Insulating Floors Joists on Addition
LESLIE: Jean listening in on WPRO from Cranston, Rhode Island, what can we do for you?
JEAN: I need some house with a bump-out. We have a 12 foot-long bump-out in the back of our house – we have a colonial. It goes out about 25 inches off the house. And we had our builder insulate it but the – we have hardwood floors in our kitchen and it’s just very, very cold. We have a dishwasher in our kitchen sink. It’s basically the length of our kitchen counter. And it just is very cold. It seems like the cold air is coming in. And I need help because the dishwasher in the sink is there. There’s one little heating vent below the sink which kind of keeps those pipes OK but I’m just worried about the cold air with the dishwasher.
TOM: So when you say bump-out, do you mean like a cantilever of the floor system that overhangs the foundation in that area?
JEAN: It overhangs the foundation.
TOM: Yeah, it’s a cantilever design with a floor joist overhang. Now, when you say your builder insulated it, did he insulate the floor joist area underneath that kitchen countertop area; in other words, the section that’s extended? I’m sure he insulated the walls but did they insulate the floor joist area?
JEAN: They had come back to insulate it but I don’t think that it’s good enough and I was wondering if there was a better insulation product or something else that we could do for that area.
TOM: Well, I mean you need to make sure that those – every one of those bays is filled up to the brim with insulation. Now, you can’t compress it. You don’t want to overstuff it because that could be an issue. But you definitely want to make sure it’s all filled up.
The second thing is you’re going to have a lot of drafts in there so you have to do a really good carpentry job of putting some sort of a soffit material over that and even so far as to caulk all of the seams so that no air gets around it.
You know, you have an additional exposed surface there. You have the exterior walls which are exposed, but now you have the floor where the cold gets underneath. And the two of those together is what’s causing these issues. I will tell you that it’s never going to be as warm as an area of your house that’s not bumped out, but you probably can make it warmer if you do a really good job insulating. If you’re going to take the soffit material off that’s there now and pull the insulation out, you can also seal up any gaps in the framing with Great Stuff; the expandable foam spray insulation.
TOM: Spray that in there first, seal up the gaps and then put the insulation in and then re-soffit it and caulk all of the seams. And that’s going to be the best you can do.
JEAN: Perfect. Thank you so much.
TOM: You’re welcome. Thanks so much for calling us at 888-MONEY-PIT.