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FileOpen 11-16-2011 07:43 PM

Newbie questions on refinishing walkup attic with knee walls
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I'm a beginning DIY'er in NJ. Thanks to all the frequent contributers, especially GBR. I've been lurking for a while but now I have to start doing.

Here's the basic idea of my 1949/1950 house. It is a ranch with a walk up attic. The attic follows the entire footprint of the house, from left to right, (see pic) in order 1) over the living room (storage) , 2) over the kitchen/bed/bath, 3) over the master bed/bath (storage) and 4) over the garage. The attic living space is part 2, there is a ridge vent. When I bought the house, the attic living space was finished with 3/4 " t/g wood paneling covering the walls, knee wall and flat ceiling . It is supposed to be real living space, there are 2 radiators. And I'm being taxed for a finished attic. The roof has gable vents, the roof does not overhang (no eaves/soffits). There is currently a ridge vent only on part 2. There are small doors that allow passage from part 2 to parts 1 and 3. The living space has a "closet" which contains some of the plumbing vents. I'm hoping to downsize the closet but leave the plumbing accessible.

A couple years ago, the following work was performed:
Installed attic fans in parts 1, 3 and 4. Added fire-rated sheetrock between parts 3 and 4. Added roof vents and insulation to the gable and floor of parts 1, 3 and 4. The old insulation only consisted of paper wrapped batts in the floor in parts 1 and 3 (no info on R-value or manufacturer). The garage attic had no insulation at all. I think someone mentioned that you should have either a ridge vent or attic fan but never both. So I guess I'm OK on that count. Question: I've gotten some comments that it was wrong to insulate the storage areas of the attic, was it wrong?

I want to refinish the attic and install drywall. I have lots of questions.

First, here are the particulars about my attic.
The gable uses 2 x 6's. The flat ceiling underneath uses 2 x 4's. The attic floor uses 2 x 8's. The knee wall uses 2 x 4's which are nailed to 3/4 " planks running the length of the floor . Inside the knee wall there were more planks over the batting. The walls used t/g wood panelling. Furring strips were nailed over the insulation.

The knee wall is about 3.5 feet high. It's about 3.5 feet from the knee wall to where the bottom of the gable meets the exterior wall. It's about 7 feet from the top of the knee wall to the ceiling. The knee wall was not insulated. The gable was insulated and the flat ceiling was insulated. The floor behind the knee wall had insulation.

Here are some points for what I was planning along with some questions.

1) I think I saw a comment from Scuba Dave that he would insulate the knee wall, the floor from the knee wall to the bottom of the gable and gable. I have a bathroom fan venting through a 4" flexible duct that goes behind the knee wall to the roof. I was going to change to an insulated duct. Would all this insulation pose a problem to venting the bathroom??

2) Insulate the knee wall (2 x 4ís). Should I use R-13.? The facing should be towards the living space, correct?

3) Add a vapor barrier to the knee wall that covers the backing. Should I use Tyvek for the vapor barrier?? What would be better?

4) To insulate the floor inside the knee wall, I was going to blow in insulation (cellulose, thanks GBR). I don't plan on using the space for storage so should I replace the planks over the 2 x 8ís and then cover them with more insulation? Note, at least one metal clad wire runs over the 2 x 8ís.

5) Would it be OK to insulate the attic floor between the knee walls?? I'd only have to take up a few boards to blow in insulation from one end to the next.

6) I will insulate the ceiling slightly overlapping the gable insulation. There is currently only 1 light fixture. I will install IC recessed lighting. I was going to use R-13 between the lighting. Should I use R-13 unfaced insulation over the lighting? There is enough headroom in the ceiling for even thicker insulation.

7) I will use spray foam to seal where the bottom of the gable meets the exterior wall and seal the ground floor light fixtures and wiring. Question, I've read on the forum that I should caulk the knee wall to prevent drafts into the livable spaceÖ but what do I caulk?

8) I will install roof vents and insulation, from the bottom of the gable to a point past the flat ceiling. I'll have 2 inches between baffles. Questions, the gable is 2 x 8ís, should I use R-19 insulation and 5/4 furring strips under the drywall? Should I only screw the drywall to the furring strips and not screw into the studs?

9) Drywall should be installed from the top to the bottom correct?? Even in my instance? It's about 7 feet from top of the knee wall to the ceiling. If I install the drywall horizontally, should the 4 foot pieces be above or below the 3 foot pieces?

10) I've read on this site that a foot of insulation should be rolled up in a garbage bag and shoved under the knee wall. Should I use unfaced insulation? Should I use R-13 ? From inside the knee wall I can see there is 2 x 8 blocking between the floor studs a couple feet into the livable space. Is it OK if there is a gap between the roll and the 2 x 8 blocking?

11) There is metal clad and Romex wiring going to outlets in the knee wall and the ground floor. All of those can be covered by insulation, correct?

12) The doors in the knee wall used the same wood panelling as the walls . And the doors were not insulated. There are also short doors leading to parts 1 and 3. Some door openings are 20+ inches (single door) wide. Some are 40+ inches (double door) wide. What is the best way to replace those doors? Some seem too wide to use a section of slab door.

13) There are a couple massive plumbing vents about as thick as the gables (2 x 6). I would just insulation on either side. Maybe add foam insulation board if it fits. Should I do anything special??

Thanks for reading. Feel free to respond to any questions you feel comfortable addressing.

Gary in WA 11-19-2011 12:23 AM

Welcome to the forums,FO!

Let's start with your Zone- either #4 or #5:

1. SD is no longer a member here. The fan duct should be insulated and plastic wrapped so the attic (outside) air doesn't lower the temperature of the ducting (smooth metal) to cause condensation inside it when exhausting the warm moist bath air. Another reason not to use flex duct- it has twice the surface area to condense on unless stretched out fully (hard to do, especially on the bends or turns).

2&3. Need your Zone..... Vapor retarder toward heated space. Housewrap or foamboard facing attic, may require ignition barrier if interested...

4. No, on replacing the floorboards for only R-1.25 per inch of solid wood and possibly creating air pathways for de-rating your cellulose;

5. Homework- study these and I will be


FileOpen 11-19-2011 11:31 PM


Technically I'm in Zone 4, but I'm really close to Zone 5.

Does anyone have a preference for insulation from Johns Manville or Corning ?

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