The Housewrap was Accepted (sigh)

After much thought and research, I decided to accept the housewrap installation done on a rainy December 10th just before the hardi siding was slapped on.  I made this decision during the following week.  Since that time, I've been mostly too exhausted dealing with that and subsequent issues to keep up with the blog, so this post is just the beginning of an attempt to catch up.

Recap: instead of the #30 felt for housewrap I specified after much research online, Lowe's plastic housewrap was used.  Seeing this going on, I called the supervisor twice.  Finally, on the north side and the corner of the east side, felt was installed OVER the Lowe's housewrap.  I'm not sure what happened on the west side, it may have had the felt also, or just in the corner like the east side.  I never got a chance to see it before it got covered with siding (and more about the siding issues later).

As disappointed as I was with the Lowe's housewrap, which wasn't what I had specified in the interest of 75 year building longevity (my dream, etc), at least it was code legal and probably satisfactory to most building inspectors.

It was the use of felt on top of the plastic seemed like it might be especially problematic.  Sure, two housewraps would almost certainly shield the house from external water better than one.  But the issue, still an unknown, is whether the use of felt on top of plastic might trap any water that happened to get through both housewraps, ultimately leading to damage to the sheathing and framing.

I posted this issue to the DIYChatroom and got some mostly useless discussion.

My best guess is that since both housewraps are water vapor permeable, this won't happen.  So, at least I can hope it won't be a problem.

Actually, sometimes limited amounts of felt are required to be put on top of a plastic housewrap for certain reasons.  For example, with Hardiplank, one option for the butt end joints is to put extra flashing behind them and on top of the actual plastic housewrap.  In this case, the "flashing" is either a special kind of plastic made specially for this purpose by Tyvek, or felt.

Famous "building scientist" Lstiburek doesn't think housewraps are the big deal they are made out to be.  They do some good, he says, and it is AFAIK that he has used Tyvek on his own house, but he says that in almost all cases, wall failures are not related to lack of housewrap or the particular housewrap but due to other building errors, such as failures to properly flash windows.  Housewrap cannot fix other problems, and it most cases it does very little.  If you have a serious water leak, housewrap is not going to fix it.  On the other hand houses got by for centuries without modern housewraps.  Housewraps simply reduce moisture intrusion a little bit over time.  They may tend to help mask tiny building errors but won't do anything for the big errors.  Basically, water shouldn't be getting into walls, and there should be no reason for significant amounts of vapor to escape from walls either, especially from the sheathing outward.

Now one issue wrt the potential water trapping of the two housewraps I have on some parts of my workshop is how the vapor permeabilities of the two different materials add up.  My first frightening though that they might multiply.  For example, if one material had permeability of 0.05 and the other 0.15, the resulting permeability if this were true would be 0.05 * 0.15 or 0.0075.  At that point we've gone from "vapor permeable" to "not significantly vapor permeable."

Thinking about this a lot, I decided that it's much more likely that the resulting permeability of a series of permeable layers is determined roughly by the least permeable layer.  So if either one was good enough, the two in combination will be good enough also.  One obvious example of this is where the same kind of housewrap is overlapped at seams.

Now regardless of whether this was a big issue or not, I had the contractor in my hands on this one.  The felt housewrap was clearly spelled out in the contract, and they recognized that mistakes had been made, and said they were willing to do it all over again to my satisfaction.  But I decided not to have them do this.  Why?

Because I decided that tearing down the siding and housewrap and putting up felt and new siding would leave me with sheathing and framing full of small nail holes.  Now that the sheathing and siding has nail holes in it, guess what, the housewrap better be done right the second time, or moisture would slowly enter through those holes and ultimately eat the structure apart.

Now of course this is done all the time during re-siding.  One can only hope that during re-siding, the housewrap and such is done correctly.  In my case, I'd have the same crew that screwed up doing the re-installation, and they'd probably make other mistakes, along with being angry about it.

I suggested that they also tear down the sheathing and framing and then do the construction, but the builder dismissed that out-of-hand, and I suspected I wouldn't be able to get them to do that even with threat of lawsuit.

There is an inherent virtue in the original construction.  Even if it's not perfect, it's better than reconstruction, unless the reconstruction is done much better, and there is no guarantee of that.  In fact, not only is there no guarantee, I could be virtually certain it wouldn't be done correctly the second time either.  Even if only felt were installed, since these guys don't like felt much, it is almost certain they would not do single-layer felt correctly.  And some people say if felt is used, a dual layer of felt should be used.  And others say that #30 felt paper for housewrap isn't what it used to be.

I also had concerns about the siding installation.  But after talking them over with the supervisor, I decided it was all OK if not exactly as I would have wanted it.  That will be the subject of a future catch-up posting.

In any case, that was the decision I made during the heat of the battle in December, and it's far too late to go back now.

The Lowe's brand housewrap is obviously a perforated reinforced plastic housewrap.  I can see why the installers like this, in addition to being the cheapest available it's also the easiest to install.  They just staple it on.  Tyvek has to be carefully taped with Tyvek tape, something that requires a special skill.  Tyvek cannot be stapled because that would make it fracture and tear apart.  One might worry for this and similar reasons that Tyvek might not hold up well over time, either, an in fact there are reports of old Tyvek having fallen apart over time.  The great virtue of Tyvek is that it has very high vapor permeability

Some online research suggested that Lowe's housewrap is actually rebadged Pactiv Classic wrap, which used to be sold as Amowrap name.  It is tear resistant and has a permeability of 15.  That's acceptible, if no where near as high as Tyvek.  Tyvek has a moisture vapor permeance of 58, the highest of any housewrap I know about.

Felt paper, when dry has a lower permeability of about 5, which is a typical code minimum.  But it rises to 30 if the felt actually gets wet.  (Actually, I'm a bit confused between Grade D building paper and #15 and #30 felt, and I'm not sure what my builder actually used, but they all have permeance around 5-8 when dry.)

So the combination of the two housewraps would be expected to have a variable permeability from about 5 to 15.  OK, if perhaps much less than optimal.  The thicker felt layer might allow actual water to drain away more quickly, though, than the perfwrap by itself pressed up against the hardi siding.  The low end of the permeance is actually determined by the felt, so possibly I'm not that much worse off than if only felt had been used.

If, on the other hand, the two wraps are incompatible and eat each other apart, the worst that could happen is that it would be like having no housewrap.  But that would actually have the advantage of greater permeance.

Another thought is that mistakes like this happen all the time.  Buildings are, in climates like mine, quite forgiving.  Lots of mistakes can be made, and a building will still go without serious problems for decades.  I'd probably get decades of use out of a building constructed only with plywood, like my sheathing.  I have truly lousy Masonite hardboard on my actual 28 year old house.  Parts of it in the front (where there was water spash) deteriorated and had to be replaced.  But the rest of it is actually still holding together with the original 28 year old paint applied by the cheapest tract home builder in San Antonio (Rayco) which no longer exists.