Do I Need to Remove Old Insulation?
LESLIE: Nancy in New Jersey listens to us on WCTC and has an insulation question.
Nancy, how can we help?
NANCY: Oh, hi. How are you?
LESLIE: Good, how are you?
NANCY: Great. Thank you for taking my call. I’m needing to reinsulate my attic. Of course with the cost of heat this year, I’m concerned. And my house is about 50 years old. The insulation in the attic of course is the original and it’s kind of compressed down and I’m thinking of having this cellulose blown over it and I’m wondering if – what do you think about that and, if not, what’s your suggestion?
LESLIE: Tom, which is more cost effective; taking out the old fiberglass insulation and laying new or covering over? Or is that a bad idea in general?
TOM: Well you know, if the existing insulation is compressed, so it’s not fluffy, that’s not going to give you any r value when you cover on top of it.
LESLIE: So you need to give a new, fluffy base.
TOM: Right, exactly.
LESLIE: Would you recommend replacing both or doing one or the other?
TOM: If the existing insulation is compressed, I would take it out. I would definitely take it out, Nancy, and then you could add new insulation on top of that or in place of that.
In terms of which insulation you use, I mean cellulose is fine. It’s a little bit more convenient to install. But if you ever want to use that attic for any kind of storage or anything like that, it’s really hard to work around it because you have to kind of plow through it and it usually covers the top of the beams.
Another thing to do is to put new, fresh insulation between the ceiling joists and then put more insulation perpendicular to the ceiling joists on top of that. And that’s pretty …
LESLIE: So cover right over the joists?
TOM: Right over the joist. One goes with the joist and one goes perpendicular and 90 degrees to it. And really, in anywhere in the northeast of the country, you want to have at least 10 inches of insulation moving in to the winter. And besides that, make sure you add more ventilation to the attic as well so that you have plenty of air to keep that insulation nice and dry. Because you’ll get condensation in the winter and that’ll saturate the insulation and make it ineffective.
NANCY: OK, but I do have to take out the old insulation.
TOM: I think it makes sense because otherwise you just have a filler there that’s not insulating at all. You told me it was sunken down, so it’s really not doing a good job. Insulation only works if it traps air and if it’s compressed and saggy, it’s just not doing its job.
NANCY: OK. OK, thank you very much.
TOM: You’re welcome, Nancy. Thanks so much for calling us at 888-MONEY-PIT.