DIY Doctor

Mono pitch kitchen roof insulation advice

Postby Arabella0802 » Sun Feb 14, 2021 10:04 pm

Hi,
Im looking for some advice on insulation best practice. I have a mono pitch kitchen ceiling. The kitchen is an extension, probably 1960's with currently no insulation. Roof covering is; slates, sarking boards, 6" rafters @ 16" (400mm) enters which taper to 4-1/2" at the lower end of the pitch. I have limited head room at the lower end of the pitch. Any advice on method and products would be appreciated. Thanks.
Arabella0802
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Postby stoneyboy » Mon Feb 15, 2021 2:55 pm

Hi arabella0802
If you need building regs approval it will probably be necessary to put on a new roof structure unless you accept a lowering of the headroom.
If not you could improve things by removing slates and sarking boards, increasing the depth of the rafters by adding 100mm timber on top, insulating between the rafters and refitting the topping. You must add top and bottom vents when the slates go back on.
Regards S
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Postby Arabella0802 » Mon Feb 15, 2021 10:04 pm

Thanks for the quick reply Stoneyboy.
I won't need building regs and I can't afford to re-cover the roof. I'm fitting a new kitchen, and thought it best to insulate before I start.
What I was going to do Was infill the rafters with 100mm kingspan type insulation, leaving a 50mm air gap below the sarking. Then staple "space blanket insulation' to the rafters, then insulated plasterboard. I'd appreciated any thoughts on this. Can you also let me know where the Top and bottom vents would be? There is plenty of air flow at the moment coming through the slates, The plasterboard is removed and I can feel a good draft.
Also is there any way of adding a breathable membrane below the sarking as an additional barrier to water.

Thanks in advance.
Arabella0802
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Postby stoneyboy » Tue Feb 16, 2021 10:17 pm

Hi arabella0802
The top and bottom vents are not necessary since you do not have felt under the slates.
Using space blanket will act as a vapour barrier but you must tape the joins. Suggest you use 50mm of the Kingspan insulation under the rafters and fix standard plasterboard under this. Since you have a ventilated space above the insulation a breathable membrane is not needed.
Regards S
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Postby Arabella0802 » Wed Feb 17, 2021 7:57 am

Thanks for the help and advice.
Arabella0802
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