Cape Cod - Re-Insulating Existing Sloped Ceiling


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Old 01-02-15, 06:02 AM
R
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Cape Cod - Re-Insulating Existing Sloped Ceiling

I have a Cape Cod built in 1953. I am working right now on updating the insulation.

There is a crawl space across the front of the house with a knee wall. I am looking to improve the insulation of the sloped ceiling running from the knee wall up to the attic. Currently there is 2" of very old fiberglass insulation between the rafters. I have since stuck Styrofoam baffles in at each end to allow for air flow. The rafters are 2x6.

Within the next year I am going to have an insulation company blow cellulose into the first floor walls (no insulation) and throughout the attic. My question is whether or not they would be able to blow insulation between the joists of the sloped ceiling or not. My concerns are 1) would the existing 2" of fiberglass need to be removed first and 2) would they be able to dense pack the cellulose without breaking or blocking my baffles?

I want to get everything setup and ready to go now.

Your insight will be appreciated.
 
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Old 01-02-15, 08:05 AM
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Hi Running,
Those 5.5" deep cavities on the slopes of a cape are impossible to bring up to current codes without filling them completely full of rigid insulation, but then you cut off the ventilation path from soffits to upper attic and the project gets much bigger.

You mention an attic space in the front of the house, what is in the back? I live in a cape so suspect it might be what I call a shed dormer where the roof pitch has been reduced so there is an outside wall instead of a kneewall. If so, is there a soffit vent on that dormer? And, are you having any ice dam issues when the snow accumulates on the roof?

Bud
 
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Old 01-02-15, 08:29 AM
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Yeah I am not looking to necessarily bring it up to code, rather just an improvement over 60 year old insulation standards. I will not be removing the baffles. We had an extremely baked roof replace a couple years ago, and the increased ventilation has significantly decreased the rooftop temps.

You are correct in that there is a dormer out the back with a reduced pitch. There are baffles running the length of the slope of the dormer. Unfortunately, I don't think I can have insulation blown into that side of the roof because the ends are not blocked off. I imagine that insulation would get blown into the soffits and block my soffit vents. The dormer faces south-southwest, so ventilation is critical due the sun it gets and the reduced slope.

There does appear to be ice damming on the dormer, but it has not caused any problems. My contractor installed ice guard underlayment in front of all the gutters.

I just got off the phone with the insulation company I plan to use. She suggested removing the exist fiber batts prior to blowing in the cellulose as the compressed fiber will result in reduced R values.
 
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Old 01-02-15, 10:21 AM
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I doubt they can really dense pack those cavities as it would crush the baffles. Heck, it can blow out the drywall if not careful. They would be fluffing it in so, yes the fiberglass would compress to some degree, but it's r-value would be its resulting depth, just like the depth of the cellulose. Do your baffles extend from the kneewall space all the way to the top attic and are they just slid into place rather than being fastened securely?

If your configuration is as I suspect, soffit vents front and rear (under that dormer) venting up to either gable vents or a ridge vent, then the question arises, are the dormer soffit vents an intake point or an exhaust point. The wind will use them for either, but static venting is more difficult to determine and in most cases results in those dormer vents being exhaust vents. That means the warm air in the attic is warming the bottom of that roof instead of a flow of incoming air cooling it, thus an ice problem. When I figured that out on paper I immediately ran out back and up my scaffolding and sure enough, there was a substantial flow of warm air coming out my rear soffit vents. Why that happens is a long story and the fix is a pain, but it has to be fixed to eliminate those ice issues.

I'm a contractor, so removing the sheetrock, padding those 2x6's to be 2x10's and then insulating and adding new drywall is a piece of cake and will make for a much better job. Remember, the r-30 or whatever the minimum code requires is well below what should be there. They are reducing the requirement due to the difficulty involved, but r-50 is what would be comfortable and save energy. BUT, I do understand, just do your best. And if you go with the blown in cellulose, be sure there is still an air path.

If you somehow remove some of the fiberglass while keeping the kraft vapor barrier in tact it would not hurt. But if leaving it is necessary to keep whatever is there as a VB then the compression should not be an issue. If it compresses to nothing, then their cellulose just fills up the extra space.

Bud
 
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Old 05-21-15, 09:18 AM
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Hey bud, I have a cape cod in Florida and it's built in 1986. Concerning the slant ceilings upstairs the truss is 2x6 and it has batting insulation but no baffle for air flow . I have vented all attic spaces including the top long triangle using different methods and seems adaquate . The only warm spot to touch is the slant part of ceiling during summer. I put off ridge vents at the knee wall to vent out knee wall space since air could not get to the top ridge vent because the slant ceiling issue. So should I just use great stuff to fill the slant part of ceiling and leave the batting also?
 
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Old 05-21-15, 10:07 AM
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Rather than tagging onto the end of this old thread, let's see if one of the nice modes will move this to it's own thread. If not, just start another thread and reference this discussion if it is relevant.

I'll wait to answer to see where this topic lands.

Bud
 
 

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