Cedar over ice and water


if the entire roof has ice and water shield over zip sheathing and you are installing a 18" 7/8 tapersawn roof, would you still use felt in a two ply application (7 1/2" show)?

If so, would you instead just do a 3 ply 5 1/2" show?


I should add that an alternative being considered is I&W in the usual places and then a breathing adhered roof membrane (Vaproshield SlopeShield). That costs more, the only advantage I see would be if moisture was trapped when the product is applied.

The roof is non ventilated with closed cell foam in the rafters and a conditioned attic space FYI, an important point to make. That means it can’t dry to the inside but also that it does not have a hot/cold attic under it.


We do a good number of cedar roofs both sawn and split. And my only offering is installing as follows… ice and water shield on usual areas with a good synthetic underlayment (I prefer OC deck defence).
Then cedar breather, yes this item alone costs the same price per sq foot as a decent 30 yard shingle. Then I do my shake with30# felt on every row (half rolls).
Stainless steel staples or galvanized ring shanks.


Cedar breather is a must if installing over a completely shielded and foamed roof deck. We use split 30# with shakes and nothing with sawn. Quality galvanized ring shanks with natural, stainless with pressure treated.


18" perfections @ 5.5" is a hell of a roof FWIW – no felt interlay needed but definitely should have breather in your application.

@7.5" code probably requires felt every row, although in practice with breather over i&w it probably would make no difference so long as the product is of reasonable quality.


MPA - I messaged you, did you see it?

I need to get the roof going, Philadelphia suburbs if you’re interested.