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416 05-14-2013 10:22 AM

Shed floor question
 
I plan on building up the floor with a layer of ply on to of the joists, then rigid insulation and finish with another plywood on top.
Question...do I build this "sandwich" before raising the walls or do I put down the first layer of ply, raise the walls and then the insulation and finish ply within the boundaries of the walls.
Thanks

MJ Force 05-14-2013 11:01 AM

Quote:

Originally Posted by 416
I plan on building up the floor with a layer of ply on to of the joists, then rigid insulation and finish with another plywood

Do you plan on heating your shed? Rigid foam can be installed inbetween the joist. Then lay 5/8" or 3/4" T&G ply. If your shed is on dirt, make sure you lay 6mil poly on the ground.

Is there a reason you want to use a foam core floor?

416 05-14-2013 11:28 AM

I figured I'd avoid thermal bridging by placing on too of the joists. Maybe a little warmer in the feet.
Yes, I plan to heat the shed in winter.

MJ Force 05-14-2013 11:48 AM

Quote:

Originally Posted by 416
I figured I'd avoid thermal bridging by placing on too of the joists. Maybe a little warmer in the feet.

I see what your trying to do however, any product will transfer cold/heat. It's the rate of transfer that's important. R-10 transfers faster than R-20. I don't know the R value of wood but its generally acceptable in construction. Log homes for example. It's air movement that speeds up that transfer. You know, like wind chill factors.
Get the R value up in those floors. A foam core floor might have an R value of 8. Whereas you could add more R value with rigid foam between the joist. Remember to add a ground sheet.

416 05-14-2013 12:01 PM

Would the r value increase because of the air gap between the foam (in the joists) and the floor or just because I could get more in there.
Also, just for reference...would you build the layered floor then raise walls in the original scenario? Or just sub floor then walls then rigid and floor top after raising walls.
Thanks.

MJ Force 05-14-2013 12:45 PM

Quote:

Originally Posted by 416
Would the r value increase because of the air gap between the foam (in the joists) and the floor or just because I could get more in there.
Also, just for reference...would you build the layered floor then raise walls in the original scenario? Or just sub floor then walls then rigid and floor top after raising walls.
Thanks.

You can get more insulation between the joist. 6-10" depending on your joist size. Even 4" is ok. The less air transfer under your floor the better.

I would not place your walls on anything that could move or crush.

416 05-14-2013 01:23 PM

In that case, I guess I'll need some ply cut to fit into the bottoms of the joist openings to keep critters from munching on the insulation?
Thanks again.

MJ Force 05-14-2013 02:46 PM

Quote:

Originally Posted by 416
In that case, I guess I'll need some ply cut to fit into the bottoms of the joist openings to keep critters from munching on the insulation?
Thanks again.

Well I don't know about your critters but my critters will eat through wood before they ever eat through rigid foam insulation.

416 05-15-2013 08:10 AM

Hmm. Well, that would be ideal if my critters think like yours. Would the rigid foam act as a vapor barrier too? Sorry...I'm still a bit of a newb.
Thanks again.

MJ Force 05-15-2013 08:33 AM

Quote:

Originally Posted by 416
Would the rigid foam act as a vapor barrier too?

The idea with a vapor barrier is not too prevent the outside moist air from coming in, it's to prevent the warm moist air inside your heated space from penetrating your walls and floors and reaching colder surfaces where that warm moist air will condense into water. Warm air holds more water than cold air.
If the area or void under your shed floors is unheated, likely, I must be allowed to breath to prevent that area from warming up. Two small openings would help prevent this.

How is you floor framing built. Right on the ground or raised slightly?

MJ Force 05-15-2013 08:54 AM

Essentially the area under your floor is like a basement or crawl space. To create warm comfortable flooring over a crawl space or slab, you have to heat those areas. Not practical for a shed. However if you insulate the flooring properly, the flooring will take the temperature of the ambient air next to it. Since warm air rises, your ceiling will feel warmer than your floor. If you really need nice warm feet, there are some electric infloor heating methods which work well with different types of flooring. Other than that, your plain ole insulated floor will transfer heat/cold at a rate determined by the insulation R factor and convection.
If your worried about critters, lay down a 6mil poly ground sheet and screen any openings.

MJ Force 05-15-2013 09:08 AM

Quote:

Originally Posted by 416
Would the rigid foam act as a vapor barrier too? .

I guess I didn't answer you question directly.

There is closed cell and opened cell foam insulation. To act as a vapor barrier, the closed cell rigid foam insulation needs to be sealed along its edges. This can be done with acoustic sealant chaulking as you fit the foam sheets in place between your joist. It's a bit of overkill in my opinion for a shed but hey...I don't know if your storing lawn mowers or gramma's favorite doilies in there.

416 05-15-2013 10:36 AM

It will be raised between 10" and 14".
It will act as a shed for storage (loft) but I also hope to use it as an office and I'm in toronto.

416 05-15-2013 10:37 AM

Great info. Much appreciated.

MJ Force 05-15-2013 10:50 AM

Quote:

Originally Posted by 416
Great info. Much appreciated.

Good luck.
Sorry aboot da Leafs.


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