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Alternatively is there anywhere I can read about wall assemblies/insulation/dew point etc specifically for Seattle's climate (figuring its nearly identical to Vancouver's (Canada)). From what I can gather that would be "Zone 4 - Marine".
When combining exterior foam insulation with fiberglass, cellulose, or mineral-wool roof insulation, the foam layer must be thick enough to keep the sheathing temperature above the dew point. Otherwise, water vapor can condense on the back side of the sheathing, elevating the moisture content of the materials and possibly resulting in mold and rot.
Answer: It depends on the temperature differential at any given point in time. Could be half way into the wall cavity, or 1/3rd. And it varies depending on real R values at any point in the wall. Adding exterior insulation simply moves the dew point more to the exterior. Adding most anything to the exterior moves the dew point further out.
This is a little counter-intuitive, but with more batt insulation, you need thicker XPS to avoid dew point problems inside the batts. I am a big fan of insulating the actual pipes that feed your radiators (and also hot water or cold water lines), in addition to the overall insulation to improve comfort and reduce heat loss.
Hi Mark. Moisture will not condense on a surface unless that surface is as cold or colder than the dew point. Dew point is the lowest temperature at which moisture will begin to condense out of the air. As air gets colder it holds a lesser volume of moisture. As it gets warmer air can hold a larger volume of moisture.
The exterior wall would have no sheathing to rot and the interior wall's OSB or CDX would have 2/3rds of the R-value between it and the weather, keeping the dew point away from the sheathing. The exterior wall would only be covered by two layers of 30# felt with hemmed and taped laps, then furring to create a 1/2" rain screen gap, then paper ...
Closed-cell spray polyurethane foam may be the best insulation available today, but it is expensive. Fiberglass batts, on the other hand, are inexpensive and insulate fairly well, provided they are installed correctly. Combining the two, in a system called flash and batt, couples the air-sealing strength of spray foam with the cost-effectiveness of fiberglass batts. Flash and batt begins with ...
Because the calculator goes beyond the limits of grade, live load, and dead load in the DCA 6 and IRC tables, you can design decks that fall outside the table limits. For instance, if you know the dead load of the deck will be less than the prescriptive 10 lb., then you can select 5 lb. or 7 lb. and eek out a longer span.
Use a dehumidifier to keep the humidity below dew point. Stop breathing, sweating, cooking and washing to keep water vapor out of your home. Leave your home empty during cold weather. If you keep your indoor temperature at 70°f and your relative humidity 65% then dew point is 57°f. If you change your relative humidity to 45% then dew point is ...
With enough rigid foam to keep the roof sheathing above the dew point during the winter, it’s safe to install fibrous insulation like fiberglass batts between the rafters. This type of roof works only when the foam layer is thick enough; colder climates require a thicker foam layer than warmer climates. Unvented roof: Pile on the exterior foam.