# Insulating under floor of FROG



## Windows on Wash (Aug 30, 2011)

Seal off the airflow. After that, the gap between the subfloor and the insulation can actually allow the floor to warm a bit.


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## Bud9051 (Nov 11, 2015)

Hi sports,
Living space (often bedrooms) over an unheated garage have long had "cold" issues.
A couple of questions.
1. Where are you?? Your climate region helps us determine how much insulation will be needed.
2. What is the current state of that ceiling, just insulation or also covered with drywall?
3. What size are those ceiling joists, 2x8, 2x10, 2x12?
4. What type of heat do you have, forced hot air, baseboard hot water, other?

If you have the depth one approach is to fill the lower 3/4 with insulation and leave a gap at the top. Although less total insulation that gap will fill with warm air from conduction through the floor. That warm air will then contribute to warmer floors.

The more common approach would be to fill those cavities completely. 

The less desirable and all too frequent approach is to install that r-19 all the way up against the floor above. This provides insufficient insulation ans subjects that insulation to air currents.

Bud
Windows is just faster than I am.


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## Sports75 (Dec 27, 2015)

Live in central Mississippi, ceiling of garage is dry walled, has 2x10 joists. It does have the r19 faced batts stapled to underside of floor, which of course will sag over time. I could blow insulation under the floor as I have pretty easy access to this part of the attic jus outside kneewalls. Just didn't know if that was necessary given I am going to seal the joists off. Will have a 9000btu mini split for heating/cooling


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## hyunelan2 (Aug 14, 2007)

If you over-pack insulation, it actually does less. You want to make sure there is an appropriate amount of insulation in there, not just keep stuffing it until it no longer fits. The airspace inside the insulation is what does the work. Compressing it solid won't help.


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## Bud9051 (Nov 11, 2015)

With kneewalls it sounds similar to the construction used in a cape, link:
http://www.finehomebuilding.com/2012/09/06/two-ways-to-insulate-attic-kneewalls

If filling those spaces would be easy that sounds fine to me. You certainly aren't going to remove the drywall. Once filled block each end to eliminate any air circulation into that space.

Bud


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## Gary in WA (Mar 11, 2009)

--------Welcome to the forums!----------------------------

Yes, fill it up, as least as much as the rental blowers will go... compacting FG makes it more dense, equals more, smaller air pockets to insulate better. Less dense equals fewer, bigger air pockets which are less effective at insulating, and full of inherent convective looping. 


The existing batts are probably held up against the floor with steel rods which solves 1/2 your problem of getting a good application, the hose should sneak right under to reach 1/2 way and fill as you pull out, seal ends as said, air-tight.

Using Jackson with a guess garage= 22 x 18= 396 sq.ft. times your design temp per that location, divided by R-19 (without air space or material R-values)= 937 Btu's to heat.

With just more insulation to fill cavity to R-30 = 594 Btu's a 58% improvement... not even figuring if you dense-pack it.... big improvement, not even figuring the cooling loads. 

R-19 and R-30 are both low density insulation; http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/ compressing it at 2.5# per cu.ft. from 0.55# will increase the r-value greatly, from a low density to a "high" density, compare in a 2x4 wall; http://www2.owenscorning.com/literature/pdfs/ProPinkAirInfiltrationSellSht.pdf Well, that is the wrong comparison link, but just do it! 

Gary


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## Gary in WA (Mar 11, 2009)

Further thoughts; if you compress existing R-19 to 3" at 2+ density, you increase it for total insulating value of R- 42, which also 'air seals" to use when figuring your "infiltration" factor heat loss and cooling gain for Btu's total. 

IF DIY on the insulation for walls, though it sounds like it is done? IMO, use some fibrous, then a housewrap to stop wind-washing. ADA the drywall and caulk the butt joints of meeting vertical wall/angled ceiling joint so more than just paper tape/drywall shim coats are air-sealing there to increase your infiltration figure because with new construction code insulation levels are fine for your location. The bigger number will be from "infiltration" compared to walls/ceiling that you can fix. 

I have a Fujitsu 12k mini, it cools way better than it heats. you'll like yours, esp. if you are DIY insulating/air sealing everything rather than builder. There is a lot of wood members in those attic room trusses for a lot of thermal bridging, add some rigid foam strips over all wall/ceiling framing before drywall to limit thermal loss, if DIY. Low-exp. foam around windows/door, caulk under wall drywall/subfloor, baseboard, etc.

Gary


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## Bud9051 (Nov 11, 2015)

Gary, you are entertaining but you're not making a lot of sense. I'm not going to spend half an hour chasing your links, but you are not going to turn an R-19 fiberglass batt (5.5") into a batt at R-42 by compressing it to 3". There is a curve that shows the R-value per inch increasing somewhat as you compress fiberglass insulation, but nothing in the range of R-14 per inch (42/3).

Bud


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## Gary in WA (Mar 11, 2009)

Sorry Bud, I thought "compressing" existing by adding the dense pack FG, readers could understand. R-19 (6.25") compressed by new blown-in FG to about 3" gives about R-10-11; http://www2.owenscorning.com/litera...ul Compressed R-Value Chart Tech Bulletin.pdf

2x10 joist (9.25") minus the 3" compression OF THE R-19 leaves 7" for two layers of 3.5" as the chart in last link before shows = R-16 plus R-16 plus R-10= R-42... pretty sure I did the math correctly. 

This would be even better for your heating Btu reduction to 424 Btu's, a 121% difference.

Gary


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## Gary in WA (Mar 11, 2009)

Reflecting on your answer in post #3 sounds like you have read (at least) one of these two links I've posted together on this forum a dozen or more times before; "If you have the depth one approach is to fill the lower 3/4 with insulation and leave a gap at the top. Although less total insulation that gap will fill with warm air from conduction through the floor. That warm air will then contribute to warmer floors." http://www.buildingscience.com/documents/insights/bsi-064-bobby-darin-thermal-performance which I use with this; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/ 

What, exactly, did you think was going to compress the R-19 by 2-1/2 pounds pressure with floor above and drywall below? Air pressure? If you added anything, you would count the R-value of that material wouldn't you? Maybe you skipped my post #7 entirely to see what I meant and HOW I got to R-42 using the Owens-Corning link for R-values. I leave links to back my answers and also be educational, but you have to read them to benefit from that... your questioning it as such doesn't make sense unless you didn't read all of it. I suppose I could have told you to read post #7 again, and look up the links, but I give credit to people expecting they read my links after major statements I make.

Sports75, last link here shows foil-faced FB under the joist, Fig. 7, over a garage, though that would require replacing drywall over it to meet possible fire code, check locally.

Gary


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