Answers to Insulation Questions #4

Q. We have a three-door car attached frame garage, with the wall between the house and the garage properly insulated. There are ceiling joists at 16" on center. I would like to insulate the walls and the ceiling because the garage gets very cold in winter, and hot in summer, and I want to be able to heat the garage easily to use as a shop. There is a lot of stuff stored among the joists in the ceiling: long 2 x 4s, conduit, tarps, etc. I like having that storage space available. That is why I do not want to drywall the ceiling, as I would lose access to that space unless I put in pull-down ladders, and even then, it would make access more difficult. Can I use kraft-paper backed fiberglass insulation stapled between the rafters and attach it to the underside of the roof instead, or will this cause moisture problems?

A. One problem with your plan is that the kraft paper being exposed that way is a "no-no" due to fire hazard. Another problem is dimension of the rafters; if these are less than 2 by 10's, it would be hard to insulate and still allow for attic ventilation. Inadequate ventilation can cause rotted roof boards, mold, condensation, limited roof shingle life, etc. Depending on how the garage is attached to the house, it may be necessary to drywall the ceiling in the garage anyway, due to fire-safety codes. One thing you might consider is insulating above a 5/8" drywall ceiling and build a loft below that ceiling at the back of the garage, where total ceiling height isn't as critical.

Q. A couple of years ago, we had a new furnace put in our attic (crawl space). Obviously, the space is getting some heat. This is very visible seeing the snow get melted form the roof above the area. This in turn will cause ice dams. Can I do some type of insulation? Maybe put rigid foam under the roof joists?

A. The best place to put insulation is around the ductwork up there. Ice problems on roofs come with the territory when the furnace is up there. A secondary insulation under the rafters will likely cause more problems than it will solve. If ice is a big problem, you might want to consider putting ice-melting grids above the roof eaves.

Q. I have converted an older closed-in porch into a laundry room. It is framed with original 2x4 construction even on the ceiling, which has no load above it. I have installed pink batting with vapor barrier in those ceiling bays, but here is my question: Instead of putting up just a plasterboard ceiling, can I just install extra rigid 4x8 sheets of insulation with a foil barrier over the pink batting that sits in the bays? The rigid stuff would attach to the exposed ceiling joists. Or should I add some strapping? Here in N.H. I'm trying to hold onto all the heat I can in this converted space. Also the underside of this space is a crawl space about 24" with no insulation in the floor joists. It would be much easier for me to maybe put some carpeting and a good carpet pad below the carpet to provide some R-value. Does this make any sense?

A. When you say "rigid insulation," I assume you're talking about foam-board. Most building codes require foam-board to be covered with 1/2" drywall, for fire safety. I'm not saying that would be impossible to do on a ceiling, but I wouldn't recommend it. For one thing, it would take a lot of very long nails or screws to get past the foam and anchor deep enough into the ceiling joists to keep that drywall from falling. Carpet and pad might make the floors seem warmer, but probably wouldn't actually make the room any warmer. Did you say if this room has any heat? Without a heat register or some other source actually in that room, it will be impossible to trap enough residual heat from the wall common to the rest of the house, to make much difference in your climate. Insulating a 2' crawlspace is tough, not only because of accessibility, but also because rolls of insulation don't last very long down there. Even with a good vapor barrier on the ground, it won't be many years before the insulation starts to rot. I think it would make a difference how damp it was down there to start with.

Q. I have a new home in New England built in 1997. The attic is a full walk up with a very high ceiling. To get to the attic the builder installed one of those fold up staircases. The roof has a ridge vent running along most of the ridge, which stops about a foot short on both ends. Soffit vents run the entire length of both the back and front of the roof. Styrofoam inserts keep the insulation back from the soffit vents. I have a LOT of condensation in the attic, to the point where the north-facing wall is wet. That's the worst area. There is moisture throughout the entire attic, some on the south facing wall and some on the roof decking between the rafters. Being the cheapskate I am, I don't want ANY of my heat to escape so I covered the top of the attic staircase with insulation. When I brought the builder up to show him the condensation, the first thing he did was ask, "Who covered the staircase door? That's your problem." Do I need to allow some interior heat to escape to the attic to help create the airflow so the attic stays dry?

A. Your builder is wrong. The condensation comes from the heat in the house and adding more air heated to the attic will only make your situation worse. The above website gives you some insights on the "Attic By-Pass Phenomena." Having that much condensation in your attic indicates you have a lot of ways for heated air from the house to enter the attic. I doubt very much if ventilation is a concern based on your statements. In other words, there is so much heated air escaping into the attic, that no matter how much ventilation you have, it would still condense in the attic.

Q. We are just getting started with finishing our basement. We are planning to paint the walls with a waterproof sealer and then glue up plastic (from what I have read, this is called a moisture barrier). We are then going to frame it out with 2x4 and use R-11 insulation with the paper side toward the room. Should we put up a vapor barrier after we install the insulation before we drywall? Why would this be necessary?

A. You can find different opinions on basement moisture barriers and where they should go. I think if you were going to use one on the base wall, I would leave a couple of inches of air gap to the wall studs and just use the paper faced to the heated side. Something else to consider when finishing a two-year-old basement is the chance of future cracks in the poured walls. Most two-year-old basements have pretty much settled out, but if you have signs of recent cracking, it could pose leakage problems in the near term, as your water-proofing probably wouldn't solve more than a hairline crack. One other thing to consider is future "rod hole" problems. Steel rods are imbedded in your walls, and depending on the moisture activity of your soil, these rods will rust through in 10 or 20 years. If you plan to live in this house for an indefinite period, you might consider having these rods drilled back and have hydraulic cement used to fill the voids. Most homeowners don't go to this much trouble, but when water problems are found behind finished walls, it's usually a leaky crack or rod hole that is the problem. Don't expect the "water-proof" coating to perform miracles 10 years. from now; there is nothing more persistent than water pressure on the back-side of this material. Water usually wins out in the long haul.

Q. My wife and I recently moved into a new house. It is about 2500 sq ft. Our old house was much smaller and our electric bills were barely anything. At our new house, our electric bills have seemed a little high (we've compared to friends and family with similar size houses). The new house has a conditioned crawl space with insulation on the sides, but no insulation between the joists under the floor. Should we put insulation under the floor? What do you think about the crawlspace?

A. If you have no immediate plans to finish the bonus room, you should insulate the wall common to this room and the second floor finished room that could be a future access to this room. If finishing your bonus room is not too far in the future, I would go ahead and insulate the entire room, but not the wall I just referred to, as that insulation will be redundant when the finishing work is all done. Any ceiling from a heated portion of your home, such as the laundry room you mentioned, needs to be insulated, as does the hatch cover. A porch ceiling is not insulated. A conditioned crawl space will waste energy because you're heating and air-conditioning a space no one can use. There is some conflicting opinion lately that a conditioned crawl space is better than a vented crawl space. Until that theory is proven, I still like a vented crawl. A vented crawl needs insulation under the floors and at any wall common to a living area (commonly found in some tri-level homes) but none at the foundation walls. If you have water lines in that crawl, that would be one more reason to stay with a conditioned crawl space, although insulation and heat tape on those pipes will usually take care of any frost problems. As the name implies, a vented crawlspace will require foundation vents on the outside. If you have adequate height down there to keep the floor framing away from the moist ground and you have a good moisture barrier on the bare ground, a vented crawl would be OK. You will save heating and AC costs with a vented crawl. You will get a stiff neck from hanging all that insulation under the floor.

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