Insulation, Radiant and Vapor Barriers - Fiberglass and humidity

Well, my wife and I have decided to settle down in Japan. My wife is Japanese and her family has some land but it is farm land. We are now finding out how fun(satire) it is to rezone the land from farmland to house land.

But my real question is about houses. We have looked at a variety of homes and it seems that many of them are quite nice. But some of them cut corners to make the price lower. Out of all the houses and companies that we have looked at we like Selco homes. They are imported 2x6 built homes from Cananda. They have solid wood floors, while 6 panel doors, vinyl windows and loads of insulation. They do use fiber glass insulation and some builders have told us to stay away from it as it can absorb moisture etc and cause problems. The builders are pushing a hard foam type insulation(expensive) but Selco does not offer it. How big of a difference is it? I am aware of all the humidity problems that many homes in Japan have. Should I go with the foam and choose another house or is the fiberglass OK?

I understand the whole vapor barier idea. The Selco home wall is as follows from the inside out.
wallboard-plastic vapor barrier-insulation-plywood sheeting-semi permiable sheet-siding
Note: there is no space(air) between the siding and the permiable sheet. Some builders have stated that this is very important. Is this true? Does it matter so much.

I would appreciate any pointers on what is needed to get a good decent home. So any opinions would be welcom.

Thanks,
Sdskinner

That Selco homes sounds good to me . And if its from canada You know it gets cold up there. I find homes dont go bad from the out side in, Its from the inside out. That poly V/B under the drywall on the inside of the home is the key for a good home. We put a V/B on a home even when the fiberglass insulation has a paper on it to room side. Also on the ceiling then the drywall. Have had no troubles this way over the years and I have seen it down to -15f
Dont forget if you are on a crawl space to also put down a 6 mil poly on the ground there ED ;)

Thanks for the reply. I too think that they are good homes. I am only a little worried about the high humidity here, especially in the summer. It gets very humid and our winters are fairly mild.
We only have a few days that are below freezing(32F). Do you think we will have any problems. And does having a space(air) between the house wrap and the siding make a difference. ? Selco doesn't have a space and some people have told us that not have the space decreases the air circulation and therefore increases your condensation problems.
And lastly the Selco home is most likely way over insulated for our area. Are there any problems that can come from this?

Thanks,
Steve

lastly the Selco home is most likely way over insulated for our area. Are there any problems that can come from this?
Not that I can think of. It should help for the AC side of things. Id look more to does the attic have vents in the over hang and out the roof also



I am only a little worried about the high humidity here, especially in the summer. It gets very humid and our winters are fairly mild. Then why are you going to this 6" wall over the 2x4" wall then? will you have AC in the home there?

I have lived down here in Florida for the past 19 years. You think you have humidity there HA. Furnace was on about 4 weeks this year

does having a space(air) between the house wrap and the siding make a difference. ? Selco doesn't have a space and some people have told us that not have the space decreases the air circulation and therefore increases your condensation problems.

This kind of wrap lets the air in and out dont need the air space

ED;)

http://www.eere.energy.gov/consumerinfo/factsheets/bd4.html

This site discusses areas where high humidity is present and the concerns with the applications of vapor barriers. When they discuss HDD (Heating Degree Days) concerning vapor barriers, they are talking about areas where they experience cold winters. This is because when heating is used a lot within a structure, the concern is with heat transported moisture. This is where vapor barriers work the best. On the othe hand, in areas where high humidity is present a good portion of the year, the site discusses air barriers and/or air/vapor barriers. This is because the concern with condensation inside structures come from air transported moisture.

So your area climatic conditions dictate the appropriate application. Since you experience high humid summers and mild winters or a low HDD for your area, it would rule out the Selco house. The foam house would be a better choice because it prohibits air movement inside the wall cavity. This does not mean that fiberglass could not be used in your area. What it does mean is that an air/vapor barrier should be applied to the outside under the siding to prohibit air movement into the structure.

Though one can easily understand that no-one wants to trap humidity inside the structure. It is just as understandable why people are confused when applying an air/vapor barrier to the outside of insulation. The thing to remember here is that vapor barriers specifically address the source of humidty. In cold climates, the source of the humidity is the heating of the house. In warm humid climates, it is the heat and humidity outside the house.