I'm nearing the decision of attic insulation for my shop. Current plans are to go R 30 (unless someone here changes my mind) and I'm leaning toward fiberglass...which is what I used in my last shop. However, there is a fair amount of opinion that cellulose is actually a superior insulation. The thought behind that was that cellulose settles over time and forms a better barrier to heat loss, whereas fiberglass packs a lot less. With fiberglass the looser pack actually allows a little heat to escape by rising through the  loose fibers. This isn't a cost question. more of a curiosity to me. Besides, I may hire this out and some installers only do one or the other. What say the collective here?

Can only offer our experience. We used cellulose in the house because installation was quicker and easier. After several years...maybe 5....the cellulose settled and we had another layer blown in. We started with 6" and the second layer was 2". It stays warm.

In the shop, I used fiberglass because there was no attic. It's also easy to heat. 

I'd think r30 would be r30, regardless of the material. But, I'm no expert.

My understanding of this is that the insulation value actually comes from dead air space.  That if you take a piece of R30 and pack it into a 4" space you have defeated the purpose as you end up with something a lot less than R30.  If this is correct, fiberglass batts should retain most of the R30 value while the blown in cellulose may loose some as it settles and packs over time.

 

Now, that said - the blown in variety will blanket everything including the ceiling joists which the batts would not do.

Cal

Would cellulose be more susceptible to humidity than fiberglass? IDK, our humidity is so low it wasn't a consideration. 

I just had fiberglass blown in above the garage. After 35 years the original cellulose in the attic space had packed down to +/- 4". The local power company subsidizes improvements if you bring it up to a minimum standard.

 

Using one of the power companies recommended contractors, the attic was brought up to R-42. While they were at it, I had them insulate above the garage (a normally uninsulated space), which, on the average, has lowered the heat load in the garage 10-15°. This makes a HUGE difference when you go from 95° to around 80°.

 

As for the cost...it was only about $250 to add R-42+ to about 500 sq/ft. No matter what the payback period is, the reduction in heat inside of the garage was well worth it. We'll see how much warmer is stays this winter when it cools down.

I bet the cellulose can be blown in by a contractor for what it would cost you to lay the fiberglass.  I would go the cellulose.

It might be six of one, a half dozen of the other regarding cellulose or fiberglass. I recently did the space about my shop, aka garage, with blown-in fiberglass. I rented the machine at HD, got the fiberglass bales at HD as well,  and did the job in a half a day with help of my son. I did prep work ahead of time by installing air intakes baffles in  between the trusses, down near the soffits to allow the air flow over the insulation on it's way to the ridge vent. I also built a barrier at the attic access to keep the fiberglass from flowing out.  If you do it yourself, you will need a person to help you to feed the insulation bales to the machine. The controls on the machine let you start and stop the flow as needed.

I should have explained...the insulation, regardless of type, will be blown in. The loose fill I used in my last shop was fiberglass. I'm not much on batts in the attic, like mentioned the loose fill covers everything. I did put those foam baffle thingys in before I had the rock installed, so we're good to go there. But this is all good input.

Glad you installed the foam baffles to keep the cold air from the eaves comming in to purge the hot air trapped under the roof.  That extends the life of the roof considerably and decreases the heat load of the conditioned space below.  Please make sure you have a ridge vent.  As for insulation choice which has a greater R value per inch of blown in insulation?  Do you have enought height in the attic to have either blown in and still get to R30?

Also be aware that at extreme cold like -20 F  the fiberglass actually becomes a conductor not and insulator.

I do not know where you live but if you can get very cold I go with Celose then reblow it in after 5 years.  

As for humidity the fiberglass is superior to celouse.

 

44 minutes ago, Michael Thuman said:

 

Also be aware that at extreme cold like -20 F  the fiberglass actually becomes a conductor not and insulator.

I

I think that is the phenomenon to which I referred. It seldom gets that cold around here, so maybe it's not an issue. As for room, there's plenty..I suspect I could go to R40 but I'd have to check the height of those baffle thingys.

Edited October 23, 20178 yr by Fred W. Hargis Jr

The baffles are around 3' long. Blowing in fiberglass to an R-42+ came up somewhere around 15-18" deep (give or take). My baffles were existing but the insulation didn't come anywhere near the top of them.

 

There wasn't much of a cost difference between the cellulose and the fiberglass. The fiberglass packs (compresses) MUCH less than the cellulose. If you have to re-blow due to compression it just adds to the end cost. Cold in Florida is a joke...I haven't seen a decent "hard frost" for several years. So, -20°F just "ain't gonna happen"

 

When I priced DYI vs. contractor installation it was less trouble to go contractor for the price difference...

 

I would check with your local power company. Many offer incentives to upgrade. I have retroed single to double pane windows, the insulation, and just replaced the almost dead heat pump. It made a noticeable difference in the power bill and the credit from the power company was really a surprise. It doesn't hurt to check.

6 minutes ago, schnewj said:

 

When I priced DYI vs. contractor installation it was less trouble to go contractor for the price difference...

 

 

That's kinda what I'm thinking. I remember when I did the last one I itched for 3 days, and probably sneezed/coughed for a week (yes, I used a very good respirator). he problem with a contractor may be the one I always face with them around here...getting the job done in some kind of acceptable timing.

Just now, Fred W. Hargis Jr said:

That's kinda what I'm thinking. I remember when I did the last one I itched for 3 days, and probably sneezed/coughed for a week (yes, I used a very good respirator). he problem with a contractor may be the one I always face with them around here...getting the job done in some kind of acceptable timing.

I had to use a power company pre-vetted and approved contractor for the insulation. They showed up, when scheduled,  in the morning, and were cleaned up and gone within three hours. They even added a R-45 batt to the drop down stair. My conversation with the rep was interesting...he, said, my power company (Duke Energy) didn't fool around. He was held to high standards, and in return got jobs he didn't have to go hustle to get. It was a win/win situation for him for just being there on-time, when scheduled, and doing the job correctly.

Fred, it looks like you have four power companies available in your area. A couple are Energy Star participants and offer some rebates. However, it was mostly for HVAC, and hot water. I didn't see anything about insulation, windows, or any other improvements.

 

It doesn't mean that they don't offer them...give your provider a call and discuss it with them. At the very least, they may have some suggestions and/or recommended contractors to do the work.

Edited October 23, 20178 yr by schnewj

4 hours ago, Fred W. Hargis Jr said:

I think that is the phenomenon to which I referred. It seldom gets that cold around here, so maybe it's not an issue. As for room, there's plenty..I suspect I could go to R40 but I'd have to check the height of those baffle thingys.

 

This is insulation time of year so they may be busy.  On the plus side the weather is cooler for them to be up in the attics.

Just wondering, if it's possible to use it, have you considered foam insulation? More costly, but it leaves no voids to eventually create problems.

I had considered it for the walls, but not the ceiling. I agree it has some real advantages but the cost is quite a bit more.

Foam has to be  very tightly and perfectly sealed.  It is NOT for ceilings (normally) now for walls the challenge is the where do you get 3 1/2 foam to fill the cavaties between the framing.  You cannot so you have to put in 2" then tape it off (Seal it)  then 1 1/2" and again tape it off (seal it).  Any voids must be filled with closed cell expanding foam and then sawed to the same thickness.  

Foam has the other great property it is rigid so when it backs up drywall it stops most impacts from breaking the drywall.

 

I thought the reference was to the spay foam technique (icynene).

We used to live in a part of AZ where flat roofs were prevalent. In the old days, rolled roofing or just layers of tar paper was the covering. You can imagine what a mess that became. Then, spray foam insulation became the go to covering. That was good for a while, until UV and pigeons began to degrade it. Eventually a white polymer coating over the foam became the usual. That protected the foam and reflected the sun's rays. Leaky roofs were rare and the homes were much cooler in the summer and, easier to heat in the winter.

If I were building a new home today, I'd use the foam in every instance where insulation was required. It's great stuff.