attic insulation advice sought

[iron]

after demoing a portion of my ceiling for a kitchen remodel, i now need to reinsulate my attic. i read through dozens of posts on this site and had some additional questions i hoped people would be able to help out with.

i'm planning to use blown in celluose. seems like a no brainer. i currently have some pink stuff in the attic (soft, about double the size of a cotton ball) with a shredded wood/sawdust layer that sits directly on the sheetrock.

1. is my existing insulation celluose or fiberglass?

2. if fiberglass, i assume i shouldn't blow new celluose on top due to its weight?
3. should i install a plastic vapor barrier in my new sheet rock area before doing the celluose? i assume the previous wood/sawdust layer was trying to act similarly to break moisture contact.
4. if i add several more inches to the current insulation, will i need to consider changing the venting? i currently have 2 gable vents and a ridge vent the full 60ft length of the roof.
5. any tips on how to best insulate around/over the attic hatch? it's a 2'x2' opening in the drywall ceiling in our master bedroom closet. i understand this to be a poor performing area in the thermal barrier.
6. for air sealing, can i use spray foam around electrical boxes? is it possible to possibly spray foam from below (not from the attic)?
7. i have proper-vents (or semi-equivalent) at my vented soffit locations. if i have insulation contact the roof, but not block those vents, is that okay? should insulation never touch the roof itself?

also, i do have have a question of insulation at my chimney chase. i noticed during some colder periods here (where it was cold enough to leave good frost on the roof), that the area around my fireplace chase (directly above the fireplace) was melted out. i had insulated my chase and drywalled before putting the fireplace in. is this melting out normal due to the hot flue and masonry on the inside of the house that really acts as a heat sink, or, do i have a problem with insulation/air leaks in this area? the spot where i notice this melt pattern is poorly shown in the attached picture.

lastly (semi-related): should i take the opportunity to use the insulation blower (that i'll have for doing the attic) and poke holes in my basement ceiling to blow insulation between the floor joists? the basement is finished, and i will be upgrading the insulation in the walls and floors this summer. so, it's a conditioned space. just not certain adding insulation to the joists is a good use of time/money. the floor above the joists is oak hardwood.

thanks!

 

[DickRussell]

1, 2. It's hard to tell from the kitchen picture, but if that pink stuff on the floor is what you are describing and is in chunks the size of two cotton balls, then it likely is fiberglass. You probably can just leave the sawdust and FG in the other areas away from the kitchen, and there is no problem with blowing cellulose over a loose-blown FG layer. While the FG will be compressed slightly by the weight of added cellulose above it, the added thickness of the cellulose more than compensates for this; total installed thickness is what counts. Also, in the case of loose-blown FG, IR studies have shown that there can be thermal looping, air currents set up within the FG layer, caused by heavier cold air above the insulation sinking downward and displacing warmer air above the sheetrock. A layer of cellulose added to the FG layer essentially eliminates that effect.

3. I don't know what the sawdust layer was trying to do, other than provide some cheap or no-cost insulation if it was available at the time or the builder wanted a disposal place for it after the ceiling sheetrock was up. Sawdust will absorb moisture in cool weather, just as will cellulose, but both will dry out as attic temperature climbs, provided there is adequate attic venting. I'd be inclined to skip any layer of poly before redoing the kitchen sheetrock. A layer of vapor retarding primer paint or even just several coats of latex paint should be sufficient vapor-retardent to avoid moisture problems due to molecular diffusion. Of far more importance is air leakage into the attic space from below, both in the kitchen and elsewhere in the house. Crawl up there before you add cellulose to what's there, move insulation aside, and foam-seal any holes where there are wiring penetrations through framing or ceiling light fixtures. I see several recessed light fixtures hanging from the kitchen ceiling framing. Put those in a dumpster and go with surface-mounted LED lighting, with wiring boxes sealed; there are boxes designed for easy air sealing. Can lights, even those rated AT/IC (air tight, insulation contact) result in air leaks and are thermal holes into the attic space. They are a terrible idea for any upstairs ceiling.

4, 7. As for attic venting, the best system is continuous ridge and soffit venting, without gable end vents. You have the ridge vent, but you ought to have soffit vents at every bay, with insulation baffles to keep insulation off the roof deck. Here is a good source of reading: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-do-everything. There also is this one on venting: http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-attic-venting.

5. As for insulating and air-sealing the attic hatch, read this one: http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-attics.

6. As for air sealing electrical boxes on outside walls and attic floor, you can use can foam, but it ought to be the type used for that (orange stuff), and you don't want to foam up the inside of the box; there must be adequate volume inside the box for the number of wires connected there. Sealing the light fixtures from attic side likely is best.

As for the snow melting near the chimney chase, that's harder to say. It could well be air leakage into the attic space from below or from the chase itself. In general, it's better for the roof not to have heat leaking into the attic during winter, as that leads to ice dams and icicle formation at the edges. But if you haven't seen that by that area of the roof or elsewhere, then there may not be anything of particular concern. What do you see during the winter in that regard?

Finally, if your basement is conditioned space, then insulating between floors won't do anything for you, other than for sound abatement.

 

[vinny11950]

Iron, make sure the sawdust layer is not leftover vermiculite insulation. It may have asbestos.

http://www.nytimes.com/2008/08/14/garden/14fix.html

 

[iron]

DR: thanks for the super detailed response more followup ?s if you don't mind:

3. i didn't put up poly with the drywall, so i guess that's not happening. but, we did already install new AT/IC can lights. those are going to stay... should i go out and buy the lids/cones that sit over can lights and sprayfoam them to the drywall before insulating? i was skeptical when my electrician friend said they were airtight...

4. i have soffit vents (more like 3 round holes in a 2x4 at the truss-to-top plate location) at every other truss. as far as i could tell (before i started ripping down the kitchen ceiling), it seemed like the attic was cold, dry, and functioning mostly properly minus not having air sealed holes.

misc: at the chimney chase, i only observed this a few times since there's only a handful of days where it's cold enough to frost over. we've only been in the house for 15 months and only recently installed the northstar ZC fireplace. i will have to pay attention next winter and beyond to see if it keeps happening and if it only happens when we have used the fireplace and all the masonry on the inside is all heated up. our masonry does go up to the drywall ceiling and it does get relatively warm, so it seems reasonably that this is effectively heating the roof cavity right where the chase meets the roof. hmm... not sure there's a good way to fix this. i suppose it's a drawback to installing the masonry all the way up the ceiling, even though it does look better to us.

PS: based on the vermiculite pictures i've seen, i don't think that's what we're dealing with here. i might take a picture the next time i'm up in the attic air sealing stuff.

 

[Babaganoosh]

Wear a mask up there!

 

[vinny11950]

should i go out and buy the lids/cones that sit over can lights and sprayfoam them to the drywall before insulating?

Yes, that's the way to go, Iron. Make sure to keep the foam away from the can light (the foam will burn after 240 degrees - even the orange stuff from Great Stuff). I did this thinking the orange fireblock stuff would not burn and had to cut a lot of it out. PITA.

Good thing you skipped the plastic vapor barrier, if not done right, it can turn into a mess. Mud and pita and good air sealing should work.

Good luck.

 

[semipro]

You can build a box out of foam board to go over the can lights easily enough also.

Edit: BTW, "airtight" recessed fixtures aren't actually airtight.

 

[DickRussell]

Here are some good links on dealing with existing can light fixtures and attic venting. The first is an introduction to a GBA blog taken from a Fine Homebuilding article, but not the whole thing. The full article discusses the pitfalls of just adding insulation domes over recessed light fixtures, worth finding and reading.
http://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/rethinking-recessed-lighting
http://www.finehomebuilding.com/design/departments/energy-smart-details/recessed-can-lights.aspx
http://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/rethinking-recessed-lighting
http://www.greenbuildingadvisor.com/blogs/dept/building-science/lstiburek-s-rules-venting-roofs

There are a great many more good articles out there on dealing with or even replacing recessed light fixtures, and GBA is a good site for searching on them. Not only do you find the blogs, but most of the time there is good discussion at the end of the blog among interested readers.

 

[iron]

thanks for all the links and feedback.

i hear you on the recessed lighting being a bad idea for an insulated air space. wish i had learned this before redoing the kitchen electrical...

anyway, now that i have new IC/AT cans in, my question is this: can i just caulk the integrated LED trim kit when installing the lights? essentially, put a bead of caulk all the way around the trim, then push it into place and never touch it again, or at least until the LED dies? seems like that would air seal it. then, insulate the crap out of it in the attic with cellulose.

 

[semipro]

anyway, now that i have new IC/AT cans in, my question is this: can i just caulk the integrated LED trim kit when installing the lights? essentially, put a bead of caulk all the way around the trim, then push it into place and never touch it again, or at least until the LED dies? seems like that would air seal it. then, insulate the crap out of it in the attic with cellulose.

That's exactly what I do. That way, if the LED trim is airtight and the gasket was installed between the fixture and ceiling then you should have very little air leakage between living and attic spaces.
If the gasket was not installed you should still be able to seal between fixture and ceiling with caulk.

 

[vinny11950]

X 2 on what semipro said about the can lights. And use high temp caulk because can lights can get very hot.