Interior retrofit of insulation in a cathedral ceiling
by Ken Ackerman
I have a 36 y/o home with 2 cathedral ceilings. A new roof was just put on (strip old roof, replace decking as needed, new 30# felt, new OC Duration energy reflective composition shingles (Shasta White). The re-roof process was on site inspected by an independent engineer to meet the Texas Windstorm Insurance Agency requirements. There was not enough time or money available to add Polyiso sheets over decking during the re-roof process. I live in Corpus Christi, TX, very hot & humid, no snow. I had continuous ridge vents installed and all old turtle backs and other roof vents removed. I am now starting to add Cor-a-Vent continuous soffit vents to balance the new ridge vent area.
1) Is it possible to remove the ridge vents temporarily and have an insulation contractor put liquid foam in each of the rafter cavities? I assume that due to the age of the home, that FG batts were probably installed originally. It's also possible to also open the soffits if that provides needed access. Just thinking about trying this approach gives me great reservations because it may actually block the venting cavities between the rafters.
2) If #1 above is not appropriate (more than likely not), then I assume the inside approach is the only one left. The current ceiling is sheetrock, is it better to take it down or just put polyiso sheets right over it? The diagram in this article above shows the polyiso put directly over the rafters. I'm assuming that taking down the existing sheetrock will more than likely allow the FG batts to fall out and prove to be a nightmare, unless the batts were stapled to the rafters.
3) What are the downsides to applying the polyiso directly over the current ceiling and then sheet rock over them, if any?
4) If the current sheetrock ceiling was ripped out and the batt insulation with it, would that allow an insulation contractor to liquid foam the back of the roof decking and still keep a vent channel to the ridge vents? If so, would it be necessary to put rigid foam inserts after the liquid foam is applied to insure the vent channel stays open?
OR install rigid foam sections one at a time prior to liquid foaming above it?
As you can see, I'm certainly not an expert in this area, but I'd like to do it once and only once, the right way, the first time.
Posted Thu, 11/01/2012 - 17:35
Edited Fri, 11/02/2012 - 05:08
Other Questions in GBA Pro help
Since drywall has a permeance of 0.02 liter/sec - m at 75 PA is ever possible to have sheathing dry to the interior of the home?