Roof Insulation, Closed vs Open Cell

[jeremywrags]

Hi All,

I am about to pull the trigger on foam insulation in my shop (30x40 Pole Barn ) and I have a suggestion from the foamer that I am not quite sure about...

His suggestions is to put 1" closed cell foam on the walls which I agree with and then do 4" open cell on the roof. His reasoning is that if one of the rubber gaskets fail (which has already happened) the open cell foam will let the water come through telling me that I have a leak. With the closed cell the water will just run down the rafter and rot the wood over time.

Does anyone have experience or a qualified opinion on the best way to apply the foam based on that concern?

I like the idea of closed cell all around for the added rigidity but I do not want to worry about rotting lumber.


Thanks

 

[Radix2]

Hi All,

I am about to pull the trigger on foam insulation in my shop (30x40 Pole Barn ) and I have a suggestion from the foamer that I am not quite sure about...

His suggestions is to put 1" closed cell foam on the walls which I agree with and then do 4" open cell on the roof. His reasoning is that if one of the rubber gaskets fail (which has already happened) the open cell foam will let the water come through telling me that I have a leak. With the closed cell the water will just run down the rafter and rot the wood over time.

Does anyone have experience or a qualified opinion on the best way to apply the foam based on that concern?

I like the idea of closed cell all around for the added rigidity but I do not want to worry about rotting lumber.


Thanks

how is your roof built ? metal over purlins, screwed on the peaks or valleys?

with purlins and peak screws, the foam will seal around pretty much every screw...if in the valleys, about all that is at risk is a small area around the screw, and it is not like a seep is going to show up through 4 in of open cell either.

I'd do the closed cell.

 

[wssix99]

I'd go with open cel foam in the roof just for the fact that closed cel would give you a vapor barrier effect. If you did closed cell all around, the humidity would be like living inside of a garbage bag.

BTW - Open cel sprayed on the roof makes a horrible mess. If you have a nice slab, I'd watch them like a hawk and make sure they have it fully covered. My contractor cleaned out their guns on my slab and left a huge chemical stain. Fortunately, I epoxied over it - but when I saw that, I was ready to kill...

 

[theoldwizard1]

Sponges are open cell foam. Sponges hold water. Yes, they do dry out.

I am not sure what your temps are there in OK, or if you are planning on heating/cooling. I would want at least 2" in the walls, and would likely add more. I would also add more to the roof.

 

[minytrker]

Getting my 24x40 shop walls and ceiling done in 2in closed cell tomorrow.

 

[rieferman]

I'd go with open cel foam in the roof just for the fact that closed cel would give you a vapor barrier effect. If you did closed cell all around, the humidity would be like living inside of a garbage bag.

I'm not an expert on this, so just thinking out loud... The closed cell would prevent vapor transfer from out to inside, and vice versa.

Therefore, if interior is air conditioned, humidity should not be a problem (i.e. no enormous new source of humidity is present). Even if not conditioned, unless you pump humid air in, there still shouldn't be a problem as the humidity is blocked from entering in the first place.

I might be thinking about this wrong though, curious to know what others think

 

[Beemer533]

I'm not an expert on this, so just thinking out loud... The closed cell would prevent vapor transfer from out to inside, and vice versa.

Therefore, if interior is air conditioned, humidity should not be a problem (i.e. no enormous new source of humidity is present). Even if not conditioned, unless you pump humid air in, there still shouldn't be a problem as the humidity is blocked from entering in the first place.

I might be thinking about this wrong though, curious to know what others think

This is correct; this is a big part of why folks use it (although to qualify as a vapor barrier, I think it needs to be a minimum of 2")

 

[Beemer533]

As far as the leak in the ceiling showing up, I don't think open cell will really be much better. Where it actually might end up dripping inside will probably be no where near the actual leak, if it shows up at all. It not like with open cell the water will just leak straight down...

 

[rieferman]

As far as the leak in the ceiling showing up, I don't think open cell will really be much better. Where it actually might end up dripping inside will probably be no where near the actual leak, if it shows up at all. It not like with open cell the water will just leak straight down...

Thanks for both replies, and I agree here. I would rather a "roof within a roof" scenario that you get with closed cell. With today's pole barn fasteners (rubber washers seal very efficiently and do not decay in the sun like the old style could) and long warranties on the roof steel, roof leaks on a quality install are not common. In the rare event of a leak I'd rather have it contained, especially with the other benefits of closed cell.

 

[wssix99]

Are we talking about an air conditioned pole barn here?

Regardless, if the OP's area does not put vapor barrier in the ceilings, I would not put in closed cell. If it's common place in that part of the country, then it's probably not a big deal other than the roof rot issue.

The think with roof rot here is not just the replacement of the roof material - since the insulation is attached, repairing the roof would require insulation repair and would be a total mess!

 

[HRJoe]

I've looked into this for my planned metal pole building. Local spray foam guy here suggested open cell on bottom of the roof 6" thick.

At that point, no need for ridge vents, etc because the whole building is now "conditioned space".

However, I (for now) have decided against all this because my builder swears I will have humidity issues inside the building. Instead, I'm going to insulate my ceiling (not roof - just vapor barrier there) and let attic breath via soffet / ridge vent.

 

[Cybeast]

Foam insulators in are area use open cell in case of roof leaks on pole barns.

 

[minytrker]

Friend has a 12,000 sq ft shop with closed cell on walls and roof and the roof leaks right through the closed cell. Open or closed cell the water is still coming in.

 

[finn]

My installer used closed cell on the basement walls of my house addition, but closed cell on the studded walls and ceiling primarily to save me money, or so he said.

Six-ten inches of open was cheaper than two inches of closed, with the same performance.