It could be the biggest single hole in the house, and one of the toughest air sealing jobs. It's the huge hole required for the bathtub drain and overflow pipes. Right next to them are the supply pipes and a plumbing vent.When a tub is located above an unheated space, sealing this hole becomes a major challenge. There's no easy way to fix this massive hole, but it's well worth some extra effort.
In most cases, these holes are too large for foam sealant. Here's an easy and effective way to block this air leakage path. And it costs less than all those cans of foam. You build a simple box under the plumbing and cover it with plywood. Here's one option for sealing the box.
The Box
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The existing floor joists form two sides of the box. Add blocking between the joists to close the other two sides. Make a cover for the bottom with exterior grade plywood. The cover should have two pieces that meet at the drain pipe. First, cut the plywood to the correct size. Locate and drill a hole slightly larger in diameter than the drain pipe. Saw the plywood into two pieces by cutting through the hole. |
Sealing
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- Before insulating, run a generous bead of sealant around joint where the framing meets the subfloor and in the corners where the joists meet the blocking.
- After insulating, staple a gasket to the face of the floor framing that forms the box. Screw the plywood cover over the gasket, so it can be removed to gain access to the pipes.
- Apply sealant wherever pipes penetrate the box.
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