Metal roofs

Hmm, Our building's manufacturer supplied two manuals with it.

Neither of them said anything about sheathing or a vapor barrier.

They did supply thin strips of rubbery foam that have the shape of the roof, and are caulked along the eave between the roof sheet and the top of the wall, so it is sealed against drafts.

Of course I sprayed Styrofoam over that, so it is all covered now anyway. [on the inside].

Yeah, a couple inches. It just staples to the outer face of the rafters, leaving a couple inches of dead air space between the insulation and the roof decking.
OOPS this is Vicker. DW forgot to sighn out.

Does it have air flow over it? It should have openings at the eaves and a ridge vent.

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"Education is the ability to listen to almost anything without losing your temper or your self confidence"
Robert Frost

I've seen that with a lot of metal buildings, but when they are manufactured they are usually not intended as houses but more as commercial applications. This usually means they aren't continually occupied and don't have showers and kitchens. I have seen a lot of insulation that is roll type with a vapor barrier that is used on metal buildings. When I speak to the insulation companies they always recommend the air space with air flow.

All of this comes from what research I've done on installing a metal roof over my existing shingle roof with adding insualtion and research for a friends metal building. He made a mistake in building his with no eaves yet he is installing an insulated ceiling. He installed a ridge vent but has no air intakes.

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"Education is the ability to listen to almost anything without losing your temper or your self confidence"
Robert Frost

I see.

Well my house is getting pretty airtight.

Right now, I have enough make-up air, but I will require a system for getting make-up air. Maybe a pre-heater.

Yep. Got that too. Vents at the bottom and a vented ridge cap. I actually ran my woodstove chimney out the wall because, there was no way I was going to cut a hole in that roof

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Vicker
If you're born to hang, you'll never drown.

If the roof is all vented, does not that allow interior heated air to leave and exterior cold air to enter?

Our roof is metal with batt insulation between the rafters. 29r I think. We never hear a sound, and our "Attic" space has 2 bedrooms and a bath.

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"The most beautiful system of the sun, planets and comets, could only proceed from the counsel and dominion of an intelligent and powerful Being." - Sir Isaac Newton
(A REAL scientist)

No. The rafters are vented at the eves and at the ridge, while the insulation installation provides an airspace between the insulaton and the roof. That provides a channel for air to move through and prevent condensation in winter. It also helps cool your roof in summer.

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Vicker
If you're born to hang, you'll never drown.

I see.

My insulation, well the first part of the insulation, the spray-on-foam, is epoxyed right onto the roof [the underside obviously]. One inch thick.

Then the fiberglass batting.

So there is no air space between the roof and the insulation.

I know this is slightly off topic, but I was helping a deacon from my church put roofing on a new addition to his barn to house some of his equipment and becareful when you put it up. Wear gloves otherwise you get some nasty cuts.

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I'm a ramblin' man and I'm ramblin' on.

BTW it was a metal roof, and cutting it was a bit of a chore, but after going through several metal saw blades as we cut it in bulk it was worth it.

__________________
I'm a ramblin' man and I'm ramblin' on.

LOL

Metal saw blades do dissolve very quickly.

I was very fortunate, in assembling our house all of the sheets were pre-cut. I only had to drill holes in them for the screws. The screws are supposed to be 'self-drilling' but all I could get them to do was spin. The directions said that if you wanted to you could drill holes, and it specified the size of drill bits to use. So I followed that.

Later when I began to cut holes for windows, was when I found that metal saw blades evaporate very quickly.

I cut ten holes for 3'X3' windows, eleven holes for 3'X6' windows, four holes for outdoor electrical outlets, two holes for outdoor water faucets in one inch pipe, one 7'X3' hole for the back door, and a round hole for the stovepipe.

So I did go through a bunch of those cheap saw blades.

We used a mini grinder and cut off wheels to cut mine. The roof overhangs where specifically extended to use the entire length of the metal panels and we just had to cut one to width on each side of the house.

Ditto on the safety equipment. I had one piece slip when we where putting it in. It fell about 3 inches sliding on the outside of my wrist just above the cuff of my glove. The cut took months to close up completely due to something on the metal and I now over a year later I have a nasty scar that looks like I tried to kill myself. If it had got me right across the flat of my wrist it could have been life threatening.