Above Roof Deck Insulation with Membrane Roofing

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!

go with a peal n stick system over 2" iso board.
tac the board down, then install peal n stick base sheet, then screw and plate the hell out of it, through the base sheet , through the iso , into the 2"
wood deck
then install 2nd layer granualated peal n stick.

then your house is ready to host the next hurricane party.



I would watch using screws. They could come through your ceiling.

The screws are suposed to penetrate the deck. They may allow you to not penetrate the deck because of the thickness.

Using Insta-stick for the iso board and fully adhered edpm is the way I would go.

If money isn’t a problem I would look into building a false deck over it. Now you have a space to insulate and you don’t have to sweat screw length. Then like Lefty said I’d go fully adhered EPDM.
I try hard to be a GAF fan-boi but I just can’t like peel and stick.

certainteeds flintlastic system----then run homasote insulation w/top deck board and install a flat system---its called homasote-easy roof ply and you can get up to r-32,you would have to build up the fascia /rakes to cover of course

Go with Lefty. Insta Stick or Olybond

hey donl,what`s wrong w/the homasote+epdm since the man has insulation problems,he could use insta stik w/that as well,and putadhered epdm—2"iso only has an r-value of 11 :!:

First of all, there is a difference between “iso board” and “extruded polystyrene.” For the record, you will want to go with the polyisocyanurate roof board insulation. Next, you will want to adhere it to the roof with a product like insta-stik like Lefty suggested. After that, you need to decide what type of membrane you want to go with. Like gweedo, I lean toward the modified bitumens membranes, but I stay clear of peel-n-sticks. EPDM membranes aren’t bad, but you’re probably looking at only 10-12 years of roof life, and falling branches and such can/will damage the membrane. A TPO membrane is another consideration, as is Sarnafil PVC membrane.

thanks cerb for half heartily agreein with me.
been gettin some funny looks lately.
maybe its somethin i wrote.

anyways, we all know the torchdown tarry substance
is the best thats ever been , yes.
but for me the fire risk has finnally outweighed the
durability superiority.

do i think peal n stick will last as long?
no. but at least there will be a house there to reroof 10-15-20 yrs from now.
peal and stick has only been out here in tampa bay
about ten yrs.
so far so good.