Metal roofs and condensation

[adamjones]

Probably. My Woods house has regular composite shingles over plywood and I get no condensation in there, but it is also a Woods house. Meaning wide open ventilation.If you go this route, you will also want to have wide open ventilation if at all possible.

Do much research and there are basically three things needed to prevent condensation in buildings.

1. Reduce the moisture level inside. (Good luck with that if you raise chickens and keep water inside, have a high population of birds inside and/or use deep litter over dirt floors. That is a high moisture environment).

2. Vent moisture to the outside. Wide open ventilation does that......moisture has an escape route to flow out, vs. having to condense out. Ventilation also tends to equalize both the moisture and temperature levels inside and out. In what seems like a contradiction, warm moist air...the culprit of condensation.....rises and flows out....as if it is on a conveyor..... if you have good ventilation that allows it.

3. Principle of insulation is to isolate any warm moist air inside from cold metal roof, siding or or other surfaces on the outside. Works like putting an insulation sock on a cold beer in summer. Insulation limits access of the warm moist air to the cold surface of the can, and water does not condense on the insulation. Concern here is if warm moist air on the inside of the building contacts cold surface, it may still condense, but then be trapped between the two as liquid. Rot, mold, etc. follows. You may not see it, but it is there just the same. So best practices would leave an air gap between the two to vent any air and condensate moisture out.

If you really want to use a metal roof, and I might if I was to do the Woods house again, I would opt for hard insulation board under it. The polyiso foil faced stuff. White inside, shiny aluminum side up facing roof. Rafters, with purlins running crosswise over those. That is how my daughters barn was done.

Instead of the hard foam, many commercial pole barn builders install a layer of bubble wrap over the purlins.......loosely to let it breath.....them metal roof over those. This type of bubble wrap is white on the inside and shiny reflective foil on the outside, facing the metal roof.

BTW, white or light colored metal roof is cooler than dark.

My current workshop has a single skin roof.

Its cold, its rattly, it leaks and it suffers from epic condensation.

The new workshop has been somewhat set back by a lack of job. So plan b is to fix the current place.

The garage is steel framed with box section tin screwed down to it.

Now the plan is to fix 2x2 timber across the top of the roof running left to right at 90º to the ridge on the tin

I am then going to drop in 2 inch insulation above the tin and then cover it with another layer of box section tin.

This will give me 2 inches of insulation and a new waterproof roof.

BUT

It doesn't do anything about the big cold steel expanse under the roof. So i don't know if will fix the condensation issue.

Can anyone else see any other issues