I noticed the AC installation by my house's previous owner left an unpatched hole in the siding, close to the ground. We have a lot of rain in the fall/winter. I don't know how long it's been like that.

Is this a concern of damage inside the exterior wall? Concern of mold? Would simply patching the hole be enough?

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2 Answers 2


Well, that's a bit messy looking!

The best repair would be to remove the two damaged planks and replace them with new ones.

Next best would be to cut back the planks away from the hole and replace the pieces that cross the hole.

Next best would be to install flashings that cover the hole.

Mold is definitely a possibility. I see moss growing on the insulation.

Pull or push some of that insulation out of the way and check for mold. The mold can probably be sufficiently treated though this hole without a need to disassemble the whole wall.

  • That looks like hardi plank not so easy to cut in place replace but a metal flashing slid up under each board in front of the hole would work work for a patch until you can properly fix
    – Ed Beal
    Aug 10, 2020 at 13:44
  • to cut it use an oscillating tool or an angle grinder with a concrete cutting disk, or if you can't afford power tools a hacksaw blade.
    – Jasen
    Aug 12, 2020 at 4:17

There are two problems to fix here:

  1. the house sheathing has been left wide open. You should put some plywood covering the hole, and attempt to seal the exposed fiberglass from critters, bugs, etc. Usually there is house wrap/water barrier over that.
  2. the weather proofing is also compromised. Patch the siding. Hardie-plank is dear, look to see if they left you any scraps. Or put a patch of pvc board over the hole.

You may have to widen or square the hole up to do a workman like job. A patch siding board should have a z flashing on top.

  • not exactly expensive, home despot has it for $10 for 12'
    – Jasen
    Aug 12, 2020 at 4:28

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