flat roof insulation

[inspectorgadget123]

redoing my 70`s house all the ceiling has been removed due to a wasps nest.

what is the best product for insulating this type of roof i would like to install some spot lights also , so it would need to be compatible with these kind of lights.

Untitled

• inspectorgadget123
• 15 May 2009
• 1

Untitled

• inspectorgadget123
• 15 May 2009
• 1

 

[noseall]

Add 100mm kingspan insulated roof deck (bonded insulation to plywood sheet) to the top of the ceiling joists, then add felt layers.

 

[inspectorgadget123]

Add 100mm kingspan insulated roof deck (bonded insulation to plywood sheet) to the top of the ceiling joists, then add felt layers.

the roof is fine itself i just need to insulate , i have already ripped down the plasterboard ceiling.

could i use this between the joists ?

http://www.wickes.co.uk/General-Con...n/General-Purpose-Insulation-Slab/invt/161197

or

http://www.wickes.co.uk/Polystyrene-Sheet/Celotex-PIR-Insulation-Board/invt/190545

do i need to vent the roof space if i used this ?

 

[noseall]

If you insulate between the joists then you are creating a cold deck and will need a 50mm air gap (on the cold side). this will need ventilating.

You may get away with fully filling the void with celotex, pressing the insulation tight up against the roof deck and sealing any gaps with mastic or foam.

 

[inspectorgadget123]

If you insulate between the joists then you are creating a cold deck and will need a 50mm air gap (on the cold side). this will need ventilating.

You may get away with fully filling the void with celotex, pressing the insulation tight up against the roof deck and sealing any gaps with mastic or foam.

well the joists are 100mm thick so i should be able to get some celotex that is 50mm flush with the joists.

should each space between the joists be ventilated ? as i can get to the overhang easily.

 

[noseall]

All joist runs will need ventilating.

50mm is just under half the (building reg's) required amount.

 

[inspectorgadget123]

only just remembered that the flue for the boiler comes out the roof just behind the area which needs to be ventilated.

so doing the ventilation is a no no

i think i am going to just reboard the ceiling as it was never cold anyway

 

[noseall]

You may get away with fully filling the void with celotex, pressing the insulation tight up against the roof deck and sealing any gaps with mastic or foam.

....or this way?