Floor Insulation Question

[Mako-SKO]

Ok, so I'm at the point in my build where I'm starting the floor. I am using 2x4's for the base, insulation in between, and plywood for the subfloor. My question is: Can I use faced pink fiberglass insulation for the floors? My problem is I am having the hardest time finding foam board in 1 1/2 inch. I've called around and it's going to be at least 4 weeks to get it in and even then it's no guarantee. this is the same problem I had with my windows. Took me 1 1/2 years and 2 1/2 times the cost to get my windows...I've delayed enough. I can easily find the pink stuff but want to know if it is a good idea or not. I know it's no biggie on the walls/ceiling (I will be doing spray foam), but is it ok for the floors? Thanks in advance for the constructive advice

 

[TheHubbardBus]

We used 1" XPS against the metal, with 1/2" poly-iso on top of that. Foam board is going to allow you a larger span between sleepers that fiberglass batt, which in turn means less wood, less weight, and since there are less thermal bridges, better insulation. Plus batt will generally be sized according to studs (3.5" min), so it might be a little tight cramming it down that tight, plus since it isn't designed to be compressed that far you might impact its insulation value. Speaking of which: Fiberglass batt @ 3.0 r-value/inch = 4.5. 1" XPS + 1/2" polyisio = ~7 - 7.5.

FWIW we also used a continous layer of 1/2" polyiso over sleepers as well.

 

[musigenesis]

We used 1" XPS against the metal, with 1/2" poly-iso on top of that.

This is a good way to go, since polyiso has a better R-value per inch than XPS (6.5 vs. 5.0) but the R-value drops off with lower temperatures. By having the polyiso on the inside, it's more protected from the lower temperatures by the XPS layer.

 

[Mako-SKO]

So you used 2 different types of foam board? That is an option for me as well. Only problem it will be at least 1 1/2 times more expensive rather than just getting 1 piece. I'm still trying to figure it out, but again trying to see if faced fiberglass is even an option or a bad idea for the floor under the plywood

 

[musigenesis]

As TheHubbardBus pointed out, layering foam board is fine to do, so you could double up 3/4" board, for example, and get the same benefits as 1.5". Problem is it's a lot more expensive this way, since foam board is cheaper per board-foot the thicker it is.

I assume you've checked Home Depot? That's where I got all my 1.5" XPS and they had tons of it (I'm not in Central Florida, of course).

 

[Mako-SKO]

Yeah, completely out. they have 1" and 1/2". I've even called other companies and being told 3-4 weeks out with no guarantee of it coming in then. I've waited long enough for this build. Time to get the ball rolling. Speaking of price, I just put Henry's Tropicool on the roof. last year it was $267 for a 5 gallon bucket, I picked it up last week and paid $374. So not only is it getting harder to find supplies, but the prices are going through the roof (no pun intended).

 

[musigenesis]

Yeah, completely out. they have 1" and 1/2". I've even called other companies and being told 3-4 weeks out with no guarantee of it coming in then. I've waited long enough for this build. Time to get the ball rolling. Speaking of price, I just put Henry's Tropicool on the roof. last year it was $267 for a 5 gallon bucket, I picked it up last week and paid $374. So not only is it getting harder to find supplies, but the prices are going through the roof (no pun intended).

Oh well, I know a way you could have saved $374. :biggrin:

 

[LargeMarge-TC]

... I'm starting the floor....the pink stuff but want to know if it is a good idea..:

.
2003, for our ExpeditionVehicle, I laid one-inch pink-board on the box floor.
On that, I laid half-inch marine plywood painted on all surfaces to seal.
.
Laid on the plywood, our visual floor has a bamboo plank perimeter with slate in the center.
.
Nearly two decades full-time live-aboard, the pink-board shows zero-zero-zero signs of compression or deterioration.
.
I think you will be OK without the 2x4 multi-layer sub-floor or any of the other complexity.
I say this with the expectation you probably will not bounce your rig for miles up rough logger tracks to remote mountain lakes nor across deserts to isolated Baja beaches.
You probably will not drop SCUBA tanks and dump weight-belts on your floor.
Your three RedHeelers will probably not dig to investigate stray scents amongst your tiles.
Nor will you utterly ignore any rational sense of decorum by traipsing-in wearing muddy farm galoshes.
.
(Pun intended...)

 

[Mako-SKO]

This is the route I have decided to take. 1" xps (R5) on the bottom, 1/2" polyiso (R3.2) on top, then the 3/4" plywood. It's almost done. It, of course is taking me twice as long to do since I am cutting 2 foam boards for each opening but oh well, it's getting done. I would have been done already if I hadn't tweaked my back the other day playing tennis...getting old sucks...lol...thanks for all the advice everyone!

 

[Carpe1]

FWIW, I bought Amvik Envirosheet- Under-Concrete special High Density EPS foam R10- 24 in. x 48 in. sheets, 2 3/8 in. thick, and going to lay OSB over it. It is typically used under slabs for frost protection, so moisture resistant and strong enough for a slab to be on top of it. No floor framing at all allowing the floor to be completely insulated and more than an inch shorter than the 2x4 frame.

 

[kidharris]

.
2003, for our ExpeditionVehicle, I laid one-inch pink-board on the box floor.
On that, I laid half-inch marine plywood painted on all surfaces to seal.
.
Laid on the plywood, our visual floor has a bamboo plank perimeter with slate in the center.
.
Nearly two decades full-time live-aboard, the pink-board shows zero-zero-zero signs of compression or deterioration.
.
I think you will be OK without the 2x4 multi-layer sub-floor or any of the other complexity.
I say this with the expectation you probably will not bounce your rig for miles up rough logger tracks to remote mountain lakes nor across deserts to isolated Baja beaches.
You probably will not drop SCUBA tanks and dump weight-belts on your floor.
Your three RedHeelers will probably not dig to investigate stray scents amongst your tiles.
Nor will you utterly ignore any rational sense of decorum by traipsing-in wearing muddy farm galoshes.
.
(Pun intended...)

What pun??

 

[Hutchy-SKO]

FWIW, I bought Amvik Envirosheet- Under-Concrete special High Density EPS foam R10- 24 in. x 48 in. sheets, 2 3/8 in. thick, and going to lay OSB over it. It is typically used under slabs for frost protection, so moisture resistant and strong enough for a slab to be on top of it. No floor framing at all allowing the floor to be completely insulated and more than an inch shorter than the 2x4 frame.

maybe a dumb question but could I use that stuff and just lay flooring right on top with no wood? I want to lose as little ceiling clearance as possible

 

[TheHubbardBus]

@Hutchy, you would not want to do that. You need a rigid subfloor over the insulation to distribute weight across its surface. Anything designed to go over a prepared subfloor will not have the necessary rigidity and strength.