the joists and stagger the joints between panels. Also do not have strips less than 16 inches wide around the perimeter anywhere.

Usa89gt
Member
# Posted: 19 Nov 2013 20:51
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Thanks Gents! I appreciate the feedback!

Borrego
Member
# Posted: 19 Nov 2013 21:04
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I did exactly the floor you are doing, it'll work out fine, but you must lay a subfloor. I'm old-school and not a fan of OSB (yes guys, I know the new stuff is better, just too many old nightmares) , I used 3/4" CDX, then glued and blindnailed the 1x6 pine. Then toe nailed the ends of the boards where they butt - it is super solid!
You can get pressure treated 3/4 ply nowadays, other wise, I'd prime both sides of whatever you use..

+1 on what Mtn Don sez , critical that you do both...
Quoting: MtnDon
Lay them long dimension across the joists and stagger the joints between panels.
Canebrake_2222413.jpg
Canebrake_2222413.jpg


Just
Member
# Posted: 19 Nov 2013 21:05
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I built one with roof deck for sub floor and covered it with hard wood as soon as the roof was on . It had 16 in spacing in the floor joists. It was a little bit soft till I got the hardwood on but it worked for me and I would do it again ..Just my thoughts

leonk
Member
# Posted: 19 Nov 2013 21:27
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While in theory I get it, sheet goods or diagonally installed decking makes the structure more rigid, but it it's not necessarily needed structurally.
It depends on the house size and the expected loads. I'd say if you plan to repeatedly ram your truck into one of the house corners - it'd be important to make it as resistant as possible to diagonal deformation.
And since we're talking small cabins here, the most one can expect is subfloor and 'finish' floor installed at 90 deg to each other, they will lock (assume nailed) and hold each other in place. If I had the funds I'd use solid wood for the subfloor instead of ply or OSB (avoid the damn glue).

Borrego
Member
# Posted: 19 Nov 2013 21:38
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That horizontal diaphram is real important even in a small structure...it makes the whole place solid from stem to stern..it'll quell racking 2 stories up......I would not do without it, but I'm a builder, always done it overkill I guess, maybe it's not really necessary, I would do whatever Don says

Martian
Member
# Posted: 19 Nov 2013 21:42
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I do a lot of home repairs. One thing I've noticed, after about 10 years, the construction adhesive is hard and doesn't adhere everywhere. The floor moves against it, and it squeaks. I've taken to using a good bead of silicone on the joist. Wood breathes. Silicone stretches, Even if it breaks loose at some point, it will still act as a cushion.

That's my thinking, anyway.

Tom

MtnDon
Member
# Posted: 19 Nov 2013 22:08
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Borrego, you are right on the money and I'm not just saying that because you and I agree. Many do not realize a building is the sum of its parts. Cheap out in something structural and sooner or later it will bite back. Of course do not follow the 'good enough' school of building. I want better as 'better' stands a chance of being passed along to future generations.

Borrego
Member
# Posted: 19 Nov 2013 22:26
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Quoting: MtnDon
Many do not realize a building is the sum of its parts.

Yes - a proper horizontal 1st story diaphragm will shore up the whole structure, all the way to the 3rd story roof deck. Create a diaphragm and strap it to the next diaphragm (either horizontal or vertical) and there you have a solid building that will last forever. Just because we are building cabins does not mean we can't make them great, right? It takes literally no extra time or money IMO.. Think of it like a wooden puzzle, it all locks together, and the tighter the bottom floor, the better the whole house will be....arrrgghhh I don't know it's hard to explain it....

Oh, and if you have already framed floor joists at 16OC, or 24OC you can add a post underneath, I had to do this...no big deal...bottom line: do it right, do it once

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