Insulated Roof Construction for Garden Room

[Co1]

Afternoon all. I could do with a bit of a steer on how best to construct the insulated roof on my garden room. It’s going to be a mono pitch roof, using profiled sheet.

From the top down I’m thinking:

Roofing sheet
Membrane
Osb
50mm air gap (ventilated?)
50mm PU insulation (should this be 100?)
50mm gap to run cables and house recessed lights
Ceiling.

Does this feel right?

Thanks
Col

 

[alex robinson]

Have you considered structural insulated panels? So much easier - single sheets to fix on rather than multiple layers. What is the span? They will do 3m without any internal structures. You can get more insulation for a given roof thickness as you don't need a ventilation gap.

You can screw stuff to them, so you could hand a false panel beneath to hide cables and recessed lights.

 

[Co1]

Hadn’t considered that. I’ll have a look.

 

[alex robinson]

Hadn’t considered that. I’ll have a look.

They aren't especially cheap, but not too different in price to a traditional roof. We got a whole roof up and attached in 1 day though...

Ridge and trims come with the kit, and you can even get guttering as part of the system. Handicraft has a good series of YouTube videos about fitting them.

 

[Co1]

Thanks a lot. Who did you get the kit from?

 

[alex robinson]

Thanks a lot. Who did you get the kit from?

I got them from https://www.panelsell.co.uk/. Went for 80mm PIR as a decent compromise between insulation and practically (they offer between 40 and 160mm).

The website isn't especially DIY friendly, but they are really helpful if you contact them. They provided a list of all the fittings and trim bits I would need, along with span tables etc.

Panels cut quite nicely with a circular saw (cut the flat side first).

 

[Jameshow]

Afternoon all. I could do with a bit of a steer on how best to construct the insulated roof on my garden room. It’s going to be a mono pitch roof, using profiled sheet.

From the top down I’m thinking:

Roofing sheet
Membrane
Osb
50mm air gap (ventilated?)
50mm PU insulation (should this be 100?)
50mm gap to run cables and house recessed lights
Ceiling.

Does this feel right?

Thanks
Col

What's your budget on this build. If your wanting recycled panels I know a place in Huddersfield.

 

[Fitzroy]

Order looks right except ideally you’re missing a vapour barrier on the warmside of the insulation, necessary in a permanently occupied space like a house, but probs overkill in a shed. Yes ventilate the cavity else no point having it. 50mm is not much insulation I’d go 75mm min and 100mm ideal. If your trying to fit in 100mm joists then I’d go 75mm insulation 25mm ventilated cavity.

 

[Co1]

I got them from https://www.panelsell.co.uk/. Went for 80mm PIR as a decent compromise between insulation and practically (they offer between 40 and 160mm).

The website isn't especially DIY friendly, but they are really helpful if you contact them. They provided a list of all the fittings and trim bits I would need, along with span tables etc.

Panels cut quite nicely with a circular saw (cut the flat side first).

Just had a quote for £1500 from those guys, but more than I was expecting. I think the “traditional” option will prove more economic.

 

[HOJ]

Couple of thoughts, try and catch up with Martin @Molynoox, he designs and builds Garden rooms, probably has the ideal solution in his portfolio.

Have you the scope in the height of the roof to make it a warm roof, leaves the structure exposed below so you can fix lighting etc without compromising your insulation.

 

[Molynoox]

Couple of thoughts, try and catch up with Martin @Molynoox, he designs and builds Garden rooms, probably has the ideal solution in his portfolio.

Have you the scope in the height of the roof to make it a warm roof, leaves the structure exposed below so you can fix lighting etc without compromising your insulation.

I think you missed battens from your build up, between membrane and metal roof sheets.
Also, 100mm insulation is pretty standard for a heated space if your joists have the room for it.
50mm ventilation gap is great, but be aware that many don't bother - depends on how much you plan to use it, same with vapour barrier, you may get away without, but then it's very cheap and easy so I would put it in.
You can possibly put your electrics in the gap above the insulation and then you don't need the 50mm gap between ceiling and insulation. But with electrics they do need to be a certain depth to be compliant, I think the guideline is 50mm inside wall. So I always try and get the cable just above the insulation inside the air cavity which then puts it 50mm below the roof but it doesn't get in the way of pushing the insulation up. If you route electrics through the centre of the joists, as is optimum for retaining beam strength, then you will probably need to do a lot of cutting of the insulation so you can still push he insulation up far enough.

Martin

 

[Molynoox]

By the way, careful when you noggin out your ceiling not to use the same timber size as the joists as this will close up the ventilation gap.
So if joists are 150mm then use 100mm for noggins and leave the 50mm at the top for the air.
Common mistake hence why I'm mentioning it

While I'm at it, might as well mention that if you use PIR, I recommend spacing your noggins at 1200mm... It's one less cut to make as PIR will be 1200 x 2400 sheets.

 

[Co1]

Very much appreciated.