Confused: 2 flat roof quotes with different insulation

[Daddy]

Hi,

We are looking to replace a flat roof approx 15m2 in size with EPDM. There is no insulation board above the joists at present but I suspect there may be some wool between the joists below.

We've had 2 quotes:

1. Local company want to place 75mm insulation board+deck combined over joists (warm roof ?)

2. Mossrid want to completely fill inbetween the 8" joists with Rockwool and not use any board on top (cold roof ?)

The latter are a lot cheaper but I'm concerned about the approach. I thought cold roof needed ventilating between the joists although I can't see any ventilation around it currently. They will do the over boarding for a price but say it's not strictly necessary but I'm not so sure. Also, is it a possibility to have both Rockwool and the board ? The room is quite cold in winter !

Many thanks,

Andy.

 

[wombats]

If you were to have both then the roof would probably sweat and cause condensation as the heat would be trapped netween the surfaces. Sound to me that the 2nd quote seems the better choice as you will be keeping the heat in instead of the roof trying to heat the building.

 

[Daddy]

Thanks for that wombats !

 

[masona]

I thought cold roof needed ventilating between the joists although I can't see any ventilation around it currently.

Flat roof should have ventilation such as cross flow vent from joists to joists and soffit vents etc