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WRB for retrofit

M S | Posted in Green Building Techniques on

I have looked through the site and most of the WRB articles seems to focus more on new construction. We have an old 1940 house in Zone 6. Wall profile is some kind of reflective silver paper WRB over 30lb felt paper with ship lap 1×6′ for sheathing and balsam wool insulation ( . 

We will be getting new siding LP Smartside.  I am looking for any suggestions on a WRB to use with shipped lapped sheathing.  For example, would I request they keep the existing felt paper and add a second layer?  If I were to go with  Tyvek can it be used over 30lb felt?

Any suggestions would be appreciated.

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Replies

  1. GBA Editor
    Brian Pontolilo | | #1

    Hi MS.

    Tyvek is one of the most vapor open WRBs, so you could install a new layer of Tyvek over an existing layer of felt if there was reason to leave the felt in place (perhaps the window and door flashings are incorporated with it). However, if you want to take this opportunity to improve the air-tightness of your home, which can help with efficiency and comfort, you could also consider stripping the house down to the sheathing and installing a self-adhering WRB, which would tighten up the sheathing quite a bit. Here's an example of a more extreme, but similar project: Self-Adhering WRB Retrofit.

  2. M S | | #2

    Of the commercially available WRB’s on market, does anyone have a recommendation. I thought I had read how some of the newer WRB's come with a pseudo rainscreen or something to that effect. Maybe I was dreaming.

    1. Expert Member
      Peter Engle | | #3

      For that wall system, Tyvek over the original felt would provide plenty of drainage, except maybe for a waterfront location. There are building papers with built-in texture that give a bit of extra space for drainage, crinkled Tyvek is one, but there are others. Not sure you need it for your walls.

    2. GBA Editor
      Brian Pontolilo | | #4

      Hi MS.

      There are a variety of drainable WRBSs available (the option that looks the most robust to me is Hydrogap from Benjamin Obdyke). Drainable WRBSs do not create rainscreens, though. Rainscreens achieve two things: drainage to get water out from behind the siding, and ventilation for airflow and to allow materials to readily dry. Rainscreens can be built with furring strips or installed with a 3D rainscreen product that creates enough of a gap to achieve these objectives. With drainable WRBs, you get only the potential for some drainage.

  3. M S | | #5

    Thanks Brian and Peter.

    Brian to your knowledge has any article been put up on the site regarding drianable WRB's (comparsion bewteen some that are on the market today. I would like to read up on some different options beyond Benjamin Obdyke product.

    1. GBA Editor
      Brian Pontolilo | | #8

      There is very little available in the way of independent testing of WRBs. FHB ran this article a few years back, which is at least, very informative: Are Drainable Housewraps Enough?

  4. Expert Member
    Akos | | #6

    Efficiency of all drainable house wraps come down to the amount of air gap they provide. 3/8 is pretty much free draining, as good as a rain screen. 1/8 is good enough in most cases.

    The crinkly type WRB still provide a fair bit of drying but the wrinkles are not enough for a capillary break. It is still better than standard house wrap.

    Because the back of shiplap siding is flat, I would use something that provides a reasonable gap. This would be the 6mm Benjamin Obdyke or 3/8 strips of plywood.

    I would definitely 2nd the peel and stick over the old sheathing. This is what I did for my wive's studio and it completely sealed up a 100 year drafty old structure. Getting a good air barrier makes a huge difference for comfort and energy use.

    1. GBA Editor
      Brian Pontolilo | | #7

      And there will soon be a draining, self-adhering product available, if the rumors are to come true. I hope so...

    2. Expert Member
      Peter Engle | | #9

      The OP mentioned shiplap sheathing, not siding. If correct, that would provide a VERY rough surface. A photo might help us understand better.

      If that were the case, a spray-on liquid WRB/air barrier might do the trick.

  5. M S | | #10

    They have started to rip off the siding. It appears the initial WRB is this Alcoa breather foil product?. It seems to be a paper based product with shiny/foil exterior to it which is very thin. Underneath looks to be the tradtional felt paper, however it has more of crinkled rough exterior to it. Sheathing looks T&G 1x6's (1940's house)

    Looking for feedback on whether to remove the Alcoa layer and have them use the tradational Tyvek WRB over the felt OR have them go over the Alcoa WRB?

  6. M S | | #11

    The housewrap they seemed to have dropped off is the following. Not sure quality or whether this is considered "drainable"

    https://www.wolfhomeproducts.com/system/files/BLOCK-IT%20Brochure_0.pdf

  7. Shawn Shumaker | | #12

    Is this (1x6 sheathing) or (1x6 sheathing / original siding)? My house is almost exactly like what you have. Under the foil stuff is the sheathing/original siding. This is not a flat contour on the exterior. This may be an important consideration, particularly if you consider peel and stick.

  8. M S | | #13

    It's 1x6 T&G sheathing. which is flat (not siding which is lapped)

  9. Tim B | | #14

    Is peel and stick untenable on T&G sheathing? I have the same sheathing on my early 1950s house.

  10. MN_JohnB | | #15

    My primary experience is with plain old Grace IWS but I think it or a similar product would stick especially in hot weather. I think it would be worth it to broom down the sheathing before application and maybe do some scraping if there is a lot of asphalt paper residue, etc. I don't know how some of the newer products would fare. I'm hoping to to a similar thing to my 1937 cape - strip down to sheathing, dense-pack cellulose, and apply a self-adhered WRB/air barrier/drainage plane and then back with LP smartside.

    1. Expert Member
      Akos | | #17

      Grace I&W is a bad idea for any walls unless there is spray foam in the wall cavity. I&W is vapor impermeable and creates true cold side vapor barrier which is a bad idea in almost any climate.

      You want a vapor open peel and stick.

  11. William Sherman | | #16

    How is a self-adhered WRB installed on an existing house with many obstacles such as electric meter, spigots, surface-mounted chases for mini-split line sets, and PV emergency shut-offs? My house seems to only have building felt installed at corners, around windows and doors, but not in the field.

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