Loft conversion Insulation

[DHFrames]

Having our loft done at present

The builders, building control, chippy etc all have their own ideas that meet regs in regards to insulation, I can get celotex any thickness and acoustic wool very cheap so based on only using that what would be best in the following places...

Dormer

Cheeks and front 150mm timber
Is an air gap required?

Dormer roof, 3 layers, 225mm running down to 175mm.
Is an air gap required?

New front elevatin roof, 150mm
50mm air gap is required

Existing part of roof 100mm
This needs to made bigger but by how much, 25 or 50mm? Then what size insulation?
50mm air gap is required

Stud walls, what size timbers & what size insulation?

Cheers all

 

[freddiemercurystwin]

What do your drawings specify?

 

[DHFrames]

Different to what everyone else is advising

Ie Drawings say 80mm Celotex between the rafters, thinsulex quilt over the top.
Builders say 100mm between rafters with 40mm Celotex over the top

Chippy says baton rafters to enable the required 50mm air space using just 120mm Celotex between the rafter.

They all have different advice for the Dormer cheeks, stud walls and dormer roof as well. Just need after a little clarification.

 

[freddiemercurystwin]

Ie Drawings say 80mm Celotex between the rafters, thinsulex quilt over the top.
Builders say 100mm between rafters with 40mm Celotex over the top.

Well for your roof I concur with your builder, as will everyone worth their slat on the forum, if a little overspec'd.

As for the others can you state the exact proposed construction for each of the elements, you've not provided enough info so far.

 

[DHFrames]

Here you Freddy

Dormer cheeks
50x150mm timbers, again is 100mm sufficient with 40mm over the top? Is a 50mm air flow required?

Stud walls
Is 50x100mm timbers, insulated with 100mm rockwool sufficient?

Dormer Roof
This is insulated externally with 116mm thermaroof, but what is required between the 175mm rafters internally ??

Lastly the existing roof rafters (100mm)
Is 75mm sufficient between after adding 25mm batons. Limited for space here so don't really want to celotex over the top, its in the void bit of the loft!

Appreciate your advice

 

[freddiemercurystwin]

Dormer cheeks
50x150mm timbers, again is 100mm sufficient with 40mm over the top? Is a 50mm air flow required?

As requested, what is the proposed make-up, from external to internal finish? So tiled or rendered or lead or what etc

Stud walls
Is 50x100mm timbers, insulated with 100mm rockwool sufficient?

Is this an internal partition within the new loft? Is its separating an ensuite?

Dormer Roof
This is insulated externally with 116mm thermaroof, but what is required between the 175mm rafters internally ??

Sounds fine. No need for anything between the rafters internally.

Lastly the existing roof rafters (100mm)
Is 75mm sufficient between after adding 25mm batons. Limited for space here so don't really want to celotex over the top, its in the void bit of the loft!

Is the this the sloping bit between the top of the dwarf walls and the eaves?

 

[DHFrames]

Apologies for lack of info

Dormer cheeks
Tiled out, 19mm ply, 50x150mm timbers

Stud walls
yes this is separating the the en suite and a walk-in wardrobe.

Dormer roof
There is now no 116mm thermaroof, instead there will be 100mm between rafters with 40mm over the top, hopefully this should be ok

Existing roof rafters 100mm
yes the sloping bit between the dwarf wall and eaves, but also this will run up to the ridge as the roof is changing from hip to gable.
The existing rafters will be battened with 50mm, allowing 100mm celotex between the rafters, 30mm will go over the top.
The void beyond the dwarf wall, is a air space required? If not i will just use Rockwell or off cuts of celotex taped at the joints.