Insulating a metal roof

[Stefan (S.T.E.F.)]

I have an old croft building (barn?) which has had a metal roof put on maybe 20-30 years ago.

In the winter I get a lot of condensation on sunny days as the building warms up and the outside air is cold.
Sometimes it literally rains indoors.
Tools in there are starting to show moisture damage and cardboard boxes are damp and collapsing.

I need to insulate the roof somehow to avoid all this condensation, so that I can install a workshop stove.

Any ideas on what to use?
The metal roof is corrugated.

[dhaslam]

The only consideration is  moisture above the insulation layer.  You would need a  moisture barrier above the insulation  to stop  warm moist air condensing on the metal roof.   Once that is done you can use practically any insulation  underneath. 

[Eleanor]

You could spray it with insulating foam. I think I gave you the name of a company that sells it a while ago but can't remember the details now. It's stopped condensation in our tin shed.

[camillitech]

Hi Stefan,

I had the same problem in my many (seven) crinkly tin sheds and solved it in the ones that matter (where the pigs are) by using 8x4 sheets of 25mm polystyrene. It was very cheap and easy to do as the roof trusses were 4' apart  I just screwed them to the wood with long screws and penny washers. As for condensation, I've never noticed it but I suppose if it's there it will just run off the insulation, probably poor practice for a dwelling but fine in a barn.

Good luck, Paul

[Stefan (S.T.E.F.)]

Yes, I remember about the foam spray stuff. I asked about that long time ago for the garage of the rented house, but the landlord wasn't keen on it...

With the barn I rather not use it as it's a historical building (not listed), but I like to preserve it as much as I can without pumping 21st century stuff into it...

I vaguely thought about putting netting over the beams and filling the void with straw... wouldn't last forever, but these croft buildings are hundreds of years old... so need some TLC every few years anyway...

[camillitech]

Done the rushes and fishing net stuff too Stefan and it does work, though I found it took up quite a bit of room, beauty of the polystyrene is that it reflects the light as well as keeping the heat in and stopping condensation.

Cheers, Paul

[qeipl]

Paul's idea gets my vote. Quick, effective and bright.

[SteveH]

 I'd go with Paul's solution as well.

 The insulation will massively reduce the temperature difference between the inside & outside of the metal roof & very little, or no condensation will form on the underside of the metal.

 The spray option is akin to the way they produce box profile metal roofing panels for use in buildings with a heated internal envelope... The new sheets arrive pre insulated & have the advantage of bringing the roof structure inside the heated envelope, protecting it from the elements & condensation issues.

 With your existing roof it would very much depend on the condition of the existing metal. if there's any sign of corrosion the roof will need to be repaired at some point & I would take Paul's suggested route.

[Stefan (S.T.E.F.)]

Sounds good.

Wonder if I could combine the too and use polystyrene AND fill the voids with straw.... Need to look at the roof structure again....

I remember that with a lot of wind and fine snow the wind blows the stuff up the roof and it ends up inside the barn due to the semi open ridge. Gotta find a solution for that as well.

The just gotta add some heating and add guttering so the rain doesn't soak too much through the floor (no foundations)...

[camillitech]

Tin of expanding spray foam to seal the ridge Stefan but if you plan on keeping livestock in there leave it open for ventilation.

Cheers, Paul