Sealing the floor of water heater closet.
fourforhome
| Posted in General Questions on
Hello everyone,
I am currently insulating my basement floor using a subfloor assembly consisting of 2 inches of rigid foam (XPS) topped with two layers of plywood. However, I have left the concrete slab exposed under the stairs, as this is where the water heater and water softening system will be installed.
The perimeter of this utility space is framed with walls using pressure-treated bottom plates directly on the concrete. The only places where the 2-inch XPS and double-layer plywood profile are openly exposed are at the two doorways leading into the space.
My concern is that a future plumbing leak in this utility area could migrate laterally, get underneath the rigid foam at these doorways, and spread throughout the entire insulated basement subfloor.
To mitigate this, I want to create a formed-in-place “bathtub” containment zone under the stairs. I have a 1-inch drain pipe installed that daylights outside. I am less concerned about sloping the floor to force water to the drain, and more concerned with achieving a seal between the waterproofing basin and the drain pipe itself so that the drain line is the only possible way of exit for the water.
I am seeking advice on the best building science approach for these two details:
Sealing the Drain Pipe Interface: How do I reliably tie a liquid-applied waterproofing membrane (like RedGard or Hydro Ban) or a sheet membrane into a 1-inch drain pipe exiting a concrete slab? Is there a specific type of low-profile clamping drain flange, a specialty flashing boot, or an epoxy-based detail that will ensure water cannot weep down the outside of the pipe where it penetrates the concrete?
Sealing the Doorway Curbs: What is the best method to construct a containment curb across the two doorways and transition it to the exposed XPS/plywood profile? If I use a liquid-applied membrane to coat the basin, what should I use to flash and protect the exposed edge of the XPS foam from potential solvent damage?
Any advice or insights on how to properly seal this plumbing penetration and subfloor termination would be greatly appreciated. Thanks!
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Replies
Schluter's Kerdi-xxxx ("xxxx" can be various things depending on what component of the system you're using) products would be a good fit for this for something site built. That particular Schluter system is intended for things like custom built showers and the like, so you can use it to build a waterproof liner. I've never used it left exposed though, so not sure how well it would handle any traffic on the top.
My personal preference for this sort of thing is to have a pan made up from stainless steel sheet. I will typically use 18 gauge stainless steel sheet, usually either 304 (cheaper) or 316 (better) alloys, with the sides formed with a bending break and the seams between the sides at the corners TIG welded. This will make a pretty much indestructible and completely waterproof pan, but it's not cheap and you'll probably need a metal fabricator to make it for you. If you do go this route, having a bulkhead welded onto a side (or bottom, if you have a floor drain), allows for a way to drain any liquid out if you ever have a leak.
BTW, whichever way you choose to go, I suggest using one of the leak alarms in the pan to alert you to any future problems. It's common for pans to be installed, and then to overflow when no one notices a leak. An overflowing pan doesn't help you any better than no pan at all.
Bill
+1
Think of this project as adding a shower on the second floor. Continue the flooring system into the closet. Use fiberglass shower pans under the equipment and connect the drains to you drain pipe. Use a p-trap and regular plumbing techniques. Everything is off the shelf.
That pt lumber on the concrete will wick moisturel.