Blowing Cellulose Into an Old House
I live in a small, two-story colonial house in New Jersey. The house was built in the 1940s. There is no insulation in the walls, and the fiberglass batt insulation in the attic is in very rough shape.
New Jersey has an energy efficiency incentive program that will help me foot the bill for air sealing and adding insulation. I had an energy auditor evaluate the house and perform a blower door test (required by the state to participate in the program.) He is recommending blowing cellulose into the walls, ceiling above the garage, and attic. He says doing these things will reduce my utility bills by 55%.
This is my first time doing work like this to my house. I have a few questions I’m hoping folks on this forum can help me with.
1. Should I have any concerns about blowing cellulose into the walls, ceiling, and attic? My biggest fear is that the cellulose will enter electrical boxes and start a fire. Or a small plumbing leak (I have no evidence that there are any leaks, but you never know) that isn’t noticable now will become a sopping wet mess of old newspaper inside my walls. Are these concerns legitimate?
2. For folks who have done this kind of work before, will adding insulation noticably affect comfort? I know it varies, but in general…?
3. I was quoted $2.70/square foot (8″ thick) to blow cellulose into the attic (700 square feet). Is this a resonable price? I’m concerned I’m getting price gouged by the contractor because he knows I’ll be getting money from the state.
4. Is it possible that air sealing will cause problems like trapping moisture?
5. Any other concerns I should have?
Thanks for your help!
Replies
There is some reason to be concerned about the electrical. In particular, your house is old enough to have some old knob-and-tube wiring and that should not be surrounded by insulation. But you'd probably want to upgade any old K&T anyway, before you insulate, just to bring things up to "modern" (1950s) standards -- much harder to do electrical work after insulation is installed.
One big advantage of cellulose in old homes like yours is that it's fairly effective at air-sealing, so there likely will be a significant increase in comfort (and the estimated heating savings is realistic).
Probably cellulose is one of the choices that is least likely to "trap moisture". Your only real concern would be if you have leaky outer walls (or a leak originating in the roof and running into the wall). You'd have to evaluate this yourself.
Thanks for the info.
Fortunately, no K&T to worry about. Most of the wiring is BX, with some NM for retrofitted lights, fans, etc. From what I understand, BX uses the metal jacket as ground. My fire concern is really about some cellulose getting into an electrical box through an opening (like a missing knockout cover), making a "connection" between the hot wire in the box and the box itself (ground), and lighting on fire.
I did some electrical work in the house a few months ago and found a gangable metal electrical box where one side of the box had fallen off into the wall. That box has since been replaced, but it's possible the same situation could exist elsewhere, so the idea of cellulose in contact with hot wires isn't a crazy one.
On second thought, I guess the cellulose would need to conduct electricity in order for my concerns to be valid. In theory, I could pack an electrical box full of cellulose insulation, and the only thing I'd have to worry about is a fire starting from the heat itself. Is that right?
Happy to hear about that the increase in comfort, potential savings, and low likelihood of trapping moisture. Again, thanks for the info.
Do note that cellulose is treated with a fire-retardant chemical.
But before insulating it would be wise to open all accessible electrical boxes in the outer walls (and they ALL should be accessible) and check that they are intact. You can even take the time then to foam holes in the boxes, as this will significantly reduce air infiltration.
40% of your heat loss is thru holes and gaps in your house envelope. I would caulk and seal whereever you can get to including all your elecrical boxes on exterior walls. I would blow fiberglass in the walls and cellulose in the attic. Cellulose will compact somewhat over time so it will help with air leakage in your ceiling fixtures and gaps in your sheetrock joints