Flat roof insulation

[Coogie]

i have a flat roof with 8" joists that i want to re-insulate with Kingspan 'slab' insulation

Will 100mm be sufficient? and should i leave the remaining 4" gap above the insulation for ventilation?

How much gap should i leave for the electric cables that run through the joists and how much free space should downlights have?

Thanks

 

[Hib]

For pitched roofs you need 50mm air gap if you're not using breathable felt. That would be plenty for your electric cable (i think)

Not sure if 100mm kingspan is enough - someone else will have to help you there.

As far as i know about 150 x 150mm is required around downlights - the manufacturers instructions will tell you. To me though - considering 250 - 300mm fibre glass insulation is reccomended (which is a small mountain of the stuff) and then you can't put it anywhere near the downlights - you have to be very fond of downlights to make them worth it. To put it another way they don't seem very energy efficient.

Check out this post http://www.diynot.com/forums/viewtopic.php?t=44479

Hope that helps

Hib