Is the upcost of densepack cellulose installation over diy mineral wool worth it?
dfvellone
| Posted in General Questions on
Having finally gotten a reputable cellulose installer to give me a quote I’m now faced with a diy mineral wool install or the pricier cellulose install, and my question is if the upcharge for cellulose compared to what it’ll cost me to use mineral wool is worth it.
The exterior walls are 1400 sq. ft. and the densepack will cost me 3000. over what the mineral wool batts will cost me. I can detail the mineral wool installation so that it’s a grade A installation.
Both will perform satisfactorily in my wall assembly as I’ve confirmed here recently.
Is the upcharge worth it for densepack?
Thanks, Daniel
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Replies
It’s probably not worth the upcharge. There is no air sealing advantage to the cellulose compared to the mineral wool here in the way you’d have if you were comparing mineral wool to spray foam, for example. You are pretty much looking at an R value comparison and nothing else. Cellulose has moisture buffering abilities that mineral wool does not, but I’m not so sure that is really much of an advantage in a wall with either sufficient exterior rigid foam for moisture control or a well detailed smart vapor retarder on the interior.
If this were my house, I’d go with the mineral wool (which is what I’ve been doing as I renovate my house). It’s easy to buy, easy to install well, has good R per inch, and requires no special equipment to install. I’d use the $3k for something else. I don’t see any advantage to cellulose here.
Bill
Cellulose has much lower embodied carbon than mineral wool, if you care about the environmental impact of your actions. As Bill said, cellulose also has some unique moisture-buffering qualities which may or may not be important, depending on your wall details. Mineral wool has slightly higher R per inch than cellulose.
How long will it take you to procure, install and clean up after installing mineral wool? Is it a task you would like, hate or somewhere in between? Could you make $3000 doing something else in that amount of time?
I would not enjoy the installation process very much at all, and I wonder if the slightly higher R per inch is trumped by blown-in cellulose more successfully filling the many cavities with the obstacles of outlet/switch boxes and wire loops which will be challenging with batt insulation. I wonder if, as well as one might detail a batt install, the quality of the finished job rivals blown-in. I don't mind paying for labor, but if I can detail as good or even better an outcome, that's what I'm here for - this has been my build from the foundation on except for the electrical.
Consider wet spray cellulose you will get 3 pounds per sqf and very good gap filling.
Walta
None of the installers in my region will wet spray.
Deleted
Cellulose does a good job of sealing up older houses (balloon frame, board sheathing etc). Much cheaper than SPF. One of the few ways to insulate walls without taking either the interior or exterior off.
Mineral wool is hard to install if your stud spacing is not standard or if you have real 2x4s.
With newer construction, the above are less of a benefit. Unless you are building very thick walls, I can't see it being worth it.
My studs are full dimension, 2x5's actually @24" centers, and I bought some Rockwool to try and it seems to fit nicely. It's all the switch/outlet boxes with wire loops and the wiring that I'm concerned with getting detailed nicely with batts. Have to also say that having had to combat carpenter ants recently that had burrowed into the foam I insulated a roof with that the borate treated cellulose has a certain appeal.
The way I detail mineral wool around electrical boxes is to cut the mineral wool to clear the box, then cut part of that piece to slip behind the box. If you do it right, you get a tight fit all the way around including with the back piece. Be careful not to squish the back piece too much.
To accommodate the wire, split the middle of the box (not exactly the “middle”, but about where the wire is), so that the wire ends up going into that slit as you install the batt. If the wire loop is too big, cut a section out of one of the batts, split that section, then install the piece behind the wire and the other in front of the wire. Exactly how you make the cuts depends on exactly what you need to fit around in each bay.
There is a cheap bread knife on amazon that I recommend for cutting these batts. I’ve posted a link before but would be happy to post it again if you would like.
Bill
If you could post the link, I'd appreciate it. Thanks, Daniel
https://www.amazon.com/gp/aw/d/B000PS1HS6?psc=1&ref=ppx_pop_mob_b_asin_title
It’s $15. Pretty cheap. It’s actually a really nice bread knife, it almost makes you feel bad using it on mineral wool but it does an EXCELLENT job cutting the stuff. The width of the blade also lets you stick it between sistered studs between cuts for safe storage on the job site. I highly recommend this knife for cutting mineral wool batts.
Bill