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The siding company is having to redo the installation of my siding. I know the wrap underneath the siding that will be removed will end up having lots of holes after the planks are removed. The installer is planning to put up HardieWrap. I originally had paid extra (5 years ago) to have them install Dow Weathermate Plus house wrap. The installer is paying for all of the materials this time.

  1. Would it cause a breathability problem to double wrap a house?

  2. How does HardieWrap compare to other products on the market?

They said they can put the new wrap over the Weather mate Plus or tear it off. I am concerned about a breathability problem if I let them install it over the top of the other wrap, but I don't have confidence in the new product because it is fairly new on the market and I cannot find much information on it comparing it to other products like DuPont Tyvek. I was just told that the company has already ordered the materials and is coming this Tues.

What is the recommendation on HardieWrap? I know their siding has a great reputation, but is their wrap adequately tested?

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There is no problem with doing this. Housewrap is "breathable" by design so you won't trap moisture anywhere. You could build a wall with ten layers of housewrap and it would be more durable, not less.

Regardless of how many layers you have, it's critically important to make sure your windows and doors are properly flashed to the outermost layer slash the one with the most integrity. When the installers complete this work, don't let them get away without re-flashing all your windows and doors to the new layer of housewrap.

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  • One caveat: what you say is true as long as all the housewrap is on the outside of the insulation -- housewrap on the inside of the insulation leads to condensation and eventually mold when you turn the A/C on. – ThreePhaseEel Jan 17 '16 at 2:00
  • I have never heard of anybody being so foolish to put housewrap on the inside, under the drywall. What would be the point? You may be thinking of poly vapor barriers, which are indeed a bad idea because they are vapor-impermeable--unlike housewrap. – iLikeDirt Jan 17 '16 at 2:43
  • There are people up in the frozen north who put their plastic on the inside of the insulation, yes... – ThreePhaseEel Jan 17 '16 at 2:49
  • Poly inside, housewrap outside. We have plenty of humidity and air conditioning in Minnesota, and mold isn't a problem in most cases not related to damp basements. It certainly doesn't cause condensation on the drywall or inside the walls. – isherwood Jan 17 '16 at 3:49
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    It will if you keep the poly in the wall and apply stucco over a single layer of tar paper in those climates! This actually happened in that region. buildingscience.com/documents/insights/… greenbuildingadvisor.com/blogs/dept/musings/… – iLikeDirt Jan 17 '16 at 4:50
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Hardie products are good quality in general. As a long-time builder and carpenter I'd have no concerns about using it (in accordance with their literature).

Here's a study that seems to indicate that two layers of housewrap should be the standard. To me, that says that adding a second layer won't cause problems. That said, they're disparate products, and it can't be said for certain how they'll react to each other. I'd consider giving Hardie a call and asking them about it.

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Dupont specifically says that covering old Tyvek with TYVEK is ok. I think the verbiage was "as long as it's Tyvek". Could be covering tail, but worth heeding, IMO.

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    Do you have a source document you could link to for that? – isherwood Dec 19 '17 at 1:44

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