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Old 09-08-15, 02:09 PM   #11
jbattenhouse
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Compressing lowers the R value considerably. It is the air, trapped in the insulation, that gives the resistance to heat flow. Compressing the insulation reduces the amount of air and the R value.

By a lot.

bottom line - don't compress!
If this was true then dense pack cellulose would provide no benefit at all. Cellulose fibers actually add the insulation value and dense packing it cuts way down on air infiltration.

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Old 09-08-15, 07:39 PM   #12
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Cellulose is different from fiberglass. Cellulose, a wood product (actually a long chain sugar) has lots of air pockets in it. It is these air pockets that provide resistance to heat flow and not the physical product itself.

Thus, dense pack cellulose is completely different from densely packet fiberglass.

Easy to misunderstand.


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Old 09-08-15, 08:08 PM   #13
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OK, dense-packed cellulose insulation is not a bad thing. Loose-packed cellulose is not a bad thing. The main difference between the two methods of installation is the particular purpose. Let me elaborate.

When a space that is already pretty airtight is filled, loose-packing will give you more insulating effect per pound, because it goes further in the same space. The r and u values are also somewhat better than dense-packing due to the higher trapped airspace. More air in between fibers equals more heat flow barrier.

When a space that has air infiltration issues (gaps around obstacles, cracks between chambers, convective channels or chases, etc.) needs insulated, dense-packing is the cure. The high velocity air that blows in the cellulose travels through these difficult-to-seal areas naturally. The cellulose travels with the air and gets lodged in all these air paths, effectively sealing them by way of injection molding. Once the leaks and voids are filled, the cellulose packs in behind the clogged airways, further sealing each chamber substantially. Resistance to airflow in older, leaky buildings can be increased by factors in the tens to hundreds of mm of water column, bringing effective leakage areas down 40-80%, sometimes more. At constant pressure, air leakage drops an order of magnitude or better (from 4 cfm before to 0.2 cfm after @ 0.3" w.c.)! This leak sealing effect adds to the added thermal mass and r-value of the insulation, tremendously reducing fuel costs. Not quite an air barrier, but a lot closer than the way things were before.

Tolerance to compaction is a critical property of cellulose. Unlike mineral based insulation, organic fiber is cellular in nature and inherently non-conductive. Trapped air between fibers is only one part of its insulating ability. Compacting cellulose insulation would ultimately reduce its R-value to that of wood. If we compact fiberglass to the ultimate degree, we would get the insulation performance of glass. When we need to get air sealing by tightly packing insulation, cellulose fibers retain their resistance to heat conduction and mineral fibers don't. Cellulose also absorbs moisture, wicking it away from specific leaky areas and spreading it out at lower concentrations, until it has a chance to dry out.

Either method of packing is acceptable in the general sense. Loose-packed cellulose tends to settle on its own over the years, kind of like snow. Not surprisingly, it doesn't lose much r-value during the process, but it does lose a little. That's OK, we can add more loose-pack in the unfinished attic later if needed. Not so in between wall studs: what's done is done. Until it gets re-done.
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Old 10-13-15, 12:32 PM   #14
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Geo NR Gee, did you ever figure out what you're going to do? Did you do it?
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Old 11-01-15, 08:44 AM   #15
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Yesterday I enlisted the help of my nephew and we tackled the insulation. You can see the 2x4 walkway down the center isle.






We discovered a opening that lead to a small room. You can see the opening. The previous insulators totally skipped over it. No wonder that room was super cold in the winter.




I took a temperature reading before and after. It was as much as 4 degrees difference between the rooms.
The rooms now have all even temperatures and the furnace is noticeable not cycling as much. I spent $300 on the insulation, rented the machine for free and woke up warm this morning! I wish we had done this years earlier.
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Old 11-03-15, 07:19 PM   #16
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Thanks for the update and the photos. At some point, I look forward to getting that much insulation in my latest project house. At the moment, I have batts that don't cover the trusses in a climate where frost was showing up in the mornings in late September.

Is the black plastic I see in some of the rafter bays against the roof decking a channel to promote/maintain airflow? In my warm climate house, I have foam channels to maintain air flow from the eaves through the attic.
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Old 11-04-15, 09:04 AM   #17
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Quote:
Originally Posted by where2 View Post
Is the black plastic I see in some of the rafter bays against the roof decking a channel to promote/maintain airflow? In my warm climate house, I have foam channels to maintain air flow from the eaves through the attic.
Yes, they were added to the cardboard ones that were already installed in the bays. Since I added several inches of cellulose, we needed to extend those up. I purchased a electric staple gun just to put them up. Glad I did because of the angle, and having to work over existing fiberglass insulation. There is a massive difference in the comfort in the house now. The $300 was totally worth the expense.

The next energy saving project is to seal above the door jams. It's amazing how much they leak at the top of the molding.
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Old 11-04-15, 08:17 PM   #18
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Quote:
Originally Posted by Geo NR Gee View Post
There is a massive difference in the comfort in the house now.
If this was better understood, we would not need building codes to force people to put a minimal amount of insulation in new houses.
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Old 01-11-16, 03:00 PM   #19
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Update: Before the blown-in, we used to have the Tstat set at 69 to 72 depending on who is home. Now it is almost always set at 63 to 65 or it gets too uncomfortably warm. Both upstairs and downstairs are pretty even except for the floor downstairs. That's tell me that I need to have my nephew come over to help insulate the crawl space now.

My electricity bill should have been a lot lower, but were finding ourselves enjoying the hot tub more this winter since all the boys are back in college.

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