Insulating Rafter's (Kingspan)

[diycooper]

I am planning on insulating my Rafter's with Kinspan in my loft. They are 75mm x 50mm. I was Planning on leaving a 25 mm airgap at the back of the Rafter then insulating and using 50mm Kingspan, flush with the rafter's. What is thebest way to fit the Kingspan. I was thinking about cutting it as snug as I can to friction fit then using 75mm dryline screws throught the side of the rafter to hold in place if I need to. Just want to know if this sounds right so I can get cracking before the cold months.



Thanks In Advance

 

[tony1851]

If it's a tight friction fit, it shouldn't need any additional fixing because it is so light.. The plasterboard will also help keep it in place.
Be careful about your ventilation; if you've no felt under the tiles (or breathable felt) you should be OK with 25mm gap. If you've got the bitumen-based felt, you need a little more clearance.
Make sure your vents at the soffit are clear; is there any ridge venting?

 

[diycooper]

If it's a tight friction fit, it shouldn't need any additional fixing because it is so light.. The plasterboard will also help keep it in place.
Be careful about your ventilation; if you've no felt under the tiles (or breathable felt) you should be OK with 25mm gap. If you've got the bitumen-based felt, you need a little more clearance.
Make sure your vents at the soffit are clear; is there any ridge venting?

thanks for reply, I have got bitumen felt but will be getting new roof in next few month, there are no ridge vent will get roofer to put couple in . Will this be ok then ?

 

[noseall]

Fix 50mm insulated plasterboards (62.5mm including plasterboard) to the rafters for now.

When the roof is stripped fix another layer prior to fitting the breathable membrane.

As said you may need ridge and soffit ventilation until your roof is vented via breathable membrane. I suppose you could risk slitting the felt if a new roof is imminent, but it may be a costly risk.

If the insulation/ventilation detail were to satisfy b'regs then additional insulation thickness and battening of the rafter would be required.