Non-destructive improvement of loose-fitting cavity insulation?
Early this fall, we had dense pack cellulose blown into the empty wall cavities on our first floor. Not every cavity was empty. In all, about 1/3rd of them had some existing fiberglass insulation. We didn’t know full from empty when we started, and our installer simply did circular cut outs in each cavity, packed insulation into the empty ones and left the already insulated ones alone.
For reasons I won’t get into, we’ve yet to have them come back to patch the install holes.
This has given me the opportunity to make the following observation. Several of the already insulated cavities are showing a fair amount of cold air leakage detectable at the install/inspection hole. None of the cavities with blown insulation exhibit this.
Our house is quite old. We believe it was built in the mid 1890s. Some of the wall cavities are a bit irregular. The “2×4” framing studs are also noticeably bigger than modern lumber. (Closer to actually being 2×4 as opposed to 1.5 x 3.5.) I’m generally aware that batt insulation is not meant to provide air sealing, but I suspect this leakage is further enabled by the somewhat deeper-than-standard and irregular cavities.
In any case, I’m curious if anyone here has suggestions for what we might do to address this, short of ripping open the walls to remove the fiberglass. Is it, for example, possible to add dense pack cellulose (or fiberglass) to an existing cavity just to tighten things up a bit?
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I see no reason why the existing insulated cavities couldn't also have been dense packed. I would go that route.
I think blowing cellulose into a partially filled cavity could be difficult. It would be fine if it was partially filled to the full thickness, but it sounds like the batted cavities have a void that is only 1/2" or so for the whole cavity. If you tried blowing a cavity that narrow it's probably just going to plug up the first few inches below the fill hole.
If the cavity has no wiring or pluming in it, a long flexible drill extension with a wire burr on the end can be inserted and rotated SLOWLY with a drill to remove the fiberglass insulation. The old insulation will wrap around the burr and shaft of the extension similar to how cotton candy is made. You can pull it out in clumps.
I got this idea while fishing wires, since insulated walls would always bring out clumps of insulation on the end of the drill with patience, it can be used to remove insulation from a cavity with several in/out cycles of the drill. If you only have a few wall cavities to do, this could be an option for you that doesn't require completely opening the wall.
Just remember that you need to be sure there isn't any plumbing (which will get in the way), and especially that there is NO WIRING (which will get damaged) in the wall cavities you want to clear.
Once the insulation is mostly gone, you can pack in cellulose. A few random bits of remaining fiberglass shouldn't be a problem once the bulk of the batt has been removed.
Bill
I’ve had this happen myself and while frustrated, I never considered the intentional application. I applaud your thinking!
The idea of removing the existing bits in clumps is intriguing. I hesitate to do it right now, in the middle of winter, but I may well try this in a few of the most problematic spots in the spring. Many thanks for the suggestion!
You can and should dense pack over low density fiberglass batts. A good installer should be able to get a a fill tube there and fill the wall to crush the existing batts. Even if they need to open up another hole in the wall to get good fill it is well worth the effort.
This will make a big difference with older homes with board sheathing that are impossible to air seal any other way.
I was unaware this was even an option or standard practice. (I may well have confused the issue by explicitly writing up our statement of work to cover "filling of empty cavities".) They're coming back to address a few cavities that were simply missed in the initial install so I will bring up the notion of doing some crush/fill of the problematic spots at that time. As I say, the holes are already there and have not yet been patched. Many thanks for the insight!
itech20,
Have you insulated at the foundation? If not, it could be that you are feeling the results of stack effect. The posts I've read generally recommend insulating the foundation, then the attic/roof, and finally the walls (if practical).
We have, in fact, insulated the foundation. I'd meant to link to an earlier discussion thread on the basement work when first posting this. That thread is here:
https://www.greenbuildingadvisor.com/question/retrofit-external-insulation-for-a-brick-foundation-ground-below-grade-interface
TL;DR: - After initially considering external rigid foam, we went with internal low GWP/HFO closed cell throughout, and the result has already been a pretty dramatic reduction in heat load coupled with a dramatic improvement in temperature and comfort in the basement.
However, we're keen to see just how much better we can still make it!
We do have reason to believe there is room for both air sealing and insulation improvement in our attic.
In a separate project earlier this year, we installed a single head Fujitsu mini-split on our second floor in the hopes that it will be a more appropriate replacement for a dramatically over sized forced air AC/gas furnace currently located in the attic. It's been working quite well over the winter and, if it holds up under cooling load this summer, we'll likely take the plunge and remove the existing equipment in the attic and use that as an opportunity to thoroughly seal up the attic/2nd floor interface and ensure that we have consistent insulation coverage as well.
(At the moment, the HVAC equipment is resting on a plywood pad that is preventing more than a few inches of insulation across about 50 square feet of the attic/ceiling interface. I also suspect there is a significant amount of air leakage where the return duct passes into the attic.)
itech20,
It seem to me like there are two issues here.
One is the lack of insulation in those cavities. That's something you may or may not feel needs remediating.
The other is whether the air movement through the holes you made indicates anything very important - and I'm not sure it does. Until very recently air-barriers were alway located on the inside face of walls. If that's where they were (or that's where you have decided yours should be), creating a hole in it would naturally cause air movement through the wall. Dealing with it is an simple as repairing the holes. Further improvements to the air-sealing at the interior face of the envelope would of course be useful.
Malcolm,
We took some steps when first purchasing the house about 10 years ago to move the air-barrier to the exterior wall. Specifically, in concert with replacing the windows and 1960s vintage aluminum siding, we had 2" of rigid foam added across the entire exterior of the house. The joints between foam sheets were taped and the installers seem to have made good use of flashing tape to seal up the interface between the foam and the window frames.
As Akos correctly surmised earlier, the sheathing is original and is horizontal boards. It's unclear to me how exactly the foam/window interface might be failing and allowing air to leak in. My guess is that it's occurring at some combination of the bottom boundary between the foam/sheathing and the foundation and perhaps also at some of the non right-angle interfaces where the foam sheets aren't fitted together particularly well.
In any event, in the previously empty wall cavities the dense pack seems to have done a good job of providing a second layer of defense. The handful of drafty cavities are now quite notably different, particularly on some of the colder nights when we've fired up our wood stove to provide additional heat (as well as a large negative pressure draw).
I take your point that this will likely diminish quite a bit if we patch up the gaping holes we've willfully created as part of the dense pack install. However, as long as the holes are already there, I'm inclined to try some combination of the "claw out the poorly fitted stuff" and "aggressively crush fill on top of anything that is left" approaches that others have recommended up-thread.