View Full Version : attic insulation

Magda Braccia
02-04-2009, 05:36 PM
I posted recently about problems in my attic, water and ice.
We sealed all the air leaks and it already made a difference, when there was moisture on the plywood it looks less visible, like it's drying, so it looks like it was all condensation, and there is no leaking roof.
But from what I read I think we don't have enough insulation and we don't have the right kind of insulation. The attic insulation we have is yellow with paper on the bottom.
Should we remove the old one or just place new layer of the pink one on top of the yellow one?

When inspector sees the drippings from the nails on the yellow insulation, even after the condensation problem is solved, will he write it in the report ? could this be a problem?
so would it be better to remove all the old insulation and just put a new one ?

Also, we plan to add radiant barrier, staple foil to the rafters, is this good idea in Chicago climate ? would it help more with any condensation problems ?

Jim Luttrall
02-04-2009, 07:04 PM
Yellow and pink just means the insulation is a different brand, do you like Coke or Pepsi?
If the insulation or paper backing (vapor barrier) is damaged, wet or molded, I would recommend replacing it. Look at the R-value recommended for your area Insulation Fact Sheet (http://www.ornl.gov/sci/roofs+walls/insulation/ins_01.html)
Insulation Fact Sheet (http://www.ornl.gov/sci/roofs+walls/insulation/ins_16.html)

Foil will not help condensation. Radiant barriers should be installed only with due consideration to cost, payback in relation to the overall insulation and ventilation levels in your house. Radiant barriers work with your attic insulation system.

David Wood
02-05-2009, 11:02 AM
Agree that unless the existing insulation has moisture damage it is OK to blow more insulation over it. Any blown-in insulation should work fine. Not sure what code is in Chicago, but here in Ontario it is R-40 or around 13-14" of fiberglass for an attic.

Radiant barriers are basically useless in a cold climate. Spend your money on air-sealing and insulation.

Jerry Peck
02-05-2009, 12:01 PM
Blown in fiberglass insulation has *much less* resistance to cold air settling down through the insulation than than batt fiberglass insulation has. Use batt fiberglass insulation, unfaced, laid perpendicular over your existing insulation. Laying it perpendicular over your existing insulation cover the gaps and openings of the lower insulation around and next to things (trusses, joists, boxes, etc.) - be cautious, though, that if you have recessed lights and the recessed lights are not IC (insulated ceiling) recessed lights they you will need to leave those open above (cut out the new insulation so as not to trap the heat into the recessed lights, otherwise they could overheat and catch fire).

David Wood
02-05-2009, 03:20 PM
Yes, blown-in fibergalss alllows air to move more freely and it does affect its R-value. NRCan suggests using an R-value of 2.88/in for loose fill and R-3.17/in for fiberglass batts. So you need to install a greater thickness to achieve the same R-value. As long as you do this, it will preform equally well.

Jerry Peck
02-05-2009, 05:26 PM
Yes, blown-in fibergalss alllows air to move more freely and it does affect its R-value. NRCan suggests using an R-value of 2.88/in for loose fill and R-3.17/in for fiberglass batts. So you need to install a greater thickness to achieve the same R-value. As long as you do this, it will preform equally well.

That's for the R-value, however, for the problem with gravity settling of air through the loose fill fiberglass insulation, the effectiveness of the insulation may be reduced by half.

There was a recent thread with posts and links about this.

David Wood
02-06-2009, 04:59 AM
I haven't read the other thread, but I do know there is some debate on this subject.

The R-values I have given are suggested by NRCan for use in HOT2000 software for energy modeling. I don't know how they got these numbers, but I don't think they just accepted numbers from the manufaturers. And the R-value does take into account how easily air moves through the material, because insulation basically works by restricting air movement.

We have strayed from the original question. I would suggest to the original poster that if you have questions, the cost of an energy evaluation, including a blower door test, would be worthwhile. I believe that Resnet is where you could start looking for someone.

Daniel Leung
02-06-2009, 05:14 PM
Hi Madga,

When I read your question, it seems a moisture and ventilation problem more than an insulation problem.

Material and/or thickness of insulation do not cause condensation, but moisture does. If moisture gets into attic and has no way to vent, then condensation will drop down from the nail and sheathing when snow/frost stays on winter roof (normally North and East slopes are the cold sides caused condensation).

Where is the moisture from? Laundry dryer, bathroom fan and kitchen fan vent into attic. May be no vapour barrier between the insulation and the ceiling.

Why no way out for moisture? The roof vents near ridge (or on the gable end) create outflow and soffit vents create inflow. Inadequate air circulation in attic when roof vent or soffit vent is missing. Most of the case is either total area of outflow or inflow is too small. (outflow area / roof are > 1/300, If means every 300 sf roof area has 1 sf roof vent)

You said already sealed all air leaks. This is not the normal way to deal with attic condensation. You said it looks drying may be not related to this action. It may be less moisture come into attic or outside temperature was not cold.

Anyway, please tell us more about your attic. For example, where is the existing insulation located, on the slopping sheathing or on the deck of attic? What ventilating system you have... The best way is attach some photos.

Hope your problem can be solved!

Daniel Leung Richmond, BC

Jerry Peck
02-06-2009, 06:01 PM
In reading Daniel's post above I realized something, something which I've either missed (hey, I'm in Florida, I'm expected to miss it ;) ) or was not mentioned ... the discussion about ventilation not being sufficient, etc.

Guys, remember, her roof is covered with snow, *half her vents are covered and blocked*, i.e., her ridge vent ... right?

Or, being a Florida person, am I missing something about the ridge vents not being blocked with the roof covered with snow?? :confused:

Anyway, worth mentioning and asking.

Tom Maides
02-08-2009, 10:49 PM
I agree with David. You would be well advised to have an Energy Rating performed by a RESNET qualified individual. Also, if they have IR (infrared) camera technology available, I would choose them over raters without the camera.