Question for builders

[Geoffrey Carter (Buttercup)]

The insulation will go flush with the bottom of the rafter and then the insulated plasterboard nails to the rafter. You may need a vapour barrier also but some insulated boards have the barrier within them now.

Thats my understanding.

[Mark (smokey mow)]

9 minutes ago, Arm said:

Hi Mark. Mind if I ask another quick question ? Have moved up with the build to the sloping upstairs ceiling and dont know if im reading this correctly.

So 100 mm pir board between the rafter then insulated plaster board (12.5 mm plasterboard bonded to a 25mm pir) underneath ?

Or an additional layer also ?

Thanks

Ash

Yes I read that as 100mm Celotex cut between rafters and then a further 25mm over the inside face with 12.5mm plasterboard and skim below that. Although you'd actually need closer to 40mm on the underside to get to the required U-value of 0.18W/m2K.

Like this:

For a vapour barrier all the joints in the insulation would need to be taped with foil tape or alternatively tou could use a foil backed plasterboard.

 

 

[Arm]

That makes sense. I will follow as instructed .

Cheers
Ash

[Arm]

Back again sorry . Celotex or kingspan or ecotherm, all much the same ? I'd go for the better one even if more expensive. 100 mm thick 2.4 by 1.2

[Mark (smokey mow)]

6 minutes ago, Arm said:

Back again sorry . Celotex or kingspan or ecotherm, all much the same ? I'd go for the better one even if more expensive. 100 mm thick 2.4 by 1.2

Buy on price and availability.

Celotex GA4000, Kinspan TP10 and Ecotherm Eco-versal all have a thermal conductivity of 0.022 so for a given thickness there's no difference between them in thermal performance

 

[Geoffrey Carter (Buttercup)]

I am just using Eco Versal in a housing development and received a great price compared to Kingspan.

[Arm]

I used ecotherm in the floor and was a good price. Will look at the relevant one for roof also. 

So many out there it’s confusing but as you look and get familiar they seem much the same.

[Arm]

Ouch. Roof insulation purchased. So expensive!

Anyway is it ok to cut led downlighting through insulation . All the way through to prevent hot spots.

Pitched roof so vaulted ceiling thus 50 mm air gap above insulation. 

[Mark (smokey mow)]

5 hours ago, Arm said:

Ouch. Roof insulation purchased. So expensive!

Anyway is it ok to cut led downlighting through insulation . All the way through to prevent hot spots.

Pitched roof so vaulted ceiling thus 50 mm air gap above insulation. 

No you need at least 50mm insulation behind the light fitting to prevent condensation and to maintain the vapour control layer. 

Have a a look at led down lighters, there's some that are only 30mm deep.

[Arm]

Ok that works as I have 138 mm total insulation and plasterboard depth to work within. Thanks