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Old 02-20-2014, 09:22 AM   #16
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Is my attic insulation adequate?


You do need an airtight enclosure around the attic stairs. They sell them or you can make your own.

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Old 02-20-2014, 05:52 PM   #17
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Is my attic insulation adequate?


Mike, you really can't compare them. IMO, batts are for limited headroom, cathedral ceilings, or over a bath fan for future replacement. The batts are fine for low slope (restricted headroom and lower insulation dams around scuttle hole access), around recessed lighting without building a cover or with standard joist spacing, but blow-in is easier with multiple obstructions. IMO, need an elevated walkway for any HVAC - OR (removable) batts just from the attic scuttle to unit for filter changes. Just raking blow-in aside for access and replacing leaves big air pockets (de-rating the R-value) because the insulation clumps up with further movement.

The FG batts are available in much higher densities than the blow-in for perimeter application where roof slope interferes with full R-value. You don't want the insulation touching roof sheathing or even framing (R-1.25 in wood-- thermal bridge)- premium to use stacked/sloped (baffles of XPS) rigid foam board over the exterior walls (1' wide) for maximum insulation in that restricted height- no conduction loss. Use of blown-in FG = R-10 at that 4" height and this is the coldest wall in the house (due to exterior location and air vents directly coupled above).http://bct.eco.umass.edu/publication...o-save-energy/

There are recirculating convective loops in all gabled attics that are vented- the cold incoming air sinks to/through the top inches of blown-in quite easily due to the low density- mixing with the heat flux rising from room below; http://digitalcommons.unl.edu/cgi/vi...ct%3Dj%26q%3Dv

The more insulation you add, the better it is as the density increases from the weight above = better product. Still, even at R-60, the density is only 0.58#ft.cubed;http://www.r-prollc.com/Documents/At...Fact_Sheet.pdf


Your local code requires R-38; http://energycode.pnl.gov/EnergyCode...state=Nebraska --------------- Six-sided air barrier required for full R-value; https://docs.google.com/viewer?a=v&q...M8l_EeA2F-qvvA

So, to counter the convective loops and the attic wind-washing, IMO add a housewrap over the top- like Tyvek as it will also work as a radiant barrier of sorts;http://www.homeenergy.org/show/article/year/1992/id/895

Or from above, at new construction; http://www.philwrites.com/AW_Manual_12_1_all_LR.pdf

Gary
PS. OR just fill it to R-60...lol.
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Last edited by Gary in WA; 02-20-2014 at 05:55 PM.
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Old 02-20-2014, 09:46 PM   #18
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Is my attic insulation adequate?


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Originally Posted by Gary in WA View Post

There are recirculating convective loops in all gabled attics that are vented- the cold incoming air sinks to/through the top inches of blown-in quite easily due to the low density- mixing with the heat flux rising from room below; http://digitalcommons.unl.edu/cgi/vi...ct%3Dj%26q%3Dv
I believe my brain just imploded trying to fully understand this.
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Old 02-21-2014, 06:52 AM   #19
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Is my attic insulation adequate?


Thanks everyone for all your comm,wents and suggestions. I'm learning a lot.
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Old 02-22-2014, 08:58 PM   #20
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Is my attic insulation adequate?


Yes, I've used that link to show convective loops are always in an attic (with passive venting), cold------ ; or hot climate; http://www.fsec.ucf.edu/en/publicati...SEC-PF-226-91/

Now I'm trying to convert the heat flux (using same outside temps) through the attic insulation (R-20) compared to heat through a 2x4 (R-13) exterior wall-- pp.86: http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja But the wall outside temp is 5*F, with 10 W/m2 loss and the ceiling (R-20) with 32*F outside and 37 W/m2 loss, and 21*F out with 48 W/m2 loss; almost 5 times more loss and temps are warmer in attic (w. 4cm vents) than wall exterior..... anybody?

Send me a PM if you want, I'd love some help on this. Thanks, Gary

PS. the colder air (less dense) settles on the attic floor being warmed by the heat loss through the insulation to rise/exit the high vents; http://learn-science.20m.com/tmyths.htm#myth2

http://www.usatoday.com/tech/columni...derquest_x.htm
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Last edited by Gary in WA; 02-22-2014 at 09:04 PM.
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Old 03-01-2014, 06:40 AM   #21
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Is my attic insulation adequate?


If you know of any painters, an extendable and retractable painters pole is handier than a pocket on a shirt for blowing in insulation. Duct taped to the blower hose and you're GTG.
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Old 03-02-2014, 12:53 PM   #22
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Is my attic insulation adequate?


going from R-19 to R-49 is not that costly. Once you have blown in that is what you need to stick with. you can have batts then cover with blown in but not the other way around.
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Old 03-02-2014, 12:56 PM   #23
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Is my attic insulation adequate?


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Originally Posted by Gary in WA View Post
Yes, I've used that link to show convective loops are always in an attic (with passive venting), cold------ ; or hot climate; http://www.fsec.ucf.edu/en/publicati...SEC-PF-226-91/

Now I'm trying to convert the heat flux (using same outside temps) through the attic insulation (R-20) compared to heat through a 2x4 (R-13) exterior wall-- pp.86: http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja But the wall outside temp is 5*F, with 10 W/m2 loss and the ceiling (R-20) with 32*F outside and 37 W/m2 loss, and 21*F out with 48 W/m2 loss; almost 5 times more loss and temps are warmer in attic (w. 4cm vents) than wall exterior..... anybody?

Send me a PM if you want, I'd love some help on this. Thanks, Gary

PS. the colder air (less dense) settles on the attic floor being warmed by the heat loss through the insulation to rise/exit the high vents; http://learn-science.20m.com/tmyths.htm#myth2

http://www.usatoday.com/tech/columni...derquest_x.htm
Huh? translate to laymen's terms please
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Old 03-02-2014, 07:18 PM   #24
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Is my attic insulation adequate?


It's all temperature differences; http://www.uwgb.edu/dutchs/EnvirGeol...EarthWorks.HTM

Warm air enters attic, colder air settles in your blown-in insulation. Convective currents formed by temp difference degrade any ceiling insulation without a cover on top or enclosed venting continuous to the ridge.

Which width for insulation rolls

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Old 03-08-2014, 07:16 PM   #25
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Is my attic insulation adequate?


With an infrared gun (Lowes has em cheap) I've seen the temp fluctuations (from air currents in my glass insulation) while aimed at the ceiling and the colder it is the wider the fluctuations.
I'm at min code here with blown R38 glass ...will upgrade to R60 I think and the link about the tyvek covering sounds like a great idea.
Great thread !
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Old 03-10-2014, 05:46 PM   #26
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Is my attic insulation adequate?


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Originally Posted by joecaption View Post
Not enough. http://www.energystar.gov/index.cfm?...sulation_table

Need to check to see if anyone air sealed before adding the insulation that's there.
Sealing up anyplace plumbing, wiring lighting was run into the attic with spray foam will be a big help.
If someone added can lights make sure there IC and air tight fixtures. If not your going to have to add some covers.
Can the OP use any type of spray foam?
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Old 03-11-2014, 01:10 PM   #27
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Is my attic insulation adequate?


Quote:
Originally Posted by High Gear View Post
With an infrared gun (Lowes has em cheap) I've seen the temp fluctuations (from air currents in my glass insulation) while aimed at the ceiling and the colder it is the wider the fluctuations.
I'm at min code here with blown R38 glass ...will upgrade to R60 I think and the link about the tyvek covering sounds like a great idea.
Great thread !
R38 is code.

There is a diminishing law of return on depths beyond that really but insulation is relatively cheap.

Tyvek does stop the wind washing but if you install cellulose, it is denser to begin with.

FYI...what you have is a Infrared Thermometer.

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