What are the best options for my insulation job?
I live in the Northeast. I live in a house about 45 years old.. I’d like to add or remove and re-insulate the attic. Attic is ventilated with eave vents and continuous ridge vent. Floor rafters in attic are 2 x 6″ and have 6″ of kraft faced fiberglass, with facing towards warm side, rooms below, in house. The insulation is a little matted in places, missing in a few, etc.. I would like to re-insulate, and willing to rip out the old stuff and start new if that’s a good option. What are my best options? Is it better to start new? I plan to add rafter vents into the eaves so that the new or added insulation does not extend over the eave vents, but covers the top wall plate. Any help would be greatly appreciated. Thanks.
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Replies
Michael,
If the existing fiberglass batts are relatively clean, without any mouse feces or bat feces, the fiberglass batts can stay right where they are. They don't have to be removed.
The first step, before you upgrade the insulation, is to perform air sealing work. This article will explain all of the necessary steps: Air Sealing an Attic.
Here is a link to an article that will provide more information on the vent baffles that need to be installed at the eaves of your attic: Site-Built Ventilation Baffles for Roofs.
Once air sealing work is complete and your vent baffles have been installed, the next step is to blow a deep layer of cellulose on top of the existing fiberglass batts. You want to aim for a total R-value of R-49 to R-60, which means that you want a total insulation depth of 15 to 18 inches. Here is a link to an article that will explain the work: Borrowing a Cellulose Blower From a Big Box Store.
Martin,
This might seem a silly question, but why the concern with cleanliness? Certainly if there are mouse tunnels through the insulation those can also provide a convection path. Or if the insulation is so thick with solid waste that its R-value is primarily determined by the thermal conductivity of excrement (which Dana can probably quote to us +/-10%). In those cases the performance would be degraded. But is there a health hazard or building performance hazard associated with letting the feces sit, aside from those?
Michael, you likely have heard that fiberglass can have performance problems in an attic. What is less well known is that if you put at least about 3" of cellulose on top of it, you not only add a layer of insulation that does not have those problems, but you actually make the fiberglass perform better. So Martin's advice to add cellulose on top of the fiberglass is a really good way to go. The problems it solves are the potential for convection air flow loops through the fiberglass into the attic air space, then looping back down, and the translucency of the top layers of fiberglass to IR radiation, going up in the summer of down in the winter.
Additionally, some people worry that the greater weight of very deep cellulose on old drywall ceilings might cause them to warp or bow. I don't really know whether that concern is justified, but it seems like another reason to prefer keeping the fiberglass under the new cellulose.
Charlie,
These days, an increasing number of homeowners are worried about odors, noxious dusts, and the possible health effects of airborne substances. I can assure you the some (not all) GBA readers worry about the health effects of feces in their attic. However, in most cases the feces are above the ceiling air barrier. Advice to all readers: never install ducts in your attic.
Do I worry about the health effects of rodent and bat feces in an attic? Not really, but someone will soon post a comment about diseases spread by these feces. Hantavirus, anyone? For years, I have cleaned out the dropping board under the roosts where my hens sleep, as well as the bedding on the henhouse floor, so I have inhaled more than my share of this type of dust.
My grandmother used to tell us that her job as a young girl in South Dakota was to help bank the foundation of their house with horse manure, before the first snow, as insulation. Of course, horse manure has an R-value -- and it also heats up as it composts, a real bonus in South Dakota.
Finally, Charlie, I'd like to point out that you need to have some compassion for the contractors who work in the attic. Mouse-infested fiberglass is really nasty stuff. It stinks -- much worse than chicken manure. If you've seen much of it -- and I'm beginning to suspect that you haven't -- you'd know that it belongs in a dumpster, not your attic.
Thanks Martin. For the record, I have seen and smelled some, and pawed around in it doing air sealing, though mostly with a HEPA respirator on, so perhaps I didn't experience the full stench, and I can certainly imagine that some is much worse than what I've seen. I have some sitting about 6 feet above my head right now, and hence my curiosity about what problems it might cause. I expect that leaving there will expose contractors to less trauma than asking them to remove it and clean up, but I could be wrong about that, and of course it depends on whether future work in the attic is needed.
Thanks for the advice. Is an option also to cover the existing fiberglass with more insulation rolled out in opposite direction? Recently in the home improvement store I've seen a product called Roxul that looks interesting. Comments? If I decide to rip out the old and start new, is it better to use faced fiberglass insulation, or to staple some poly into each cavity and then use maybe the Roxul type? Thanks, Mike.
Michael,
Q. "Is an option also to cover the existing fiberglass with more insulation rolled out in opposite direction?"
A. Yes, but the performance of fiberglass insulation will not be as good as the performance of cellulose insulation, because the fiberglass batts or blankets are more air-permeable than cellulose, and because it's impossible to fit the fiberglass batts or blankets close enough together to prevent gaps.
Q. "Recently in the home improvement store I've seen a product called Roxul that looks interesting. Comments?"
A. Roxul is mineral wool insulation. You can do a search on the GBA site for "mineral wool" and you'll find plenty of articles to read. Roxul is a good insulation material, but (like fiberglass) it will never perform as well on an attic floor as cellulose.
Q. "If I decide to rip out the old and start new, is it better to use faced fiberglass insulation, or to staple some poly into each cavity and then use maybe the Roxul type?"
A. You don't want to staple polyethylene in each cavity, because this type of insulation application does not require a vapor barrier. For more information on this issue, see Do I Need a Vapor Retarder?
If you decide to use rolls of fiberglass insulation, you can choose an unfaced product or a kraft-faced product; either product will work. (The facing is unnecessary.) As I wrote before, neither fiberglass nor mineral wool will perform as well in this application as cellulose.
Don't worry about vapor diffusion and vapor barriers. Instead, worry about air sealing. Here's a link to an article that explains what you need to know: Air Sealing an Attic.
Michael
Roxul is great product, but not for your application. A continuous layer of cellulose is far superior to any form of batt insulation laid on top of your existing insulation. There are no voids/joints. It can be installed more easily in tight attic spaces. Cellulose will install much easier than batt insulation done correctly.
I have done a lot of this work. My decision to keep vs. dispose of the old insulation varies from job to job. Sometimes its just easier to get rid of it. Air sealing requires removing all the existing insulation in order to access the ceiling surface. If it comes up in useful sections, my preference is to reuse it. If is a mess, then get rid of it.
Most importantly don't skimp on the air sealing. Expect that to take 4-5 times as long as installing the cellulose. Sealing everything is a nasty thankless job, but not doing it completely is a mistake.
Cellulose is inexpensive, so I would recommend R-60 or better.
Roxul is better than fiberglass, mostly because it is less floppy and fits into the bays more neatly, which makes it work better in the end, with fewer gaps and weak spots.
Placing batts crossways to the bays on top of already-filled bays works best if the insulation fills the bays neatly to the top. But if the top of the
Something Martin mentioned in his first reply that should not get forgotten is the importance of air sealing. That is a lot easier to do with the fiberglass all removed. So if you are on the fence about whether to remove the old fiberglass, that could tip the balance.
Removing rodent feces, or any sign they have been there, serves two other practical functions. Later on it allows you to see if they have returned, and it mitigates the chances that the rodent infestation will appear on a home inspector's report when you sell. Past infestations are often flagged because of the possibility that they may have caused damage - especially to wiring.