Replacing old fiberglass insulation
The fiberglass batt insulation in my attic seems quite old, and I am thinking of replacing it. In addition, the way in which it was laid seems incorrect. There are 2 layers of 3 1/2” kraft faced insulation. The lower layer(closest to the second floor below) has the kraft facing towards it (correct), while the the upper layer (facing the open interior of the attic) has the kraft facing upward. (incorrect?) Seems like the second layer should have been non faced, I thought there might be a potential for moisture to be lessening the effect of the insulation.
The attic is currently open, though I plan to put a little bit of light storage up there using 2 4×8 sheets of 1/2 plywood.(for empty boxes, clothes, etc)
I should mention that we have a slate roof, with deep eaves. Older building (1915) with 7″ ceiling joists.
I was initially planning to purchase r19 batt insulation and lay it in the bays, however, I thought that I could strip the kraft facing off the old insulation and lay it perpendicular to the new stuff to give an added layer of protection. Not to mention that I would then have less to bring to the landfill.
Does this seem like a logical plan? I thought about loose fill, but wasn’t sure whether that would work.
Any comments would be appreciated. Thanks
Replies
There's no need to remove the old insulation unless it's contaminated.
Re having the kraft facing up, that's a mixed bag. If the seams between adjacent sheets aren't sealed (eg, with tape) then likely it's leaky enough that it doesn't matter, from a VB point of view, but the kraft facing up DOES improve the insulating value of the FG considerably. (Open-faced FG loses considerable insulating value due to convection.)
If there has been condensation in the insulation it will be visible as water stains on the kraft of the bottom layer. (Check areas where air circulation above is worst and humidity is most likely to be seeping up from below, such as above bathroom and kitchen light fixtures.) If you had drywall ceilings you'd also be able to see water stains on the DW facing.
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Edited 11/1/2005 4:10 pm by DanH
i'd leave the FG in place, cross your joists with 2x6 , and blow 6" of cellulose right over the top of your old fiberglass..
then put your plywood floor down , only 6" higher than you were going to
you really want to air-seal movement into the attic from the conditioned space before you top your insulation up
is it balloon framed ?
any pipe penetrations... wall/ceilig intersections, etc.
Mike Smith Rhode Island : Design / Build / Repair / Restore
Edited 11/1/2005 6:52 pm ET by MikeSmith
Thanks for the suggestion about crossing the joists Mike. My guess is that you are thinking the perpendicular change will help to seal in the heat below.
The house is made of brick, double thick walls I believe, no ballon framing. Also, one of the reasons the eaves are deep has to due with the roof framing. The outside walls on the second floor are not full height, more like 7 foot, which causes the interior rooms to have a sort of vaulted look. I will still need to ensure this section, approximately 2 feet long, also receives additional insulation. Perhaps I can just add the batts to this slanted area, and do the loose fill as you suggested in the flat parts.
In terms of attic penetrations (into the attic as opposed to through roof) there is a pull down attic stair, a bathroom exhaust fan, stink pipe, and some wire chaseways from basement. I was planning to build a plywood box to cover the pull down attic stair to lessen the heat loss through that section. I can also stuff the chaseway to lessen the air flow movement from below.
Any further suggestions?
crossing the joists with 2x6 will reduce the thermal bridging, it's true.. but mainly, it's just easier to do it by crossing them than trying to stack them parallel
your kneewalls would be a good place for some foam sheets , like 2" EPS
the box on top of the pull down stair could also be made out of foam... glued together with gun foam
get some gun foam to seal those chases also..
there is even fire-rated caulk for certain applications ..Mike Smith Rhode Island : Design / Build / Repair / Restore
Don't remove the inulation. It would not be a good use of time or money. If the vapor barrier facing the wrong way on the top layer really bothers you, just take a rasor kinfe and slice some venilation in it, or strip the paper off entirely. Really the craft facing is not a very good vapor barrier anyway. If you want more insulation do what Mike said.
It should also be pointed out that the multiple layers of oil paint in an old home makes an excellent vapor barrier. Moisture gets out through penetrations, wall tops, etc, not through the ceiling in most cases.--------------
No electrons were harmed in the making of this post.
We've replaced most of the deteriorated FG in our 1949 home. Someone had the bright idea before we bought the place to dump styrofoam packing peanuts all over to supplement what insulation there was. This was certainly a special challenge to remove (shop vac sucking through a garbage can to a flexible dryer vent hose to yield 40-50 contractor bags of combined peanuts and FG).
The one thing no one has mentioned in terms of sealing is to get all air leaks, not just at obvious openings. We found that cracks at connections between the ceilings and both interior and exterior top plates were moving air into the attic from the wall cavities. You'll want to get these too.
So, is gun foam really OK for gluing foam sheet material? I was always worried it would just melt the EPS I used in a couple of places.
Thanks for the suggestions everyone. Halfway through the project now, using the bad weather yesterday as an excuse to work inside :-(.
I need to create the foam box for the attic stair, and also for the bathroom vent.
Next step after this will be to paint the exterior trim of the house. Including the aluminum cladded windows. We were going to use 'gripper" first, then apply our chosen paint. Anyone with ideas on that?
Thanks again,
David