Help with pitched metal roof on garden room
Information, help and tips on many areas of roofing including trusses, tiling, venting, insulation etc....

4 posts   •   Page 1 of 1
jamie1234567
Labourer
Labourer
Posts: 2
Joined: Mon May 15, 2023 1:20 pm

Help with pitched metal roof on garden room

by jamie1234567 » Mon May 15, 2023 1:33 pm

Hi,

I’m planning to build a music studio in my garden.. I’m 80% there with the design, but need some advice regarding cladding the roof. I'm keeping it small enough that I won't have to meet building control requirements, but I still want to do the job properly.

The plan is for a pitched roof design and I want to use either box profile or corrugated metal sheeting to clad it.

I’m thinking from an acoustic and thermal insulation perspective, to go for a decent thickness of PIR insulation between the rafters, then a layer of OSB sheathing on top, then a membrane, but I’m not sure of the correct way to then attach the metal sheeting on top.

All the manufacturers guidelines I can find for this type of material suggest attaching it to thick purlins, but they are all aimed at building a barn or workshop roof with no mention of wood sheathing or insulation below. I have found several videos on youtube (all from America), where people are using this material on houses and are laying the metal directly on top of the OSB (and membrane) and are using foam packers at the ends, but I feel like restricting airflow beneath the metal might be an issue?


Basically my question is:

On top of the joists should I go OSB>membrane>metal roofing sheet or OSB>membrane>some sort of battens (or larger purlins)>metal roofing sheet.

I feel like any sort of horizontal battens will prevent any drips from running downhill, but no battens might restrict airflow. What’s the proper way to do this?

Thanks,

Jamie

stoneyboy
Project Manager
Project Manager
Posts: 6444
Joined: Wed Dec 10, 2008 6:44 pm

Re: Help with pitched metal roof on garden room

by stoneyboy » Tue May 16, 2023 10:47 pm

Hi jamie1234567,
Suggest you go - acoustic panels - vapour barrier - rafters with insulation between - osb (suitable grade) - breathable membrane - steel topping (not flat sheets)
Regards S

jamie1234567
Labourer
Labourer
Posts: 2
Joined: Mon May 15, 2023 1:20 pm

Re: Help with pitched metal roof on garden room

by jamie1234567 » Wed May 17, 2023 9:26 am

Ok thanks!

So if I'm understanding correctly I can just fix the metal directly on top of the breathable membrane, without any battens?

Also should I leave an air gap between the insulation and the OSB (and ventilate at the soffits), or completely fill the gap between the rafters with insulation?

stoneyboy
Project Manager
Project Manager
Posts: 6444
Joined: Wed Dec 10, 2008 6:44 pm

Re: Help with pitched metal roof on garden room

by stoneyboy » Wed May 17, 2023 10:50 pm

Hi jamie1234567,
Assuming the metal sheets have some form of corrugations going up and down the roof, fix direct. Maintain ventilation up the corrugations ie do not seal the ends.
Provided you fit a continuous vapour barrier fill the space between the rafters with insulation.
Regards S

4 posts   •   Page 1 of 1
It is currently Wed May 22, 2024 3:02 am