Garage roof idea-approval or advice etc required

[chestercity]

Just taken down asbestos roof off lean to garage and wish to put on new one.
Have added wood purlins etc
Want a metal roof- corrugated steel.
I wish to be able to add some insulation beneath the roof, in between the timbers. With corrugated or box steel profile being an issue as cold air would penetrate I thought I could attach WBP 9mm board onto beams before corrugated or similar steel is attached.
Does this make logical sense?
Thanks for any input
Tony

 

[theprinceofdarkness]

Corrugated iron drips condensation very badly. The only way to stop this is to seal the underneath to any air, which is impossible. I think a possible cure might be to run a plastic membrane directly under it , so the drips are intercepted by the plastic, which will follow the roof slope so will run out. The plastic must be laid like roofing tiles with the overlaps going in the correct direction and all overlaps sealed and taped.
Likewise there should be a vapour control membrane on the inside of the roof, to stop any moist air getting into the insulation and condensing within it.

Soooo, pin up your VCL with drawing pins on the underneath of the purlins, screw up your 9mm WBP under the VCL. Go on top, fill all joist gaps with glass fibre or WHY. Drawing pin your damp proof membrane to top of joists. Fix corrugated on top..

I would recommend this stuff :- http://www.tatasteelconstruction.co...structural-decking/building-envelope/trisomet
There are places that sell it as surplus. Its the stuff they use for the cladding of big box supermarkets
Frank

 

[chestercity]

Hi Frank,
Condensation was something I overlooked, although i saw a website selling under roofing for this reason since posting the thread!
The issue i would have with your idea is 1. It would be wasteful and counterproductive to tile and have corrugated 2. The roof is flat (to flat for any tile at least), so tiles are out.
I would seem that I would be better to go for flt on board. Less hassle but ugly. However it is pretty well out of view.
I would have built a pitched roof for fun and tiled it BUT it abuts to a garage and would therefore be problem with drainage/guttering.
Thanks for your ideas though

 

[oldbutnotdead]

You can get insulated corrugated sheets- quite pricey (£12/sq m) but quick and easy fix, no faffing with many layers.

 

[chestercity]

Sounds much more promising. Do you know suppliers?
I know some are plastic coated...maybe that helps? Though plastic coated metal windows can condensate I believe.
Thanks

 

[oldbutnotdead]

You can get bare corrugated metal (usually galvanised).

Next up is the plastisol coated- looks prettier

Next up is the stuff treated to prevent condensation (some sort of cottony stuff on the underside of the sheets). But you're into quite serious cash for that stuff.

I've bought GRP panels from this lot before http://www.ebay.co.uk/itm/Insulated...91?pt=LH_DefaultDomain_3&hash=item4d317ee7f3, Ebay is your friend