Use Tyvek Over Building Felt Under Siding

While some believe that the original product was made from cotton rags or felt the original was made generally from squares of paper way back in the 1800 s used during the gold rush period even on the prairies for shanties roofing.

Use tyvek over building felt under siding. The industry standard for two coat stucco underlayment at least on the west coast is two layers of grade d building paper. This product soon evolved into being made in rolls using felt then fiberglass now we are back to using paper albeit a. Felt is preferred by some but i ve seen a lot of felt that has crumbled into dust so i prefer other things. Tyvek has its advantages personally i prefer it to typar because it s more durable on site in my experience.

Plastic housewrap is not advised for use under stucco because it reacts to the surfactants in cement plaster. Tyvek and r wrap lost about 10 of the soapy water column in 2 hours. Who knows what tyvek typar or the random felt you get at a random supplier tomorrow will do over the next 100 years though. Tyvek and r wrap lost about 3 of the cedar extractive mix in 2 hours while felt again lost 30.

We limited our tests to tyvek r wrap and felt since these were the winners of the first round of clean water tests. One disadvantage is that they can be damaged by the extractives that leach out of wet cedar and redwood siding a problem shared to a lesser extent with asphalt felt. Felt seemed unaffected by soap still loosing 30 of its water. Another problem with using asphalt saturated felt is that it is difficult to seal the seams unlike with plastic house wraps which can be sealed with specialized tapes that are bombproof.

Tyvek will not allow moisture to pass through it unless it is in vapor form essentially requiring it to evaporate before it can be transferred. Felt paper will absorb moisture to some degree and wick it through. The original wrb was tar paper. It is also much heavier than house wraps that are made from thin light weight plastic fabrics such as polyethylene tyvek and polypropylene typar.