Roof construction

[CPdiyer]

Hi, having some quotes done on a single extension pitch roof and for my own sake would like an unbiased answer to how it should be done, as different builders have given me different answers.
It will be a cathedral roof (no roof space).

My understanding from the outside in is tile/batten/felt(or what ever its called today)/insulation/ply/plasterboard.

Considering there is a wall of glass windows what type of insulation should be there

 

[^woody^]

Any type. It's the thickness that matters.

 

[CPdiyer]

Any type. It's the thickness that matters.

Yes so I hear!! - but seriously I am thinking of 6x2 rafters as its a reasonably long span so space isnt a great issue - am I assuming that its none specific just the best I can afford?

 

[freddiemercurystwin]

Timber size is dependent on the span not what you think will be OK. If you don't know what you want how will you judge what a builder says will do?

 

[CPdiyer]

Timber size is dependent on the span not what you think will be OK. If you don't know what you want how will you judge what a builder says will do?

The structure wasn't the issue, I will be getting an SE at some point it was more to do with building regs as to what insulation/felt type etc so I can have it clear in my mind, so I can be 100% clear when I finalise this with the builder.

 

[^woody^]

Celotex or Kingspan. 100 between rafters and 50 along the underside. 50mm air gap below membrane, vented from eaves to ridge/abutment

 

[Ian H]

Use separate insulation and plasterboard rather then the combined stuff.

 

[catlad]

Use separate insulation and plasterboard rather then the combined stuff.

why?

 

[Elastomeric]

This is 140mm with TLX Gold giving me a U Value of .16. 9" Rafter with the correct air spacing. All foil taped with normal plasterboard going on.

 

[noseall]

why?

Because it is easier and more economical to do so. You have greater positional freedom and no waste issues (regards the underdraw layer of inso') when they are fitted separately. You can also seal the secondary layer of insulation gaining a bonus VCL. Joint bonding becomes more robust also.

 

[noseall]

This is 140mm with TLX Gold giving me a U Value of .16. 9" Rafter with the correct air spacing. All foil taped with normal plasterboard going on.

What is the point in insulating an already insulated loft? All you are doing is protecting an already cold space.

 

[Elastomeric]

What is the point in insulating an already insulated loft? All you are doing is protecting an already cold space.

Loft conversion. Floor insulation predominately for acoustics.

 

[noseall]

Loft conversion. Floor insulation predominately for acoustics.

Gotcha.

 

[Elastomeric]

https://www.diynot.com/diy/threads/bungalow-loft-conversion.480018/