DIY blown fiberglass

Exeric · 11-01-12, 07:01 PM

I'm also about at the point of putting in blown insulation that I was going to do myself. I was going to do fiberglass using the machine from Home Depot since it seemed cheap and relatively easy for a diyer. Is there anything wrong with using fiberglass over cellulose? I already got the 1/6" mesh netting from JR instead of the insulweb. Maybe I screwed up there? I'm new to this also so I don't pretend I'm not trying to figure it out as I go along. Any help would be appreciated. Thanks.

S-F · 11-01-12, 07:09 PM

The problems with all fiberglass, as opposed to cellulose are that mice love the stuff, it's not recycled material and fiberglass doesn't have the hygroscopic value cellulose has. It also might be more expensive. I'm not sure because I have never (well, only once) used blown fiberglass.

Exeric · 11-01-12, 07:20 PM

Hmm, interesting. If I stayed with blown fiberglass for the convenience factor do you think that the mesh netting I got will work? It sure was cheaper and my understanding is that blown fiberglass is more compressible so it doesn't put quite the strain on the netting.

I plan on putting a layer of 1.5" xps over that using 2.5" plasticap nails directly to the studs. No stringers will be used. That is, it will be (from outside) siding, housewrap, plywood sheathing, blown insulation inside 2x4s, xps, and finally drywall. Drywall will also be with 2.5" drywall screws.

Hopefully I don't need to worry so much about dew points and drying times in my climate, northern California.

S-F · 11-01-12, 07:45 PM

The double vapor barrier sounds like a bad idea as well as not having the sheathing directly attached to the studs. That's a major code violation and for good reason. You will HAVE TO install let in bracing or else your house will lean over. Why not just put all of the XPS on the outside of the sheathing?

Also this should have its own thread. If a mod would be so kind as to split this up?

Exeric · 11-01-12, 07:57 PM

Well, I'll explain myself here while waiting for the subject to get split. It is standard construction, sheathing attached to 2x4s. Maybe I didn't explain myself well. Also i'm not seeing where I have two vapor barriers. The house wrap is standard tyvek air barrier. The xps has low to moderate vapor permeability. So even that doesn't act like foil backed iso.
We generally don't use vapor barriers in Cali because we don't need them here.

Also, to answer your other question. I just installed new windows and doors within the existing structure and matched to the existing siding, and the interior walls are stripped to 2x4 studs. So it is much more practical at this point to install the xps on the interior side.

Do you have any ideas on the questions I asked you?

S-F · 11-01-12, 08:24 PM

Sorry, I misread your previous post and said a bunch of things which must have seemed nutty. I don't know about the netting you're using so I can't comment on that and I also don't have much experience with blown fiberglass for the reasons previously mentioned.

I just went back over your first post in this thread and I can tell you that the machines they rent at Home Cheapo, at least in New England, aren't capable of dense packing cellulose. They simply don't have strong enough blowers. Also they don't have a tigerflex hose so even if they were strong enough, you'd have to go out and buy your own adapters and a hose. You might want to check out lumber yards to source a suitable machine. But maybe you only need 1 pound per ft. with blown firberglass. I doubt it though.

Exeric · 11-01-12, 08:51 PM

Thanks a lot. I just wanted to find out if there was a big hole in my plan for using blown FG. It sounds like it will work for me with the proviso's you've given me. The main reason I'm tending that direction is just because it seems to be slightly more forgiving for a diy install, even though in a lot of ways it may be inferior to cellulose for the reasons you gave. It's also a lot cheaper here than blowing cellulose, especially if I had to rent a big honking machine for it. I'll keep an eye out for those damn rats and seal it properly before they start hanging their hammocks behind it and bringing their picnic lunches.

S-F · 11-01-12, 08:59 PM

I think you will still need that big honking machine. I find it hard to believe that you can dense pack anything with one of those anemic Home Cheapo machines. Get a tester and make sure it can blow 2.8 or get a different machine. That stuff WILL settle and then you're worse off than if you just putt FG batts up.

Exeric · 11-01-12, 09:22 PM

I'm still thinking out loud about all of this. It may be that HD machines are just for loose fill in the attic. If so i will might just end up paying some one to do it and go the cellulose way. I'll do some more research to see what's available locally for rental. So far I don't see much apart from HD and that just might just be for loose fill.

S-F · 11-01-12, 09:45 PM

These machines are strictly for a slow open blow. God it must take all day to blow an attic! Where I live none of the rental centers have good machines or machines with TigerFlex hoses. But.... The local lumber yard does. They have a great machine and rent it for $50 a day. Hoses, adapters and all.

11-01-12, 07:01 PM	#1
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	DIY blown fiberglass I'm also about at the point of putting in blown insulation that I was going to do myself. I was going to do fiberglass using the machine from Home Depot since it seemed cheap and relatively easy for a diyer. Is there anything wrong with using fiberglass over cellulose? I already got the 1/6" mesh netting from JR instead of the insulweb. Maybe I screwed up there? I'm new to this also so I don't pretend I'm not trying to figure it out as I go along. Any help would be appreciated. Thanks.

11-01-12, 07:20 PM	#3
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	Hmm, interesting. If I stayed with blown fiberglass for the convenience factor do you think that the mesh netting I got will work? It sure was cheaper and my understanding is that blown fiberglass is more compressible so it doesn't put quite the strain on the netting. I plan on putting a layer of 1.5" xps over that using 2.5" plasticap nails directly to the studs. No stringers will be used. That is, it will be (from outside) siding, housewrap, plywood sheathing, blown insulation inside 2x4s, xps, and finally drywall. Drywall will also be with 2.5" drywall screws. Hopefully I don't need to worry so much about dew points and drying times in my climate, northern California. Last edited by Exeric; 11-01-12 at 07:35 PM..

11-01-12, 07:57 PM	#5
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	Well, I'll explain myself here while waiting for the subject to get split. It is standard construction, sheathing attached to 2x4s. Maybe I didn't explain myself well. Also i'm not seeing where I have two vapor barriers. The house wrap is standard tyvek air barrier. The xps has low to moderate vapor permeability. So even that doesn't act like foil backed iso. We generally don't use vapor barriers in Cali because we don't need them here. Also, to answer your other question. I just installed new windows and doors within the existing structure and matched to the existing siding, and the interior walls are stripped to 2x4 studs. So it is much more practical at this point to install the xps on the interior side. Do you have any ideas on the questions I asked you? Last edited by Exeric; 11-01-12 at 08:05 PM..

11-01-12, 08:51 PM	#7
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	Thanks a lot. I just wanted to find out if there was a big hole in my plan for using blown FG. It sounds like it will work for me with the proviso's you've given me. The main reason I'm tending that direction is just because it seems to be slightly more forgiving for a diy install, even though in a lot of ways it may be inferior to cellulose for the reasons you gave. It's also a lot cheaper here than blowing cellulose, especially if I had to rent a big honking machine for it. I'll keep an eye out for those damn rats and seal it properly before they start hanging their hammocks behind it and bringing their picnic lunches.

11-01-12, 09:22 PM	#9
Exeric Apprentice EcoRenovator Join Date: Aug 2012 Location: California Posts: 274 Thanks: 19 Thanked 37 Times in 28 Posts	I'm still thinking out loud about all of this. It may be that HD machines are just for loose fill in the attic. If so i will might just end up paying some one to do it and go the cellulose way. I'll do some more research to see what's available locally for rental. So far I don't see much apart from HD and that just might just be for loose fill.