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Attic R value Insulation Questions
Last Post 20 Apr 2010 01:39 PM by Dana1. 43 Replies. |
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Eric Anderson
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Posts:441
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| 15 Apr 2010 09:16 AM |
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Blackflag,
I think what a lot of people are saying is that from an economic standpoint, adding geothermal is probably not as cost effective as reducing the demand for energy. The economics of this change if you have to replace the heating and AC systems anyway. Depending on where you live, and the quality of the installation, geothermal can range from a lot cheaper to marginally cheaper than other heating sources. On the other hand reducing demand is always going to lower your costs. Most houses in this country have a lot of easily correctable flaws from an energy consumption perspective. Priority #1 is usually air sealing. Next is likely adding insulation to accessible spaces like attics and accessible Knee walls.
One possibility I have seen done around here in retrofits is to blow cellulose to the top of the bottom cord of the trusses, then staple mesh to the top of the bottom cord of the trusses and blow cellulose on top of that. Now weight is not much of a factor and you can blow in quite a bit without worrying about drywall bowing or screw pops.
As far as as cellulose being blown into attics wet, usually on horizontal surfaces the cellulose is blown in dry(at least the big contractor around here). Wetspray for walls only.
In my own house the difference between cellulose blown to R38 and R 50 was ~ 250 dollars for 1150 ft^2 of roof area.
Eric |
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| Think Energy CT, LLC Comprehensive Home Performance Energy Auditing |
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Dana1
Senior Member
Posts:6991
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| 15 Apr 2010 11:47 AM |
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Posted By cmkavala on 14 Apr 2010 06:16 PM
Adding 12" (~R40+) to R20 of fiberglass, reduced that fiberglass from R20 to only R16 for a net- R56+ result instead of a potential theoretical max of R60+ it's not so adverse in my accounting. Adding R40 of fiberglass to it would also "crush" it, just not as much since it's ~ half the density call at R58. The true performance of the result has far more to do with the quality of the installation, how evenly is it installed, etc, that whether the original R20 was reduced by only 10% instead of 20%- it's still
I think your predicted percentages are skewed, with the human element is involved, installations are less than perfect.
Cellulose is heavier when first installed because it has moisture introduced to it and a mist is applied to keep it in place, so the initial weight is heavier than the dry weight , it is also hygroscopic. It’s able to soak and hold liquid water. Undetected leaks can wet cellulose causing it to sag within framing cavities. Water leaks can compress the blanket of fiber and in extreme cases, can create a void space, degrading its thermal value. Another concern is that chemicals used to protect cellulose from fire make it potentially corrosive in wet environments. Tests conducted by the Oak Ridge National Laboratory show chemical treatments used to treat cellulose can cause metal fasteners, plumbing pipes and electrical wires to corrode if left in contact with wet, treated cellulose insulation for extended periods of time.
The fact that R-value of cellulose is slightly better than fiberglass is perhaps a minor issue. Fiberglass batts and cellulose used in walls earn similar conductive ratings between R-3 and R-4 per inch depending on density. And while the low-density fiberglass insulation used in attics rates lower – there is typically very little space restriction in attics. So you can simply pile fiberglass deeper to achieve the R-value you need.
I state in the very clip that you're quoting that installations are less then perfect, that the true performance depends more on the quality of the installation type. The metals-compatibility issue is only related to sulfated fire retardents (banned in some countries, still allowed in the US), and can be avoided by specifiying borate-only material. Very few of the installers in my area use sulfated material anymore- even if they're only thinking of potential liability. (YMMV) Open blow in attics is rarely done with wet-spray mist (at least with the contractors I deal with), and dry-blown installed densities don't change appreciably with humidity until/unless there is a roof leak. Also ALL wet-blown material sold as wet-blow is sulfate free. Dry blown density does change with time due to settling issues, but that too is a human-factor related to the installer's abilities and is independent of fiber type. When wet spray cellulose IS used, the settling factor of the cellulose goes away due to it's water-activated adhesives, and it keeps it from being moved around by wind in the soffits, etc. Some of the better fiberglass blowing wools like JM Spider are also often wet-blown to take activate the adhesives & limit settling over time. Wet-spray cellulose starts out ~35% water, by weight, so a 1.6-2.0lb settled-density app might start out at 2-2.7lbs density if wet-sprayed. Dry blown, it'll rarely be more than 2lbs/ft^3 even for the crummy stuff. Spec on most dry blow is more like 1.6-1.8lbs these days. Fiberglass is quite elastic, and the tiny amount of loft lost due to a somewhat higher density wet-spray should return as the density drops with drying. The elasiticity of fiberglass is relied upon to save space in shipping- both loose-fill material & batts are shipped bundled tighter than the pressures of a foot of wet-spray cellulose overblow, yet they maintain their ASTM R-rating after shipment. If you can point me to independent test data that gives the actual compression/degradation of fiberglass due to a cellulose overblow, I'd be glad to replace my WAG percentage numbers with real data. But merely asserting that they're skewed doesn't reliably demonstrate even in which direction they might be off, eh? We may both have opinions/guesses- show me the data. (It's not tough to do your own bench test with a some weights on a square foot of thin plywood and a hunk o' R19 batt to get a ball park figure. I'd be stunned if it compressed it more than an inch, which would be a ~20% reduction in R- the high end of my WAG you find so skewed.) ASTM C 518 ratings are not the same as the relative performance over the actual temperature ranges encountered, which become relevant in attic applications, but are a far bigger issue in low density fiberglass in low-R applications than newer denser blowing wools and R-values >40. The IR translucency issue has not been beaten down fully, despite additives to the glass mixed in for that purpose, but again, above some R value it becomes a "who cares?" sort of thing, only relevant in lower-R applications than what we're talking. Sure, you can go much higher R with blown fiberglass in an attic without causing the ceiling to sag, but if we're only adding 6" the loading factor is less, and the R-stability issue more relevant. But bottom line, it's all good, and the notion that you can only blow cellulose over cellulose or only fiberglass over fiberglass and get a good results seems to be at odds with actual practice. If it's been a problem in the real world, again, data would be useful. |
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buck3647
New Member
Posts:85
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| 15 Apr 2010 12:18 PM |
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Closed / open cell foam save 30% immediately on your energy bill |
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cmkavala
Veteran Member
Posts:4327
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| 15 Apr 2010 12:18 PM |
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Dana1;
as you stated these are both our opinions neither one is backed with by any data, just pracical experience, You may have had good experiences with cellulose, Myyopinion is based on 40 years in the industry , I have not had good expriences using cellulose, especially when blown over fiberglass.
But, I no longer get involved with renovations, rehabs, block or wood frame construction , we stick with what we do best in metal based SIPs
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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Eric Anderson
Basic Member
Posts:441
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| 15 Apr 2010 02:34 PM |
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Buck
Saying the same thing over and over does not make it true. font size doesn't help the r value or air sealing either. Foam can be a great material and insulator. It is not always better, not does it automaticaly save you money. There is no perfect material nor magic bullet.
Peace,
Eric |
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| Think Energy CT, LLC Comprehensive Home Performance Energy Auditing |
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Dana1
Senior Member
Posts:6991
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| 15 Apr 2010 05:01 PM |
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Posted By eric anderson on 15 Apr 2010 02:34 PM
Buck
Saying the same thing over and over does not make it true. font size doesn't help the r value or air sealing either. Foam can be a great material and insulator. It is not always better, not does it automaticaly save you money. There is no perfect material nor magic bullet.
Peace,
Eric
Sure it does- repetition makes all overselling mis-statements true over time- just ask the folks with the nano-particle paint goo, or the reflective insulation guys! (You know, the guys who try to convince you putting radiant-barrier under a basement slab will reduce the heat loss there by 56%! It sort does if you have a foot of dry gravel under the slab, and your house is on fire so that it's 125F in the basement according to their modeling. An isothermal plane of 125F at the slab isn't a likely condition in your basement until the first floor is fully engulfed, eh? At lower delta-Ts the insulative value of the stuff is too low to have any practical value in that application, yet they persist... ) Unfortunately this is what we've come to expect from the insulation industry, and why the FTC requires ASTM test data to back up claims (not that it slowed down the marketing BS machines by a whole lot.) There's a wealth of disinformation & hype in the spray foam biz too- a lot of foam installers that tell you "(x) inches is all you need", and who insist on removing fiber insulation even where it doesn't interfere with their installation, etc. Sometimes it's just a poor understanding of the issue on the installer's part, but sometimes not. Insulating the roof deck with half-pound foam might be worthwhile here, but it's not the first, most cost-effective solution to a low-R problem that comes to mind. |
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blackflag
New Member
Posts:24
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| 15 Apr 2010 05:21 PM |
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just had an insulation guy out. it turns out i have about 7 inches of cellulose in attic. he recommened another 7 to get in the high r40's.
opinions? |
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blackflag
New Member
Posts:24
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| 15 Apr 2010 05:22 PM |
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and yeah that foam spam fails |
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Dana1
Senior Member
Posts:6991
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| 15 Apr 2010 06:15 PM |
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Posted By blackflag on 15 Apr 2010 05:21 PM
just had an insulation guy out. it turns out i have about 7 inches of cellulose in attic. he recommened another 7 to get in the high r40's.
opinions?
Sounds about right. The 7" sitting is ~ R25, doubling it to ~ R50 that would usually be cost effective in PA, for homes with high-efficiency heating systems (even more so for those with low efficiency systems.) Or you could just squirt a few inches of half-pound foam on the roof deck and "save 30% on the heating bill!"  If going to 14" covers the tops of the joists/truss-chords by at least a few inches and they're currently exposed or only have a couple inches of cover, the blow-over will cut the conducted heat loss by more than half, since it provides a thermal break over the framing timber (which only gives value on the order of R1 per inch of thickness, compared to the R3.5-3.7/inch for the cellulose.) I assume the insulation guys took a look before making the proposal but a total of 14" of cellulose gives you a static loading of a bit over 2lbs/square foot. What's underneath, holding it (plywood? OSB? 3/8" sheet rock on 24" centers?) Did the geo guys give you a room-by-room heat-loss calculation on which they're basing the system size, or (hopefully) are they waiting until you fix up all of the cheap & easy building envelope stuff before determing the size & firming up the quote? If you have a full season of heating-fuel, system type & size from prior heating seasons, with historical weather data from a station near you it's usually pretty straightforward to calculate a whole-house heat loss number as a reasonable starting point, and with the square footage of the attic you can calculate how much of a reduction in peak load this one change is likely to reap. Reducing the peak load 6000BTU/hr here, 8000BTU/hr there starts to add up, and peeling off even a ton of heat exchange/well-capacity would be a not-insignificant change in system cost. If they gave you a heat-loss calc it probably has the outdoor design temp it's calculated against too, which could be useful. (I suspect it is mid to high single digits F, but I'd have to look it up to be sure.) |
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blackflag
New Member
Posts:24
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| 15 Apr 2010 06:27 PM |
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thanks. insulation guy was up there for like 45mins - he was thorough. Didn't ask what was on floor but he said it could handle load with no issues.
Would you know fair price per sq/ft for 7 inches of blown in cellulose?
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On geo i got 3 quotes. 2 said 5 ton (rule of thumming it..). one said possibly 4 ton but no smaller. i didn't do a blower door test.
i was told that a *slightly* larger system will run mostly on 1 stage, which can work out to cost less than an undersized system running on both stages and/or backup as well.
I also feel more comfortable being slightly oversized in case of sever cold weather snaps - which can happen where I am. and paying a few grand more for a 5 ton to insure I don't have to hear my wife complain if it's too cold if system can't keep up is very valuable indeed!
I found out the largest cost in geo for me is drilling as i need vertical holes. i sourced the heat pump my self and was able to cut 3-4k off what some of the hvac guys wanted to charge me - so left me some room for the larger system to be safe.
And if i ever biuld an addition the larger system is good for that - that is why i am erring on larger system - even though there are people who say smaller is better. |
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cmkavala
Veteran Member
Posts:4327
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| 15 Apr 2010 06:58 PM |
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blackflag;
Oversizing the HVAC too large will cool down quick and fast, but it will not run long enough to get enough moisture out. Too much moisture will ultimately cuase mold and mildew to occur. It is the reason why many commercial buildings feel cols and clammy inside. They are required to design for max load (bodies) but rarely does that happen and consequently the humidity runs high and you can smell mildew, motels/hotels .....same problem.
I would rather have a slightly undersized system than a grossly oversized system. Just be very careful about oversizing I would not go more than 1/2 ton uless you are going to be adding on soon |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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insulateright
New Member
Posts:17
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| 15 Apr 2010 09:06 PM |
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Adding Blown cellulose over the existing attic insulation should work very well. Blown cellulose has an R value of R3.8 per inch. A total of 14 inches will give you a settled R value of approximately R50. Cellulose typically settles about 12% in the first year. A good installer will compensate for this. We base the R value on the settled R value which is always lower than the installed value. Make sure your rafter vents are not restricted, and also add styrofoam insulation to the top of the trap door. Add weather stripping around the the hatch or seal with silicone to stop air leakage (if you don't need to go in the attic very often).
A rule of thumb for this type of work is typically $1 a square foot or less depending on attic size, difficulties of moving around in the attic etc.
For the master bedroom, I would suggest having your cellulose installer add dense pack to the garage ceiling. If the garage ceiling is not drywalled then two or three inches of closed cell spray foam would be the best. This depends on the code requirements in your area. Closed cell spray foam is typically R6 per inch. This would also improve the air barrier between the house and garage. Dense pack cellulose could also help in the cathedral ceilings above the master bedroom.
It doesn't matter how good your furnace or geo thermal systems is if you have poor insulation. You will still need to produce lots of heat, most of which is lost to the outside without the insulation in place. Correcting the insulation deficiencies is a cost effective way of reducing heating costs. |
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Matt G
New Member
Posts:93
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| 16 Apr 2010 07:08 AM |
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All:
Regarding this discussion of adding dry blown in cellulose over fiberglass and possible adverse effects, I was recommended not to do this by an insulation contractor with possible moisture problems being the reason. I have an ongoing working relationship with this guy and trust him to a certain extent - limited by his experience - which is extensive in the insulation field. BTW - he sells/installs cellulose, fiberglass and open cell foam.
I'm not saying this is right or wrong - I'm just wondering... My thought was that if you put a cellulose air barrier on top of fiberglass could it be possible for air circulating within the fiberglass that is carrying moisture to be stopped at the cellulose and end up with a condensing "surface" between the stratified layers of fiberglass and cellulose? |
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Dana1
Senior Member
Posts:6991
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| 16 Apr 2010 10:31 AM |
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Posted By Matt G on 16 Apr 2010 07:08 AM
All:
Regarding this discussion of adding dry blown in cellulose over fiberglass and possible adverse effects, I was recommended not to do this by an insulation contractor with possible moisture problems being the reason. I have an ongoing working relationship with this guy and trust him to a certain extent - limited by his experience - which is extensive in the insulation field. BTW - he sells/installs cellulose, fiberglass and open cell foam.
I'm not saying this is right or wrong - I'm just wondering... My thought was that if you put a cellulose air barrier on top of fiberglass could it be possible for air circulating within the fiberglass that is carrying moisture to be stopped at the cellulose and end up with a condensing "surface" between the stratified layers of fiberglass and cellulose?
This is something to consider only if the ceiling leaks air and has no vapor retarder but even then it would be highly climate-dependent: The dew point of 68F, 30% RH conditioned-space air is in the high-30s F. If the average outdoor January temp is in the mid-20s (as it is in SW PA) the average condensing point within the insulation during the worst-case month within the insulation layer is where the temp is ~38F, which is ~1/4-1/3 of the way in from the top of the insulation. If the overblow is at least 30% of the total R, the amount of interior-air infiltration into the cellulose is limited. If the overblow is 50%+, it's EXTREMELY limited. But if it's less than 25% of the total there is some potential of seasonal moisture accumulating in the cellulose, particularly if the ceiling has lots of air leakage. Cellulose is a very good hygric-buffer- it's fibers are hollow, and it can tolerate over 15% water (by weight) without suffering thermal performance or long-term degradation. (There's good data on this.) It wicks any condensation that does occur, distributing it evenly through the material over time. As either side finds drying conditions, moisture will move from wetter-to-drier layers. But air-sealing at the ceiling plane would still required to be sure you don't end up with localized issues. Also, interior side vapor retarders are always a good idea under any fiberglass layer in 5000+ heating degree-day climates. The practice of capping fiberglass with 3" of cellulose to eliminate R-value loss in the fiberglass may not be the best long-term convective air-barrier if it's still air-leaky at the ceiling, or without warm-side vapor retarders in colder climates. (Vapor retardent paint at the ceiling + air-sealing would be sufficient mitigation for most of the lower-48). SW PA has a ~ 6000HDD climate, and interior-side vapor retarders (or vapor retardent paint) should be standard practice in new construction. It needn't be a Class-I vapor retarder such as polyethylene sheet (at 0.05perms). Kraft facers are fine (~0.4 perms), as is vapor retardent latex (~0.5 perms). If any of those are applied and the ceiling is reasonably tight there shouldn't be any moisture issues related to condensation in the cellulose. |
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ksagan
New Member
Posts:3
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| 16 Apr 2010 11:36 AM |
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Hello, I understand what you are attempting to do, but there is not enough information to make a "Valued Decision". I strongly reccommend that you hire an energy rater to do a blower door test before you do anything. A good one in your area is Comfort Homes in Lancaster Pa.( I live in State College, so I have no association with this firm). They will advise you of the priority you should make in tightening your home and any potential problems that may arise in tightening the home. I myself have problems with homeowners tightening up a home and not checking to see if there is enough "combustion air" for appliance ( water heaters stoves and furnaces) and fireplaces. What you are attempting to do is tightening the house that may need to be intentionally leaky. Have you thought about the stale air inside the home and what you will do about it? Then there is the issue of humidity. Not just from the bathrooms where you probably have exhaust fans , but the occupants that raise humidity. How about VOC's. If you continue to try and DIY, then I reccommend that you read ASHRAE 62.2 Indoor Air Quality for Residential Homes. (I sit as a voting member on this committe) and make your decisions after you have reviewed this document. It makes a lot of sense, especially if you have children.
Yes , insulation is the low-hanging fruit. But it may not be ripe fruit. Caulking and sealing may be cheaper and reap better results. One must look at the whole-house as a system and not just a few entities. Remember, the home is only as good as it's weakest link.
Energy Raters have all this information and know what to expect. If I do this, I get this or If I do this, then I need to do this also.
In summary, You may be able to say a few bucks by adding insulation, but you may also cost you more elsewhere. Get someone that is an expert in these things before you go and spend good money! |
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cmkavala
Veteran Member
Posts:4327
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| 16 Apr 2010 12:26 PM |
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Posted By Dana1 on 16 Apr 2010 10:31 AM
Posted By Matt G on 16 Apr 2010 07:08 AM
All:
Regarding this discussion of adding dry blown in cellulose over fiberglass and possible adverse effects, I was recommended not to do this by an insulation contractor with possible moisture problems being the reason. I have an ongoing working relationship with this guy and trust him to a certain extent - limited by his experience - which is extensive in the insulation field. BTW - he sells/installs cellulose, fiberglass and open cell foam.
I'm not saying this is right or wrong - I'm just wondering... My thought was that if you put a cellulose air barrier on top of fiberglass could it be possible for air circulating within the fiberglass that is carrying moisture to be stopped at the cellulose and end up with a condensing "surface" between the stratified layers of fiberglass and cellulose?
This is something to consider only if the ceiling leaks air and has no vapor retarder but even then it would be highly climate-dependent:
The dew point of 68F, 30% RH conditioned-space air is in the high-30s F. If the average outdoor January temp is in the mid-20s (as it is in SW PA) the average condensing point within the insulation during the worst-case month within the insulation layer is where the temp is ~38F, which is ~1/4-1/3 of the way in from the top of the insulation. If the overblow is at least 30% of the total R, the amount of interior-air infiltration into the cellulose is limited. If the overblow is 50%+, it's EXTREMELY limited. But if it's less than 25% of the total there is some potential of seasonal moisture accumulating in the cellulose, particularly if the ceiling has lots of air leakage.
Cellulose is a very good hygric-buffer- it's fibers are hollow, and it can tolerate over 15% water (by weight) without suffering thermal performance or long-term degradation. (There's good data on this.) It wicks any condensation that does occur, distributing it evenly through the material over time. As either side finds drying conditions, moisture will move from wetter-to-drier layers. But air-sealing at the ceiling plane would still required to be sure you don't end up with localized issues. Also, interior side vapor retarders are always a good idea under any fiberglass layer in 5000+ heating degree-day climates. The practice of capping fiberglass with 3" of cellulose to eliminate R-value loss in the fiberglass may not be the best long-term convective air-barrier if it's still air-leaky at the ceiling, or without warm-side vapor retarders in colder climates. (Vapor retardent paint at the ceiling + air-sealing would be sufficient mitigation for most of the lower-48).
SW PA has a ~ 6000HDD climate, and interior-side vapor retarders (or vapor retardent paint) should be standard practice in new construction. It needn't be a Class-I vapor retarder such as polyethylene sheet (at 0.05perms). Kraft facers are fine (~0.4 perms), as is vapor retardent latex (~0.5 perms). If any of those are applied and the ceiling is reasonably tight there shouldn't be any moisture issues related to condensation in the cellulose.
all ceilings leak air |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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cmkavala
Veteran Member
Posts:4327
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| 16 Apr 2010 12:32 PM |
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ksagan;
good point, many power companies will do a free energy audit with blower door test and make recommendations free of charge. They may also assist in paying for sealing of ductwork, adding insulation and upgrading HVAC equipment
I took advantage of such a program myself about 20 years ago, I could not do the work myself for what I paid to have mastic put on ductwork and an additional 6" fiberglass blown in over top of existing |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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Dana1
Senior Member
Posts:6991
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| 16 Apr 2010 01:21 PM |
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Posted By ksagan on 16 Apr 2010 11:36 AM
Hello, I understand what you are attempting to do, but there is not enough information to make a "Valued Decision". I strongly reccommend that you hire an energy rater to do a blower door test before you do anything. A good one in your area is Comfort Homes in Lancaster Pa.( I live in State College, so I have no association with this firm). They will advise you of the priority you should make in tightening your home and any potential problems that may arise in tightening the home. I myself have problems with homeowners tightening up a home and not checking to see if there is enough "combustion air" for appliance ( water heaters stoves and furnaces) and fireplaces. What you are attempting to do is tightening the house that may need to be intentionally leaky. Have you thought about the stale air inside the home and what you will do about it? Then there is the issue of humidity. Not just from the bathrooms where you probably have exhaust fans , but the occupants that raise humidity. How about VOC's. If you continue to try and DIY, then I reccommend that you read ASHRAE 62.2 Indoor Air Quality for Residential Homes. (I sit as a voting member on this committe) and make your decisions after you have reviewed this document. It makes a lot of sense, especially if you have children.
Yes , insulation is the low-hanging fruit. But it may not be ripe fruit. Caulking and sealing may be cheaper and reap better results. One must look at the whole-house as a system and not just a few entities. Remember, the home is only as good as it's weakest link.
Energy Raters have all this information and know what to expect. If I do this, I get this or If I do this, then I need to do this also.
In summary, You may be able to say a few bucks by adding insulation, but you may also cost you more elsewhere. Get someone that is an expert in these things before you go and spend good money!
If you read the thread entirely, you'll discover that there already is an HRV system installed in this house. Over-tightening it would not be much of an issue. |
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Dana1
Senior Member
Posts:6991
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| 16 Apr 2010 01:35 PM |
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Chris: Sure all ceiling leak air, but it's a matter of the volume of air leagage at any particular leak location that would make it a problem or not. I can imagine an insulation contractor in some climate zones wanting to avoid the air-sealing issue entirely. In other climate zones it's a complete non-issue. Condensation with cellulose is only problem if there's sufficient air volume moving through there to saturate it. The volume of air infiltration might be high in a 3" overblow, but dramatically less in a 6" overblow, and much attenuated in 12".
If air sealing at the ceiling is too complicated/expensive, that's a time to consider foam-insulating at the roof and foam-sealing the vents rather than blowing over insulation. The convective forces between a roof-insulated sealed attic and conditioned space are very low compared to a basement to ridge-vent stack-effect, minimizing the air flow into the (now warmer) attic space. But humidity would have to be monitored in the attic during the first season of cold weather to assess the condensation risk in the attic (again, a function of the local climate averages, indoor humidity levels, and R ratio between roof deck and attic floor.) |
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Matt G
New Member
Posts:93
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| 17 Apr 2010 09:27 AM |
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Posted By cmkavala on 16 Apr 2010 12:26 PM
Posted By Dana1 on 16 Apr 2010 10:31 AM
Posted By Matt G on 16 Apr 2010 07:08 AM
All:
Regarding this discussion of adding dry blown in cellulose over fiberglass and possible adverse effects, I was recommended not to do this by an insulation contractor with possible moisture problems being the reason. I have an ongoing working relationship with this guy and trust him to a certain extent - limited by his experience - which is extensive in the insulation field. BTW - he sells/installs cellulose, fiberglass and open cell foam.
I'm not saying this is right or wrong - I'm just wondering... My thought was that if you put a cellulose air barrier on top of fiberglass could it be possible for air circulating within the fiberglass that is carrying moisture to be stopped at the cellulose and end up with a condensing "surface" between the stratified layers of fiberglass and cellulose?
This is something to consider only if the ceiling leaks air and has no vapor retarder but even then it would be highly climate-dependent:
.
.
.
Thanks for your thoughts. Again, I don't know if moisture could be an issue. I'm just discussing. With that said, I'll say: We don't use ceiling vapor barriers in our area - Raleigh NC. And BTW - wall vapor barriers are quickly going out of vogue as well. Regarding ceiling air sealing - it is a matter of what is practical. Sure it is fairly easy to seal well around ceiling penetrations like electrical, plumbing, etc, but when you start looking at sealing above the partition walls - particularly in a retro-fit situation, to get these long slits of air leakage sealed is very difficult, impossible where the partition passes under the many ceiling joists. So yes. there is always going to be some ceiling air leakage with fiberglass loose fill insulation. |
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