My water heater is located in an alcove on the back corner of the house. Today I found water line leaking from the heater, replaced and it is good now. I have always just assumed the walls and ceiling of the alcove was stucco (it is a closet with a door on the outside of the house). But after replacing the line and looking at the damage, I found it was just drywall with a texture coat. The drywall is wet and will need to removed but I'm stuck with what to replace it with. Doing a stucco coat seams out of the question since the family will be out of hot water for a couple of days. So what should I put up in this 2' by 2' closet? It has a door but I don't consider this closet to be weather proof but only mostly weather proof. Is there another acceptable wall covering for this alcove that I can up in day or two.

Edit: I'm going to have to get insurance involved. I have water damage in the bathroom that is next to the water heater closet.

2 Answers 2


For exterior applications, fiberglass faced gypsum board is commonly used. Fiberglass, unlike paper, is resistant to mold growth and ordinarily does not deteriorate when exposed to moisture.

For protected locations such as an exterior shed, this is almost certainly adequate as is indicated by the service life of the current installation.

Fiberglass faced gypsum board is a commodity material available from major gypsum board manufacturer's such as National, USG, or Georgia-Pacific under a variety of trade names.

As with any building material, following manufacturer's instructions when cutting fiberglass faced gypsum board is recommended.

  • Just did some research on the fiberglass faced gypsum, that also looks like something to consider. I'm going to have to work with my insurance on this one as I have internal damage as well. So depending on what they allow and what I can upgrade I will keep this as an option. The location is actually internal to the home but has an external non weather proof opening. I'm just completely baffled that this was allowed when they built the home. I've assumed this last two years that the textured drywall I was seeing was the original stucco coat of the home.
    – diceless
    Nov 17, 2014 at 4:43
  • @diceless Cement plaster is not commonly used as an interior finish material. The class of techniques "allowed when they built the home" has a non-empty intersection with "what the inspector did not see" and "what needs to be done on Friday afternoon so checks may be cashed and drinking may commence". Honestly, though, it's the leaking plumbing that deteriorated the gypsum not normal service conditions. I'd have bigger issues with the plumber.
    – user23752
    Nov 17, 2014 at 13:56
  • This is weird spot on the house. It is definitely not interior but more like an alcove (like an inset front door with a small landing in front). But yet the floor of this alcove is the slab of that section of the house. Normal drywall is out of the question since the door can not be weather sealed. Plumbing failed because of age. I should have removed the insulation when I bought the house and inspected the supply lines but keep putting that off as one of my projects was to replace the water heater (30+ year old unit).
    – diceless
    Nov 17, 2014 at 18:12
  • Thank you for the answer. It seems fiberglass gypsum is the only suitable option for this closet when it comes to providing a firebreak.
    – diceless
    Nov 18, 2014 at 5:54

Cement board, tile backer board - or use the exterior siding flavor of "otherwise pretty much the same product"

  • I like the idea of cement board, do you know what it's fire rating is?
    – diceless
    Nov 16, 2014 at 21:33
  • Not exactly, other than our local (or possibly state) code allows it to be used where they used to ask for asbestos board in wood stove installations, which leans to the "effectively fireproof" end of the scale. Of course fire ratings are for "wall assemblies" not just panels. If you cannot find one to suit via USG or James Hardie you may need to fall back to firecode gypsum or "toughened" firecode gypsum and then use the cementboard over the top (which seems to be a common approach in the listed assemblies with cementboard I have found so far...)
    – Ecnerwal
    Nov 17, 2014 at 3:09
  • Typical install of water heaters in this area is either garage or exterior with an aluminum enclosure. This house is different with closet inset into the house with the exterior door. My preference would be to treat this closet as part of the exterior skin of the home. But my preference is probably not going to happen so having to come up with a secondary. The drywall in there looks like 5/8 which i'm guessing is for fire code. So will need to check with local regulations on what is acceptable in this location.
    – diceless
    Nov 17, 2014 at 4:13

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