Attic Vapor Barrier & Insulation
Attic Vapor Barrier for Insulation in Cold Climates?
Insulation details change about as often as the weather here in New England. One question that seems to come up is whether or not to use a vapor barrier with attic insulation in cold climates? The answer to this question seems to have changed in recent years and may surprise you.
For this article, I’m strictly focusing on vented attics in a cold climate. The details will be different for un-vented attics and/or warm climates.
Air & Water Vapor Movement
The key to this discussion is understanding the movement of air and water vapor. In a perfect world none of the conditioned air (from the house) would enter the attic and none of the unconditioned air (from the attic) would enter the house. In addition, ideally all water vapor would be managed with mechanical systems. Unfortunately we do not live in a perfect world and building construction is FAR from ideal.
Water vapor wants to move from warmer to colder air. That means in the winter time water vapor inside the home wants to move to the colder attic space. In the summer the warm humid air will want to move to the interior of a cooler home.
Ideally ceilings in homes would be perfectly sealed with drywall and good quality latex which would drastically reduce the movement of air and water vapor. However, in reality most ceilings today look like swiss cheese. Ceilings are riddled with holes from lights, mechanical vents and access hatches. Each one of those “penetrations” typically allows a significant amount of air and water vapor to move back and forth from the conditioned to unconditioned spaces.
Attic Vapor Barrier Detail for Cold Climates
Even though we apply vapor barriers to exterior insulated walls in cold climates it’s no longer recommended for ceilings (floor of the attic). Because it’s nearly impossible to seal penetrations in the ceiling, the reality is water vapor will get into the attic. Due to this inevitable fact it’s actually better to omit a vapor barrier between the insulation and drywall of the ceiling below the attic.
The best approach for a vented attic, in a cold climate, is installing a layer of drywall with a good coat of latex paint (the paint creates a semi-permeable vapor barrier). The insulation (fiberglass or cellulose) is then placed on top of the drywall with no vapor barrier above or below.
The latex paint allows the ceiling to breath a bit but still help prevent significant movement of air and water vapor. This really helps prevent trapped moisture between a traditional vapor barrier and the drywall.
Should A Vapor Barrier be Used Over Attic Insulation? The answer is no. Either install un-faced fiberglass, loose fill fiberglass or cellulose directly on top of the drywall.
In my attic I currently have USG Thermafiber insulation in the 5.75- 6.75″ between joists with 9″ unfaced fiberglass batts on top. Below the joists is 1×5 16″ center to center supporting lathe and plaster for ceiling below I am trying to create some walkways and storage space by placing boards on top of the joists. What is the best way to get r value in the space between the joists. I believe in most places drywall has covered the original plaster ceilings.
Joe – First off, be careful you don’t overload that attic. Many attics are not designed to handle anything more than occasional access, and certainly not storage. Having said that, many people do create storage space. When we create a space like that, we typically build a frame to get the floor up high enough to allows the proper depth insulation. Good luck.
Hi Todd- My hubby and I own a small (15x 30) cottage in southern Vermont. We are using the attic for storage with easy access via pull-down stairs. We wanted the attic to be somewhat part of our living space i.e. there’s some carpets on the floor of the attic with no insulation between the attic floor and main floor. (It’s about 50 degrees in the winter.) As part of an energy audit program last year a contractor told us to install 8″ thick fiberglass paper-faced insulation between the rafters to keep any heat that came through the attic floor from escaping through the roof and to also install 6 ml plastic over all the insulation. There’s no soffit (not open anyway) and no ridge vent. There are 2 normal openable windows.
Big Problem is: with warmer weather and the sun beating down on the roof , there’s a lot of condensation forming on the inside of the plastic and dripping down from light sockets. As a stop-gap measure we’ve been using a dehumidifier to keep the water and mold at bay but we want to fix the problem itself. What do you think?
Linda – Can you be more specific about where the insulation is, where the paper facing is, and where the poly is? Sounds like a double vapor barrier problem.
Thanks for your time on this problem, Todd. The insulation is between the roof rafters with the paper facing inward. The plastic is stapled to the rafters, covering all the insulation. The few places that we didn’t seal well with the plastic actually drip with condensation on sunny days. (Like around light fixtures at the peak.) We’re also not sure when and if we should open the windows.
Thanks so much! Linda
Linda – Not sure where to start with this so I’m going to toss out some thoughts.
– First off, here in this part of the Country, 8″ of insulation is NEVER enough for an insulated rafter application. Doesn’t even begin to meet code. Attics today are typically insulated with R30 to R49 at a minimum. You’ve got probably about R25, well short of the required insulation value.
– Secondly, I’m not sure why he installed plastic on top of the paper. This is trapping moisture that’s caught between the plastic and roof surface.
– It’s odd that moisture is trapped in that space, it makes me think that either the roof has some leaking, the plastic isn’t sealed well and moisture from below is getting behind the plastic and trapped, or there was moisture in that space prior to the installation that got trapped.
A dehumidifier won’t fix this problem. I’d inspect the roof, remove the plastic, and be sure to install the appropriate amount of insulation. Furthermore, batt fiberglass against a roof without ventilation is BAD!!! Each bay should have a vent, tied to soffit and ridge venting.
Good luck.
Thanks, Todd! Your comments make a lot of sense and line up with what a local roofing guy told us this week. We will be making some changes (for the better!) for sure. The dehumidifier has worked quite well as a stop-gap, symptom – not problem- fixer. It will be good to fix the problem. Thanks for your excellent input!
Stay cool–Linda
I have faced fiberglass insulation batts in my attic. While the R value was to code when the house was built, I’d like to increase the R value in order to maximize the efficiency of a geothermal climate control system we recently had installed.
My thought was to temporarily pull up the fiberglass batts in between the ceiling joists, install 2 inch blue board in the joist cavities, then place the existing fiberglass batts back on top of the blue board.
Will this cause issues down the road?
Larry – I would leave the fiberglass, and blow in additional cellulose over that. You can rent a blower and do it yourself for cheap money. We still use a ton of cellulose in attics and it works quite well. good luck.
I’ve bought a 40 year old semi-detached and noted that at in winter, 3 rooms form condensation at the end of the ceiling and drops of water.
An expert company advised replacing our vents with a Max Vent, add baffles, remove all insulation and put a spray foam vapour barrier and blow cellulose insulation. This was too much to remove all existing insulation.
Another company came, insulated my dry walls (I think retrofit), ie spray foam insulation between drywall and bricks, put the MAX Vent, 21 baffles and blow cellulose insulation. They advise not to put the vapour barrier which will be costly to remove all existing insulations, etc.
Last winter, it was better but the condensation continues in the 3 rooms.
Is the vapour barrier the only solution? Is there an alternative type of vapour barrier where we can shift the existing insulation part by part and put the vapour barrier? Please advise the most economical way.
Thanks
I think you’re miss-understanding the issue. From what I can tell, you’ve got two problems.
1. You have too much humidity in the house. You need to deal with lowering the relative humidity. Showers, baths, cooking, washing clothes and dishes all generate high humidity. You need better ventilation.
2. It’s likely the insulation value is not high enough at the “pinch” point where the walls meet the roof, this results in the ceiling being cold, so when the damp warmer air hits it, it condensates. So….you likely need to increase the R value, if there is not enough space for cellulose to get a proper R value, then you need spray foam.
Hello, I just wanted to understand your words (in quotes further below) —
The drywall is installed on the attic floor itself? And, below that drywall, would be open space/wiring/light outlets, ect…
The drywall is painted, and then insulation is put on top of it. Is this correct?
And, it would not add to much weight to attic (size is 550 sq. feet); Victorian Home… Much Thanks! M
(RE: Attic Vapor Barrier Detail for Cold Climates) —
“The best approach for a vented attic, in a cold climate, is installing a layer of drywall with a good coat of latex paint (the paint creates a semi-permeable vapor barrier). The insulation (fiberglass or cellulose) is then placed on top of the drywall with no vapor barrier above or below..
You misunderstood.
The approach is basically ceiling joists with drywall below (living side). The drywall is painted with a good latex paint. There is NO vapor barrier other than paint. Insulation is installed above that.
your description was confusing. it also sounded to me, like you were saying install drywall on the floor of the attic/ painted one side.
Mack – It’s pretty straight forward…the drywall is attached to the house side of the attic floor joists or the bottom of the ceiling joists, typical location.
Hi, I live in Montana and our climate is pretty arid. We bought a 1960’s house with batt insulation which is faced. The contractor used two layers of insulation one is R13 the other is R11 which gives us R24 (no where near what is recommended for our area). First, I noticed that both layers of batting are faced (the facing is towards the drywall) and I am curious if it is a problem that the second layer of batting is face and am curious if it should be removed? I am also wondering if it is okay to blow cellulose over those layers of insulation to bring the R value above 50, or if it would be better to remove all of the batting and then blow in cellulose. If I do remove the old batting and blow in cellulose it it necessary to paint the drywall first as it is very dusty and dirty up there and I have doubts about how well the paint would stick. P.S. I am planning on air sealing the attic first.
Bill – It’s not ideal, but I don’t think it’s a huge deal, if it was a wall I’d be more concerned. I’ve seen cellulose blown over it with success.
Hi Bill,
Was is the best material to be used when creating a vapor barrier in the attic? I’m installing new bathroom ventilation fans and want to make sure they are air tight, especially under the duct exhaust of the fan. I didn’t want to compress the fiberglass, and was thinking of putting blown insulation around the fan box, then put unfaced fiberglass on top. Should I use the backing that comes on the “faced” insulation and tuck under or is there something else that would do a better job, like the “Frost King” Self-stick vinyl foam with aluminum foil backing?
Hi Todd,
We have a commercial building with a flat roof and a vented attic with cellulose insulation. We just added 4″ of polyiso to the roof deck since we put on a new TPO roof. I am looking to close off the attic vents and turn it into a sealed space. Currently the floor below the attic is un-occupied, but when we renovate we will put up drywall and paint on the ceiling. Do I need a moisture barrier on the ceiling or attic? Is it OK to close off the vents now, or should I wait until we also seal up the ceiling so as not to trap moisture in the unvented attic?
Thanks for your advice
I would wait until you’ve got that sealed from below.
HI Bill
I’m from new york, and I have a condensation issue in my attic. I had an energy audit and they said I was also losing a lot of heat through my attic because I only have r19 batt insulation between 2×6 joists. They recommended raising my attic floor and putting cellulose blow in insulation and capping it off with 2 inch xps foam board. So my question is will that cause problems covering the insulation with the foam board. Will the inulation get moldy from moisture or will the foam board prevent the water from condensing on the bottom side?
I would NOT install that foam board. I’d just install the proper depth of blown in insulation.
I live in Bismarck, nd. Cold winters. Hot summers, rarely humid. Finishing upstairs remodel with spray foam on walls and either blown in fiberglass or cellulose in attic. So your saying no vapor barrier at all, not even a thin poly or product like certainteed membrain? Thanks.
Hi, Todd. Thanks for your time and help. The attic now with went and attic floor insulation. We are planing to finished the attic and insulate the roof. The roof is gable.There are no soffit or ridge wents. Rafters are 2×6 ( 16inches between). What is best way to insulate the attic to make it livable and avoid mold problem. We think to use polyiso RMax boards since they have high R.
Really depends on where you live. 2×6 isn’t very deep. You need to know minimum R value suggested where you live, then come up with a plan
Hi Bill,
I have a house that was built back in the 60’s and the entire attic floor is covered with plywood. I want to add Radialnt barrier to the underside of the Roof rafters and also add Foam board to the bottom side of the roof rafter. If I do this should the radiant barrier go up first then the foam board or vice versa? Is this a good way to help insulate the attic space or should I leave it alone?
Thank You for any recomendations you can give me.
I’d install the radiant barrier first, then the foam. Good luck.
Professional spray foam is the most expensive and effective way to insulate your attic, but could a homeowner do it himself with a specific type of Great Stuff spray-can foam that I spray directly over the drywall and wood beams that make-up of the attic floor underneath the existing pink rolls of insulation?
I live near Chicago in zone 5 and our bath fans exit out to the attic and not through the roof unfortunately. So we stopped with turning those fans on. We turned off our whole-house humidifier that runs with the furnace now as well because we found a lot of ice build-up on the north wall eves and roof nails and some thin frost on the south walls. We don’t have gable vents, just the 5 or 6 round metal flat air vents. It’s too much money and work to make bath fan pipe to the roof so I want to seal the vent stack opening and conduit openings at least to seal the attic floor as much as possible and Great Stuff spray foam might be an easier option than caulking and painting the attic floor. What do you think of that idea?
There’s really no DIY product on the market, and that’s for a good reason. These materials can be dangerous. The costs are dropping every day, and we seldom insulate projects now without foam as it’s so much more cost effective, and the pay back is so fast.
We recently purchased a farmhouse in Vt built in 1865. It has slanted ceiling in the bedrooms with a 30″ knee wall. We are getting condensation where the ceiling meets the knee wall. This is only in the winter. No soffit vents but there are gable vents in the tiny attic space. We are thinking of using blown in insulation but we were told that without vents the moisture would be trapped between the roof and inside wall which would eventually lead to rot, mold etc. We had a guy come out that does spray foam insulation and he said the spray foam would ‘help’. I want it to be 100% fixed. If spray foam won’t fix it I don’t want to waste the money doing it. Tonight I was told to use a blown in insulation that is like a vapor barrier. I have never heard of this. The bedrooms were updated in the 90s and do have drywall instead of plaster. There is no heat upstairs though. Home repairs add up quickly, especially in an old house. Any information would be appreciated so we aren’t throwing our money away.
Without seeing the details it’s hard to give you much advice. But…with no venting I’d likely tear out the drywall, use closed cell foam (do not get talked into open cell), and be done with it.
Hi there i have a house i bought 4 years ago, and it has a finished attic, in that it is fitted with tongue and groove ceder planking throughout. the house was built in 1948 and i suspect this is the original flooring up there. My question is what would be the best way to re-insulate this attic as i believe it needs doing, but the thought of having to pull up all the planking seems excessive. what would you suggest? my house is about 25m x 20m so thats a large enough floor area up there.
thanks
Typically holes are drilled in the planking so insulation can be blown in.
Hi, Todd. I live in southern NJ and we have a 40 yr old two story dutch colonial(gambrel style roof). We are having a problem with moisture and mold forming on the ceiling of the attic and gable walls in the attic. There were no soffit vents, but there is a ridge vent. There is also an old roof vent(no fan)and 3(yes, three) gable end vents..two on one end, one on the other with a big thermostat controlled vent fan. Insulation is in between the floor of the attic, paper faced fiberglass with what looks to be around r-19-paper is on the bottom against the drywall from the second story ceiling below. Also noticed the insulation is pushed up too close to where the joists meet the roof rafters.
We are having a remediation company remove the mold and the insulation. I just installed vented soffit on the eaves at the bottom of the gambrel roof. What is the best way to go about reinsulating the attic and should I remove all of the other vents except the ridge vent?
Any suggestions you could offer would be greatly appreciated.
Hey Todd, my name is Robyn. I live in Georgia so loss of cold air in the summer is my main issue. I just bought a 1930s brick bungalow and the seller ripped out the old plaster ceilings to reveal beautiful original heart pine boards. She left the boards uncovered to function as the ceiling for aesthetics. I love them like that and don’t want to change them, but I’m worried about loss of cool air into the attic as the boards have small gaps in some places where you can literally see through to the attic. The seller thought she fixed this issue by using roll out insulation in the attic with the paper backing placed down against the boards. I’m not sure I feel like this is good enough, especially since I’m unsure if this is a safety hazard for me breathing in any fumes that may come off the insulation…(?) I can’t seem to find any information on this as it seems like an uncommon issue. Your advice would be greatly appreciated.
Hello I have no insulation in my attic. If I want to put blown in fiberglass do I need anything between the drywall and the insulation?
nope
Hi Todd. I just moved into an old brick house (1912) in Duluth, MN (very cold winters) and the attic is insulated with fiberglass between the roof trusses, held in place with a thin layer of styrofoam (1/2″?). Makes sense to me to insulate the floor instead, as the space will not be used for storage or anything else, so I’m planning on placing foam between the floor joists and covering that with lots of cellulose. I’m planning on removing the fiberglass from the ceiling, so my question is…do I need to install vents in the ceiling/roof once I’ve removed the insulation? I’ve heard mixed reviews on vents in the attic ceiling. Any input would be appreciated. Thanks!
You always need ventilation regardless
Hello,
Just curious…is it recommended to have vents in the attic ceiling (ie. roof)? I have foam covered in cellulose between the joists, and the previous homeowner, for some reason, sealed off the vents in the ceiling. I’m assuming I need to open those back up again? Thanks for you advice.
Well it really depends on the details. If the roof rafters are spray foamed, maybe not, if your insulation is at the ceiling joists then you need venting. Every roof is different.
We are having the current insulation removed and it will need to be replaced. There currently is no vapor barrier (central Ohio) – if we go with blown-in cellulose would you suggest one? Having to repair n=vents from upstairs bathroom as they previously weren’t vented properly and caused moisture in the attic. Blown-in at R-49 will end up being almost $1200 cheaper than kraft-faced batt insulation at R-49. I have read to install a vapor barrier previously and now you say don’t…which would you do & why?
An attic doesn’t require a vapor barrier….the vapor retarder is the painted ceilings below.
I just want to say how much I appreciate articles like this, especially in my area where it is a violation of code not to use a vapor barrier and, when people follow such advice and don’t, it creates a nice business opportunity when they discover the mold growing near the ceiling penetrations at the drywall/insulation interface. They always seem shocked–shocked!–that not following code had a consequence.
Hi Todd,
I live in northern NJ in a new construction with a flat roof and metal access hatch to the roof. The first winter I was here I noticed condensation would form on the inside of the metal hatch when the temp dropped below 40. I had the builder come back and insulate the exterior of the hatch with two layers of roofing material and a 1/2 inch thick insulation board in between those layers. They also installed a sheet of that board on the interior ceiling of the hatch and even put a piece of painted plywood to hide the hatch at the base of the opening in the ceiling to further keep the hot inside from the cold outside. While all this definitely helped, when the temp drops below 30 some condensation still accumulates on the interior metal walls that are still exposed. It would be difficult to insulate the interior with insulation boards all the way around because it would interfere with the opening and closing arms. Should I stuff some fiberglass insulation on the topside of the plywood board to help keep the cold on the outside of the plywood, or will it just trap the moisture further. Any recommendations? Thanks.
Jake – Part of the problem may be the humidity levels in the house. Have you checked to see how high they are? Are you doing anything to control moisture in the home? New construction is so air tight that this can be a real problem.
Thanks Todd. No, I have not checked the humidity levels. In fact, generally in the winter months when this hatch condensates, the forced air heating system makes the air quite dry, and I was thinking of getting an air humidifier just for comfort. Part of the problem is that the hatch is at the absolute highest part of the ceiling and the warm air naturally rises to this point. Perhaps I can replace the wooden board with a different insulation board that has a high R value to keep the hot air from rising beyond that point.
If you have condensation…you have a high humidity level. It’s part of the equation…i’d test it just to see!
Okay, what is an example of a high level and what can I do about it. Thanks!
Upstate New York here. I have tongue and groove planking above six inch joists in the attic. No insulation underneath. I’m sure I’m losing heat in the winter, but what’s really noticeable is in the summer when the temperature in the attic can exceed 130ºF and I have to blast air conditioners constantly in every room below.
Thank you for this advice on vapor barriers, because I could not find good advice elsewhere as to whether it should be on top (as in a warm humid climate, like our summers) or bottom (as in a cold climate, like our winters). Not using one at all solves that dilemma!
Most advice I’ve seen also says to completely rip out the planking and just blow insulation between the joists. You mentioned in a comment that holes could be drilled to blow the insulation under and I would prefer to keep the planking as it makes the attic more accessible for the occasions that I need to get up there. So, I guess two questions: 1- would 6 inches blown in have enough of an effect in this climate, or should I consider going above the joists? And 2- assuming 6 inches would be enough, is there any drawback to blowing under the planking versus removing it entirely?
6″ isn’t very much insulation, so it won’t make that big of a difference unfortunately. Yes holes will work, but again it’s not a very large r value.
Hello Todd,
We have painted the ceilings under our attic 9 years ago with latex and we may still need to do some vapor barrier sealing. Now we have quite a cold drafty attic and would love to know if VISQUEEN (sp?) or other plastic barrier would help on top of a thorough surgical approach of “many a can of” great stuff foam leaky trouble spot sprays for the entire attic floor. Could one also apply a (primer first) but latex after painting of the attic floor rafter bays right up to the baffling if Visqueen/plastic is not appropriate before blowing in cellulose? The attic was formerly very hot in the Summer as a former homeowner converted a former Jalousied porch into a vaulted ceiling living room at one end of the circa 1958 Ranch (Woodbridge CT). However that vaulted ceiling completely blocked off one former of two large gable vents at both ends of the house. Now after adding an attic fan due to the former stifling heat in the attic we now have a proper ridge vent (after replacing the asphalt roof) and will check the soffits for non best practices type blockages. Now the house more than ever seems to lose very much heat through the attic floor. Please advise on our vapor barrier strategies. Thanks for your consideration.
Hi Bill,
I live in Toronto, and winters get pretty cold and summers fairly hot. We’re currently using our attic for storage. The underside of the roof is not air tight. air gets in and there is a ridge at the peak of the roof.
I’d like to insulate the space to try and maintain and reduce temperature fluctuations. I’ve completed half the space, where I’ve put insulation batts right up against the underside of the roof and a vapor barrier overtop. Floor previously had insulation, so I’ve left it in place and added plywood on top to cover the space.
One issue is that the one area over the drop down stairs has started condensation. All other areas seem fine. Looking for some advice as to how to overcome this? Not sure if fully finishing/ putting up either drywall or a thin wood piece to cover ceiling would help reduce moisture build up or just hide it.
Also, I had put some rafter vents in some locations but was advised they would not matter as air seems to flow throughout the roof (instead of the typical from soffit to peak). As I’m not bushing the rest, wondering if this is something I should add to each section? If so, should I return to the old areas and add back in?
Thanks in advance and hoping you’re still responding to this old thread.
Hi Todd,
I have a 60 year old ranch. The attic has cellulose insulation that is smashed down and held down by a radiant barrier. I am planning on having a company come in and remove the old insulation and air seal the attic. I did read where you said no vapor barrier, I had a mold remediation guy tell me to put down batt insulation with the vapor barrier (I think he said facing down). The only ventilation in the attic is 3 gable end vents. My insulation guy quoted me blown in insulation but I think I would rather have batts rolled out. Fiberglass or Rock Wool? What do you recommend? We are in southern Ohio. I believe we need R49
Another Upstate New Yorker, in an 1832 story-and-a half house with an 1849 addition. The original part of the house had some batt insulation in the small attic space, but with wide gaps. Our contractor blew in additional insulation to seal between the batts, and there is a ridge vent, but no gable vents. In the sloped part of the ceiling, we put backed insulation, but, because it’s a timberframe, there was no real way to vent that space, and now I’m worried … The other bedroom, with a similar sloped ceiling, is currently mostly uninsulated, although we blew in some insulation where there’s attic. We caulked the baseboards to seal drafts.
The biggest issue is the addition. Because the plaster was bad and the wiring had to be redone, we gutted the room, used foam to seal between the sheathing boards and {after much research} put unlined fiberglass behind painted drywall. The ceiling is tongue-and-groove pine above the antique timbers, so there’s no drywall to paint, and there are a few gaps where the boards shrank and around the edges. Since we don’t have gable vents (we will have a ridge vent installed when we insulate), I only sealed the walls up about 20 inches, so the attic can breathe once insulated. We are fine with blowing in cellulose, but how do we keep it from coming through the gaps, and how do we keep too much moisture (it’s a kitchen) from getting in? Should we put painted plywood or drywall over the tongue-and-groove?
Hi Todd,
In Michigan’s Upper Penninsula, zone 7. New construction garage with Attic Trusses for loft living area above. Planning R-60 Bat/blown between the level. Loft is vented. Concern is the insulation in the loft. Plan on backing knee wall with foam backer and paper bat insulation (inside living). On rafters (6″) connected to living space was planning vented foam board + paper batt insulation. Ceiling using paper batt. Putting tongue and groove on walls and ceilings. Worried about lack of air barrier and condensation with T&G. Suggestions?
I currently have faced fiberglass insulation in a vented attic. The facing is down against the ceiling. I would like to add additional insulation and was looking at rock wool. Would there be any issue with putting rock wool batts on top of the existing fiberglass insulation?
Not at all….it’s a good option.
Fantastic article! Thanks for creating it. Now I feel fairly confidant about what I’m going to do. My ranch attic gets mice every Fall. I’ve read that mice love to nest in fiberglass insulation. The floor of my attic has fiberglass rolls face down between the studs with loose cellulose thinly, sparsely and poorly applied over top.
Fiberglass rolls were also folded into the 12″ x 22″ open areas, from the vented soffits below the baffles, and used as windblocks and to support the deteriorating egg carton type baffles which were only haphazardly laid down here & there. (A derecho laughs at this style of setup.)
While the two insulation experts I had look at my attic say things looked fine enough (from an insulation perspective) I plan to remove all the insulation, air seal as best I can, and then put in 24″x 6′ OSB as baffles, then shimmy in and try to put 12″x 22″ OSB as wind-blocks beneath the baffles, then lay down 100% loose cellulose insulation in the attic.
I was concerned about condensation being a problem on the OSB baffles, but not anymore.
While mice might chew through the OSB, it’s not gonna be an easy hop, skip and a jump from my soffit into my attic and hopefully they won’t enjoy the cellulose and decide to stay.
Also, my attached uninsulated garage has OSB in place of drywall. I’m going to air seal it & insulate it because I occasionally heat it with a portable heater. I’m thinking the OSB does not need paint like drywall would, the glue in OSB is the paint? (Depends on which class it is?) However; I will likely paint it anyway. Maybe.
What if the ceiling is cedar T&G as opposed to drywall – still no barrier between ceiling boards and insulation?
– Construction dates to 1960
– Zone 4 (Portland OR)
– Attic is vented
– T&G is varnished only on the conditioned-air side and the joints were not caulked or otherwise sealed on the unconditioned side
Currently have a mix of loose and batt insulation in attic, but we’re removing it all (to make electrical and hvac work easier during a kitchen remodel) and replacing (upgrading). So now’s the time to add a barrier if there should be one.