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Old 10-16-2014, 11:17 AM   #1
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Cathedral Ceiling Insulation


We have a cape cod and are having a new roof installed. The stairs leading up to the second story, the cathedral part, with two rafter bays of 2x6's had no insulation in them. The roofers pulled the roofing deck and put in some batt insulation, (R30 with a plastic wrapping that had holes) and some attic cat they put in by hand. They also put in plastic baffles between the decking and the insulation. Unfortunately at the bottom of the rafters it is completely blocked off. So there will be no air being pulled in from the soffets. There isn't a way to get them open. Not to mention, there will be no ridge vent since there is also the dormer.

Not an ideal situation at all, but since the deck is off, should we do something different? There will at least be some gap between roof deck and insulation with the baffles. We are in climate zone 5.

Not ideal, but are we looking at a disaster down the road?
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Old 10-16-2014, 11:34 AM   #2
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Did find this on Certainteed's website (that is the shingle going on). The method used should meet that requirement.

http://www.certainteed.com/resources/30211199.pdf

"The need to leave space between the roof deck
and the insulation has been debated for years.
This depends in part on where you live, however,
it is the recommendation of the CertainTeed Home
Institute that, when practical, some space be left
for ventilation.
The amount of space has also been the subject of
some debate. As stated earlier, some codes require a
minimum of 1", however, there is no basis technically
for this number. The CertainTeed Home Institute
recommends that some space, say 1⁄2", will suffice.
Finally, the best form of ventilation is a system
utilizing a combination of eave (or soffit) vents
and continuous ridge ventilation. This allows for
the movement of air under the roof deck which
can minimize moisture problems and prolong the
life of the roofing."
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Old 10-16-2014, 12:37 PM   #3
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Sounds a bit like a cluster you know what.

With the venting, the roof should have been insulated along the floor and vented via gable vents or spray foamed.

There is a bunch of stuff wrong there.
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Old 10-16-2014, 12:57 PM   #4
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It really is only those two rafter bays that were uninsulated and unvented. Now they are insulated with a gap via the baffles. On either side of the rafters, is the typical cape cod with knee walls. The floors on either dide have r49 in them that we had installed this past May. I even air sealed the knee walls as all they had was batt insulation. There is a gable on one side too, and the other side will be getting a ridge vent with the new roof.

Just trying to make a less than ideal situation better as we saw no savings after the blown in was installed since those stairwell/cathedral ceiling had no insulation at all.
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Old 10-16-2014, 05:38 PM   #5
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We typically dense pack the slopes and make sure the upper attic is vented via gable end vents.

On the kneewalls, many folks want them as conditioned storage so we spray the underside of the roof (after we install some foam) and make sure it gets come conditioned air and a thermal barrier.
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Old 10-17-2014, 08:08 AM   #6
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Any changes now will have to be from the inside. The stairwell and its cathedral ceiling splits the upstairs attic. The left side is open with a gable with insulation on the floor and kneewalls, the other side is mostly opened with the newly installed ridge vents. The right side is about 50', and 15' of those feet are the dormer with no ridge, the remaining 35 feet of the house has the ridge. With the soffits there should be plenty of air on either side of the stairwell.

The stairwell isn't completely sealed, as it is slightly narrower than the rafters above it. There are actually three rafters, with the middle rafter only about 12" OC and the rafters to the side are both 16" OC. On the outside edges of the outter rafters, is about a 2" gap. So both of those rafters will get some air infiltration, albeit from the bottom. It's that middle rafter that will probably see the least if any air movement.

While there should be some gap with the baffles between the roof deck and the insulation, there won't be much if any air movement in the middle rafter, but the side rafters are opened a bit.

Besides not being the most efficient insulation (albeit better than zero that was in there to begin with), is potential mold issues the biggest worry? Hot and humid air permeating through the drywall of the stairwell, going through the newly installed insulation, past the baffles and hitting the cold underside of the roof deck. It'll condense and with the little air movement (especially that middle rafter), will get mold in there?
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Old 10-17-2014, 01:01 PM   #7
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Here are the pics of the gap on the outer rafters. I used tyvek there when air sealing the kneewalls.
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Old 10-18-2014, 05:21 PM   #8
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Condensation is your biggest concern here.

Not sure what can or cannot be done now.
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Old 10-19-2014, 01:42 PM   #9
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I'm thinking I'll just have to drop the drywall ceiling in the stairwell, pull the insulation, and have it sprayed with closed cell foam. They are 2x6 rafters, so that should get me about an R30. Not quite code, but I'll take R30 over the R-whatever 1/2" drywall, 5 inches of air, 1/2" plywood and shingles give you. May even be able to drop the ceiling height somewhat in the stairwell and pick up an extra inch for insulation. Have to be careful or upstairs furniture may never get back down.
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