Our house has all vaulted ceilings with no insulation. The interior design makes below the ceiling insulation undesirable, so we are looking at above the roofdeck insulation on top of the approx. 2" wooden roof. One suggestion we have received is to use a membrane roofing (Duro-last) over a 2" extruded polystyrene insulation board (Isoboard) on top of the roof deck.
As some extra information, the roof has a very low slope (less than 3" on the front, and less than 2" on the back). The front currently has shingles on a 1" board over the roof. The back has roll-roofing on the 1" board over the roof. The location is central South Carolina, so snow and hurricanes are both a rarity, but high temps are months on end.
I understand that if shingles were used spacing would be required for ventilation. Is it correct that a memberane roof wouldn’t require the spacing? Anyone notice any structural/maintenance things we might be overlooking in considering this option?
Thanks in advance!