I am using Roxul insulation for ceiling and walls in a post-and-beam barn home
I plan to use this insulation in a 2×8 ceiling and 2×6 stud walls. Roof is sheathed in OSB, with a Titanium underlayment with standing seam on top. Walls have OSB and Tyvek house wrap. My question is can I use a poly vinyl vapor barrier on the interior after installing the insulation and then cover with 1×6 tongue and groove pine board. I have seen conflicting information on this. We are in Kansas which I think is Zone 6. This is a full post and beam barn structure. It has a gambrel portion with a loft. Loft has 12′ high ceilings. Lean to portion has 9′ high ceilings. Not sure there will be a lot of moisture buildup. The Roxul material is called stone wool. It is relatively new to our market but I like it because I can get R-30 in a 2×8 batt and R-19 in a 2×6 cavity. I am worried about what I have read requiring sheetrock first. We have 2900 square feet of ceiling and rocking it first would be a lot of labor and extra expense to do both. I would prefer to simply insulate, put up a vapor barrier and then go over it with the T&G. What do you think?
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David,
I to have read many conflicting answers regarding this issue. A vapor permeable membrane seems to be the correct answer. It can be purchased here...
http://foursevenfive.com/product-category/air-sealing-system/interior-membranes-air-vapor-control/
So no sheet rock is needed if a vapor permeable membrane is used?
David,
You cannot install Roxul insulation in this type of ceiling unless you first install a ventilation channel between the underside of the roof sheathing and the top of the insulation.
In Zone 6, building codes (the 2009 IRC) require ceilings to have at least R-49 insulation, so you'll need to do something to thicken your roof assembly.
For more information, see How to Build an Insulated Cathedral Ceiling.
You don't want to install any interior polyethylene, but you do want to pay attention to airtightness. I recommend that you use 1/2-inch gypsum drywall as your air barrier directly above your tongue-and-groove ceiling boards.
Actually, we do not have to meet code in our county so I am not too concerned about using R-49. This is a weekend use only barn home and the primary area for use will be the downstairs area covered by the loft which is fully decked. I am more concerned about needing a ventilation channel between the Roxul and the OSB. Because the Roxul is 7.25" deep, as is the 2x8, we have no room. So that tells me we would have to tack furring strips on to the 2x8. And then put on sheet rock. Would a 1x furring strip be sufficient?
Actually, we are in Zone 4, I just checked. Sorry
I was thinking as I was reading Martins post he must not know most of KS has not adopted an energy code, so we don't have to comply with the non-sense yet :) All insulation applications are not created equal. Lav rock or man made iron slag has different properties than glass or cellulose believe it or not and making general rules may not apply. There is alot of controversy related to what materials need what level of air flow or CFM to prevent freezing, condensation, fungi and rot. I have seen no prove that shows any less than guess work other than what the OEM has on their website that seems to be the most credible vs opinons. Roxul @ lowes and Themafber @ Menards are the same product, either will work depending on the best price. It has an incredible ability to wick water away in every cavity and evaporate it and some of that is a function of the roof pitch and drainage paths.
Your OSB-TI underlayment is not a barrier I believe unless it is Hubard ZIP, so there will be some air flow towards it, and MW will not freeze as long as there is flow, air and/water paths. Putting interior T&G allows the wool to breath both directions or resperate which some subscribe too. If it were a loose fiberglass batt that degrades r-value in moisture this would be a bad idea, but not the case with wool. Also wool is chemically inert and will not promote fungi growth in the presence of other material reactions, heat, and moisture.
So the most cost effective plan is as you stated, put wool in the 2x6 roof cavities as is, you can add the interior barrier if you want but since Z4 KS does not see real harsh freezing temps for long periods of time I would not be too concerned, nor with the hot humid summers.
David,
Even people who live in areas without a building code should still think twice before installing less insulation than code minimum levels, in my opinion. But of course, it's your house.
You can tack on wooden strips to deepen your joists, as you suggest, or you can install a continuous interior layer of rigid foam, as AJ suggests. AJ's method has the added advantage of reducing thermal bridging through the rafters.
Unlike Terry Lee, I do not think that the use of mineral wool is enough to keep you out of trouble from a moisture perspective. This type of installation still requires (a) ventilation channels above the insulation, and (b) an airtight barrier below the insulation.
A cathedral ceiling with inadequate ventilation channels and no interior air barrier is the classic recipe for failure -- dripping ceilings, mold, or rot.
Just slapping up ventilation channels with no plan to produce ventilation in each bay can perhaps be a total waste of time. You need pressure differentials to produce air flow. If you are trying to get cross-air flow perpendicular to the rafters with furring strips between OSB-Rafters don't count on much, towards the soffit in EACH BAY perhaps if you have a high flow ventilation channel across there or big holes to in the rafters to connect soffit vents and create low pressure, along with a ridge vent that allows flow into each bay. Otherwise, what I described can have more or less air flow than adding the channels with stagnant air to promote fungi and freezing.
The best you can probably do is consult the manufacture, ask about there hot box testing and CFM requirements. Roxul has some good engineers. Hempcrete is another natural mineral that takes moisture, needs no barrier. Not everything is a chem treated loose low density batt that needs high flow. I'd put that smart barrier up against MW Richard posted before I used poly if I had a ventilation path/ again ask the manu. Last I talked to them the only surface that would collect moisture is subjected to the elements and a very small percentage of thickness, the interior surface would not 'drip" and even if it did to a barrier you would need a drainage path since there is not guarantee of complete evaporation.
Here is a good read for those against an air space above dense pack materials:
http://www.applegateinsulation.com/Product-Info/Technical-Pages/249234.aspx
You have raised an issue about air movement that, frankly, I am not aware of. We are installing a standing seam room on top of the Titanium underlayment and I am not sure if there are ridge vents. If there are, that would be the only way to create a means for the air to move behind the insulation. We will have soffits in the lean to and on the gambrel end. I have contacted Roxul to get their take on this but they have not answered yet. So, Terry, if I cannot effective create the air cavity and air movement between the Roxul and the OSB, you believe that effectively I am packing it tight and would not bother with any membrane before attaching the T&G? The T&G is going to move with the temperature and breathe somewhat.
David,
Building science principles and the building code both require the type of roof you are contemplating to have a ventilation channel below the roof sheathing. That means you need soffit vents as well as a ridge vent. You also need to have the right roof configuration -- one without valleys, hips, dormers, or skylights. These principles are explained in my article, How to Build an Insulated Cathedral Ceiling.
If your roof lacks ridge vents, you'll need to switch your design to an unvented roof assembly. That means that you will need to use use spray foam insulation.
David,
You wrote, "Effectively I am packing it tight and would not bother with any membrane before attaching the T&G? The T&G is going to move with the temperature and breathe somewhat."
I am not going to try to speak for Terry. But here is my advice: If you are planning to install tongue-and-groove boards as your finish ceiling, and Roxul for insulation, you absolutely need a bulletproof air barrier directly above your ceiling boards. You don't want any air to sneak through the cracks between your boards, or you are asking for trouble.
Of course, if you switch to spray foam, then the spray foam is your air barrier, and you'll be fine.
Thanks for all your advice. I have some checking to do with my roofer/builder and with Roxul.
David when roxul calls you back ask to speak to a senior level engineer please update us on what they say...they just opened a new facility ms I think it was I know they're hard to get ahold of keep trying
The water vapor permeance of Titanium is 0.06 perms, which makes it a true Class-I vapor retarder AKA "vapor barrier":
http://www.interwrap.com/Titanium/udl_30_tech.html
Putting interior side poly vapor barrier without venting the roof deck creates a severe moisture trap, even if the roofing above were ventilated metal on purlins or something. Most roofing stackups have less than 0.15 perms anyway, and in cold climates they spend most of the winter with snow/ice on top, creating an exterior side moisture drive as well.
There are no magical properties of rock wool that will somehow protect an OSB roof deck from moisture damage if you left the interior side more vapor open.
Cellulose has the ability to buffer some amount of seasonal moisture, but will not work in every case. Both the climate and the density of the cellulose matter.
I will let you know what Roxul's technical department says. I had to leave a message. I am still at the point when I can make changes but I already bought the Roxul so I am stuck with this insulation system which I think is good stuff. I am assuming that if I use in the wall I can use a poly vapor barrier. It is a 2x6 studwall and we have Tyvek on the outside.
David,
I don't think that you should install an interior polyethylene vapor barrier on your walls. For more information, see Do I Need a Vapor Retarder?.
Terry is correct in that ventilation channels without ridge and soffit vents would be a waste of time, but who in their right mind did or would suggest you do that?
Roof structures are usually sized not for the structural load but to provide an adequate depth for insulation and venting. The first thing I'd do is upgrade from 2"x8"s to 2"x12"s, provide at least a 2" ventilation space and make air sealing the ceiling your main priority.
AJ. Thanks so much. I just shipped off to the Roxul rep my plans, photos of the inside of the gambrel and lean to and questions about this. So your suggestion would be to put the 1/2" rigid foam over the purlins after establishing an air cavity, say about 1.5", and then run the T&G over the foam, which is sealed? I am thinking of furring on wood strips so I can create the cavity and then putting in some kind of venting cavity, perhaps wood strips that hold the insulation out from the OSB. I just found out that our metal roofing system does have a ridge vent but I need to make sure the builder has allowed for venting along the ridge to make sure that if I do the cavity, it will have a place to go. This is all very helpful. I certainly will let you know what Roxul says once I get ahold of a senior engineer. The rep wants to feature our barn so I told them it is in their interest to make sure this system is properly designed and works. I like the 1/2" rigid foam idea. Funny thing is that the Roxul rep seemed to think poly was okay over the studwalls and you say don't use it. I will get some prices on the 1/2" foam for walls and ceiling. We are talking about 2900 square feet for ceiling and about 2200 square feet for walls. Thanks again for your advice.
AJ, thanks a lot. I feel better already. No poly on walls at all will be a lot easier. Any suggestions on a cost effective way to make an air channel? The Roxul is pretty firm and holds in place. If I staple in 1x on either side of the purlin, do I need to bridge them with something rigid or is it okay for the canal to be created by itself, assuming the Roxul stays fairly rigid? I suppose I could staple sturdy cardboard to the 1x lumber.
David,
I strongly urge you to read my article on insulating cathedral ceilings. I have provided you the link twice already. That article provides the answer to your latest question -- the one about the best materials to use to create a ventilation channel -- as well as answers to many questions that you haven't posted yet.
If you read the article, the information you learn could keep you out of trouble.
For your convenience, here is the link again: How to Build an Insulated Cathedral Ceiling.
Actually, I did read the article and, in particular, the part that says a vent space "can be created by installing 1 inch by 1 inch 'sticks' in the upper corners of each rafter bay, followed by stiff cardboard, thin plywood, OSB, fiberboard sheathing, or panels of rigid foam insulation." So, to keep in mind that I want to avoid unnecessary expenses but do this right, I really do not want to sheetrock 2900 square feet only to have to go over it with T&G because of labor and expense but I want to do it right. If I establish a good ventilation channel, as you have suggested in article, then put in the batt and then cover the whole thing with 1/2" foam board that is sealed at all of the perimeter areas, is that sufficient to then install T&G on top of the foam board? And do you have an opinion, Martin about whether I should treat the stud walls any differently than AJ suggests, which is to just go over it with foam board and T&G?
David,
I agree with AJ's advice -- as long as you pay attention to air sealing when you install your ventilation baffles and when you install your rigid foam. To make sure that the foam layer is as airtight as possible, it's worth investing in high quality tape.
Why not just go with a SIP roof? They work really well on cathedral ceiling homes.
Okay, then, to summarize: In this order on the roof: (1) Standing seam roof with ridge vents; (2) Titanium underlayment, (3) 5/8" OSB, (4) ventilation cavity of either 1" to 1.5" with material that is stiff enough to hold the insulation or "sticks" or something like AccuVent, (5) Roxul insulation, (6) 1/2" foam board taped to for airtight seals and then (7) the finished surface such as sheetrock or T&G. For walls, Tyvek, 7/16" OSB; Roxul insulation, 1/2" foam board; and T&G or sheetrock. I just checked on line, they make a 1/4" foam board. Can that be used at all? Otherwise, gentlemen, I thank you very much for all of your help. I will still share what Roxul says about its recommendations so you know what the manufacturer indicates.
AJ, do I need to use a vapor sealing paint on the foam board after it is sealed with tape or is the foam board enough by itself? You said above: "3- install 1/2" of foil face rigid foam, tape the seams, seal the perimeter as best you can.
4- Install your T&G, poly it first sand between coat 1 and 2. use satin, oil darkens, water base does not." Do I need a foil faced foam board and two coats of a vapor sealing paint on top before T&G?
David, when Roxul Engineer gives you there solution please email me it at [email protected]. Been a while since I talked to them, I call too next week and we can compare notes. I won't be using any foam there are other solutions despite popular opinions I don't care to debate. I live in KS too my son and I own a pretty big construction company in SE, Z5, so I'm familiar with the climate zones and wind speeds. I'm also a big fan of post and beam, farm homes, so I'm interested. I got some KS farm boy magic potions I can tell ya about too ;)
Terry. You are adding confusion. Stick to discussing theories. Talk about builds you have decades of experience with. Your noise on some threads is just that.
AJ, you are correct I am confused and it seems you have ALOT of experience with mineral wool, fungi, and rot. Can you please clear up this statement below with respect to FG, how would mineral wool thermal and mechanical properties acts differently given the same set of circumstances? Or better can you please give me the CFM requirements to prevent this 'bead' from occurring on iron slag? I have a home in San Diego too situation very simular to Daves, but the wind very rarely blows and I am by the salt ocean we see alot of acidic rot in vented attics. If the bead does occur will it freeze? Also, if moisture is entrapped at the interface to Dave's T&G or rafters what fungi spore would potentially be created there? Is foam rigid foam cause or resist fungi, how about spray foams, what spores in Dave assembly you are suggesting? How about the same question for my home in San Diego? And how? We don't want structural rot now do we so I need to completely understand in detail. Thanks! Terry
There are two main problems with this ventilation strategy. First, excess heat loss is incurred because by ventilating above the insulation, a suction effect is created which encourages air movement through the low density fiberglass, increasing the convective heat loss and air movement. This warm moisture-laden air is drawn through the fiberglass and is cooled until it must "dump" the moisture it can no longer hold. This is usually on the strands of fiberglass as beads of water form on the insulation, similar to the effect seen on a glass of iced tea on a pleasant summer day. This propensity of fiberglass to "bead up" moisture that has condensed was pointed out in a study prepared by Steven Winter Associates, Inc
Steven Winters since 1972: http://www.swinter.com/ Wow, big city of Philly developer, lived there too, Media, 1992-1994, not far from AJ.
Geez, puts me to shame I only been around quantifying fungi and rot three decades Just "theory" tho :)
I'm just messing with ya AJ relax, you must of fallen off a roof today. Did I tell ya I grew up a little in Long Island, NY back in the 60's when it was nice, Brentwood. :) then we moved to sunny SO Cali crazies! 70's-90's, then KS...last fungi test lab I was in 3 months ago, Eaton Global, Jackson, MI. USA homes child's play.
Malcolm wrote: Terry is correct in that ventilation channels without ridge and soffit vents would be a waste of time, but who in their right mind did or would suggest you do that?
I have ways to vent an air sealed vaulted much more effectively than a environmental vent through soffit and ridge vents if I wanted to but now you are getting into my trade secrets. The technology has been around since 1923.
Terry, This "I learned a deadly martial art at summer camp but swore to keep it secret" stuff is becoming a bit tiresome. I'm also can't understand why insulation would be subject to air washing if the ventilation is separated by baffles or a membrane.
Malcolm, read the article I posted air transports moisture from point a to point b. Common that is common sense. Sometimes that air can contain acids a membrane or anything will not stop. I'm sorry I am not a one-off builder, Engineer, I am trying to make a retired living out of designing and building of homes so I don't have to go back to consulting corporate,. I have competition the average home owner that builds one does not care about. I have 30 years into this, it was not easy, and I am not willing to just give it way. Unless there is a ROI. I am a business man, man. I agree Maritn is smart and I have learned, so I give back what feels comfortable. We can tap into free clean air if we think about it, the pioneer did it back in the 20's.
That’s what I LOVE about this industry it takes no qualifications to get into the “DESIGN ENGINEER” door, even the uneducated non-experienced, most states allow ANYONE to design up to a duplex, an unexperienced person that has no glue of basic design engineering principles can be, or at least act like a “Design Engineer” can come to the internet and be such a qualified person fictionally, to the point they have the job description required to post. Take that same persons resume to the corporate world, submit it and there is no way in He$$ they get the job. Because of that, I can go to your world, push you aside, you cannot come to mine. Be my guest try it. That is where I have the most respect for Maritin and his kind, that differs from your respect AJ and Malcom, I’d never have the tolerance nor patience for it. I’d rather work in corporate, quite, no questions, no bs, sit behind a 3d terminal and design, do my job go home in 8-12 hours. Time and half for OT. Done! Weekend’s family time.
BTW, the AHJ has the power to decide if code intentions have been meet, nothing is a hard rule if you are smart enough to explain the reasoning why. I just did it before a code board with a PE licensed in several states, fire Marshall, etc, they are now following my lead in light of adopting 2012 IRC chapter 11. "Terry, we agree no barrier required, requirement waived" your assembly needs to breath in both directions as proven over the past century+. They want evidence. Been that way for "decades" ! In most code there is a prescriptive and analytically path, and "alternate material and methods" paths, CH 1 Admin.
Perm ratings play a small part in dynamic material properties and behavior in an assemble, especially at the "whole hose level", Dana. I'd be interested in seeing where you used perm ratings in the past alone to determine a spore growth?
Does it really matter how this guy builds his house as long as it's built safe for his family? If the house does not have constant air movement 24/7 and proper RH management (mechanical dehumidification) you risk the mold issues every builder fears most. Well they do now because their insurance does not cover mold. The smart choice is to build with proven techniques rather than experimentation when it's your own home or even a clients.
AJ seems to be steadfast on his method and insults everyone who disagrees. This shows the mentality of most builders who think they built 100 homes and never had a call back. This is perplexing. I gutted 1980's bathrooms with these suggested rigid panels installed on the interior face as suggested and found mold many times. (ie; fiberglass-foam-mold-drywall) No joke! Why is this? Lack of moisture management by the occupants... That's right the people who live in the building are creating this moisture. Is it their fault or our constant change in energy efficiency design methods and the lack of knowledge associated with proper ventilation?
A few months ago I had an opportunity to inspect a friends Icynene house. Here's the building lay out from the inside out.... 3/4"x6" T&G poly coated fir, 1/2" drywall, 1/2" aluminum coated polyiso, 1/2lb Icynene spray foam cavity fill, 3/4"plywood, Tyvek designed for thinstone veneer, 1/2" thinstone drainage board, mortar and thinstone veneer. The interior of the wall (1/2lb Icynene spray foam) was covered in black mold! In fact the mold seemed to be eating the foam away. The cause... No interior exhaust ventilation (Air Exchange), NO dehumidification, NO HVAC, NO air movement during the winter month's, summer relies on open windows, winter heated with natural gas from a ventless fireplace. Where did all the moisture come from? Fireplace, shower and kitchen use. A true occupant failure in a 6 year old extremely energy efficient 1-1/2 story 1800 sq. ft. home and I have the rusty interior nails and drywall screws to prove it happened!
How many kitchens and bathrooms have you visited where the paint looks striped from dew running down the walls after a shower or from boiling hot water? Where do you think that evaporated moisture ended up? Interior of the Roof, interior walls or do you believe it remains in the room attached to the face of the drywall and then it miraculously disappears? Drywall allows moisture vapor to penetrate it's surface even when painted. In fact, Certainteed has created drywall to do just that, adsorb indoor VOC's which allegedly alters the VOC to a non-toxic substance. Showers need waterproofing because most tile and grout is not 100% waterproof. Hence the success of Schluter Systems Kerdi and Ditra.
With this said, if you follow AJ's method you risk trapping moisture that penetrates the roof assembly in the core. This is providing you do not mechanically manage your moisture generation from the living space 24/7. You better be certain you do not puncture those foam panels after spending all that time installing it and taping those pesky seams. My spray foam investigation of a friends house illustrates reality. This includes sealing all nail penetrations. Yes, they need to be sealed to! I have the rusty nails and screws to prove this.
Today blogs are saturated with rotting roofs from either open and closed cell foam used in roof assemblies and Martin continues to promote spray foam even after writing about the failures which are clearly not understood by top building experts. Is this to salvage advertisers? Why promote something when the product isn't understood by top building scientist or even top government researchers (EPA, CPSC, CDC, OSHA, DPH) regarding public health? Today these same building scientist are investigating with computer sensors in affected homes to find out why these roofs are rotting and why people are getting sick. Our government has constructed homes with tax dollars to evaluate the entire building on human simulated computer models because they do not understand modern energy efficiency building standards. More so they are attempting to create standards for every builder to abide by. A responsible professional builder would stop suggesting foam as a means of encapsulation of the interior of the home until the theory / testing stage is complete and proven safe and for which there are standards to safely build by. Our current code does not do this. Reality shows if it fails your not insured for the damage caused by the product and it's installation and it certainly will not cover your medical expenses.
"Experts". I have news for you all.... No One fully understands the product performance aside from energy savings and this seems to be where the learning stops for many. Regardless of those perm ratings foam traps moisture and will influence premature rot and mold in unconditioned spaces. Our current government administration is steadfast on air sealing 80% of all housing stock in this country by 2030 and no one dares to get in the way of this goal.
Roxul / Mineral Wool, Fiberglass and Cellulose are already proven methods used in the residential sector for many years with proven results. David is on the right path.
In closing vapor permeable materials allow a building to dry out when wet, foam does not and it's proven to exacerbate a problem when high RH occurs outside of visual sight. If you care less or your wallet can not sustain ventilation and dehumidification, fan noise and elevated utility bills you better build a home the old fashion way or pay the consequences!
David to answer your question on line 2... The answer is follow your codes if you abide by any and certainly consult with Roxul engineers. Be sure to get all the advice in writing! No matter what we say here there's no warranty to protect your building when disaster strikes and it certainly will hold no water with your insurer should a claim be made in the future. Did I say builder GL policies do not cover workmanship failures? Neither does your homeowners policy.
"I learned a deadly martial art at summer camp but swore to keep it secret." :) Thank you for making me laugh today. Stuck at work and needed a good chuckle!
see my first post
see my first post
This is how I have built similar to your project in zone 6a northern NY
Cathedral
1- Install vent channels from the lumber yards
2-install high density R-21 unfaced fiberglass or use your Roxul is fine
3- install 1/2" of foil face rigid foam, tape the seams, seal the perimeter as best you can. Use thicker foam if you can and then you will need to add 1x3s or whatever, plywood strips etc to nail the T@G to
4- Install your T&G, poly the T&G first sand between coat 1 and 2. use satin, oil darkens, water base does not choose either it is a personal preference thing.
Done
Walls do the same except no vent channels. The walls should be permeable to the exterior which they will be if your siding is permeable.
This set up works. Of course the exterior needs proper moisture proofing and proper flashing etc. Same with inside moisture, controlled moisture, bath fans, normal cooking, not boiling water daily for hours, no huge plant set ups getting watered by the gallon... If the home is low ACH it needs to be addressed. Other threads go into this.
There are many other builds that would work or possibly not. Martin has great advice and links to builds that work.
This is my only post I am going to have on this thread. Good luck. I am willing to debate elsewhere. See the debate thread.
aj builder... posting what has worked for me. Lawyers and engineers and bears oh my.... debate link to follow
see my first post
Peter, Hope it's sunny tomorrow and you can get out and enjoy the fall.
Why not push everything outside? I have 38 years building experience and realize that every house I build is complex and an opportunity to try to perfect simplified enclosures (yes, I am cheap) and HVAC systems (really cheap, as in I only use Goodman or Payne).
Martin has supreme patience, hearing, the same questions, over and over again: https://www.greenbuildingadvisor.com/blogs/dept/musings/getting-insulation-out-your-walls-and-ceilings
I think (yes, an opinion not a stated fact) peel and stick can be replaced with Sto Emerald Coat over Zip Wall system with no degradation in performance.
I am really warming up to Roxul, it seems like a great product. Unfortunately the more exotic forms of it are not available here yet. In Germany and UK Mineral Wool is the first choice for exterior insulation.