Insulating roof rafters wont help heating costs — The Boston Globe

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Q. My girlfriend is convinced that we would save on heating expenses if we insulated between the roof rafters. My contention is that only the attic floor needs to be insulated because we only use the attic as storage space. Are there any advantages to insulating the roof rafters? Is moisture build up in the attic an issue? Would insulating it increase the risk of ice dams?

RC, Melrose

A. You are correct and your girlfriend is wrong. Insulating between rafters will do no good because the attic should be ventilated, and the rafter insulation would be between two unheated spaces. You can add insulation to the floor, the more the merrier. Just dont put it in the eaves. Also, make sure the attic is well ventilated. And you are right that cold roofs prevent ice dams.

Moisture buildup in the attic is a concern because it can condense into water, often causing mold. Good ventilation will stop that. Good ventilation comes from soffit vents and a ridge vent. Soffit vents are in the under part of the roof overhang.

The only time when insulation is installed between rafters is when Icynene is used, and everything, except the attic floor, is insulated with Icynene. It is against traditional thought, but apparently it is effective. It is very expensive, and any payback from what you will save in fuel costs will take decades to accomplish.

Q. My 60-year-old family room has two mildly warm heat ducts and one cool-air return, and the room is about 6 degrees cooler than the rest of the house. Why is that? Another pipe in the basement runs from the furnace to the chimney, and is very hot. Why is that?

A. First things first. That super-hot pipe is a smokestack, so leave it alone. You can heat the family room with a portable electric heater or a gas fireplace with a power exhaust right through the wall. If the family room is an addition, the cool room is due to a furnace that is too small to handle the extra space created by the addition. You could insulate those ducts with duct insulation, and that will help some.

Q. My plumber is charging $1,500 to build a sump in my basement (a hole in the floor) and a pump. Isnt that kind of high?

Q. Is hydraulic cement the right stuff to fill some cracks in my concrete steps? Most cracks are between tread and riser, 1/4 to 3/4 inch wide.

CLAIRE USKEL, South Boston

A. Hydraulic cement expands as it sets, so be careful that it doesnt expand where you dont want it to. Instead, try Top n Bond, a high quality mortar that does not expand as it sets.

Q. What is your opinion of composite wood for decking? Is there a brand you prefer? Or do you like natural wood?

GUEST, in Hottons chat room

A. Ah, its nice to talk about something other than winter. There are many kinds of composite floorboards available since Trex came out with the first, using ground-up plastic bags and wood. Much of it is pretty good, but I have heard that it can get damaged looking with small cracks. I think most of those complaints are from people who want a pristine deck. Perfect forever, that is. That is impossible no matter what you try.

Q. I have a funny one for you: My Cape Cod-style house has heavy snow on 5 feet of roof along the bottom edge (good) and 5 feet at the top (also good), but with a bare shingle band right across the middle of the roof. Weird. My contractor said it was because the ceiling below has little or no insulation right along that band. He said he would add insulation to that part of the ceiling.

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