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Old 05-19-2017, 01:05 AM   #1
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Can Roxul insulation be teared to shove in tight areas?


When placing batts say where there's a big pipe and there's gaps, is it ok to just uses shreded pieces to fill in those gaps? Ex: does it have a grain like fibreglass where it won't insulate well if it's not in the right order?

From cutting and such I end up with small chunks and rather than discarding them I'm shoving them in awkward spots like behind electrical boxes, will this work ok?

Can't find much info on this. Trying to avoid those situations but while putting batts in really awkward spots it's hard to avoid. Like some rim joists it's hard to wrap fully around a pipe going outside without there being gaps so I just shove some extra in there. Is that going to do a decent job? I already spray foamed those areas so there's still some decent R value and I'm just adding to it really so I'm thinking it's fine. Was just curious to see what others think and since I can't find much online on this figured it would make for good conversation. :P

I have this say this stuff is wonderful to work with though. Cuts nicly with the proper knife and it's not itchy like the fibreglass and while it does have a mild smell it does not irritate my breathing.
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Old 05-19-2017, 02:31 AM   #2
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Re: Can Roxul insulation be teared to shove in tight areas?


The trick with placing pieces of insulation, whether Roxul or FG, is to get enough in there to do some good and keeping the air pockets fluffy.
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Old 05-19-2017, 08:03 AM   #3
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Re: Can Roxul insulation be teared to shove in tight areas?


Along with what jl said I would prefer to replace the word "shove" with "carefully fit". When insulating a home neatness counts. In fact an energy efficiency rating will look at various walls with an infrared camera and assign a quality rating because they have tested homes to know it is important.

But fiberglass and Roxul are both very air permeable so an important part of their performance involves eliminating air pathways into and through those cavities. Pipes and wires pass through holes in the framing. Even the perimeter of each cavity allows air to seep between framing and sheathing. A couple of cases of well placed caulking is a good investment.

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Old 06-20-2017, 11:30 PM   #4
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Re: Can Roxul insulation be teared to shove in tight areas?


I was speaking more about the oddball areas where you can't place a whole batt or it's such a small and irregular shape you can't reliably cut one to fit fully, so you cut one as best as you can, then fill in with smaller pieces.

I ended up doing it anyway, any oddball areas where it's too small to actually cut and fit a piece I would use scraps from when I was cutting and just push them in, while trying not to squish them too much.

The vapour barrier and spray foam mostly takes takes care of air sealing.
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Old 06-21-2017, 04:34 AM   #5
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Re: Can Roxul insulation be teared to shove in tight areas?


I have dedicated an old 12" long bladed bread knife for cutting Roxul. Smooth cuts and no boogers. This may help with the smaller pieces and will keep it from falling apart.
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Old 06-21-2017, 10:26 PM   #6
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Re: Can Roxul insulation be teared to shove in tight areas?


Yeah I bought the proper knife for it, goes pretty well. The basement side is all done now except for laundry room, and vapour barrier all installed. Crawlspace is next. Laundry room will wait as I need to redo the plumbing, I was not thinking when I originally did the plumbing and plumbed it inside the walls but all those pipes will make insulation and vapour barrier hard to install as I want the pipes on the warm side. So I'll just rip it all and redo it surface mount. Have to move electrical panel too as I want it on the warm side as well to avoid so many penetrations in the vapour barrier and having to build an insulated door etc.

Some pics of progress:










The more awkward areas were rim joists, but those are all spray foamed, so the insulation is just to add extra R value and act as fire block.
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Old 07-03-2017, 02:32 PM   #7
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Re: Can Roxul insulation be teared to shove in tight areas?


I install insulation professionally (new houses), and unfortunately insulating spaces with obstructions is one of the drawbacks of Roxul. FG is much more forgiving if you know what you're doing, understand how insulation works and don't compress it too much around the obstructions. I've seen various tutorial videos on installing Roxul, but they are set up under ideal conditions with perfect framing (everything 16" on centre), no obstructions (or very simple obstructions) or impractical cutting tables/equipment that no professional is going to drag around a jobsite. That's not real life. Most new houses I'm in now have 3,4 or 5 bathrooms (lots of plumbing), tons of electrical, which means there are tons of obstructions to insulate around in every room, with all that plumbing and electrical ending up in the basement.

If you're talking about small gaps (1 inch or less) between stud where you can't place a full batt, you can try your best to carefully cut the Roxul to width using a serrated knife and a straight-edge, but it will likely just crumble apart on you when the piece is that narrow. You'll probably end up just stuffing the small gaps with scraps. It won't give you the full R-value, but if you push enough in there (I use the back of my Olfa knife to push it into the narrow gap) it will slow the air movement so it's better than nothing. In the grand scheme of things you're talking about a relatively small area that has a little bit lower R-value, it's not going to be disastrous to the overall improvement of your house (as long as your not completely leaving/skipping difficult areas with no insulation at all). Just take your time to stuff enough and you'll be fine. Personally, if it's a house that is using a mix of FG and Roxul (some builders use FG on main levels to save money, but prefer Roxul in the basement since it handles water better) I'll use scraps of FG for any super tiny (half inch or less) gaps in framing, and builders have always been OK with that, simply because tiny pieces of Roxul are generally a PITA to work with and they understand that.

For obstructions involving pipes, it's best if the pipe is somewhere is not too far towards the front of the framing. If it's somewhere centered (not to far forward or back) you can just cut where the pipe is and sandwich the two pieces around it. I've also seen some better builders place a piece of 1 or 2 inch foamboard behind pipes, so then you just batt either side of the pipe, since the foamboard behind the pipe is providing some R-value. Even more extreme, I've seen 1 builder just have the spray team spray insulate any hard to access areas when they are spraying the garage, and don't even bother trying to batt the really difficult areas.

All in all, it looks like your job was professionally done. I don't even do rim joists with Roxul. The bulder can accept fiberglass, or find someone else. It's just too much of a PITA, and most builders don't want to pay the $$$ to sprayfoam all the rims (so no need for a Roxul fire-block), so standard practice is insulate the rims with FG and then install a vapour barrier.

Last edited by SilverBulleT44; 07-03-2017 at 02:41 PM.
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