Do *any* metal roofed sheds, NOT sweat?

[shen]

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 chinasteelbuildsales 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,

Option 1 is the better choice. A breathable roofing membrane under the steel helps reduce condensation by allowing vapor to pass while limiting contact between moist air and cold metal. It also helps manage any drips and works well with your planned ventilation gaps. Option 2 (polystyrene) is not ideal because it can trap moisture and is harder to keep fully sealed long-term. Good ventilation plus a proper breather membrane is the more reliable approach for corrugated steel roofs.

 

[Ivor Windybottom]

Not building a metal shed is a much better choice.

Plastic would be preferable for a small shed, brick for a bigger one. Or wood if you're over 60, otherwise it won't outlive you.