I have worked on many homes and the rule for vapor barrier was “nearest to heated space”! This is the rule for cold climate construction. It is supposed to stop migration of moisture from the heated space into the insulated space. Right? If insulation becomes saturated with water, it looses its’ efficiency. Also, it will cause the framing members to rot!
My problem is: I work in an area that is cold in the winters and very humid in the summer months. The reverse occurs during summer months when there is very high humidity. The vapor barrier is to the inside, the homes are air conditioned so a condition exists where the humidity within the house is low but the humidity outside is very high. The hot humid air penetrates the house wrap and migrates inward and condenses on the outer surface of the vapor barrier. It is acting the same as a house with an improperly installed vapor barrier (many leaks)! Now you have moisture in your wall cavity and it is short circuiting the insulation and causing rotting conditions or at the very least (mold conditions).
Dupont distributes a product in Japan that is used as the vapor barrier. It is similar to Tyvek or other house wraps where it allows a certain amount of water vapor to pass but not water as a liquid. They claim that this vapor barrier will allow a certain amount of water to pass to the conditioned space and the air conditioning will remove it by dehumidification. In that way preventing moisture from accumulating within the walls.
In the United States, I have only worked in very cold climates. For the past 10 years, I have worked in Japan and the problem keeps coming up. Many companies have different solutions for the problem and get government certification for their processes. How are vapor barriers used in Mississippi, Alabama, Florida, Georgia (ie the southern states) where the winters occasionally have temperatures near 0 degrees F, but summer temperatures and humidiies that are extremely high? I build 2×4 American Style homes in Japan and want to give the best product to my customer.
Does anyone know the proper placement of a vapor barrier in hot humid climates?
Edited 11/29/2005 6:00 pm ET by mikku
Edited 11/29/2005 6:45 pm ET by mikku
Replies
Start here and see what if closes to your climate. My guess is Mixed-Humid.
http://www.buildingscience.com/housesthatwork/hygro-thermal.htm
Then look that the recommendations for that climate and representive house designs on this page.
http://www.buildingscience.com/housesthatwork/default.htm
Also look for background information and research papers in the Technical Resources page.
Thank you for the links. It is going to take quite a bit of time to navigate that website. I'll report back after thoroughly reviewing the information.
Thanks again
Man after looking at those links, and the one below ,I ordered the bulldozer for the shack in the mixed-humid zone. (:-) In the spring I am going to pull some of the vinyl siding and see what is going on with my house I built in 98. I do not see any problems at this point.
Starting from inside : 1/2 drywall, 6 mil poly, 2x6 stud cav with cocoon cell, 5/8 osb, a 3/8 polystyrene foam, a foam wrap with thin poly and expanded foam, vinyl siding. Ceiling is 1x6 white pine t&g then 6 mil poly and blown cocoon cell (supposedly to r41). The more I read the more I am not sure this was the right approach.
http://www.jlconline.com/jlcupdate/2005/0511/0511fg.html
Edited 11/29/2005 8:37 pm ET by rasconc
I know what you mean.I built in 79 and had 2x4 walls with FG. But poly "vapor barrier" on the inside and 5/8 polyiso on the outside.And I did not know anyhting about detailing and neither did the builder.Now I don't KNOW of any probems, but I expect some when I open up an outside wall.I did find out 2nd story window where the poly had been pushed throug the rough open and formed a pocket that held water and rotted out the exterior trim.And I have 2 doors on to a 2nd story deck and had problems with them leaking and water coming casing on the windows below.
We will see what happens. I think I will pop a couple of pieces of siding and do a core sample. Or I can let the heirs worry about it.
I looked over the links at building sciences and they are very interesting. It is difficult to make a decision of which zone to use, probably mixed humid. We get a lot of rain here though, over 72" a season!
I have concluded that siding with an airspace, house wrap as a drainage plain, foil faced foam (vapor barrier?), wall sheathing for shear (seismic/wind), fiberglas batt insulation, and drywall taped and painted may be the best solution. Best? or safest is unknown. Maybe another layer of house wrap beneath the drywall but still undecided.
Anyway, thanks for the information and keep helping!
Mikku
(next discussion, mandated by building code air exchangers?)
Edited 12/3/2005 5:38 am ET by mikku
Check out this recent thread.
http://forums.taunton.com/tp-breaktime/messages?msg=65988.1
Thanks, I just read through it. I will have to take a little time later to respond because my response is a case study of a project that I did about 15 years ago.
mikku
I have a few minutes now and I will tell you a few horror stories of my experience with vapor barriers.
Case 1: Around 1980, I was contacted to do some repairs to a dome house. The house had been constructed about 8 years earlier and the customer was very happy with the structure, except for the fact he was having some leaks that he needed repaired. The dome had been constructed with large OSB panels sheathing over 2x6 structural grid. All the 2x6's were connected to metal hubs. It was a giant erector set, with a diameter of about 30'. Also, the exterior surface of the dome was covered with an elasmeric type paint (spelling???) The surface was really thick like 1/8-1/4" and extremely rubbery. I had to check around some of the triangular skylites because of leaking. This was in late October when I first looked at the job. I poked around and the owner finally allowed me to open the exterior and see what was going on. When I started cutting the rubber membrane, the entire surrounding area felt spongy. When I tugged at the membrane, the sheathing came off along with the rubber. Most of the sheathing had disintegrated in that area. Once opening up one of these triangle sections of the roof, I found that it had been insulated with some kind of foam. But the foam had no strength to it. It held its' shape until you touched it then it fell apart also. The more I dug, the worse things appeared. The 2x6's that formed the framework for this dome were rotted 2/3 the way through. The poly vapor barrier to the inside was intact and the interior surfaces of the dome (3/8" plywood) seemed undamaged except for some staining where water had leaked. This is scary, The place where I was working was about 30' in the air, I had a rope tied onto an eye bolt that was at the very pole of the dome and I am seeing that the structure is being held together at some points by 1 1/2" of wood! Now this is Northern Minnesota and heading into the winter! We decided to make some hasty repairs and leave the work go until spring. Who wants to be on top of a dome when the outside temperature reaches -40F and occasionally -60F in January. On top of that dome, the only thing breaking the arctic winds were some Poplar trees (leafless in October). Over the winter, I met with the customer several times to try to figure out what to do. In my mind, it would be better to demolish the structure than to just repair parts. Any repairs only would be like band-aids and really no fix. The customer said that they loved the house, that they intended to retire there and live there the rest of their lives. They wanted me to fix their problem.
I came up with a solution that would re-build the roof; section by section. We determined that we wanted to increase the circumferance to allow for 12" of glass fiber insulation to be installed along with 4" of airspace. We would open an area; remove the foam insulation; replace or repair damaged 2x6 struts; use plywood gussets to extend the structure outward 16"; install an exterior 2x4 strut and frame in the triangle so that it could be re-insulated and sheathed. This was a major undertaking. Also, I needed to create an air opening at the lower section of the dome to allow air to enter and an opening at the top for it to escape. This was done by installing ventilating aluminum soffit at the bottom and constructing a 5 sided cupola at the top that mimiced the appearance of the dome, except that it was raised about a foot above the roof structure. I constructed it, flashed it as I went and installed insect screening at the very top to keep bugs out, yet still allow air to circulate. Once all this work was completed, a roofing contractor finished off the job with asphalt shingles. They did a real nice job and the project looked great. That was a long time ago. I believe the customer is still living there, retired and happy (I think)! We are still friends but live in different parts of the world now.
That was a case of a poorly installed interior vapor barrier. In theory, the system should have worked great. No water in the structure, no damage, no need to ventilate. But the vapor barrier was not continuous, the foam was inadequate and the structure was severely damaged. "Double vapor barrier" no place for the water to go!
I really try to solve problems when I build, or remodel. Next time, I'll talk about a modular home that needed similar repairs (only 7 to 8 years old!)
Now I have to go study those links.
I am an hour out of Tokyo where the plains meet the mountains. This area gets a lot of rain. Sometimes during storms, you can easily get 4" of rain per hour! I do not have access to temperature degree days or annual rainfall amounts. If someone has some ideas how to get these figures in English, that is another challenge. We are now entering into the winter months. Morning temperatures are near or at freezing but the afternoons are still pleasant. The cold temperatures don't come here until late February or March when the southern Alps fill up with snow and the cold from the Japan Sea Side works its' way over. We had 21 or 22 typhoons this season, similar to the U.S. Gulf Coast.
The summer starts with the rainy season --usually all of June, extending into July, sometimes later. You can have rain every day, or several times per day. It is usually overcast and muggy this time of year. When the rain clouds disappear, you are hit with scorching heat and humidity that suffocates you. The heat lasts until late August when it can start raining again. But not like the spring. The fall is great! The winters are mild and dry. You try to schedule your work around the weather, that is have finishing work that carries you through the rainy season. But that cannot always be the case.
Back to the links,
mikku
Hi, Mikku,I'm also in Japan, out west of you, in the good part.Having made the rounds of Japanese builders recently, and drilled down into their literature pretty deeply, I'd say they are a pretty confused and confusing lot. There are over 600 different patented techniques for housebuilding. It's also pretty clear that their way of using fiberglass insulation results in a black soggy mass in about 15 years--which is about when a house is normally written off anyway.I figured out one time the degree days for central Honshu, and it works out to a climate roughly the same as DC. Somewhat cold in winter and hot and humid in summer. Building Sciences calls this a "Mixed Climate", in other words, you have to both heat and cool. In the end, though, heating bills are higher than cooling.There's a Taunton book out called "Builder's Guide to Mixed Climates"--you might want to get a copy of that. The wall systems illustrated in the book have a couple of inches of taped and sealed exterior rigid insulation as the vapor barrier, or "air flow retarder". This corresponds to the Japanese "sotodannetsu" (external insulation) approach, 3 to 5 cm of high performance rigid foam, taped and sealed, then house wrap, rain screen, fiber cement panel, paint/stucco. Rather more expensive and seldom done in my area, but I think this is probably the superior approach, among all the 600 different Japanese approaches.One up on this approach, though, the other day I was in a tract development and I saw some carpenters installing Asahi "Power Wall" 60 mm hebel cladding on the outside of a stick framed house. They were screwing it down right over the housewrap with 90 mm screws. I think this is a very high performance and ideal approach for a stick framed "urban" Honshu house, because you've got everything in one inexpensive layer--4 hour fire rating, soundproofing, insulation, projectile and rain barrier. Plus it can all be installed by the carpenter, and you don't need to call in another skilled trade. If you want more insulation, then you just sandwich in a layer of the yellow foam under the housewrap and voila you've got a very airtight R-2O wall with no place for black mold. Big discount on fire insurance, too.Anyway, I think you will have a hard time selling these more expensive wall systems to Japanese customers. They seem to be willing to splurge gadgets and gizmology in their houses but not on sound construction (most of em) or proper insulation. For goodness sake, single pane windows are still the norm for new construction in Japan!
Hi Talkingdog!
Out west of me? Where? I am now in Tochigi-prefecture but have worked in Japan from Nasu to Naha but my farthest west was Wakayama-prefecture, Shingu-shi. Much of my time I spent in Shizuoka-prefecture. Tochigi still has some inexpensive land available, fresh air and great scenery--some of the reasons I'm here!
At a recent energy fair, sponsored by Tepco, I saw one companies idea of "sotodonetsu". At first, I did not know what to think and now am still undecided. They fur out the exterior of the house after the sheathing is installed; apply the rigid foam (similar to thermax); tape the joints; fur the wall again (leaving a space for air circulation-behind the siding); then install the siding material. The wall sheathing has holes drilled through it to allow for circulation of air from the stud cavity to the outside and no vapor barrier is installed to the inside.
The roof system is as complicated! Roof is normal rafter construction with foam directly attached to the top of the rafters; then furring strips (or an additional set of rafters) are screwed down to create an air space; then normal sheathing/roofing system.
There is some other detail about insulated crawl space and heat tapes in the "doma slab" with an outside air inlet. This is way too complicated to process in my mind--cost vs benefits. It all looks good on paper but will the craftsmen do their jobs according to design or just sluff through it?
The homes that I have built here all use "pair glass/with argon", energy efficient doors, imported doors and trim, cabinets (sometimes lighting & plumbing fixtures), and more insulation. That is why I am inquiring about the vapor barrier! I have to see and believe what I see before presenting my case to a customer. Some customers are very savy to construction techniques. Others could care less about the design, or operating cost of their homes. Some care "only what it costs to build" and what color it is (like buying a car!)
I am very possessive with every home that I build, like it is (my house) until I turn it over to the customer. I am a craftsman who builds houses, a bad businessperson because I'll never be rich from all my efforts. I worry too much about the product and not enough about what is left when the day is done.
Maybe there is "no answer" to the vapor barrier question. Or maybe the answer is "no vapor barrier"! Houses never had problems with indoor polution, excessive humidity, mold and spores ..... the list goes on. When the houses were not insulated. Lots of cool fresh air, or hot humid air! And these structures lasted lifetimes, rather than years. Maybe just install enough insulation to make the interiors more comfortable, use "Tyvek" as an air infiltration barrier/drainage plane; and "Tyvek" on the inside as a "semi-permeable vapor barrier". Then the question comes up-- "Does tyvek or any other house wrap still trap water in the wall assembly?"
Like you said, there are 600 different Japanese approaches. I have seen "Power Board" but that is a light-weight concrete siding panel. I have not seen "Power wall". Power board needs all the joints to be caulked and the surface painted. It is very absorbant to paint and I have seen several projects where the caulking failed. As you know, both caulking and painting is usually left to professionals only.
What are you ? a builder; architect; engineer? Maybe there should be a group of foreigners building homes in Japan association!
No vapor barrier, you say? I live in an ancient Japanese house in Khhotthat meets that description. Our vapor barrier is newspaper rolled up and stuffed in the cracks! Actually, we do have rice paper windows in some places, but the kids often punch holes in them with their inquisitive fingers, so we have to go around gluing on little paper patches. Great house until you start wanting heating/AC. Then it costs you. We burn massive amounts of kerosene to keep the main rooms of this place warm, even though it does not get what I would consider real cold, rarely even a hard frost.Your description of sotodannetsu sounds a lot more complicated than what I have in mind. People are so unscientific. On the one hand they want high performance insulation, then at the same time they want to let the house breathe.I guess I had that AAC cladding wrong, it is "Power Board". You are right, it's held together by caulking joints. But there should also be housewrap behind that. I think it should be installed rain screen style, but the last one I saw had the board nailed right to the housewrap.
Hi again!
I said "no vapor barrier", I didn't say "no insulation or air filtration barrier"
The ancient Japanese house that you speak of would probably be alot warmer with just tyvek house wrap covering the outside (or inside). At least it would not be drafty any more and the kids would have a lot harder time poking their fingers through it. You might not be able to use unvented kerosene heaters inside either. I am not sure though.
Also this ancient house if you stripped back the wall coverings, if it is old enough it might be "doro kabi with bamboo reinforcing". That is a mud wall, something like the make-up of a birds nest. You would probably find the framing timbers in excellent condition (great wood for recycling into other things). The only exception would be around wet areas- like a bath, kitchen, or laundry area. You might find "shira-ari" or some other damaged wood. But nothing like some of the projects I have seen and repaired.
About two months ago, I had to do some work on a house in Shizuoka-prefecture that was only 7 years old. There was some problem with water leakage around a kitchen door. When I opened the wall up, the vinyl vapor barrier had been installed in the inside and wrapped around the door opening and stapled to the exterior sheathing. The stud and trimmer in that location had completely rotted. That is only seven years! The customer still has 23 years to pay on his house mortgage! This is the kind of stuff that scares me. A little mistake here, another there and pretty soon you have big problems. Luckily this was not a house that I built or finished.
I am trying to determine a "happy medium" for dealing with insulation/ vapor barriers here. What I have seen examines the "building envelope" but doesn't take into account opening and closing doors and windows and the effects of human occupancy. People here use their air conditioning for cooling while they are at home only and do not recognize the benefits of dehumidification. They come home; turn on the aircon; cool everything down quickly; sleep under a futon and open all the windows up in the morning! Then they hang their futons outside to air out and put water absorbing chemicals in the closets to prevent mold.
I believe the proper use of airconditioning is for humidity control mainly. If you can maintain an indoor temperature 3 to 5 degrees F lower than the outside, and bring down the humidity you will feel comfortable. But that means 24 hour per day conditioning to be effective. And you need a structure that will maintain reduced humidity levels and slightly reduced temperatures, without condensation in the wall cavity.
There must be a way to accomplish this easily and inexpensively. This should not be rocket science!
Most houses here, either zairai or my style (2x4), apply some type of a furring strip on top of the tyvek before siding. This creates an air space for the siding to breath. Installation specifications show how you should keep this air space open from bottom to top so that air will flow freely. Many of the installers ignore the rule though.
I have been in the building trades for a very long time but every day must be a learning experience. Always happy to hear new things and try them out!
Actually, this old house is pretty much in its historic condition. That is, the mud walls are "in play" and the bamboo is visible in corners. I could renovate it, but then I would destroy what's left of the historic quality. Anyway, the ants have eaten the cores out of most of the posts by now--some are just a rind. I've patched it up over the years but I just cannot keep up.As for the subject of heating and cooling, the average Japanese household uses about 25% of what an American one does, and part of this must be due to the Just-In-Time approach, exemplified by the tankless hot water heater. Or the mini-split ACs, hot carpets, etc.If you propose something like central HVAC, people look at you like you are crazy, the running cost is thought to be too high. Actually, though, in a well-built house, and optimized central system such as Takenaka produces will get through the year on less than $150 mo. Which is not bad, considering the high cost of electricity. They really do need to have aggressive dehumidification four of five months out of the year, no matter which of the 600+ types of construction they have.
Actually, if you read the Building Science recommendations for mixed climates, you should not be putting vinyl wallcovering up everywhere, which is what 99.99% of Japanese houses do. Vinyl wallcovering is a vapor barrier. No wonder the houses rot.