Metal roof sheet queries?

[Ruggers]

I'm going to build a large detached storage shed constructed from solid block and externally clad in fibre cement board onto battens. 6.3 x 3.6m external. The roof will be dual pitched at 36 degrees. My options are to slate it like the house or to use some type of corrugated sheets which would be much cheaper.

My 2 concerns are, is it possible to prevent the condensation issue i read about a lot? Ideally i'd like to leave the trusses open so i can use for light storage.

-As the ridge covers seem to just sit over the gap where the sheets meet from each side, then what stops the rain blowing back up and under on a windy day. They don't seem very large and don't form into the corrugated sheets to seal?

 

[Burnerman]

Last summer I replaced a box section metal garage roof with Cladco products.....unfortunately the pitch of the box wasn’t the same as the original so I had to put new roofing timbers in.
The material was .9mm thick if I recall and polyester coated.
Anyway, they supplied eaves fillers made from high density closed cell foam which worked very well and I stuck them in with expanding foam.
For condensation issues you must under clad the sheets, leaving a gap between the cladding and the metal, and preferably ventilate these.
I held the sheets down with a large headed torx screw by Spax as I didn’t want the hammer shock.
John

 

[Alastairreid]

https://www.steelroofsheets.co.uk/categories/profiled-foam-fillers/

 

[Old Salt]

Don't go for steel use a corrugated rubberised roof. Use marine ply to form the roof and then fasten the rubberised sheets onto it and through into suitable timber supports.

The rubberised sheets will keep condensation down but go limp in the heat hence the ply backing to help support. Slight gap at the apex provides ventilation.

 

[Ruggers]

There seems many ways to construct a roof using sheets but it's which causes least issues. If the trusses are sheeted in ply first then the metal sheets added on top, will this stop the condensation inside or will moisture just form between the ply and the metal sheet causing rot? I take it the foam fillers are added between the top of the ply sheet and the underside of corrugated sheet to stop insects? Do they not block the air movement between both sheets?

@Old Salt thanks for the photos, looks a neat job. Are they the black bitumen sheets? I've attached these vertically on the back of my summerhouse and screwed on to OSB board. They've been good for 7 years so far but quite shielded.

 

[catlad]

You can buy fleece lined anti condensation metal sheets
antorcondenstop.com/condensation-solutions/?gclid=Cj0KCQiAx9mABhD0ARIsAEfpavQQQTT-7J2MzbYGe4JLNTnlujW4iKzm6jBn3D9yLGp4s5wPfvRlDOkaAmFcEALw_wcB

 

[catlad]

https://lantorcondenstop.com/conden...lujW4iKzm6jBn3D9yLGp4s5wPfvRlDOkaAmFcEALw_wcB

 

[Old Salt]

@Old Salt thanks for the photos, looks a neat job. Are they the black bitumen sheets? I've attached these vertically on the back of my summerhouse and screwed on to OSB board. They've been good for 7 years so far but quite shielded.

That’s the ones, had brain failure last night and couldn't remember what they were called, lol. My roof has only been up about 18 months but seems to be wearing well. I used the foam inserts at the ridge to prevent leaves being blown under the capping into the garage. They were fitted after installation and just tucked in. They will still allow some air movement, at least they do in my garage.

 

[Ruggers]

@Old Salt, was there a reason you chose them sheets instead of metal? I thought metal would of lasted a bit longer. Have you not had any issues with the wind blowing rain back up and it leaking in from the ridge?

I priced up doing it all in bitumen and it came to £900, slate would be £1000, but then I'd need a lot more trusses plus the fitting labour.

 

[Old Salt]

Metal sheets will be really loud when its raining. Rust over time and look sh1t. The capping overlaps about 150mm each side of the apex and I have only ever had leaves blowing in hence why I fitted the foam corrugated fillers

 

[Old Salt]

Some more pics of the roof construction

 

[Harry Bloomfield]

Metal sheets will be really loud when its raining.

Then can be noisy in heavy rain when you are inside, but does it really matter?

Rust over time and look sh1t.

Rust maybe, but over a very long time. Corrugated galv roofed sheds are still in use, from the last war. Modern ones are galvanated and painted.

 

[JohnD]

galvanisers can calculate how long the coating will last, and offer different thicknesses.

I think my BiL needs a new one.

 

[JohnD]

Fixed now.

 

[Old Salt]

I rest my case