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Integrating new sheathing into a house sheathed in Celotex fiberboard

evantful | Posted in General Questions on

Hi, I have a 1955 Ranch in Ellenville, NY that my wife and I have been renovating for about a year that was sheathed in 3/4 Celotex Fiberboard.

I just completed a 11ft long rim joist and sill plate repair due to 65 years of extensive water damage from the front entry door. In the process I had to remove a brick accent on the front wall next to the door which damaged a 4x10ft section of the Celotex (along with the Celotex that had to be removed along rim joist area and all around the door and window next to it, which will be replaced within the month).

As a homeowner I have been unable to locate Celotex Fiberboard (sold under Blue Ridge now) panels to purchase so I’m looking to install 3/4 plywood and trying to find a barrier that would give me similar performance properties as the rest of the building in regards to water, vapor and air resistance , I don’t know if having one section of wall have different would cause an issue.

Also there are any good diagrams showing proper flashing detail around a door opening I would appreciate it, there are plenty of videos online but they are only as good as the actual logic behind it. I plan on using a jambsill pan under the door.

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    It's still possible to get asphalted fiberboard from other vendors (more often marketed as roofing substrate for commercial roofing than sheathing these days, but it's the same stuff, often using waterproofing less nasty than the traditional asphalt):

    https://www.continentalmaterials.com/images/Data/data_ecoboard.pdf

    https://www.menards.com/main/building-materials/panel-products/fiberboard-panels/1-2-x-4-x-8-fiberboard-roof-substrate/1630991/p-1444435987504-c-13329.htm?tid=-8540043040233476529&ipos=3

    https://images.homedepot-static.com/catalog/pdfImages/95/958dd23e-8bdf-4340-a701-61b855d9c5df.pdf

    Half-inch Blue-Ridge branded stuff is even available at the big orange box store in my area.

    Plywood is FAR more vapor tight and moisture-susceptible than asphalted fiberboard, and no WRB is going to magically make it similar. The closest approximation would be exterior grade fiberglass faced gypsum board sheathing (GP DensGlass).

    Are you re-building the brick accent?

    Is the house air conditioned?

  2. evantful | | #2

    Dana,

    I've had a tough time locating any of it in my vicinity. I did find this about an hour and half from me:
    https://www.homedepot.com/p/Continental-Materials-8-ft-x-48-in-Fiberboard-Roof-Panel-STR1281/202280452

    My house (1080sqft) is air conditioned with a Mitsubishi FH-12NA Mini Split.

    The brick will not be going back, the rest of the house is sided in the original 8" Cedar Bevel clap boards (with no rain screen). I was going create a contrasted look with narrower shiplap in that area around the window and door.

    If I had to use a 1/2 fiberboard, should I just fur out a 1/2in to have the faces be on plane to the original 3/4 stuff?

    If I had to use 3/4 BCX Ply in the area under the window and around the door, would roofing felt/tar paper be a good choice as a WRB?

  3. Expert Member
    Dana Dorsett | | #3

    The STRUCTODEK HD asphalted stuff at the box store will be the most similar to the sheathing you have elsewhere.

    Furring or shimming it out 1/4" between the sheathing and framing may leave a thermal bypass channel. Two layers may in fact be better, if you can tolerate the additional 1/4" of thickness there. If the siding is going to change there it's probably fine. If it's only a few sheets and you really need it to be flush, cutting 1/4" dadoes in the fiberboard so that it's only 3/4" thick at the framing might be worth the trouble. If going with only one layer of shimmed/furred half-inch, make it a 1/4" rainscreen gap behind the ship-lap siding.

    Using #15 felt as the WRB over plywood sheathing is a tried & true solution. Just be sure the window flashing details are correctly lapped with the WRB.

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