Do *any* metal roofed sheds, NOT sweat?

[Safety First]

I have made a treated timber 8'x6' shed. Pent roof.
Plan is to clad walls and roof with corrugated steel. Eaves bays (gaps between rafters, resting on wall plate) front and rear are going to be left open. So that's front and back wall, 5 x 70mm x 200mm openings hidden (from lashing rain) behind facia and roof covering. Corrugations around walls where vertical panels meet stud walls should mean additional outrageous amounts of airflow and equity in heat, and moisture-inside Vs outside.

I've been searching for solutions...to what I read is inevitable sweating and dripping inside.

Base is concrete slab, with 2x2 battens set on recycled plastic. I can lay vapour barrier over most of the under floor concrete as an afterthought to reduce moisture coming upwards, but the design is 'loads of air and no direct rain in'?

Surely though, if ventilation was ever enough, this topic would not be so old and regular, right?

Option 1. Staple breather membrane over rafters and under batten. This (hopefully) allows some moisture through, presents a warm(er) surface preferential to the cold steel, and when drips do comes off the steel, they run out via slight sag in membrane between rafters.

Option 2. Under board the whole roof with 25mm polystyrene. I.e glue /screw and foil tape to make a single piece barrier, so water vapour cannot find any cold steel that is roofing. Walls can run all they like-just goes outside.


Any thinkers?

Cheers,

 

[Koolpc]

Spray the underside with a good brand antiperspirant. It should stop them sweating!

 

[ajrtd]

Look for anti condensation sheeting.

 

[Harry Bloomfield]

I now have three such rooves, using that galv, painted, box section. None of them sweat, except in really exceptionally freezing conditions, it seems to be promoted in warmer weather, by moisture in the building. A solution seems to be, to buy the sheet, either pre-insulated, or to add insulation.

 

[Safety First]

Look for anti condensation sheeting.

I already have the plain stuff ready to fit.

So it's option 1, 2 or no fangled attempts to mitigate the condensation. Just relying on plenty of air exchange and little ingress.

 

[Safety First]

I now have three such rooves, using that galv, painted, box section. None of them sweat, except in really exceptionally freezing conditions, it seems to be promoted in warmer weather, by moisture in the building. A solution seems to be, to buy the sheet, either pre-insulated, or to add insulation.

Thanks, so that's +1 for the polystyrene, Vs the breather membrane option then.

 

[Harry Bloomfield]

Thanks, so that's +1 for the polystyrene, Vs the breather membrane option then.

Polystyrene sheet was what I used, slotted and wedged, in between the roof joists. There are two types, the usual, highly flammable version, and a slightly more expensive, flame retardant version. You need the latter.

 

[Ivor Windybottom]

Ventilation is probably a better idea than polythene and/or insulation. The outside air is usually dry when it's cold.

Also don't put wet tools in there.

 

[catlad]

You bought the wrong sheets really. They do fleece-lined anti-condensation sheets.

 

[Wayners]

Spray metal with foam as stops the condensation and quieter when it rains is one solution

 

[robinbanks]

Metal doesn't sweat, it's just a surface that can form condensation of its colder than the surrounding air and that air is laden with enough moisture that when cooled it exceeds the air's ability to hold the moisture

To stop condensation you either remove the water from the adjacent air or you remove the cooling effect so the water stays in the air

 

[Harry Bloomfield]

Metal doesn't sweat, it's just a surface that can form condensation of its colder than the surrounding air and that air is laden with enough moisture that when cooled it exceeds the air's ability to hold the moisture

In my case, it only became an issue, when there was a frost. Ice would form, build up on the underside, then when the thaw came, it would melt and drip.

 

[Safety First]

Metal doesn't sweat, it's just a surface that can form condensation of its colder than the surrounding air and that air is laden with enough moisture that when cooled it exceeds the air's ability to hold the moisture

To stop condensation you either remove the water from the adjacent air or you remove the cooling effect so the water stays in the air

Thanks,

Can you do 'The funny bone', next?

 

[Safety First]

You bought the wrong sheets really. They do fleece-lined anti-condensation sheets.

Awesome!

 

[robinbanks]

In my case, it only became an issue, when there was a frost. Ice would form, build up on the underside, then when the thaw came, it would melt and drip.

Your dehumidifier was in turbo

Had the same in my dad's garage, a huge tin roof that used to helpfully drip all over the classic cars he kept, until the entire garage received an all-round insulation upgrade

Thanks,

Can you do 'The funny bone', next?

Option 3; insulate the entire thing, so it becomes a pleasant place to be/work. It doesn't have to cost a fortune, especially if you use the cheapest/nastiest seconds grade kingspan you can find and cut it to form a consistent thickness. If this is a mostly unoccupied space, 25mm may do but if you'll spend any length of time in it, go for more

If you want a fast, easy but more expensive result, you can get a 2 part spray foam insulation that comes in a couple of gas bottle type things and mixes in the fun you spray it with. Phenomenal stuff, very fast to fit. Google for AB Building Products to get an idea for some variants