Attic Ventilation: How Much is Needed

Attic Ventilation: How Much is Needed

LESLIE: Richard in Rhode Island, you’ve got The Money Pit. How can we help you today?

RICHARD: I had two qualified and established insulating companies come to the house. One was some $400 to $500 less than the other. When I looked further into it, turns out one was not putting in those Styrofoam baffles in each of the rafter bays, claiming that it is not necessary. It’s a two-story Colonial built in 1951. Please, who is right? Do they need to be there for breathing or not?

TOM: So, yes, you need a lot of ventilation in a 1950s house because, typically, the natural ventilation is not nearly enough. In a house that was built in 1950, usually you’ll get two gable vents at the ends of the roof structure, right? Those sort of triangle-shaped ends to your roof?

RICHARD: Exactly.

TOM: You have those couple of gable vents. You may have some ridge – you may have some roof vents. Is that right? Do you have roof vents?

RICHARD: There is only two gable vents and they’re two square – I would guess they’re rectangles instead of the (inaudible at 0:03:14).

TOM: Right. OK. Do you have soffit vents at the underside of the roof, where the overhang is?

RICHARD: No.

TOM: You have no vents there. So what you should have here – I mean adding insulation is great, Richard, and so it’s a smart move. But you also need to add ventilation. And the best type of ventilation would be a ridge vent that went down the peak of the roof and then soffit vents that went at that overhang. Because what happens is the air should be going into the soffits, passing through those vents that you described – the baffles; and that basically keeps the insulation from choking off the soffit ventilation – and then exits at the ridge.

Now, it might be that the insulation company said, “Well, you don’t have any soffit ventilation, so I’m not really putting these baffles in because there’s really nothing to let the air in.” But the project here might be that what you need to do is to have soffit vents put in and a ridge vent. And this way, you’ll have plenty of airflow in that attic. And then you can go ahead and beef up the insulation from that point.

If you put all this insulation in there and you don’t have enough ventilation, it’s just going to get damp and humid. And that insulation, once it’s damp, is not going to be effective. When you have insulation that’s damp like that, it loses a tremendous amount of its R-value.

RICHARD: Alright. Wow. As usual, great information and advice. I appreciate it. Good day. Great show.