Patch House Exterior Wood (Board)


Old 02-22-19, 01:34 PM
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Patch House Exterior Wood (Board)

Somehow, can't seem to find a secure way to prevent any water infiltration, so here goes:

The exterior sheathing is 7" wide (3/4" thick) tongue and groove boards (Circa 1954, Douglas Fur ?). I have to patch a hole, about 2 feet by three inches to make the in wall A/C opening smaller.

I do not know what would best where the new pressure treated wood butts the old wood to make sure of any water penetration.

- From inside, cover the hole with a slightly larger piece of pressure treated plywood, silicone or OSI Quad where it overlaps
- I could cut to size pressure treated 3/4 wood to fill the hole (add silicone or OSI Quad where the seams are
- Cover area to match: Add flt, add new cement shingle, add foam, add new siding

The big question is what to use where the new and old wood joins or if I am over thinking it. I can use silicone, OSI Quad, or some type of wood epoxy but not sure the best stuff to last a long time.

Notes: Not worried about the siding (have spare), will use new cement shingle to match the 1950's type that I am not disturbing.
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Old 02-22-19, 01:41 PM
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Welcome to the forums!

Normally flashing is better than caulking. If the PT wood isn't good and dry the caulk will fail even earlier. If you post a pic or two we'll have a better idea of what you are dealing with -
Old 02-22-19, 02:06 PM
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Flashing is a good idea, thank you. I can look for flashing tape.

I cannot take pics at the moment. But what is there now is the in-wall A/C sleeve.

I was going to remove the old AC and sleeve (from 1973) because the new ones are smaller. I am going to see if I can reuse the old sleeve and properly insulate the above gap between the sleeve and the new unit (width is the same). I will then visit the back and flash & calk as that was prob never done. It is on the second floor, so it is about 16 foot off the ground.
Old 02-22-19, 03:14 PM
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Not really picturing why you are trying to use identical siding, and not making a picture frame from trim... if you need to make it 3" smaller, why not use 5/4x2 trim or similar to make a frame around the opening?

And no, don't use any silicone! OSI Quad will work well, but don't caulk it until you're done.
Old 02-22-19, 06:05 PM
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Thanks for the recommendation on the OSI. I used it several times on a recommendation from a roofer and it works well.

There is currently a j-channel around the sleeve. I can shorten the sides and reuse the top. I can fill the space by cutting a piece of siding from extra the previous homeowner left behind. I also have spare felt, shingles, and the foam.
Old 02-22-19, 07:57 PM
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OK, so I took another look. A new window sleeve is 3" shorter than the original, therefore:
  1. Take out the old sleeve
  2. Add two 2x4 to the sill (if needed, shave it down) to bridge that 3" gap
  3. On the exterior, add two strips of pressure treated plywood
    1. The first fills the 26" x 3" gap where the exterior sheathing would be
    2. The second builds out where the shingle and foam would be
  4. Cover the area with white flashing
    1. Flashing will protect the area; and
    2. blend in nicely to the exterior siding an j-channel already there
  5. Install new sleeve (it will be dry fitted before flashing, etc.)
  6. Add OSI Quad (white) sealant where necessary per A/C sleeve instructions
This will take care of resizing the hole that is there, ensuring the patch is covered, and blend in nicely with the exterior. It will save me time on the ladder as I can the flashing from the inside.

Many thanks for the contributions and point out using flashing.

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