Exterior air barrier makes a tight house
I would like to discuss the exterior air barrier approach to constructing an air tight building. I’m splitting this off of a discussion we were having about unvented attics, in the construction techniques section. This approach to air tightening is an alternative to the drywall air barrier method. This method is used in structures with unvented attics as a partner in the high performance building envelope.
There are variations of this application, but I will discuss two methods. In my hot humid climate, I have used the first method with great success. This first method is definitely not recommended in a climate with average monthly temperatures much below 45 degrees F. The second method is safe to use in any climate from Fl to Ak. There are few building methods that are appropriate to any climate but I believe this second one to be just that.
The predominant air tightening procedure in the US is the drywall air barrier approach. With this method the drywall acts as the air barrier. There are many problems with this and the devil is in the details. Let me just mention a few areas where this method is impractical. 1. It is very difficult to seal plastic electric boxes to gypsum dust with latex caulk. If the wire penetrations are ever sealed, the electrician will compromise that seal when installing the electrical device. 2. Intersecting interior walls break the continuity of the drywall and allow leakage. 3. When stairways are built on exterior walls, the drywall that is installed behind the stair stringer is virtually impossible to seal. 4. Furr-downs on exterior walls are generally sealed for fire-stopping but not to be air tight. The gaps that are left allow a path from the wall cavity to the attic and to the exterior. 5. Exterior sheathings and drainage planes are built with an eye towards water intrusion but not air tightness, so failures at the drywall allow air to leak in or out easily through the exterior skin. 6. Bathtubs on exterior walls are difficult to air seal with a drywall air barrier due to contruction sequencing. 7. Bottom plates are sealed with foam which is often removed by the carpenter running baseboard. 8. Floor cavities between floors are very difficult to seal and are almost impossible to inspect, which brings me to…. 9. Current air sealing methods are tedious and impossible for a superintendent or building official to fully inspect. 10. With the drywall air barrier approach, there is a requirement that the drywall on exterior walls be applied with a sealant to exterior wall studs and plates to avoid wall cavities being connected to adjacent cavities, which allows a path to the exterior. I invite anyone to make the claim that they adhere(pun intended) to this guideline. Most builders have never heard of it.
Modern homes are tighter than older homes due to attempts to overcome these deficiencies with sealant and foam applications at penetrations and around windows and doors. We have invested a lot of effort in creating tighter houses and have still failed to do so. Blower door testing on new construction consistently illustrates our failure to achieve a truly tight building envelope. The results are higher levels of moisture in the south, overly dry houses in the north in the winter, frequent dusting, higher energy bills, and introduction of outdoor allergens.
PERSIST is a method of applying an air barrier to the exterior of the structure. The exterior side of a wall is simpler, has fewer penetrations, and is protected from being compromised later by the homeowner or remodeller. The methods I use are borrowed from the developers of PERSIST.
In the first method, cellulose insulation is used inside the wall. The exterior of the wall is covered with plywood or OSB sheathing. The entire surface of the wall is then covered with a rubberized asphalt membrane. A foil face can be included as an outer face when appropriate as a radiant barrier. The rubberized membrane is turned into window and door openings and with the help of flexwrap and a sloped bottom sill, creates a pan flashing. A loose flap is left at the top of the window opening and is later used as a head flashing. A felt fabric wicking strip is attached below the window that extends into the window pan to allow water from a leaking window to escape to the exterior. After windows are installed, a 4″ strip of membrane is adhered to the bottom of the window, over the wicking strips and down onto the wall. More strips are applied up the sides and are capped by the head piece that was left earlier. This seals the window in from the exterior, providing a superior barrier to air and moisture, while allowing water from a window failure to escape to the exterior. Interior air sealing methods are foregone and the time and money is put into the exterior. Inspection is very simple with this approach. The membrane is run down onto the concrete slab and sealed to the brick ledge, or overlaps the waterprofing that extends from below grade in a pier and beam structure. At the top of the wall, the membrane extends up to the bottom of the roof decking and is cut around rafter tails where it is sealed with an asphalt based mastic prior to soffit installation. This first method is not recommended for use in a cold climate due to the failure to control the temperature of the first condensing surface in winter. (inside of exterior sheathing)
The second method is similar to the first with one big difference. There is no insulation used inside the wall cavity. Instead, we use a 2″ layer of polyisocyanurate foam on the exterior. A foil outer face is used when appropriate as a radiant barrier. Window and door openings are oversized and lined with a 2×6 that is installed out to the level of the face of the foam. This 2×6 allows the windows and doors to be installed at a typical plane for siding or stone. Brick lugs are poured with a 2×8 instead of a 2×6 to allow for the thickness of the foam. Special masonry wall ties are attached with 3 1/2″ screws through the foam. On sided walls, a 1×2 furring strip is screwed to the wall with 4″ screws as a base for the wood siding. EIFS may be used but real stucco is not used with this system. The wall has the appearance of a 2×6 wall thickness with the lumber costs of 2×4 construction. There is very little thermal bridging. Fasteners that penetrate the membrane are self sealing, unlike other house wraps. Mechanical and plumbing penetrations are easily sealed to these membranes, unlike other housewraps and felt paper.
Moisture and condensation problems are eliminated and all lumber is kept at room temperature and humidity levels, year round. All drying is to the interior. Wetting is exclusively limited to anamolies such as plumbing and roof leaks. Plumbing can now be safely placed in exterior walls without fears of freezing. The advantages are numerous and the airtightness is phenomenal.
Blower door testing on these structures ranges from .75 to 1 ACH at 50 Pascals. Mechanical ventilation is required and with proper filtration of the outside air source, dust and allergens are substantially reduced. All infiltration is now from backdraft dampers and windows and doors. Infiltration through the walls is eliminated. We prefer to provide a make-up air source when large kitchen venthoods are used. Make-up air becomes critical if a fireplace is installed and we prefer to use only sealed combustion units. Waterheaters(tankless) are installed outside or in a sealed combustion installation. Gas furnaces if they are used, must also be sealed combustion units.
We have had great results with this system and are continuing to refine it as we go along. My personal home is 4200 conditioned square feet and has an average energy consumption of 1000 KWh and 10 gallons of propane. This includes minimal use of fluorescent lighting and pumping the domestic rainwater through an ultraviolet light. We use a hot water circulating loop on a timer and have an eight year old refrigerator that could be improved on. These factors push the parasitic loading to 10 KWh per day. Peak usage in July, August, and January averages about 1200 KWh per month. On a day that reaches 100 degrees, we can turn the AC off for 12 hours while we are away and only experience a 2.5 degree rise inside the house. On a 108 degree day we experienced a 3.5 degree rise. We use a 14 SEER heat pump and a DEC ultra-aire UA150H dehumidifier to maintain the relative humidity in the house to less than 50% year round.
I will stop here so I can go work outside. I welcome your questions and comments as I am sure I have left out alot of info on a fairly complex subject. For further reference, here is a link. http://homeenergy.org/archive/hem.dis.anl.gov/eehem/99/991108.html
You can get more info on building science and moisture issues at, www.buildingscience.com.
If you made it this far, thanks for your time and your patience.
Ray Moore
Replies
Your system sounds good in line with accepted state of the art in southern climates, but not so good for northern heating climates.
Did you intend this to be a discussion or a lecture?
I'm chuckling because my wife accuses me of being too wordy. Says if she asks what time it is, I am likely to lecture on how to build a clock, or the history of time-measuring devices.
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This is a sequel to the recent discussion of unvented attics.
Ray says that he types slowly, so I am really grateful he is taking the time to share his ideas and invite discussion.
In general I am looking for insulation techniques that are not climate specific, since I personally believe that global warming is a reality.
So I am interested in Approach #2, moving insulation and air barrier outside the skeleton. How bad would it be to retrofit this to an existing house? Right now the only alternative approach I can see is removing (some or all) siding and spraying (open-cell or preferably closed cell) foam into the cavities. This might best be done as part of residing the house, since I have no air/rain barrier. The main complication I can see with Approach #2 (and it's a doozy) is extending jambs and sills for doors and windows.
RE retrofitting - that depends on the house, but I can imagine a wide open market because of the number of massproduced homes built in th esubdivisions by large builders who ignore simple things like housewrap and then use cheap vinyl siding. There are no doubt hundreds of thousands of homes out there that will need an exterior up grade in the next 15 -20 years.
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In general I am looking for insulation techniques that are not climate specific, since I personally believe that global warming is a reality.
Have you considered insulating with straw bales? The R-value is at least R-28, making for a very cozy house requiring a minimal amount of additional heating, which would save considerably on utility bills.
This would also address your concern of global warming, since you would be using an agricultural byproduct that would otherwise be burned in the fields. (In some areas of CA, burning straw is illegal because of the great pollution it creates.)
THis might sound like a crazy idea, I know, but check it out. Here are a few good links:
http://www.strawhomes.com and http://www.strawbalehomes.com/
To see strawbale homes around the world, go to
http://sbregistry.greenbuilder.com/search.straw
--Justy
From what I have read, a straw bale house is really just temporary shelter. Huge problems with mold/musty smells. Difficult/impossible to waterproof..may be makes sense in the Southwest.
Just as with any construction technique, straw bale construction is quite durable and long-lasting if done correctly. There are straw bale houses still being occupied that are 50+ years old. And, if you looked at that database,(http://sbregistry.greenbuilder.com/search.straw) you would see that there are SB houses in nearly every state and in many countries around the world.
Water is an enemy to straw (just as it is to wood and other building materials), but with proper detiailing and construction, it shouldn't be a problem. The plaster skins on both sides of the bale wall serve as a moisture barrier, as well as protecting against fire and air infiltration.
Straw is actually quite similiar to wood in composition (cellulose-based).
Straw bale construction works - just don't let a pig build your house!
From what I have read, a straw bale house is really just temporary shelter.
Apparently some straw bale homes in where they originated-Nebraska are still standing and some are still occupied! They were built in the late 1800's...doesn't sound very temporary to me!
One built up the road from me about 8 years ago (damp, coastal climate) is performing well, especially heat wise, and is not mouldy and dusty.
The finished home looks liked a southwest adobe style.
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Here's a pic of a post war straw bale house in Nebraska. Completely falling apart...barely 50 yrs old.
I am not saying you can't build out of straw bale.
But why would you do it?
Why use something that rots? Say your neighbor has a leak in the stucco that goes undetected. How would you even begin to repair something like that?
Yeah, energy savings, you say. But you could build a house out of stone and concrete that would give you the same r values without the rot/mold issues.
I could probably build a house out of lettuce and stucco it too... if I wanted to.
Jimboy:
One picture of a failing house of a certain construction is not proof of failure of the concept nor it's application. What do we know about this particular house? Was it built like the 50 year older older ones still in use? Some are still standing without having been lived in for a few years (anectdotal to me).
A lot of wood framed houses have had severe rot. Recently, I consulted on a brick facade failure in 9 year old house (actually manse for a minister). The repair cost for this barely 25 foot wide, 2 storey front was over $40,000!! Standard platform frame construction with brick veneer- its been around since the 1920's- why did it fail so miserably???
A lot of people think that houses are being built "too tight" and that's why they're rotting, have interior mould problems and are making people sick. That's very far from the truth!! Go to the American Lung Assoc. sub-website: http://www.healthyhouse.org .
Funny they advocate "airtight" houses for already sick people!! Pretty odd, ain't it?? All is not what it seems. Most people have gut reactions to the new and odd without really understanding or learning about what they've encountered.
Given a choice between a house built of insulated concrete, and straw bale
you would actually choose the strawbale?
Obviously, wood framed houses have rot issues too. But imagine structural repairs to a straw bale house with poor flashing details. How do you do it?
Or, how does your house fare, when say, rising waters from a nearby creek flood your home? Does it dry out? Nooooo.....it stays wet. Your first floor is soaked.
So...what do you do? Doesn't the fact that there is no easy solution in this instance (compared to stick built) speak to s.bales being unsuitable as a building material?
Apparently, the assumption made with straw bales is that every single cladding system and penetration on the building will never fail. Because if it does, the potential for virtually unsolvable problems is there in terms of moisture.
After seeing this local house go up and speaking to the owner occasionally (since I designed the HRV system for the one storey on slab home), I would certainly consider it over the ICF.....certainly in terms of its green, sustainable value.
It uses local straw (60-70 miles away) that may just rot in fields. It is definitely an owner/builder sweat equity edeavour due to its high manual labour content. The outside uses an old proven high lime content "stucco" that is easily maintained/repaired.
Compared to:
(1) the oil and energy in the foam blocks;
(2) the cement who's clinkers had been heated to 3,000 deg F before being pulverized into the fine cement dust;
(3) the aggregate that may have been shipped hundreds or even 1,000's of miles using oil based transport (we have a world wide shortage of aggregate beginning- it is being shipped from Alaska to Japan and California. There's a fight brewing in my own province of Nova Scotia about a proposal for a large aggregate quarry in a very scenic area. Destination of the aggregate- New York);
(4) oil based vinyl siding or other high embedded energy siding such as cement based , metal or manufactured wood fiber based sidng
Personally, I think that, given that one's home is your most expensive asset, I would think that it's permanence would trump its "sustainability". In fact, a straw bale house, IMO, is not "sustainable", compared to a house built out of stone (like I have) or concrete.
Your quote that it rots in fields if not put into someone's home speaks to that.
Certainly, I could forward you, but I am sure you are aware already, of wood housing that still survives from the Middle Ages. Obviously, there are stone shelters that are thousands of years old.
Yet, as far as the longevity of straw is concerned, we only have a few examples dating back 150yrs or so. No example using modern claddings/hvac systems to really tell the durability of this type of constructions. What you essentially have with this house is a bunch of "IF'S"
IF thehouse has large overhangs. and if the house isnt in a climate that is very humid, and if your wall/roof penetrations never fail, well, yeah, we think it can work. But since it's a fairly new technique, we really have no historical basis for this assumption.
Why use something that rots?
Well, most houses are built out of materials that rot because they're cheap, easy to work with, and are often a good compromise for a house that may be torn down and replaced with a mcmansion in a few decades anyway.
I agree with you that there are better building materials out there, but experienced is right- there are some 200 year old strawbale houses out in the sand hills of nebraska. I've got a friend who has built a few strawbale houses, here in eastern washington where the climate is great for keeping strawbale houses dry and rot free.
I would say that for a strawbale house to be long lasting takes a lot of attention to detail- drainage, roof overhangs, windowsill flashing, are all very important. But for some it is important to build with a low embodied-energy product like strawbales. And they're comfortable, beautiful houses, at least the few that I've been in.
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Takes all kinds in this world.zak
"so it goes"
" I would say that for a strawbale house to be long lasting takes a lot of attention to detail- drainage, roof overhangs, windowsill flashing, are all very important. But for some it is important to build with a low embodied-energy product like strawbales."
I agree.
Thats why I jokingly said before that I could build a house out of lettuce and stucco it.
And for the average lifespan of my flashing systems, stucco finish, and sealants, it would probably fare pretty well.
As the lettuce house passes out of my meticulous care and into the hands of someone less so, things could start to leak as these systems fail. Then what, was my point.
So how good is straw bale as an air barrier?Oh wait a minute. "And he huffed and he puffed...."
If I could weigh in on Tyvek... it's currently out of vogue up here in Alaska - too much condensation on the inside surface. I say currently cause it's kind of like clothes fashions. I don't know if that's code or not, but the fashionable builders frown on it :)
Are you involved with the Alaska Building Science Network?
My friend Marquam is working with the Persist system up there. Ya'll have some real problems up there. I've read about the SIPS failures and other problems that occur in that extreme climate. Of course, there are some areas that are only very cold instead of "Oh my God, it's insane to live here" cold.
I can't wait to get up there for the annual summer conference. I can't make it this year, but John Straube, Joe Lstiburek, Mac Pearce, Gary Nelson, et al will make it a great learning experience.
I have some of their materials and am a little familiar w/ the group, but try to stay away from non finish carpentry type stuff, ie framing in November.
It actually doesn't get all that cold where I am (SE Central) maybe a couple weeks of -30f in a cold winter. I think Minnesota probably has more severe winters. Ours are just loooong. (Although I did see -45f one winter)
FWIW I did do the interior vapour barrier poly tremco airtight elec. boxes sealed everything w spray foam etc. etc. I have 2x4 framing with 2x2 strapping inside, 2inch rigid foam between the strapping. Yes it is a very tight house, and no I would not do it again. The amount of extra work involved was too much. SIPS are probably the best bet up here.
I wanted to give an update and a brag on the performance of this system. We left town for the Memorial Day weekend. We left at 6am Saturday and returned at 7:30pm on Monday. We left the AC turned off while we were gone. Temperatures were low seventies in the mornings and mid nineties each afternoon.
When we left, the interior temperature was 74 degrees. When we returned after three days of daytime heating the interior temperature was 79 degrees on the living area side of the house and 78.5 on the bedroom end. I'm guessing that the refrigerator added a small amount of additional heat to the living area side. The two areas are separated by doors.
When we arrived at home, the AC took 2.5 hours to cool the house to 73.5 degrees. I couldn't be more pleased. The relative humidity was 45% when we got home even though the outdoor dewpoints remained above 70 for the time we were gone. This is only possible with an airtight building.
In the hottest three months of the year, this home requires less than 600 KWh to air condition. That's pretty good considering the dozens of days over 100 degrees and the remainder of days very near 100 degrees each summer. The home has been slightly remodelled since the original post and is now 3400 feet of living area and 4200 feet of conditioned space.
Edited 5/30/2006 6:33 pm ET by RayMoore2G
I don't like Tyvek either.
It's a popular club.
The method with the foam exterior to the membrane is being successfully used in Canada and Alaska and can be used anywhere. The method with the cellulose installed in the cavity is suitable to the gulf coast and south Florida, so long as interior moisture levels are controlled in winter months.
If you think my posts are wordy, you should try me on the phone. Lecturing is something I do a lot of.
The problem is that you are placing the VB ( the foam) on the exterior of the framing so moisture can be collecting in the stud bays
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Piffin-
Thank you for replying. The membrane is actually the vapor barrier and is inboard of the insulation. The first condensing surface will always be within a few degrees of the inside ambient temperature. The risk of condensation within the wall is nil. This is probably the safest system ever developed for prevention of condensation within a wood frame wall cavity.
Condensation forms within the wall cavity in cold climates when inside humidity is allowed to come in contact with the cold exterior sheathing. If the temperature of this surface falls below the dewpoint of the air in the wall cavity, then water vapor will begin to collect on this cold surface as condensation or frost. With this new approach, the exterior sheathing and indeed the entire wood frame is kept warm throughout the winter because it is inside the insulated thermal envelope.
It's actually pretty bulletproof.
I missed the interior membrane part of this, but it still relies on installing it seamlessly - sealing any and all penetrations - or did I mniss something else.
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Piffin-
Two things. First, the vapor barrier and air barrier is a layer of rubberized asphalt membrane on the exterior of the plywood sheathing. This is on the warm in winter side of the insulation. Second, the foam insulation is exterior to the wall and needs to be continuous; however, perfection is not required on this installation. It would take a substantial gap in the insulation to cause a significant vapor drive unless you were in the arctic.
One other advcantage to this system in cold climates is it's resistance to cold corners that often occur in walls with cavity fill insulation. In high humidity conditions in cold climates, ghosting can sometimes occur on studs due to thermal bridging. This is most likely to occur behind furniture and in the backs of closets where the temperature of the sheetrock is not maintained above the dewpoint due to the insulative value of the furniture or clothing. Exterior insulation prevents this phenomena.
I like the foam panels on the interior side of studs to act there as thermal stop and VB on the inside of wall. That way, there is only one VB
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You need a VB in the first place because (in a conventional house) the dew point will be in the stud cavity. If there's insulation there, it'll hold the condensation and there's your source of problems.The "exterior air barrier" moves the insulation and the dew point outside the sheathing. If I understand right, it is the equivalent of completely filling your stud bays with foam, but you still have your stud bays for wiring, plumbing, recessed radiators, etc. And you've eliminated (a lot of) thermal bridging. You put your thermal break on the inside, that's why you have to worry about dew point in cavity...not in your location (yet!) but would be in more mixed climate area with AC in summer.There was a thread recently about experience with 1/2" foam panels over sheathing. People did not like it, houses felt flimsy and attaching siding was difficult. I don't know if this approach would be subject to the same problems.
You misunderstand me. I do not worry about condensation with the foam on the inside. it is when it is on the outside that I worry about condensation, as ( I think it was armin who observed ) was mentioned in an earlier post here.You are in a location where the warm moist air wants to be drawn towards the interior cool surfaces, so you need the VB and iunsulation on the outside of the packlage, but here in the north, the effect is opposite. The interior air is warmer and moister and moves to the outside, so it must be stopped BEFORE it gets into the stud cavity.
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I'm in Joisey, still basically a heating climate, though summers are heating up and AC is spreading....In the exterior air barrier approach, the stud bays are the same temperature as the rest of the house. No condensation. Your thermal break on the inside lowers the temperature of the stud bays (in winter).Imagine there's no DW or plaster on the walls. Just stud bays open to the interior, and empty. Your only worry now is condensation on the sheathing. But the insulation on the outside pushes the dew point outside the sheathing.
The interior air is warmer and moister
Isn't that true only in properly humidified heated homes? I know it's supposed to be that way . . .
I know that radiant systems are supposed to be "less dry," too.
But, other than the latent heat fro mthe occupants, and moisture from their activites--aren't those the only primary sources for indoor humidity in primary heat climates (other than air-to-air air quality devices)?
I'm having to run on memory, not being in a heating sort of environment--and many of those memories involve very dry heat/heating situations, and in ancient, under or non, insulated houses. So, I know I'm behind the curve in experience.Occupational hazard of my occupation not being around (sorry Bubba)
Cooking, showering, and breathing create a significant amount of moisture, enough to cause problems in tightly-sealed homes.The type of heating system really has nothing to do with it.In more conventional (not so tightly sealed) homes it's fairly common to have a humdifier installed on the heating system. For comfort it's generally best to have the humidity as close to 35-40% as possible, without causing undue condensation on windows, etc.
the humidity as close to 35-40% as possible
We have a special word for humidities like that: drought <g>
Yeah, the problem I'm having is in having learned all of the "old" info on heating three decades ago, but never having had to live amongst it.
That means I'm havign to remember what the latent heat load for steam heat is in my head why trying to remember various thermal transfer diagrams & graphs. "School" stuff rather than "used every day, I could almost write the textbook" stuff.
Ray has some very intriguing ideas, and the science of it is more fascinating every time I take a deep look. It's out of the box, too.Occupational hazard of my occupation not being around (sorry Bubba)
You know your stuff, and write well. I think the main difference in our5 respective points of view is just in the local climate we each work in
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A couple of minor points:
1) Homes in northern climes have been built with an exterior air barrier for a decade or two now -- housewrap is generally required. The details of doing this right are about the same as with your rubberized membrane. Of course, the housewrap is moisture permeable, and a separate vapor barrier is used inside.
2) In the far northern parts of the country 2" of foam is not really sufficient for insulation, and I suspect that the technique gets more complicated as thickness is increased.
Hi Dan-
Housewrap ie. Tyvek is not an air barrier. There are hundreds or even thousands of holes in it after it is applied. An air barrier must be perfect to be effective. That is why the air barrier in these houses is the plane of the drywall. When using this approach, there is no need to concern yourself with sealing penetrations through the drywall, such as electrical outlets. This is a major difference between this method and the typical way of creating a building envelope.
This system was developed by the Alberta infrastructure department and they specify 2" of polyisocyanurate in their climate. This gives an R-14 with almost no thermal bridging and no air leakage, which will far surpass the performance of a conventional wall with insulation rated at R-19.
This system was developed especially for cold and extremely cold climates to overcome the problems associated with interior vapor barriers that can cause problems in summer when air conditioning is used and to provide a superior air barrier.
The link that I provided about PERSIST will address your northern climate concerns. This is one of the few building methods that is safe for us southerners to import from you northerners.
Well, no air barrier is perfect. Tyvek, properly installed, is probably 5-10x better than classical drywall+sheathing construction. The worst leaks that do occur are apt to be in places like the mud sill, where I'll grant you a self-adhesive membrane would do a significantly better job.Does your technique carry the membrane across the edge of the mudsill and onto the foundation?
Yes it does. We seal it to the masonry lug. It fuses so well that it can't be pulled loose by a strong man.
Tyvek is not an air barrier.When you take apart a wall with tyvek on it, that becomes abundantly clear. Hundreds of holes in a sheet of spun polyolefin does not an air barrier make.
Ray,
just curious, do you work for Building Science?
This Persist idea is intriguing. I like the ability to remodel spaces later. Any concerns with a/c use in the summer? I'm in Philly, we run it usually for 3 months or so.
I would love to see the energy usage of a house done this way.
Maybe I need a paradigm shift, but the conventional side of me wants to fill the stud bays full-if you know what I mean.
Homer-
I'm a builder in Austin TX.
You can do this method in South FL and set the AC at 50 degrees and there will not be an issue with moisture in the walls.
My house uses just less than 1/4 KWh per conditioned sq ft per month.
I know what you mean. I fight against change more than most. I actually went up to Boston to tell Joe Lstiburek that unvented attics in the south were just crazy. There was no way that it would save energy. I spent 5 days with Joe, learning all I could about this subject. I have been back several times to learn from the experts in the field. Building Scientists from around the world, gather at conferences and share ideas. I try to attend annually. I now build every home this way. I more than tripled the size of my personal home, but the electric bill is the same as it was before.
Dumb it down for me.
How much is your electric bill for your house & sq. footage?
Also, is the membrane just ice and water shield, or something fancier? Thanks.
My average monthly operating costs are around 90$ in electricity and 10 gallons of propane(hot water and cooktop). I have 3400 feet of living area and 4200 sq ft of conditioned area.(includes 800 sq ft of usable ht. conditioned attic space). I put it in terms of KWh per sq ft per month because electric rates vary and I wanted you to be able to caompare to houses you are familiar with regardles of price structure.
The membrane I use is a peel n stick product made by polyguard. There are several different formulations. The one I use is a little tackier than others. Brand named peelnstick by polyguard, it has a foil outer face. There are others that don't include the foil that I use when a radiant barrier is not needed. Ice and water shield is another brand name, which I have not used on walls but have used on the roof. The product I use was developed for mobile home reroofs and roof top duct wrap. In a roof application, it is warranted for 10 years. Behind a masonry wall, I would give it 50. I'm sure that eventually the volatiles will oxidize and it will start to resemble a potato chip but that is just a WAG.
Thanks for the reply. Saves me from looking at my utility bill. Impressive numbers!
Ok, next question. Whats the compatibility of synthetic stucco to the membranes? (I am assuming its put right on top). To put it another way, how are you applying stucco to the system?
As you said, conventional stucco wouldnt work, I guess both from a lack of bond as well as putting several thousand holes in the membrane from attaching lath, right?
The synthetic stucco is so sticky I would think it would work, but you touched on using it before.
Holes in the membrane are not an issue. In the south, where cavity fill insulation can be used, traditional stucco is applied per normal practice over the membrane. I do; however, us a felt fabric over the membrane(mirafi protection course200) or two layers of felt paper.
I only said that EIFS may be used over the exterior foam but traditional stucco is not recommended. I have not tried a synthetic stucco over the exterior foam approach and would have to do some research before I tried it but I have no doubt that it would work. Perhaps it could be used over a polyiso board designed for roofing applications or perhaps over an additional layer of foam substrate designed for EIFS.
So on the new homes you're building w/Persist, you're putting up the membrane, then felt/wire lath/stucco-did I get that right? Thanks.
In my climate, yes. Persist uses the insulation on the exterior. When I put the insulation in the stud bays in my climate it would be a modified version of Persist.
Again thanks so much for the information! This really makes you think "outside the box".
In your opinion: For new construction, how would this technique compare to SIPS? With PERSIST, you have a typical frame structure but less insulation than SIPS. But, shouldn't SIPS be faster and more effective? I don't have a clue regarding cost between these 2 approaches. Do you?
FF
My experience with SIPS is limited to observations of friends' projects. Sips are not as air tight as Persist. The Persist method allows a more conventional approach to wiring and plumbing installation as well as being more common to typical framing methods. Changes are easier. Cost of Persist is somewhat less, depending on some variable related to shipping costs and the availability of skilled trades. Insulation value is similar to a 4" SIPS. With this system, a small percentage of your heat loss will be through the walls.
The installation of the membrane is a new skill set for residential construction and the cost to implement it the first time will vary widely. My helper can install it on a 3400 sq ft house with 25 windows and 4 doors in 8 days by himself. The materials would cost around 1000$. The labor around 1000$. The labor could easily run to 2000$ depending on experience level and payscale in your area. From this, you can subtract the cost of interior foam sealing, pan flashings, head flashings, window wraps, and housewraps. We have developed detailing for doors and windows over time that are quick and effective. I have some pics and QT video clips that can help explain it. They are very unprofessional in nature. They are large files so are not appropriate for e-mailing and uploading to this site except in a very limited way.
thanks for the schooling,
my head is swimming but i was hoping you could clarify some points for me,
i am hoping to reinsulate our home here in south central bc. it is hot and dry here most of the time and the winters are coldish and freeze up....basically it is dry and the moisture comes from us humans mostly....the house is (from outside to inside) stucco, tarpaper, ship-lap wood sheathing, 2x4 studs insulated with vermiculite (which has probably settled greatly)(the house is cold), ship-lap wood sheathing, 3/4x6 vertical boards with 1/8" gaps between. The house also has alulminum windows. We have bought new argon filled vinyl windows to replace the aluminum windows.
I was thinking of two options. 1- screw foam board over the stucco with strapping, and screw board and batton siding with long screws threw the strapping and foam. I don't like this idea much and fear the sag. 2- remove the vertical boards in the interior of the rooms of the house and screw foam board insulation onto the ship-lap wood sheathing with strapping, screw dry-wall onto the strapping, then build out the wall with built-in cabinets/shelving and window seats. We are doing this because we like the window seat look, and it opens up the room, and i feel it will provide a little bit more r-value/air barrier.
I appreciate your advice.
kind thanks,
michael hollihn
traditional timber frames,
ecoforestry,
sawmilling
I am hesitant to give any type of advice without personally seeing the project. I'll be right up. Can you e-mail the directions? Seriously, I view a building as a complete system as opposed to a wall system, roof system, HVAC system, etc. I look at the site the climate, and even the lifestyle of the client; although that can change, so I don't lock myself into that criteria. I try to visualize the ramifications of one approach related to the other components being considered.
Based on the info that you have supplied and being limited to these two options. I would agree with you on the second option. I would tape the foam. Using this layer as your air barrier will require careful detailing in all the areas that I outlined in my original post. The first option that you outlined seems rife with potential problems.
Please specify the type of foam you are thinking of using as they have diferent R-values and working characteristics.
Best of luck with your project.
Thanks for the attention. We live on the border of Washington, B.C. in Midway.
If you are close the invitation is always there for any builder who likes to travel and visit. We are great entertainers :) Anyways, not knowing if you were serious, the foam board we are wanting to use is certified by Greenguard as being the lowest detected for off-gassing, as my wife is pregnant and my daughter is 3 and i have a hard time trusting the powers that be (paranoid yes) :) LOL. The product is Foamular by Owens Corning. I want to use the 1" to keep the width down and i believe it will be sufficient if i seal it well.
Thanks again for your timely advice.
Michael Hollihn,
Traditional Timber Frames,
Ecoforestry,
Sawmilling
What is the R-value?
5 per inch
From a couple of thousand miles away, it sounds like a good option to me.
I spoke to a friend of mine that has used both systems (this one and SIPS) about the cost comparison. He said that SIPS can be competitive in a simple home that is designed around SIPS. Electric in the SIPS is no problem but plumbing is. He went on to say that in custom homes like the ones we build, SIPS is at a cost disadvantage.
It works better when you leave the nails in. :)
Don't get me wrong, I can see how a self-healing barrier would be better than Tyvek. But I've personally seen how Tyvek is an order of magnitude better than conventional construction. There is a question of how much "better" one needs to be in a given set of circumstances.Also, I've seen with Tyvek that the devil is in the details. Without familiarity with your system (and, more particularly, without builder/inspector familiarity with it), it's not not clear how robust the system is in the face of (typical) less than ideal attention to detail.The failures of many past "systems" trace to improper real-world building practices more than they trace to inherent defects in the systems themselves. A good system must be able to tolerate some degree of error.
Our new approach has cut our energy consumption to half that of our old method of using vented attics and tyvek housewrap. Dusting is much less frequent and indoor air quality is improved. That should answer the question of how much better it needs to be.
Tyvek is not an air barrier. When using Tyvek, the air barrier is the sheetrock. The detailing is very difficult to inspect. With an exterior membrane system, inspection is easy, with a quick walk around the outside of the house. Damage is easy to repair with a caulk gun loaded with mastic. The final defense is to use the mason to repair anything they see before covering up. They keep a mastic gun nearby and repair nail holes from framers scaffolding that has been removed etc.
It sounds like I'm not going to convince you and that's fine. I really appreciate the opportunity to address your concerns. This is a very strong system, and can stand up to intense scrutiny. We are very excited about it as you can tell. It has solved so many problems for us. We simply haven't had a single water intrusion issue with this system. For a builder, that is worth a huge source of relief. One part of that is the head flashings and pan flashings around windows. Remember, window is a french word that means water in your house.
Thanks for your post.
All I know is that when we Tyveked the outside of our 70s frame, air infiltration (as noticed by drafts from outlets, etc) essentially disappeared. Parts of the house that were uncomfortably cool in cold weather became comfortable. And several places where frost would actually appear on the walls in extremely cold weather no longer developed frost (in spite of an exceptionally cold winter the year after we did the work).Frankly, despite the fact that you make a lot of sense in general, your statement that Tyvek isn't an air barrier and drywall is just doesn't hold water (or air). I'll grant you that, in previous eras, there was an attempt to make the DW **be** an air barrier, but it never was very good at that, for many of the reasons you mention.An exterior membrane, be it Tyvek or "rubber", is superior since it can be installed with a minimal number of seams (which can be sealed if carefully applied) and because it can be more effectively sealed around window and door openings. Plus none (well, hardly any) of the dead area problems you mention with drywall.Your argument about nail holes is only partly valid. When a nail penetrates Tyvek the fibers spread apart and press against the nail fairly tightly. Granted, a rubberized membrane would be better at this, but again it's a question of what's good enough.
Dan, Ray:
You guys are both right. Sorta.<g>
Dan, doing what you did (Tyvek on an older house) will definitely show an improvement regardig air infiltration, and that improvement will be reflected in the additional comfort inside the living space as well as with lower energy usage to keep the living envelope comfortable.
Now, about Tyvek being an "air barrier."
"Air barrier" needs to be defined. Some local codes don't specifically define it at all. Some do. One area where I've worked defines an air barrier as having an air transferance rate of (if I recall correctly) less than 0.004 cfm/sqft.
Does Tyvek meet that number? Sometimes it does, sometimes it doesn't. Regular Tyvek has a rate of something like 0.007 cfm/sqft, but commercial is something like 0.001 and the product sold in Canada is also less. I forget what that number is though.
Numbers aside, in practical terms bulding inspectors all over acccept Tyvek, as well as most of the other spun polys as a wrap, and they accept is as an air barrier.
Is Ray's membrane a more worthy barrier? Sure it is. But Ray also needs to be diligent in dealing with vapor since his air barrier won't allow through-drying like a spun-poly product like Tyvek allows.
But again, there are regional differences with Ray in the south and with me in New England, we need to detail our houses differently in regards to how nature directs air movement and the carried vapor with it through a wall. In essence, he's trying to keep it outside the envelope, away from the cool interior, and I'm trying to keep it inside, away from the cooler exterior.
So...it's a tie. You're both right.<g>
My point about Tyvek not being an air barrier refers to "as installed". Once the mason gets through putting a few hundred masonry anchors through it, it is no longer an air barrier. It is not even a great drainage plane. The fact that many people in the industry regard it as an air barrier has to do with marketing. The marketing people at Dupont pushes Tyvek in areas that it has no business being installed.(gulf coast region)
The issue of climate and vapor drives is moot once you put the insulation (polyiso) outside the membrane. It is now on the warm on winter side of the insulation. All your lumber is warm and cozy inside the hygro-thermal cocoon.
The use of interior poly vapor barriers in the north has confused the issue of vapor drive in the minds of many practitioners. The issue has become "how do I keep vapor out of my wall" instead of "how do I keep condensation from occuring in my wall". The best approach is to ensure that the water vapor in your building will not come in contact with a surface that is below the dewpoint of the air.
Controlling the temperature of the first condensing surface is a safer way to address the issue. There are many homes in New England that have moisture problems in their walls in summer because they have a poly VB behind the sheetrock, air conditioning in the summer, and have a strong vapor drive in the summer due to wetted claddings and Tyvek type housewraps. Persist was designed to avoid this problem.
Tyvek is not an air barrier.
Ray:
You've said that twice already in posts and I'm only at #30. The R2000 manual in Canada lists the permeances of Tyvek/Typar and they are acceptable as part of an air barrier system. Part of their design purpose was to be able to stop wind infiltrating in through batts and then into the house or back out of the cavity (as in walls parallel to the wind). Both of these scenarios do not allow air in the batts to move reducing R value.
About 2 weeks ago, I spoke to a leading builder here that won the local R2000 builder award for the tightest house in the province three years in a row. The best house of the three had an ACH of 0.25 at 50 pascals. I've only seen one other house this tight- one that an electrician did for himself!!
The builder used the exterior sheathing membrane (Tyvek/Typar) as his main wall air barrier (yes, even with nails through it!!). The interior wall vapour barrier which was required by code was left loose and not sealed. If these products are not air barriers, why did he win these awards?
That's really interesting. .25 ACH50 is what I had through the three bath vents, the gravity damper for the exhaust hood and the two spring loaded and gasketed dryer vents. The remainder was assumed to be coming in through the windows and doors as the walls and roof were presumably airtight with the rubberized membrane applied.
Of course tyvek itself meets the definition of an air barrier by passing less than 0.02(l/s*m sq) @ 75 Pa, but in practice it is difficult to achieve acceptable performance. It depends on tape at the seams and does not play well with other materials that it must join to. It does not self seal at penetrations and can be damaged easily by on going construction, wind, and even some materials that it comes in contact with. I know that you know all this and I assume that you wish only for a dialogue so I will continue.
In the house that you mentioned, were the vents sealed for the testing?
What type of windows were used? What were their ratings?
Was a foam panel used exterior to the tyvek/typar?
Do you believe that the tyvek tape will hold up in the long term?
What method did he use to seal the roof/ceiling?
In your work, you see air testing figures on a regular basis. Doesn't something strike you as odd about these numbers?
On Dupont's website they have a test house that they prepared to show the airtightness that can be achieved with tyvek. Their test results came in at 1.437 ACH50. That was a house that was used as marketing for the manufacturer. I would assume that they paid particular attention to detail. They used only casement and fixed windows according to the pictures.
Builders here that try really hard for air tightness with taped tyvek and sealed drywall for an air barrier typically do not get much below 5 ACH50. Spray foamed houses with tyvek get down around 2 ACH50 and sometimes 1.5 ACH50. Spray foam manufacturers only claim 1.5 ACH50.
I look forward to your hearing your thoughts on this.
Ray, what is your "rubberized asphalt membrane"?
What are the other products you're using?
Any guess as to the cost of the exterior coating cost?
Joe H
Joe please refer to these links. Thanks, Ray
http://forums.taunton.com/tp-breaktime/messages?msg=58800.24
http://forums.taunton.com/tp-breaktime/messages?msg=58800.25
Good stuff.
Just wanted to help (perhaps) by clarifying that with Ray's system, the wall cavities are INSIDE the weatherization boundary.
They could be left open, like in a classic New England seasonal home. The drywall, framing, and even the sheathing are not participating in the weatherization effort here.
It's sort of like building a second weather 'wall' outside the structural wall. This second weather 'wall' is complete with vapor barrier, insulation, and siding.
That is why this design can work, even in cold climates.
An important advantage here is that interior framing and mechanicals do not interfere with, breach, or conflict with the weatherization boundary, so the interior detailing work is far less fussy.