Insulating pole building roof help

[Mustangous]

Hey all!

Ive been reading these forums for a long time and love the site!

I finally pulled the trigger on a 34x60 pole barn from Conestoga with 6/12 roof with 1' over hangs all around. I got the 6/12 roof pitch and 2x6 bottom cords on the trusses to support extra weight of storage up there so I am planning on keeping the ceiling open for the most part.

There seems to be so much back and forth about insulation, use closed cell or don't, just vapor barrier, double bubble vapor barrier, vinyl backed bats and so on. Obviously i want to do this as cheap as possible, but want to do it right. What would you all recommend?

Also for the walls, Should i put the house wrap up before the metal tin goes up?

Thanks!

 

[Mustangous]

1 other thing, Conestoga quoted me $1350 for the double bubble vapor barrier installed, so i figured i could put that towards a better solution so i don't get rained on inside...

 

[bgarrett]

$1350 would get about you 1/2 done with closed cell spray foam if you do it and would be the very best thing to do

double bubble is better than nothing but I say its just barely better

 

[Highbeam]

Yes on the tyvek, no on the double bubble ****.

 

[Mustangous]

$1350 would get about you 1/2 done with closed cell spray foam if you do it and would be the very best thing to do

double bubble is better than nothing but I say its just barely better

Thats kindof what i was thinking as well, but could i just spray it right on the roof panels without any issues, like panel warps in the future or somehow seperating and falling off? Would an inch be fine or would i need more? Should i not get the ridge vent option then?

I was looking into TigerFoam/ for a few reasons, they are semi local, and it has an E-84 fire rating(what ever that is... ) I calcualted roughly 2400 sqft for the ceiling so i would need 4 jugs at min for 1" coverage.

Yes on the tyvek, no on the double bubble ****.

Not sure if I would use the spary on the walls because of the cost factor, but if i did decide on the close cell spray foam for the walls, would it be better to spray directly onto the tyvek or metal walls?

Thanks guys for your help!

 

[williaty]

1) House wrap (tyvek et al) is not meant to be used as an air barrier or vapor retarder. It forms a drainage plane. The idea is that the house wrap is there to convince the water to drain to the ground when it inevitably makes it underneath your cladding. All sidings leak eventually. The tyvek just helps the liquid water end up on the ground not in your wall.

2) Closed cell spray foam is your insulation layer, your air sealing layer, and your vapor retarder all in one product. In theory, spray foam works because it forms an air-tight barrier to prevent air infiltration/exfiltration and prevent the movement of moisture into the walls (that's being carried in the moving air). So long as the spray foam is thick enough to keep its inside surface temperature above the dew point, it works very well. The problem people get into with spray-foam insulated buildings, ESPECIALLY outbuildings like being discussed here, is that the designer or owner fails to live up to their responsibilities of having a building that's sealed that tightly. If you air-seal a building that tightly, you MUST mechanically ventilate the building! To illustrate the problem, think about breathing into a plastic bag. Even if it's quite warm, you're eventually going to breath so much water vapor into the bag that you'll get condensation on the inside of the bag. Where outbuildings like this go wrong is that people let the humidity in the building rise (either from humans breathing or other sources such as combustion heaters) to the point that the dew point rises up into the 70s or above, or at least above whatever temperature the building is being held at. The problem isn't anything to do with the spray foam, it's that the idiot using the building didn't either ventilate the building to bring in new, dry air or use a dehumidifier.

So 1) wrap the building to provide rain shedding in case you get a leak in the metal skin 2) insulate and air seal the **** out of the building (spray foam) and 3) make sure you ventilate and dehumidify.

 

[Mustangous]

So 1) wrap the building to provide rain shedding in case you get a leak in the metal skin 2) insulate and air seal the **** out of the building (spray foam) and 3) make sure you ventilate and dehumidify.

Great!

So ill definitly tyvek the walls before they put up the metal outside wall panels.

The roof Ill spray foam and seal everything up tight. How think can i get away with? I am hoping 1" because that is gonna cost me about $2500 or more for 2400 sqft.

As for venting/dehumidify, any recommendations or examples? Is that basically conditioning the space? I am planing on putting in my old furnace and ac from the house upgrade, but it isn't going to be running all the time.

Right now my main concern is the roof....

Thanks for all the replys

 

[williaty]

1" Is probably not going to be enough 3" is more common for exterior walls and even thicker for the roof.

You really need to consult a professional on this. Even though I'm a strong proponent of DIY, having a professional come out to consult and tell you what to do is just smart, even if you then do the work yourself.

 

[mtwaterguy]

Yes on the tyvek, no on the double bubble ****.

^^^^^^+2. Put your money towards insulation.