Best way to insulate attic that will have storage space
I live in a 1921 brick and stucco house in climate zone 5a. It has a gable roof with 2 large shed dormers (1 front, 1 rear). Attic floor joists are 2×4 with blown insulation which is spotty in areas, meaning none. Roof rafters are 2×6. There is an air handler with one large return and 3 ceiling grills (1 in each bedroom ceiling) Gable end walls are clay block with stucco on exterior. Dormer walls are framed with stucco on exterior, plaster/lathe interior and no insulation. Dormer walls on gable ends are balloon framed.
I need what little attic space there is for storage. Existing max. height is 5 ft. at the peak.
I was thinking of removing blown insulation and air sealing all wall plate penetrations and ceiling electrical boxes. I want to construct a rigid foam box around bath vent fan. After air sealing, I plan on insulating 2×4 joists with Kraft face fiberglass and then framing another floor perpendicular to existing and insulating with unfaced R-19 fiberglass, then adding sheathing.
I would like to avoid spray foam other than the small cans.
A couple of concerns:
1. Do I need to air seal top plates being that there is plaster (no visible joints like drywall corners)?
2. The A/C unit- No way to move it anywhere else in the house…was thinking of possibly framing
a small insulated room around it. What details are needed if feasible?
3. Rafter/wall plate connections. This is the weak point. Not much room for insulation so was
thinking possibly stacking polyiso in joist bays with canned foam to seal the edges.
Thanks in advance for any advice.
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Replies
Johnathan,
Partition walls under attic floors are filled with conditioned air, and this air leaks up through cracks around the wall top plates. I don't think that plaster walls are exempt from this leakage mechanism, so I recommend sealing the partition wall top plates from above.
Whether or not it makes sense to build partition walls around your attic air handler depend on factors that we can't judge without a site visit. Remember, you need access for maintenance -- which means that maintenance personnel need a way to get to the attic, a safe way to approach the unit, and access to all sides of the unit, with room for a person to work. In any case, careful duct sealing work (and air sealing of leaks in the air handler itself) is essential.
At the perimeter of the attic, where the rafters meet the attic floor joists, it's hard to improve on spray polyurethane foam to address air leaks and to provide R-value in a tight space.
This type of air sealing work is routinely performed by weatherization contractors. If all of this is new to you, you might consider hiring a crew that does this type of work every day.
Finally, I strongly urge you to consider using cellulose insulation rather than fiberglass batts. Cellulose will fill every nook and cranny of your attic floor, unlike batts, and will do a much better job reducing air flow through the insulation layer.
Martin,
Thanks for the reply. After reading it, I realize that maybe a site visit to address these issues may be a good thing, so all of the variables can be taken into account. Not sure who to contact about this. Any suggestions?
I am in the Dutchess County area of NY.
Jonathan
Jonathan,
You need to hire a home-performance contractor or a weatherization contractor with air-sealing experience.
A good resource in New York state is NYSERDA. Here is a link to a relevant web site for more information:
http://www.nyserda.ny.gov/Contractors/Find-a-Contractor/Residential-Contractor.aspx