I have a small, 60-year old house with original wood siding covered with vinyl. The roof is fine, the windows are (mostly) newer, and I had new gutters installed this spring.
However, last year’s brutal winter left me with some serious ice dams and the snow was melting off the roof from the house’s heat even when it was consistently below freezing. There is currently about 10-12" of blown-in cellulose insulation between the attic rafters but that’s clearly not enough.
I am planning to buy rolls of fiberglass insulation and just roll it out over the existing. I can’t find anything reliable online indicating this is a horrible idea, or a good strategy, or what. I know that moisture retention is also a consideration when insulating and I don’t want to end up with a mold issue, or rotting plaster.
How’s the ventilation ? Given blown in insulation I am assuming you have an unfinished attic, with insulation on the floor. You can add insulation on top of existing as long as it is unfaced (no moisture barrier), but you also need to make sure you have good ventilation with soffit vents and ridge vents sufficient for the size of your attic. You can also just blow in more insulation, they rent the machine at home depot/lowes, and usually that is cheaper.
IE, basically to stop ice dams you need to both ventilate and insulate (and seal).
It’s very important that you install vents between the rafters.Like this. That gives the air a chance to leave the soffit and get into the attic. Preventing mold and dry rot.
The vents are very cheap. You use a big Arrow Stapler (like in the picture) to attach them. Short staples. Maybe 3/8" at the most.
Oy, see, it gets confusing already! Thank you, jacob. Yes, unfinished attic with only insulation on the floor (or, whatever you call whatever is right above my ceiling.) There are attic and ridge vents but no soffit vents.
See, I am still confused. But it sounds like at this point my choices are down to unfaced insulation, or some additional blown-insulation?
As jacobsta811 was saying, if you have 10-12 inches of blown-in up there, I would check the ventilation. You need soffitt vents, baffles to make sure the blown-in insulation isn’t blocking the soffit vents and roof vents.
I would start by making sure the soffit vents are there and unobstructed.
Also, if the house is 60 years old make sure none of the insulation is vermiculite. If you see anything that looks like gravel, back away. A lot of that old vermiculite insulation contained asbestos and it’s my understanding that that’s the most dangerous form of asbestos.
Ah, thanks aceplace. I need to go back up there and see if I have those vents already. I’ve owned this house for four years but last winter was sort of a wake-up call.
Guess I need to go clambering around in my attic.
**
Joey**, yes - I am pretty sure it’s just cellulose/vermiculite; it looks like shredded gray paper or cardboard - I think the blown-in job was done within the last ten years. It sounds like I need to check on the ventilation status of my roof.
They roll out the insulation in both directions in really cold climates. Around here only one layer is needed. This guy is laying a second layer by rolling it out in the opposite direction. I guess when it’s 5 degrees outside that second layer is needed. Thankfully we don’t experience that kind of extreme cold. 20 is what we call cold around here. http://www.greenenergyofsanantonio.com/wp-content/uploads/2014/05/Before-Pink-Insulation-11-e1343325036523.jpg
I guess that took me too long to type. If you don’t have soffit vents, you need to add them, or call a handy man or roofer or insulation person to do it. It’s an easy job and shouldn’t take more then a few hours to go all the way around the house. It doesn’t matter how good your insulation is, heat is going to make it into the attic and it’s going to need to escape. With proper venting, it’s just be carried away with the draft instead of melting the snow.
Also, you should have roof OR ridge vents, but not both. Otherwise air comes in at the roof vents and leaves at the ridge vent. It needs to enter at the lowest point and leave at the highest point. It’s not only carrying out heat, but as it travels along the sheathing (the plywood on your roof), it removes and moisture so you don’t end up with mold.
soffit vents are best. along with some vents up high.
check to see if your soffits are ventilated, all or a good number have holes. even if the are vented then make sure the insulation isn’t blocking the airflow into the attic; there should be troughs to hold the insulation back from the roof between the attic and the soffit.
when you add insulation then it should be unfaced if rolled and laid perpendicular to the ceiling joists if rolled.
also make sure the attic door or hatch is insulated and sealed. the door or hatch should have the same insulation value as the ceiling. it should have a weather seal as if it is an outside door because it is.
I guess it’s worth mentioning not to put your foot through the sheetrock or plaster. Keeping your feet on the rafters can be a bit tricky. Especially when you are distracted rolling out the insulation. I’ve seen guys drop hammers and other tools through the sheetrock too.
Keeping your feet on the rafters can be a bit tricky. Especially when you are distracted rolling out the insulation. I’ve seen guys drop hammers and other tools through the sheetrock too.