Cedar shingle install

odo53September 10, 2008

I am planning to install white cedar shingle siding on an exterior wall. I have read that the preferred underlayment is #30 felt and I have read elsewhere that I must use house wrap for wind protection. I have read that cedar shingles should not be put directly over house wrap and I have read that they should be put directly over house wrap.

Choices are:

sheathing-#30 felt-shingles

sheathing-house wrap-shingles

sheathing-#30 felt-house wrap-shingles

sheathing-house wrap-#30 felt-shingles

Any advice is much appreciated.

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Modern housewrap is made to "breathe" by allowing cool air and moisture that builds up between the siding and the sheathing to escape. The industry that makes the product claims that the micro-fiber construction allows for moisture and condensation to escape while not allowing air and moisture to enter in. Its hard to know if this is true as we just install the stuff, cover and that's it; we don't normally go back and do a check later. If your house is air-tight, moisture penetration and condensation build-up can be a real issue.

I've taken clapboards off of 100 year old houses with the rosin paper still intact underneath.

I wouldn't use felt paper as a house-wrap material. I don't know of anyone who does. It is saturated with oil and it is made to not allow any penetration of air either way and does not have any moisture wicking properties like house-wrap is designed to have.

That's my take, I just wouldn't use felt paper, I'd go with housewrap and definitely wouldn't combine the two; one or the other.

    Bookmark   September 10, 2008 at 10:26PM
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Wow, that's a lot of misconceptions in one response.

Housewrap is not designed to breathe; it is an air barrier. It does not allow moisture to escape from the space between the sheathing and siding; it allows moisture vapor to escape from inside the wall cavity toward the outside of the house.

Building paper/felt is saturated with asphalt, not oil and has the ability to wick moisture where housewrap does not.

There is nothing wrong with building felt as an underlayment and it is often favored over housewrap under cedar shingles becasue the surfactants tend to break down the surface tension of water and that allows it to pass through housewrap. If housewrap is used it should always be the non-woven, non-perforated kind like Tyvek and Typar. Typar is the most resistant to cedar surfactants.

All underlayments are susceptible to surfactants but building felt has the ability to dry out after getting wet where as housewrap traps moisture behind it.

There is no reason to use two layers of underlayment.

I have often used building felt behind cedar shingles and clapboards and many contractors still believe it is better than housewrap.

    Bookmark   September 11, 2008 at 8:13PM
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