If I don’t cool my home on summer, should I think like I’m in a cold climate when I design my wall assembly?
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| Posted in General Questions on
In regards to vapor difussion, in a mixed-humid climate, where no AC will be used in summer, should a Cold Climate wall assembly design work just fine?
In other words, does the special concerns we have to consider when designing a mixed-humid wall assembly, have to do with being able to work succesfully and withstand both heating and cooling seasons? What if I don’t have a cooling season (No AC in my home), should I just use a cold-climate approach?
This is for Pucon, Chile, which has a climate like US’s 4-C, or Marine.
Thanks.
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In Pucon the mid-summer outdoor dew point averages are about 50F, so it kinda doesn't matter whether you air-condition it or not.
http://weatherspark.com/#!dashboard;q=Pucon%2C%20Chile
During the cool July/August period the mean outdoor temperature is about 46F, and the mean outdoor dew point is about 40F. This is more akin to a Crescent City CA winter climate, if a bit warmer in summer, which is more like the WARM edge of zone 4C, maybe even cool edge of 3C.
http://weatherspark.com/#!dashboard;a=USA/CA/Crescent_City
So basically, you don't need any true vapor barriers- latex paint would be a sufficient interior vapor retarder. Roof overhangs of 12"/30 cm per story of height would be useful for limiting the direct wetting from the exterior. If it is a sheathed studwall & siding type of wall assembly it's useful to leave at least a 6mm (10mm is better) gap between the siding and the sheathing as a capillary break between rain-wetted siding and the sheathing, and as a drying path for both siding & sheathing.
Wow you certainly did a quick research! The thing is that, in Chile, we lack the comprehensive climate info and facts you have all around the US... mostly we have to guess. And try to compare to the US zones and parasite your data by trying to find analogues.
As you can see the weatherspark link relies on Temuco info, which is nearer to the coast, gets more rain and doesn't get as cold as Pucon. To get things even harder, I could tell you that my actual building site is not Pucon, But Reigolil, which is further east, just by the Argentina border. Less rain, More cold (and Heating Degree Days). That's why I jumped to 4C confidently.
Anyway, I think your advice applies to any of these, as the differences should not be much, but could I expand my question? What if, as you say, I use sheathing under siding (I totally agree with leaving the gap, and making a rain screen system), but if I use some 2" or 3" inches of EPS as that external sheathing, would a semi-permeable interior vapor retarder, as latex-based paint, be the fit?
Thanks for your advice
PS. the main question remains answered.... generally speaking, for a mixed humid climate with no cooling system, would a cold climate design work just right?
Jose,
In many cases, walls that work in hot climates also work in cold climates. The wall design doesn't necessarily need to change based on whether a home is air conditioned -- especially if you avoid the use of interior polyethylene or vinyl wallpaper.
Your plan to include 2 to 3 inches of EPS foam on the exterior side of your wall sheathing, and latex paint on the interior, will work fine. If you ever change your mind and install an air conditioner, it will still work fine.