hybrid attic insulation scheme remediation


Old 05-30-08, 10:48 PM
Thread Starter
Join Date: May 2008
Posts: 74
hybrid attic insulation scheme remediation

I recently purchased a home. Specifically, it's a 2.5 story A-frame with a 2-story addition (with walk-out basement, and attic). The a-frame's roof pitch is about 23:12, and the addition's roof has a pitch of 8:12. The addition's roof ridge perpendicular to the a-frame's roof ridge. The property is located in the frontranges of Colorado at 8700 ft elevation.

Unfortunately, there seem to be several things about the roof's design that have hurt it. On the A-frame, which dates back to the 60s, there are two layers of shingles; the bottom layer was nailed directly to the decking with no underlayment.

On the addition, which was built in the mid-to-late 70s, there may or may not be underlayment, but under the decking is R-19 fiberglass batt insulation between the 2x6 rafters. The paper side faces the attic, but was covered with a sheet of plastic and then some kind of low-density fiberboard.

The end result of this strategy appears to have been a 'perfect storm' of exposing the decking, and to a lesser degree, rafters to extremes of heat (under high altitude sun with no gap for air movement between the decking and fiberglass insulation) and moisture (with the insulation sandwiched between the underside of the decking and plastic).

While there are soffit vents, they are effectively sealed off by the insulation batts. There are three apprx. 1.5 sq ft louvered vents, one each per gable, but with the insulation and plastic, what good they did isn't clear. I suspect later in the roof's life, a half-hearted attempted was made to add a dome vent, but after cutting a 8" square hole in the decking, they didn't bother touching the fiberglass batt insulation, plastic sheeting, or fiberboard below prior to adding the vent, so it was strictly a roof ornament. (When I pulled down that batt tonight, I found the original square of decking sitting on top of the insulation batt!)

So it seems like a totally schizoid approach to attic insulation design; elements of cathedral attic ventilation, but no ridge vents to complement the soffit vents, no rafter baffles to provide air passage to cool and dry the decking, vapor barriers to trap the moisture, and thick insulation to trap the heat. Rivulets of congealed tar can be seen on the underside of the decking, where it heated and flowed into the cracks! A lack of effective ice and water barrier underlayment has led to extensive moisture penetration, particularly in the valleys formed where the two roofs meet. They half catheralized the attic, but left gable venting; what could the point of that have been?

At this point, I'm working with professional roofing companies to come up with a quote to replace the roof. It's going to be expensive to rip up two layers of asphalt composite shingles from this 19 squares of roof, much of which is steep. An estimated 25-50% of the decking is going to need to be cut out and replaced, and ridge vents added. I'm happy to let the pros handle the exterior. At the moment, I'm aiming for 100% ice and water barrier underlayment and 30+ year architectural composite shingles (almost halfway between shingle and shake) suitable for the occasional winds up at 8700 ft...

What should I be doing with the interior? One thought is to simply pull down ALL insulation between the rafters, exposing the decking to view in the attic. I'll be doing this anyway, to make all the decking and rafter issues visible... Should I leave it this way?

Another option would be to let the roof work be completed and then add rafter baffles and replace the insulation (sans plastic sheeting) such that the soffit vents had air channels between the rafters to the ridge vents. Presumably, then, if I covered the gable vents, I'd get the benefit of additional insulated space above the attic floor (which appears to currently be joists with batt insulation covered with plywood flooring). I do like the 500 sq ft of dry storage under the 8:12 pitch roofing...

On the A-frame side of things, the situation is possibly a little more complex, as the roof is also the walls for the 2nd floor's (and top half of the 1st floor) eastern side; I believe it's mostly filled in with R11 fiberglass batts between the decking and the interior drywall (masonite faux wood or wood paneling, depending upon the room in question). Fortunately, the house is surrounded by lodgepole pines, so only the top .5 stories of the a-frame get the most intense sunlight. It'd be simple enough to pull down the R-11 in the a-frame's attic section, leaving the decking exposed...

Well, this is a big chunk of information, but I'd love to hear your thoughts on how to proceed, best practices, etc.
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Old 06-01-08, 06:35 AM
Join Date: Nov 2001
Location: USA
Posts: 1,873
Your problem here is that this has apparently been going on for some time. Some of roof decking or substrate may appear to be good but to the age and prolong exposure to moisture due to the lack of adequate ventilation will make it a poor nailing surface. Even if it appears to be in good shape. In other words the degrading of the substrate does not provide enough surface tension for the nails on the shingles and the nail lifts or what some call pops. This is compounded when such surfaces are exposed to high winds and snow.

My advice would be that you ask the contractor how much it would cost to replace all the substrate and compare the costs.

If you decide to go ahead and replace all the substrate the contractor can inspect and repair/replace any damaged rafters. You can replace all the insulation and install baffles with limited damage to the interior fiberboard.
Old 06-02-08, 09:55 AM
Join Date: Jul 2005
Location: USA
Posts: 124
Ask the contractor what you'll need to do to keep the warranty (material and/or workmanship) intact. He should tell you how much work you need to do without going overboard.

I had to add soffit vents, ridge vent, AND tear out the insulation to insert baffles in order to keep the warranties alive!


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