42x48 insulation question

[rpm1]

i've been a garage journal stalker for some yime and now i guess it's my turn to ask for advise. i have a 42x48 x16 high pole building and its time to insulate this thing,i had an insulation company stop out and give me a price and he said after they spray the walls and insulate the celing that since the builder didn't install a vapor barrier under the metal roof that i was gonna have to install a fan in the attic space so i didnt have a wet celing from condensation and ruin the insulation. i live in central ohio the building hasvented soffit and a ridge vent.if thats what i need to do then so be it.any info you can help with would be appreciated

 

[rpm1]

can't believe no one has an opinion on this issue,or did i not supply enough information

 

[Fueler]

Forum moves so fast it probably just got shuffled back a few pages before anyone noticed. Wait for it.

As far as vents I have been studying Solar vents so I would not need to run more wire.

Oh, go to your profile and put your location in there. That helps with a lot of answers.

If it has soffits and a ridge vent I figure treat and insulate it like an attic. Spraying those shut makes no sense to me.

 

[Chris705]

rpm1 - were you only going to spray the walls and then use fiberglass or some other form of insulation for the ceiling? If that was your thought I think you are losing one of the biggest benefits of using spray foam and that is an air tight seal. You would have it at the walls but lose it in the ceiling. Please ask/see if your foam installer would also spray the roof deck (and if you can afford it - expensive). There are a couple other builds on GJ where foam has been sprayed on pole construction (assume metal siding / roofing). then you can eliminate your soffit vents and ridge vent. Everything that I read about this approach seems to indicate a supperior install purely from the "air-tight" results. I will definately being doing this in my wood frame constructed garage once I save enough. But I know the metal roof topic has differing thoughts with closed cell spray foam applied directly to it. My thought is you can get away from having to use an equal r-value in foam as you would in fiberglass because of the lack of air movement thru the foam like you would have in fiberglass batts. However there is potentially a concern w/ metal and rusting if leaking from the exterior as in most closed cell foam applications you would not know you have a roof leak. The other possibility in why you may not want to go with spraying the roof deck is your heated air will rise up into this space if not using a hydronic floor heat.....

Just a possibility. And I guess it makes sense you could conceivablly end up w/ wet fiberglass in the ceiling plane if the vapor from the humid air in the attic condenses on the underside of the metal roof deck. (summer months???) Soffit vents and ridge vents size properly (1sf of vent to every 300sf of roof used to be the rule of thumb) should eliminate that from happening. Others can probably say better what they have experienced in their metal roofed pole barns w/ ceiling insulation.

 

[rpm1]

yeah spraying the celing is an option (expensive option tho). I just wanted to add my celling and insulate it. but thats not gonna happen soon.I always tell my employees some of lifes best lessons learned are the one's that cost you money... vapor barrier

 

[kj_mustang]

Having vented soffits and a ridge vent, I would not spray foam the roof. I would install a vapor barrier at the ceiling, insulate the ceiling, and then you should not have a condensation problem on the roof if the air flow is good through the vents.

 

[Chris705]

kj mustang - I just looked at your build pictures and see that you spray foamed your roof. Can you elaborate on why you now say not to spray a roof deck, did you have problems? Just want to better understand if it is a metal roof/deck vs. plywood & shingles thing..... and what led you to spay your roof and now persuade someone else not to?

 

[Highbeam]

No need for a fan with a ventilated attic. Consider this to be a house.

 

[kj_mustang]

Because I planned mine for spray foam on the roof, it has solid soffits and no ridge vent and the foam totally seals the attic space. The attic will be conditioned air along with the living area. Highbeam's comment is correct but you will need the vapor barrier at the ceiling to block condensation from reaching the metal roof.

 

[1grnlwn]

You want vapor barrier on the warm side of the insulation. That would be in the ceiling not the roof. Not a bad idea to put a exhaust fan in attic but his reasoning does not appear sound.

 

[b4z]

I've had closed cell foam in our bungalow roof deck since 2009. It is revelatory.
Ina 1620 sqft brick house with no insulation in the walls or floors it holds the heat in so well that when the temp is in the 50s we can heat the house with the interior lights and cooking on the stove.
The negative for us was that since the heat was not running we had crazy condensation on the original single pane windows. So much so that every morning and evening we had to wipe down the windows with towels.
Windsor legend series double pane low e replacement sashes added $4200 to the $4900 cost of the spray foam. And because our house is now so tight our HVAC system is oversized. In the summer it doesn't run long enough to take the humidity out of the air so we turn the temp down lower than we normally had in the past.

 

[sands35]

I've had closed cell foam in our bungalow roof deck since 2009. It is revelatory.
Ina 1620 sqft brick house with no insulation in the walls or floors it holds the heat in so well that when the temp is in the 50s we can heat the house with the interior lights and cooking on the stove.
The negative for us was that since the heat was not running we had crazy condensation on the original single pane windows. So much so that every morning and evening we had to wipe down the windows with towels.
Windsor legend series double pane low e replacement sashes added $4200 to the $4900 cost of the spray foam. And because our house is now so tight our HVAC system is oversized. In the summer it doesn't run long enough to take the humidity out of the air so we turn the temp down lower than we normally had in the past.

You need to add a HRV and a dehumidifier to change out air and control humidity even when it's not AC temperatures.

 

[b4z]

You need to add a HRV and a dehumidifier to change out air and control humidity even when it's not AC temperatures.

We are going to add about 500 sqft to the house. That should take care of the oversized hvac issue. LOL.