Didn't want to hijack the thread on radiant barriers so I thought I'd start this.

We have a new pole building going in soon and I'm still going back and forth on whether or not to vapor barrier under the roofing and if so with what.

It's a typical pole frame construction with metal siding and roofing. It will have 12" vented overhangs, with a ridge vent. Floor will be a slab with 2" foam with taped joints underneath. Walls will be wrapped in vapor barrier prior to siding.

The barn will be un-insulated and unheated for a few years until we finish it off into a living space. At that time I'll put in a ceiling on the truss chords with vapor barrier, and blown in or batts above.

So my question is should I put a vapor barrier on the roof now? If so what should I put there? Second, if I do a vapor barrier now should it go on the framing below the purlins, or on the purlins in contact with the roofing?

In response to your question from the other thread, they put my foil outside the framing. Between it and the metal.

There was a lot that I was going to do myself to try to save money, but looking up at that 14' ceiling now, I'm really glad that I just paid for them to do it then. It was a whole lot easier for them, already up there, to just unroll the stuff, staple it down, and throw on the metal. I can't imagine what a PITA it would be for me to try to get up there now to do it myself.

quote:

Originally posted by Gustofer:
In response to your question from the other thread, they put my foil outside the framing. Between it and the metal.

There was a lot that I was going to do myself to try to save money, but looking up at that 14' ceiling now, I'm really glad that I just paid for them to do it then. It was a whole lot easier for them, already up there, to just unroll the stuff, staple it down, and throw on the metal. I can't imagine what a PITA it would be for me to try to get up there now to do it myself.

Do you just have the foil then? Is it just foil or is it the bubble wrap stuff?

Any condensation with it up there?

quote:

Originally posted by ubelongoutside:
Do you just have the foil then? Is it just foil or is it the bubble wrap stuff?

Any condensation with it up there?

Foil insulation (R4 or something like that as I recall). I also had them put up a metal ceiling and then put in R35 batts. I did not want to get that high up there and try to do that myself. Very happy I paid extra for it. They left the walls unfinished and I'm currently in the process of finishing those off now with R19 and 1/2" plywood sheathing now that I've got all of the electrical/plumbing work done...finally.

To be honest, I haven't been up in the attic since they closed it up, so I can't say about the condensation up there. However, when they poured the floor a few weeks later, there was condensation running down the walls. It was damn near raining in there for a week or two while it cured up. I had to keep the windows open and the heater blowing to dry it out some. I had it done last December and we got a real cold snap a day or two after they poured. I was worried about keeping it from freezing, otherwise I'd have just left the doors and windows open.

The foil stuff clearly works as a vapor barrier.

I paid to have it done when they put up both my pole barns.
They work, except when as in the case of my first barn, they drove some nails in the roof crooked and they caused the roof to leak. The vapor barrier just hid the leak for a while. I am still chasing one leak and it have been over 20 years that the barn has been up.
The second barn never leaked.

quote:

Originally posted by Aquabird:
I paid to have it done when they put up both my pole barns.
They work, except when as in the case of my first barn, they drove some nails in the roof crooked and they caused the roof to leak. The vapor barrier just hid the leak for a while. I am still chasing one leak and it have been over 20 years that the barn has been up.
The second barn never leaked.

What did you use for the condensation barrier?

I had this roll insulation put under my metal roof. Not sure if it was needed since I didn't insulate the walls but it was reasonably priced as I recall.

quote:

Originally posted by doublesharp:
I had this roll insulation put under my metal roof. Not sure if it was needed since I didn't insulate the walls but it was reasonably priced as I recall

Any idea what it was called?

quote:

Originally posted by ubelongoutside:
Didn't want to hijack the thread on radiant barriers so I thought I'd start this.

We have a new pole building going in soon and I'm still going back and forth on whether or not to vapor barrier under the roofing and if so with what.

It's a typical pole frame construction with metal siding and roofing. It will have 12" vented overhangs, with a ridge vent. Floor will be a slab with 2" foam with taped joints underneath. Walls will be wrapped in vapor barrier prior to siding.

The barn will be un-insulated and unheated for a few years until we finish it off into a living space. At that time I'll put in a ceiling on the truss chords with vapor barrier, and blown in or batts above.

So my question is should I put a vapor barrier on the roof now? If so what should I put there? Second, if I do a vapor barrier now should it go on the framing below the purlins, or on the purlins in contact with the roofing?

If I understand your description, you'd do a vapor barrier under the roof sheathing, then a vapor barrier later on the ceiling plane. Don't do that. Just do the vapor barrier at the roof plane, and batt or blown in on the ceiling plane, with soffit and ridge venting, or adequate gable venting. Doubling up vapor barriers is a recipe for trapping condensation.

To a degree, wallboard is somewhat of a vapor barrier, and some types of roofing are as well. Depending on the construction conditions, we will use an underlayment that is vapor impermeable like Ice & Water over a whole roof, or a waterproof but vapor permeable membrane.

You either want to make sure you've got proper venting and no doubling of vapor barriers, with conventional insulation, or you could foam the heck out of everything.

My insulation of choice for non-foam applications is Roxul. I prefer it over fiberglass for sure, and it is easier to deal with than blown in.

quote:

Originally posted by ubelongoutside:

quote:

Originally posted by doublesharp:
I had this roll insulation put under my metal roof. Not sure if it was needed since I didn't insulate the walls but it was reasonably priced as I recall

Any idea what it was called?

I bought a Menards pole barn package and this was the option for roof insulation. I could not find it on Menards website. You could probably open the pole barn design center and work your way into it but that takes time. I had a pole barn built in the 80s and they used the same stuff.

If you don't insulate the roof it will sweat...I guarantee it.