Question about insulation

[HilltopDaisy]

I'm going to use the pink rolls of insulation in my new cabin's floor (pre-built Amish shed). I'll try to explain this.... I had originally thought that I could simply put down 2x4's across the width, roll out the insulation, and add a second floor of plywood. The walls are actually only raised off the sub-floor by 2", so it would work out better if I could lay the new 2x4's on their sides rather than upright. That would mean the insulation would have to be tightly sandwiched between the two floors. Will this work or does the insulation need to stay "fluffy"? Thanks.

[The Paw]

If you compress the pink insulation, it will lose its insulating value. The air pockets in the "fluffed out" insulation is what actually helps keep you warm.

If you have to lay the 2x4 flat, fill the gaps with rigid foam insulation (Styrofoam or related product). You can buy that in 1 inch thickness and cut to fit flush between the 2x4s.

Or, you could pour in loose cellulose insulation till it is flush with the top edge of the 2 x 4. The cellulose is usually treated with Borax, so you don't get insect and rodent nesting problems.

[Micahn]

Well you might be better off with the stuff made for that width. For example in a block home they put 3/4 inch strips on the walls and then a insulation made for it. Even if you got that stuff and used 2 layers of it (A 2x4 of the side is 1.3/4 inch) might be better then using the pink stuff and compressing it.

[cc-rider]

I'd do a hybrid of two of the above. If I only had 1-1/2" to work with (the side of the 2x4), and I were on a budget, I'd buy the cheapest solid insulation board I could buy (whether it be the white stuff, the foil-backed black stuff, whatever is on sale), at whatever size I could afford - 1/2" or 3/4", and put that in the bottom of the cavities. That gives you a solid wind barrier - especially if you spray foam around the edges to fiill in all gaps. THEN I'd finish filling the cavity with the stuff that you normally blow in and put a layer of visqueen (sp?) on top to hold it all in (plus giving you another vapor barrier -- "warm in the winter" side). In NY, you want all the insulation you can get. When you put the blown-in cellulose, you can mound it, put the visqueen on top, and then compress it when you put your flooring on. There is a technique for blowing in the insulation called "dense pack" where they cram it in as tight as possible, so evidently that stuff doesn't need to stay loose and fluffy!

[Alice In TX/MO]

About blown cellulose....

It only is rodent and bug resistant for a while. We built in 1979. Our blown cellulose has LOTS of rodent tunnels through it, and we have to treat the attic for roaches regularly.

[SolarGary]

Hi,
I'd use 1.5 inch rigid insulation board between 2X2's.

Using 2X2's instead of 2X4 will reduce the thermal bridging you will get from through the wood.

The 1.5 inch rigid foam will give you the best R value and best sealing. You can seal any gaps between the 2X2's and the foam board with Great Stuff polyurethane foam.
The "pink" and "blue" foam is stronger, and has a higher R value than the white polystyrene foam. The "polyiso" foam board has an even higher R value than the pink and blue -- it is usually tan colored with aluminum foil face sheets.

white polystyrene is R4 per inch
pink and blue are R5 per inch
polyiso is R6.5 per inch

I don't think it would be a bad idea to put a layer of poly over the foam and 2X2's to act as a vapor barrier. This should be on top (heated side) of the foam board.

You can get a rough idea of the reduction in heat loss with this calculator:
http://www.builditsolar.com/Referenc...sulUpgrade.htm
The calculator does assume you heat the space all the time, so if you don't, dial it down accordingly.


Gary

[cc-rider]

Can I edit my previous response? If so, Yeah...what Gary said.

My version is the cheap route. Gary's is the "good" route. I hadn't thought about using the 2x2's to save with thermal bridging. That's a good idea. I wonder if you can rip 2x4's down -- that'd be cheaper than buying 2x2's.

[HilltopDaisy]

Thanks to everyone who responded, I really appreciate all of your help! You all are awesome!

[The Paw]

Originally Posted by Alice In TX/MO

About blown cellulose....

It only is rodent and bug resistant for a while. We built in 1979. Our blown cellulose has LOTS of rodent tunnels through it, and we have to treat the attic for roaches regularly.

I don't know this for sure, but it is my impression that they might not have been treating the blown cellulose with Borax back in the 1970's. It might have been an improvement based on people's experience with it. But that is just an impression, it would certainly bear further research.

UPON RESEARCH: According to Wiki's History of Cellulose Information (boy I love the Internet), the energy crisis of the 1970s caused a huge expansion of the insulation industry. There were many small scale manufacturers of cellulose insulation, but they had trouble getting enough borax or boric acid to meet demand, and there were no prevailing national standards at the time. Right around 78/79 the government brought in standards for fire retardant content, and a lot of the small scale manufacturers closed down.

The Wiki article also says cellulose with Borax has "superior" resistance to rodents and insects, but it does note that if the insulation gets wet multiple times, the Boric content can start to leach out.

[HermitJohn]

Sprayed in foam (modern kind) is most efficient and last indefinitely, but pricey. Rodents like the other kinds of insulation except maybe the poured in expanded vermiculite thats mostly just used in concrete block construction.

[roachhill]

1.5 in isn't much insulation. I would go with the foam boards. IF you have an Amish lumber yard around you can buy 2x4s that are actually 2in and only cost half of a store bought 2x4 thats only an inch and a half. Then you could use 2in foam panels it's not much extra insulation but every little bit helps. I've heard they make an interlocking foam panel that can go under the floor without the wood supports but I don't know anything about it.

[Ross]

Use the pink board the closed cell foam not the open cell (little white white balls stuck together) and no 2x2's or 2x4's to eliinate almost all thremal bridging. It should have the shiplap edge. Fill all the gaps the foam board leaves with low expansion spray foam. Top with 1.25 inches of plywood T+G in staggered layers (2 5/8s sheets) screwed on 6 inch square pattern to the under laying existing floor using 2 inch screws. The thick ply floor will distribute the weight across the foam enough you'll not compress it.

[MELOC]

i think you should go with the most convenient route for the floors. i assume you will be insulating the entire building, so i think you will be ok no matter what you choose to do with the floor. your building isn't going to be very big. i have no idea what you will use as a heat source, but i think you will actually have to plan for ventilation in that building. depending on the heat source, you may find it difficult to control the heat. i'm not saying not to insulate, i'm just saying not to be worried about it too much. 2 x 4 's ripped in half on a table saw and spaced 16 on center on the floor and 1 inch rigid insulation should work. you are already adding a lot of expense by doubling the floor.

i'm curious, what plans do you have for utilities... plumbing, electrical and heating?