watch the best practice video on installing flashing. the announcer describes installing house wrap over flashing in which the carpenter is leaving it underneath the flashing allowing water penetration.. unless they are going to pull it out and over later???? but it seems they already nailed thru it. I see this all the time resulting in water damage..............
do you know how many times i have heard that, then why install the house wrap. If you put the house wrap under the vertical section of the flashing any water penetration above the flashing will allow water to penetrate. it will run down the side of the house until it meets the flashing and go behind not over the surface of the flashing and out. around windows for example is a way for water to penetrate and run down behind the siding. We are not talking about gallons of water but this does pose areas for termites to congregate for water supply knowing it will remain damp for extended periods of time. Most of the time when you see house wrap under the flashing you also find it over the plastic around a window installation where the water penetration is right at the window and on onto the sheathing behind the house wrap=carpenter ants and termites. quite frankly house wrap and flashing serve a very specific purpose and it only takes a few seconds to wrap a house properly to minimize water penetration extensively.
House wrap is not intended for use as water control, and that is not its purpose. Its purpose is to mitigate aginst air penetration and drafts. Neither is typical flashing intended for control of water that may have penetrated the finish. The purpose of the flashing is to protect the intersection of two materials or planes of costruction. As I said, if these items are being depended upon for control of water, then something is SERIOUSLY wrong somewhere else, and needs to be corrected.
Architect (NY) and Home Designer (PA)
Posts: 2507 | Location: Tobyhanna, PA | Registered: 24 October 2005
House wrap and flashing do serve to help in decreasing water penetration. show me a house without it and i guarantee you will have serioous damage and water penetration. Let me ask you another question? why do you install house wrap or felt from the bottom of the structure working your way up so the next layer overlaps the lower. is that to prevent drafts?
Richard, you mention that house wrap is not intended for use as water control and flashing is not intented to control water that may have penetrated the finish. As the house we are building will have all brick veneer, I would like to get your take on "best practices" for water control. First off, it has always been my impression that the job of proper flashing is to control water after it has penetrated the finish since the brick veneer in itself will not stop water from penetrating. Second, it has also been my impression that house wrap or building paper serves the same purpose (with the proper flashing) to also control water after penetrating the brick veneer and allow the water to exit through weep holes after it has traveled down the plane containing flashing/house wrap/building paper. Now I'm concerned with what I am planning to do. Recommendations or clarification would certainly be appreciated. Jeff
Housewrap is designed as an air infiltration barrier and is not designed as a weather barrier.
When used as a secondary weather barrier, housewrap functions to repel water only by the surface tension of the water upon it.
The problem is, that surfactants used in the adhesives of structural sheathing in contact with the housewrap will actaully break down the surface tension between the molecules of water and allow the water to penetrate housewraps quite readily, holding water tight up against the home where it will do damage to the framing structure.
Housewraps in general can actually add more to water damage of a home than they can help prevent it.
And because modern building codes, such a New York State's, also require that all seams in structural sheathing be sealed and/or taped, (See New York State Residential Code section 1102.4.1) there is actually no requirement at all for a secondary weather barrier such as housewrap or anything else to be used under exterior wall coverings depending on the exterior wall covering material used. The sheathing itself is enough to act as the secondary weather barrier when sidings such as aluminum, steel, vinyl, or wood are installed.
See Table 703.4 of New York State Residential Code:
In such cases, properly installed and sealed flashings without housewrap or any other barrier are all that is required to provide the structure with adequate water protection around door and window openings, roof/wall intersections, above foundations and elsewhere.
Water that does penetrate the wall covering material simply stops at the surface of the structural sheathing and runs down and out of the structure without damage.
Other exterior wall covering materials such as brick do require secondary weather membranes, but these membranes are not typical housewraps but other specialty wraps designed for the specific application.
So I agree with Rich.
If you are relying on secondary weather barriers like housewrap to be the primary water intrusion protection for the structure, the structure isn't being built right.
The structure should be waterproofed without the need for housewrap by the exterior wall covering and the flashings alone.
Housewrap should only be there for an added level of protection and not serve as the primary one.
And for what it's worth, tar impregnated felt still remains a better product than housewrap for secondary water intrusion protection, if one insists on using a secondary barrier at all.
When required, I only use felt paper, never housewrap.
So while the best practice video may be technically incorrect, it shouldn't make much of a difference if the flashing is installed properly.
This message has been edited. Last edited by: homebild,
Homebild, thanks for the reply. To reiterate, I certainly understand the need for proper flashing as well as the need for secondary weather-resistant materials but my confusion is I was under the impression that building wrap and felt provided that. What I am gathering from you and Richard is that building wrap does NOT provide me the protection but felt DOES. You also mention there are other specialty wraps that will provide this as well as properly sealed structual sheathing. So my question now is if this was your home what materials would you choose. As it currently stands the house is to be 2 story, 2X4 construction over 10" poured walls with brick ledge with walkout area on the back side. Walls will have R-13 fiberglass insulation. I had then planned on using 7/16 sheathing with building wrap and brick veneer. I am certainly at a stage where any of this can change (except the brick veneer) but want to do it right. BTW, I did go through Chapters 7 and 11 of the New York State Residential Code. Thanks for the link. Also, if it makes a difference regarding your recommendations, I am in the Baltimore, Maryland area.
Well, this topic is full of technical intrusion, if you listen to the commentator and look at the drawings they conflict with the carpenters practice in the video (be careful). In the event water does penetrate the exterior finish to the wrap or felt and down a wall it is the best practice to overlap the wrap on the flashing to avoid any possible water penetration at the seam. Since water does have surface tension (and in the event of penetrating the exterior finish) it will run down a wall on the wrap and it will go behind the flashing as the video displays. The intention of my entry was simply to make sure the housewrap/felt is overlapped as the commentator directs and the drawing displays not as the carpenter is doing. Just trying to point out a miscommunication the video displays and a simple technique to avoid possible penetration. Richard & Homebild I was not promoting wrap or felt as a primary barrier. My advice is to carefully and easily overlap all seems to avoid water penetration. Just visualize the water running over the layers not in between as gravity pulls water over the surfaces, you dont want the seems overlapped where lower layers are over upper whether it be between flashing, wrap, or felt. A very easy task to practice and could prevent water penetration to unwanted surfaces. Richard and HOmebild, let me ask you this, if someone were to install wrap on your house from top to bottom overlapping bottom layer over top would you continue the job? Yes, why? No, why?Just trying to point out a technical anomaly but still curious of your answer......
This message has been edited. Last edited by: rich ny,
