Walls and floors, Roxul or cellulose ?

Started by Arky217, November 09, 2011, 10:02:24 PM

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Arky217

My house is one story, 24x48, with 2x6 walls and 2x8 floor joists.
It sits on 3' posts with an open crawlspace.
The location is western Arkansas.

The wall sheathing is Zip panels; vinyl siding will be applied directly over the Zip panels. The drywall is not installed yet on the walls.

The subfloor is Avantech T&G. OSB will cover the bottom of the floor joists.

Roxul batts for the walls and floor will cost $2200 just for the Roxul (with me doing the installation).

A company will blow cellulose in the walls and floor for $1150.
(They seem to be the only co. around this area that does this)

Financially, it seems like a no-brainer, but is cellulose going to be better for this situation than Roxul. (Especially for the floor)

How can I tell if the cellulose installer is blowing it dense enough to prevent settling ?

When I asked him if he installed it to 3.5 lbs/cu.ft., he seemed confused and said that he had no idea.

What to do ? (can't rent a high pressure blower around here)
(Can't afford any type of foam, neither blown nor panels)

I would actually rather have cellulose, but not if it will be loosely blown like in an attic.

Opinions ?

Thanks,
Arky

MountainDon

I really like blown in cellulose as it packs into all the nooks and crannies nicely. But I wonder what that guy does and if he knows what he's doing. I haven't studied the details much but here I saw that after the cellulose had dried (it was wet blown) someone had cut out a couple of squares from the wall and weighed them. Then stuck them back into place. The contractor told me that was how they checked if it was packed densely enough. The moisture content was also measured in several spots before they'd sign off on the okay to let the drywallers do their thing.

Just because something has been done and has not failed, doesn't mean it is good design.


KWillets

It's not hard to calculate the density based on the number of bags blown. 

IMHO most of the determinants of good quality are in the prep work, which you will do in new construction. 

Alan Gage

Is this dry or damp blown cellulose? If dry I'm assuming that price is for putting up the insulweb as well?

I blew my walls with cellulose a couple weeks ago. 10" thick double stud. It was messy and not particularly fun but I had the same concerns as you. There was a guy in the area that would do it but I was worried about it being dense enough. He said he used to dense pack dry cellulose quite a bit but that no one is doing it anymore, it's mostly either wet blown or foam. I was afraid he'd get done and I wouldn't think the walls felt firm enough but since I don't have any experience what could I say? He's the pro. Another big reason for doing it myself was my schedule. I didn't have a clue when I'd actually be ready for the insulation so I couldn't set up a time in advance. So when I was ready I needed it done pretty quickly. The local lumber yard where I buy all my stuff has a couple blowers they loan out if you buy the insulation from them. I'm surprised no one in your area does that. We're pretty rural here (whole county has about 10,000 people).

I estimated mine would take 100 bags (25 pounds each) going off some charts I found online. I ended up stuffing 130 in the house and that turned out to be too much. I couldn't get the cellulose to flatten out between the studs. The only way I can flatten it out is to cut off the insulweb first and then push it in by hand. Otherwise you can't push it in far enough because the insulweb gets taught as you push it past the face of the studs. It's a pain but it's going ok. About half the exterior walls are sheetrocked now.

Everything online says it's supposed to feel like a firm mattress when the density is correct. That sounded all well and good until I started feeling my walls while blowing it in and realized I didn't have a clue what a firm mattress felt like.  I don't go around pushing on mattresses with my hand so I guess I went a little overboard.  I didn't think they felt firm enough from only the force of the blower packing it in so I'd ram the tube back down into the wall like I was performing liposuction in reverse. Maybe the density from only the blower would have been good enough, I really don't know. It certainly would have been easier to sheetrock.

I guess in hindsight I should have done a couple cavities each way and then tried to flatten them out. They make a special roller on a stick that's supposed to flatten it out with just a quick roll. I didn't have one but it would have been a tip off at the time that I was packing them too dense if I couldn't get them flat no matter what. Oh well, live and learn. I'm still glad I did it myself. Probably didn't save a lot of money and certainly cost me more time but I like doing everything I can by myself.

If I had just regular 2x4 or 2x6 walls I think I'd go with wet blown cellulose. I couldn't do that by myself but it seems like it would do just as good of a job and be a lot less prep work ( nearly 20,000 staples to put up my insulweb in a single story 1,000 sq. ft. house) and a lot less mess. Well, probably still messy but at least not a dusty mess and the installer would clean it up before he left. Sounds like too much water in the mix is more of a problem than not enough. Too much water and the cellulose gets so heavy it starts to sag down from the top plate.

Good luck whatever you go with.

Alan

Arky217

Quote from: Alan Gage on November 13, 2011, 01:15:45 AM
Is this dry or damp blown cellulose? If dry I'm assuming that price is for putting up the insulweb as well?

I blew my walls with cellulose a couple weeks ago. 10" thick double stud. It was messy and not particularly fun but I had the same concerns as you. There was a guy in the area that would do it but I was worried about it being dense enough. He said he used to dense pack dry cellulose quite a bit but that no one is doing it anymore, it's mostly either wet blown or foam. I was afraid he'd get done and I wouldn't think the walls felt firm enough but since I don't have any experience what could I say? He's the pro. Another big reason for doing it myself was my schedule. I didn't have a clue when I'd actually be ready for the insulation so I couldn't set up a time in advance. So when I was ready I needed it done pretty quickly. The local lumber yard where I buy all my stuff has a couple blowers they loan out if you buy the insulation from them. I'm surprised no one in your area does that. We're pretty rural here (whole county has about 10,000 people).

I estimated mine would take 100 bags (25 pounds each) going off some charts I found online. I ended up stuffing 130 in the house and that turned out to be too much. I couldn't get the cellulose to flatten out between the studs. The only way I can flatten it out is to cut off the insulweb first and then push it in by hand. Otherwise you can't push it in far enough because the insulweb gets taught as you push it past the face of the studs. It's a pain but it's going ok. About half the exterior walls are sheetrocked now.

Everything online says it's supposed to feel like a firm mattress when the density is correct. That sounded all well and good until I started feeling my walls while blowing it in and realized I didn't have a clue what a firm mattress felt like.  I don't go around pushing on mattresses with my hand so I guess I went a little overboard.  I didn't think they felt firm enough from only the force of the blower packing it in so I'd ram the tube back down into the wall like I was performing liposuction in reverse. Maybe the density from only the blower would have been good enough, I really don't know. It certainly would have been easier to sheetrock.

I guess in hindsight I should have done a couple cavities each way and then tried to flatten them out. They make a special roller on a stick that's supposed to flatten it out with just a quick roll. I didn't have one but it would have been a tip off at the time that I was packing them too dense if I couldn't get them flat no matter what. Oh well, live and learn. I'm still glad I did it myself. Probably didn't save a lot of money and certainly cost me more time but I like doing everything I can by myself.

If I had just regular 2x4 or 2x6 walls I think I'd go with wet blown cellulose. I couldn't do that by myself but it seems like it would do just as good of a job and be a lot less prep work ( nearly 20,000 staples to put up my insulweb in a single story 1,000 sq. ft. house) and a lot less mess. Well, probably still messy but at least not a dusty mess and the installer would clean it up before he left. Sounds like too much water in the mix is more of a problem than not enough. Too much water and the cellulose gets so heavy it starts to sag down from the top plate.

Good luck whatever you go with.

Alan

If I go cellulose, it will be dry packed and blown in holes in the drywall. The company I contacted wants considerably more to blow it using insulweb. Even If I did the prep work myself, by the time I buy the Insulweb, I might as well go with the Roxul. Besides, I'm not keen on shooting 20,000 staples; I guess that's a big part of why the insulation company wants quite a bit more to use the insulweb.

And as for blowing it wet, there's just something about wetting the cellulose that just kind of goes against the grain for me.

At this point, I'm trying to find another company that sounds like they are more certain about blowing it to the correct density; if that fails, I guess I'll go with the Roxul batts.

As to the blower at the lumber yards or box stores, I have always heard that it is not near powerful enough to blow the cellulose dense enough for walls and/or floors.

Arky


Alan Gage

All the yards around here use Force blowers. From what I've read the Force 2 is acceptable and the Force 3 is perfect. Our yard has both. They don't normally let the Force 3 out but I talked them into it. It was awesome.

I was surprised how cheap the insulweb was (under $200 for way more than I needed).

http://www.jrproductsinc.com/shop/pc/InsulWeb-c31.htm

Shooting the staples was way easier than I thought it would be. I'd read about gluing it on instead of stapling and that's what I'd originally planned on doing. I first tried one wall with glue and the other with staples. I think the staples were faster. They were also more fun (pneumatic stapler) and cheaper ($6.50/box of 5000).

I'd be a little leary of blowing it behind sheetrock too. When I asked my semi-local installer if he did it behind insulweb or sheetrock he said insulweb only. But maybe you're guys know what they're doing and can get it done.

Alan

Squirl

In addition to all the great advice from others here, dense packed or wet blown cellulose resists air infiltration performing close to an air barrier.  As don stated about its abilities to fill all the small cracks and crevices.  From what I read, wet blown is the better than dense pack, but there is almost no place to get the wet blown equipment to rent.  Air leakage is as important as R value in energy efficiency.  I both read stories and talked with a few individuals that were installers.  Many thought it was overkill to spray foam walls for air sealing if I was also going to go with blown cellulose.  If done right, the cellulose should outperform the Roxul.  The Roxul is a way that people are meeting the higher R value requirement of the energy code (R23 2x6 stud) without exterior foam and get the labor saving of batts.

Also Alan had posted some interesting articles once on moisture in crawlspaces.  An air gap between the insulation and floor was recommended.  A little bit of settling in the cellulose for the floor might be a good thing.

Arky217

Quote from: Squirl on November 14, 2011, 12:00:06 PM
In addition to all the great advice from others here, dense packed or wet blown cellulose resists air infiltration performing close to an air barrier.  As don stated about its abilities to fill all the small cracks and crevices.  From what I read, wet blown is the better than dense pack, but there is almost no place to get the wet blown equipment to rent.  Air leakage is as important as R value in energy efficiency.  I both read stories and talked with a few individuals that were installers.  Many thought it was overkill to spray foam walls for air sealing if I was also going to go with blown cellulose.  If done right, the cellulose should outperform the Roxul.  The Roxul is a way that people are meeting the higher R value requirement of the energy code (R23 2x6 stud) without exterior foam and get the labor saving of batts.

Also Alan had posted some interesting articles once on moisture in crawlspaces.  An air gap between the insulation and floor was recommended.  A little bit of settling in the cellulose for the floor might be a good thing.

"An air gap between the insulation and the floor" - That's interesting; everything I've ever read about insulating floors has always emphasized that you make sure the insulation is tight up against the subfloor with no air gaps.
The reasoning being that air gaps would provide a path for air movement that would devalue the insulation's ability to keep the subfloor warm.

Could you provide a link to the articles that recommend an air gap ?
I am curious to know the reasoning behind it.

Arky

Alan Gage

These are the links I'd posted for Squirl:

http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces

http://www.buildingscience.com/documents/reports/rr-0401-conditioned-crawl-space-construction-performance-and-codes

I've only glanced through them since I'm not dealing with a crawlspace. I don't know where they mention a gap between the insulation and floor.

Alan


Squirl


From the article:


Figure 7: Cavity Insulation with Vapor Barrier—Adding impermeable foil faced insulating sheathing over fiberglass cavity insulation is a hybrid approach that uses the best qualities of both materials. Note that the optimum location for the airspace is above the cavity insulation. Are you folks paying attention at the EPA Energy Star Program? Makes for warmer floors—this is the same detail that should be used under bedrooms over garages.


MountainDon

The key item there is the mention of a radiant layer, the foil. Those require an air space to work. No radiant, no air gap.
Just because something has been done and has not failed, doesn't mean it is good design.