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Old 02-24-2014, 12:46 PM   #1
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Which width for insulation rolls


Hello everyone. I'm continuing my attic project I came up with a situation that I haven't come across in the forums. My attic trusses for the most part are 24" OC. My current insulation is ~R22 (R19 batts + a little blown in) I was going to add at least one layer of R30 and potentially some more. As I understand each layer of insulation should be laid out perpendicular to the layer below. Ok, so when I'm perpendicular to the trusses can I use the cheaper 15" wide rolls as opposed to the 23" wide rolls? Would the extra seams be an issue or am I making a mountain out of a mole hill?
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Old 02-24-2014, 02:57 PM   #2
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Should be using more blown in not batts for less air leaks.
Also very important to have air sealed and place where wiring, plumbing, ceiling fixtures where run before adding more insulation and add baffles for air flow from the soffits to the ridge for ventilation.
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Old 02-24-2014, 03:10 PM   #3
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I prefer loose fill as well.

Easier to work with and easier to get installed correctly.
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Old 02-24-2014, 03:33 PM   #4
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While I appreciate the sentiment of using loose fill I would rather not. I have spent more time in my attic than I care to admit and dealing with even the limited amount of loose fill is driving me nuts.

I am in the process of adding baffles and air sealing the protrusions as I find them. The baffles were the main reason for this project as I found many of my soffits to be clogged or partially blocked which was causing some really cold temps inside my house as the wind blew through the insulation.
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Old 02-24-2014, 09:20 PM   #5
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Using the lowest density insulation of fiberglass they make, be sure to add a lot more; http://www.diychatroom.com/f103/my-a...196546/index2/

R-19 - 0.44# cubic ft. --- R-30 -0.50 #cu.ft. --- R-15 = 1.41# cu.ft.

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Old 02-25-2014, 09:23 AM   #6
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You lost me Gary. I've seen the articles that you've posted always an interesting read for sure. Part of the reason why I expected everyone to say loose fill and cellulose which perhaps if I built the house and put everything where I wanted it when the house was built I'd do but that just isn't the current reality.
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Old 02-26-2014, 12:07 AM   #7
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I agree; it takes some extra planning to work around/over others mistakes...

In a nutshell; batts/blown-in FG comes in different densities. The lower densities will allow air/moisture through them easily. FG REQUIRES a six-sided air barrier to meet the rated R-value. Use a high-density batt (especially on top layer) or cover with house wrap or cellulose to prevent wind/moisture coming in vents 24/7 from degrading the R-value. Or add way more than code-required minimum R-value to counter the currents in attic.

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Old 02-26-2014, 11:04 AM   #8
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I'm not sure that the 15" batts are cheaper than the 23" batts pre unit area.
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Old 02-26-2014, 11:28 AM   #9
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Quote:
Originally Posted by Gary in WA View Post
I agree; it takes some extra planning to work around/over others mistakes...

In a nutshell; batts/blown-in FG comes in different densities. The lower densities will allow air/moisture through them easily. FG REQUIRES a six-sided air barrier to meet the rated R-value. Use a high-density batt (especially on top layer) or cover with house wrap or cellulose to prevent wind/moisture coming in vents 24/7 from degrading the R-value. Or add way more than code-required minimum R-value to counter the currents in attic.

Gary
Yeah I've seen your comments about 6 sided air barriers in the past and it makes sense. How would one determine if they had high density vs low density FG? I can't say I noticed it on the package last time I was buy. The plan as it is right now is to add at least one layer of R30 to the current R22ish. Depending on time and how my budget and other projects are coming another R30 layer is not out of the question.

Quote:
Originally Posted by Anti-wingnut View Post
I'm not sure that the 15" batts are cheaper than the 23" batts pre unit area.
I probably should be saying rolls to begin with but what I've been finding is:

15" x 25' is ~$14 or $0.44/sqft
23" x 25' is ~$40 or $0.83/sqft

Actual batts work out to roughly the same cost for either width, so you are correct there because I was saying one thing and meaning another
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Old 02-26-2014, 08:30 PM   #10
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Change all the figures to feet, divide the total weight by total square footage; http://www.homedepot.com/p/Owens-Cor...6?N=5yc1vZbay7

R-30 @ $13.85 15" x 300" x 9.5" in specs. =15" or 1.25ft. x 25' x .7917 (thickness, 9.5") = 24.74 sq.ft.

14 # / 24.74 = 0.57# per cubic ft.

A low-density insulation, very poor at slowing/stopping any air-flow.

R-13 = 0.76# (medium density)
R-15 = 1.41# (high density)
R-19 = 0.44# (low density)
R-30 = 0.50# (low density)
R-30c (cathedral) = 0.80# (medium)
R-38 = 0.48# (low)
R-38c = 0.80# (medium)

Read page #41; http://www.huduser.org/Publications/pdf/walls.pdf

R-13 is just R-19 compressed...

Gary
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Old 02-26-2014, 11:46 PM   #11
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Is it just me or is it a PITA to find high density fiberglass in anything but pre-cut batts?
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Old 02-28-2014, 06:22 PM   #12
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Lol, they sell mostly what sells.... nobody cares for the higher densities, except you (and me). First one to even acknowledge concern about wind-washing, good for you! May need to buy from a supply house or online search for local distributors.
Also make a R-21, 22, 25, and 26, immensely better than R-19....; https://docs.google.com/viewer?a=v&q...Sl4MDm_aao1YUg

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Old 02-28-2014, 07:38 PM   #13
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That's what I figured, and it's kind of hard to blame the system for working in such a way. I searched locally for suppliers and most of them want to either sell me way more than I'm interested in or they want to deal with a contractor.

Wind washing is what actually got me started down this path. I found that in a few rooms there was some water staining. I couldn't find any evidence of leaks from above and then as the weather got a lot colder I noticed that wherever the staining was it was really cold. I found no missing insulation but after looking at the situation noticed that a lot of wind was blowing through the soffit in those areas which I always thought of as good thing but then realized that the air was effectively turning the already low R value to R0. I added baffles (Accuvent ones that staple to the top plate and roof decking) to most of my attic (a few places left) and have noticed significantly better temps in those rooms. It's nice when things work out.

I guess the width of the insulation doesn't matter a whole lot. Even more so if it's probably not going to be the last layer. Even adding low density will be a help, but at least I understand the limitations of it. Eyes wide open kind of deal.

Ok so philisophical sort of question. When they come up with energy codes and recommend something like R60 for an attic there is no spec that it prevent wind wash is there? I assume not since LDFG is sold everywhere, so is this taken into account or just blindly done? I'd guess blindly done but am not sure.
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Old 03-02-2014, 06:40 PM   #14
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The only reason they stopped making R-11 is because all areas require more R-value per inch in a 3-1/2" wall space. R-11 was low density; http://www.diychatroom.com/f98/bigge...ulation-90438/

If your insulation is in a six-sided box, it will function as rated; https://docs.google.com/viewer?a=v&q...M8l_EeA2F-qvvA

Thermal bypass;http://www.greenspec.co.uk/thermal-bypass.php

Air wash reduction of 40% R-value in attic; https://docs.google.com/viewer?a=v&q..._NGatSVo3wzmAQ

If in an air-tight container, you will achieve R-value, after a certain R-value, the gains vs. cost enters the picture; http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja

The R-60 is to make up for; lack of air sealing before insulation/lack of baffles/lack of an air barrier (vapor permeable) over the insulation/ lack of air sealing basement/crawl- between floors to stop natural/forced "stack effect"; http://www.wag-aic.org/1999/WAG_99_baker.pdf

Just use a top layer of cellulose or foam board under the drywall before insulating....stops heat leaving in winter/heat gain from above in summer; http://www.explainthatstuff.com/heatinsulation.html

Final thought; http://www.greenbuildingadvisor.com/...cience-podcast

Gary
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