Attic re-insulation in December?

[greg13]

How do you plan on removing the vermiculite? IF it contains asbestos you will need an approved and licensed asbestos contractor and hauler to dispose of it.
I would have it tested first to find out for sure what you are dealing with. The cost difference could more than pay for the new insulation.

 

[lml999]

The machine loader got almost as Dusty as the blower. After the first few bales we stopped, ran to the store and bought a second set of goggles (the high school chemistry type) and the dust mask that has cartridges. Those two pieces of safety gear plus a good led head lamp are critical.

Post pics or it didn't happen.

 

[lml999]

I don't understand either comment - at all.

Cellulose blows FG away, let's count the ways:

- Cellulose seals some air infiltration, FG doesn't. One reason they call it "filterglas".
- Cellulose is a much better fire retardant. Search youtube for the video of the guy melting a penny in his hand with cellulose and the video of the three "houses" set on fire. Cellulose wins hands down
- Cellulose has an intrinsic insulation value, even compressed; FG doesn't. It's only claim to fame is holding air, which does insulate. Compress FG, there goes your insulation value.
- Cellulose repels rats and mice, FG doesn't. This is opposite of your last statement. Install FG, get ready for the mice and rats in winter.

I'm getting ready to install about 50 bags of cellulose this winter; no way I'm waiting on summer or even spring, way to hot. And they don't even sell blown FG around here, I already checked before I did my research.

Good luck!

I've got fiberglass bats installed between the joists in my attic, Not sure the width, maybe 10" rafters. I'm having the attic top-sealed and then new insulation blown in. Would you spray cellulose *over* the existing FG? Or would you pull up the FG bats and discard them, then fill the space (and more) with cellulose? The workers are going to have to move some of that batting to do the sealing...

Thanks!

 

[mcdougy]

I've got fiberglass bats installed between the joists in my attic, Not sure the width, maybe 10" rafters. I'm having the attic top-sealed and then new insulation blown in. Would you spray cellulose *over* the existing FG? Or would you pull up the FG bats and discard them, then fill the space (and more) with cellulose? The workers are going to have to move some of that batting to do the sealing...

Thanks!

Toss it , pretty much useless

 

[lml999]

Toss it , pretty much useless

I'll explore that option. Mass Save quoted "adding 6" of cellulose over existing FG" on the attic floor. Pulling all of the FG, disposing of it, and then supplying the additional cellulose may run into some $. $1200 for 1000 sq ft. of attic was retail cost cited. I'll talk with service provider about the additional work, wonder if it's worth the cost...

By the way, they cannot start the work until a HRV is installed. I'm hanging it now, in my utility room, and the service provider will install the ducts and vents.

I have a feeling that this $800 (net) job is going to run me $3K+ (HRV cost $900, wall control another $100, rebate of $500 to be received...)

 

[FTG-05]

I've got fiberglass bats installed between the joists in my attic, Not sure the width, maybe 10" rafters. I'm having the attic top-sealed and then new insulation blown in. Would you spray cellulose *over* the existing FG? Or would you pull up the FG bats and discard them, then fill the space (and more) with cellulose? The workers are going to have to move some of that batting to do the sealing...

Thanks!

I'm going to seal what I can (bathroom vents and fans, lights that easy to get to etc.) but for the most part, I'm gong to leave the R-19 FG in place. Way too much work take out and then dispose of. As it is, I'm going to need about 140 bags to get to 12" cellulose depth i.e. an added R-38.

 

[lml999]

I'm going to seal what I can (bathroom vents and fans, lights that easy to get to etc.) but for the most part, I'm gong to leave the R-19 FG in place. Way too much work take out and then dispose of. As it is, I'm going to need about 140 bags to get to 12" cellulose depth i.e. an added R-38.

Makes sense to me.

A related question...we have a couple of exposed cathedral ceilings (ie, I can get to the topside of the ceiling in the attic). They have the FG batts installed...what's the best way to add additional insulation to these areas? Am I limited to running batts perpendicular to the celing joists? If so, should I just go with FG batting? Will blown in cellulose "stick" to the sloping section? Is there another strategy to keep cellulose in place?

Thanks1

 

[FTG-05]

Lml, I too have cathedral ceilings. I plan to add plywood "dams" to mine that will hold back some cellulose. The good news about the "dam" material is that was all leftover boards from my new neighbors house building a couple months ago, all of it was free from his burn pile.

Having said that: I don't see why a combination of FG batts set perpendicular to the ceiling joists and current FG batts, then blow cellulose on top and in between; in other words, use the FG batts as a "dam". I don't see why it wouldn't work.

You do want the cellulose blown everywhere you can: Cellulose will seal far better than FG, especially batts.

 

[lml999]

You do want the cellulose blown everywhere you can: Cellulose will seal far better than FG, especially batts.

Agreed. I'm going to ask the insulation company if they would pull the FG batts out on the opposing side (where the cathedral ceiling meets the roof, then blow cellulose in, upgrading the insulation in that section.

With regard to the accessible side, I'm reluctant to add fiberglass batts or dams as I think the cellulose top layer would be uneven, and might still move.

What we need is a fabric retaining sheet (something heat/age/moisture resistant) that would attach to each of the joists, or perhaps every other joist, and float at an even height above the surface. (ie, not attaching the sheet directly to the joist, but using an intermediate attachment. The cellulose would be held against the sloping surface and would not tend to move.

Or I could build a lightweight box structure with 2" semirigid 4x8 insulating panels and fill that...

The two rooms in question are the most important in the house -- our great room, where we spend much of the day (and where our wood stove will be installed) and the master bedroom, where we spend most of the night.

Or I could just build a passivhaus with a flat grass roof and be done with it!

 

[lml999]

Lml, I too have cathedral ceilings. I plan to add plywood "dams" to mine that will hold back some cellulose. The good news about the "dam" material is that was all leftover boards from my new neighbors house building a couple months ago, all of it was free from his burn pile.

Service provider said they'll just slap 2" semi rigid board on the slopes, will pick up R10 plus be more airtight. Quick and easy.

I think the stuff (the semi-rigid insulation panels) loses efficacy when it gets really cold.

We intend to be in this house 25 years, then leave it to the kids, so I want to do it right. Once.

 

[DickRussell]

A good read on insulating a cathedral ceiling is here: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

 

[lml999]

A good read on insulating a cathedral ceiling is here: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

Thanks, that's useful. I'm talking with the service provider about how to do this...looks like I need vent chutes and then I can blow in cellulose. I may already have the vent chutes over FG batts. A question is whether Mass Save will underwrite part of the cost of pulling the FG and then blowing cellulose.

My prior posts focus on the portion of the cathedral ceiling that is lower than the roofline. I have two ceilings where, on one side, I have access to the top portion of the cathedral, in the unheated attic...so I can add an insulation layer without concern about ventilation...

 

[FTG-05]

Service provider said they'll just slap 2" semi rigid board on the slopes, will pick up R10 plus be more airtight. Quick and easy.

I think the stuff loses efficacy when it gets really cold.

We intend to be in this house 25 years, then leave it to the kids, so I want to do it right. Once.

It's FG that has the upside down U-shaped temp vs. efficiency curve. In other words, as it gets colder, it gets less effective. The worse numbers are below zero so probably don't affect a lot of people here unless you live where it stays well below zero for days on end. Cellulose has a flat to slightly upright U-shaped temp/efficiency curve. Another reason to stick with cellulose.

 

[FTG-05]

A good read on insulating a cathedral ceiling is here: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

My cathedral ceiling is interior to my attic. In other words, it's no different than the rest of the attic other than it has a pretty good slope to it. Maybe it's not a real cathedral ceiling then, don't know.

 

[DickRussell]

It's FG that has the upside down U-shaped temp vs. efficiency curve. In other words, as it gets colder, it gets less effective. The worse numbers are below zero so probably don't affect a lot of people here unless you live where it stays well below zero for days on end. Cellulose has a flat to slightly upright U-shaped temp/efficiency curve. Another reason to stick with cellulose.

Loose blown chunks of FG can suffer from thermal looping, especially on an attic floor, as cold air above it sinks downward and warmer air above the ceiling below rises into the attic space. More dense FG batts don't suffer as much from this, and even a covering of a few inches or more of cellulose over loose blown FG pretty much eliminates thermal looping. The R value of loose blown FG is not as high as that of cellulose for the same thickness.

But I suspect the comment about insulation that suffers a small loss of R value as temperature drops was referring to polyisocyanurate foam board (polyiso). That discussion can be found here: http://www.greenbuildingadvisor.com/articles/dept/musings/cold-weather-performance-polyisocyanurate. If that type of foam board is added to the warm side of a wall or ceiling below an attic, its average temperature won't be low enough to be affected. It's when it is added to the exterior that the thermal degradation is seen.

My cathedral ceiling is interior to my attic. In other words, it's no different than the rest of the attic other than it has a pretty good slope to it. Maybe it's not a real cathedral ceiling then, don't know.

Well, yes, if there is venting above the insulation, then it's just like a horizontal ceiling, as long as there isn't "wind washing" of the insulation, as soffit vent air flows through it enroute to the ridge vent.

 

[Highbeam]

My cathedral ceiling is interior to my attic. In other words, it's no different than the rest of the attic other than it has a pretty good slope to it. Maybe it's not a real cathedral ceiling then, don't know.

Those are typically called scissor trusses. The bottom chord is just not flat.

Cellulose will hold on with quite a slope. Worse case, it slides down some over time and you need to put more on top. That just means a really well insulated toe of slope!

There is no reason to remove the old FG. Simply blow on top of it with cellulose and you will soon forget that it is even down there. I left the old batts in my attic when I had loose FG blown in. I sometimes wonder if I should go back in and dust a few inches of cellulose over the top to air seal it better. That would be three different types of insulation! It's additive. No reason to remove it.

 

[semipro]

There is no reason to remove the old FG. Simply blow on top of it with cellulose and you will soon forget that it is even down there. I left the old batts in my attic when I had loose FG blown in. I sometimes wonder if I should go back in and dust a few inches of cellulose over the top to air seal it better. That would be three different types of insulation! It's additive. No reason to remove it.

2nd this!

 

[iron]

i agree with HB. i blew in about 40 bags of cellulose over the existing FG. worked great. i seem to recall that 15" was the max depth for 1/2" gypsum, so heads up.

and, if you're worried about heat, i would just crank up the stove. while i was remodeling my kitchen in the middle of winter (30-40 degree temps), i had a hole in the ceiling for about a week. the hole was 16'x10'. kept loading the fireplace and kept the inside of the house around 58 degrees. not the most efficient thing in the world, but better than 30 degrees.