Insulate slate roof

[Andy_r2o3]

Hi

I am looking to create a warm storage space in my loft.
House dates to 1900
Original slate roof
I want to insulate the rafters and eventually add plasterboard etc.
There is no felt beneath the slate roof.
I have not noticed any leaks up there.
Can I add the insulation boards into the rafters and leave an air gap, or does the roof definitely need felt?

cheers

Andy

 

[freddiemercurystwin]

No it doesn't need felt but the downside is that if you get a leak it might track it's way down the rafters and leak out further down the roof and you may have to remove the insulation to find it. It's not all that unusual though, you would do the same in a loft conversion that didn't have felt.

 

[Andy_r2o3]

No it doesn't need felt but the downside is that if you get a leak it might track it's way down the rafters and leak out further down the roof and you may have to remove the insulation to find it. It's not all that unusual though, you would do the same in a loft conversion that didn't have felt.

Thank you... so I’m presuming as long as I leave 50mm between the tiles and the board for air, I won’t get damp caused by condensation?

Cheers.
Andy

 

[Alastairreid]

The air gap between the insulation will be even more efficient without felt.
Drawbacks as fmt pointed out.

 

[datarebal]

Might be worth looking at super foils
Easy to fit inside ..

 

[Andy_r2o3]

Thanks for all the replies.
So change of plan. I’m Working from home more now so turning it into a bit of an office... plugs Lights plasterboard and plastering etc ..
So I can use superfoils? I believe they’re rather new to the industry? I can put those in between the rafters, below the slate, and then stick some celotex below them? Then plasterboard.
Would that do the trick?

 

[datarebal]

Doesn't quite work like that ---> https://www.superfoil.co.uk/insulation-guide/

And --> https://www.superfoil.co.uk/case-study/loft-conversions-made-easy/

What about your floor? joists up to it?

 

[Andy_r2o3]

Doesn't quite work like that ---> https://www.superfoil.co.uk/insulation-guide/

And --> https://www.superfoil.co.uk/case-study/loft-conversions-made-easy/

What about your floor? joists up to it?

Thanks for that I’ll have a look.
I’m now having a professional coming in to reinforce floor, I believe they’re ‘strapping’ the joists with new joists for reinforcement. And fitting a velux. I am just trying to find out as much as I can with regards to the insulation for the roof. Concerned for damp from condensation etc and want to do as much as possible myself.

 

[Bargain Bucket]

If it's becoming an office, does this not make it a "habitable space" that required buildings regs?

 

[Andy_r2o3]

If it's becoming an office, does this not make it a "habitable space" that required buildings regs?

Looks like it’s now going down that route.. Having a stair case Now too.
And will adhere to building regs with regards to the insulation, still want to do the majority myself to save the pennies. Waiting back for a couple of quotes still.
- for building regs do I need felt under the slate?
- Is it 125mm of insulation I need at the roof?
- Is it 25mm airgap from slate to insulation board?

I of course will ask the tradesmen doing the Velux but want advice from accross the board.
Cheers

 

[frutbunn]

If it's becoming an office, does this not make it a "habitable space" that required buildings regs?

Yeahits a habitable room and will require b Regs,

 

[datarebal]

habitable or not you can still use superfoil and some pir

 

[Andy_r2o3]

Cheers mate.
So superfoil (still not sure which) with any gaps taped, with a 25mm air gap between that and the slate,
then celotex/kingsman boards
then plasterboard (or insulated plasterboard)
.. will this stop any condensation? I don’t want to mask any leaks etc just don’t want any condensation or damp.

 

[frutbunn]

Be aware some multi foils may not be acceptable, or at least do not achieve the standard of insulation claimed, you must check it has been independently tested ie BBA certification etc. If in any doubt check with building control, assuming you are doing the loft conversion legally of course.

 

[freddiemercurystwin]

What's the point in using a superfoil? Once you add in the required air gap above and below any space saving advantage is lost.