Generous holes are often cut through subflooring, walls, bottom plates, and top plates for plumbing pipes and vent stacks. These gaps are often hidden from view in under-sink cabinets, beneath tubs, behind shower enclosures, behind washing machines and dishwashers, or within wall cavities. If not properly closed up, large amounts of air can pass through these gaps, encouraged by pressure and temperature differences between conditioned and unconditioned spaces. These air leaks represent energy losses; they could also potentially allow warm, moisture-laden air into wall cavities or attics where it can condense on cold surfaces, creating moisture problems. Conversely, air leaking into the house from unconditioned sources such as the garage or crawlspace can affect indoor air quality and cause drafts. Air barriers need to be continuous to be effective; this means sealing all penetrations in exterior walls and in walls and floors adjoining unconditioned spaces.

Be sure to schedule sealing of plumbing holes after the pipes and plumbing have been installed and before the drywall is completed. Responsibility for sealing air leaks around plumbing should be included in the contract for the appropriate trade, depending on the workflow at a specific job site.

How to Air Seal Holes around Plumbing

1. Use caulk or canned spray foam to seal piping holes through the top plates, bottom plates, and subfloor. Avoid running water pipes along exterior walls. Run piping next to floor joists in floors if insulating with batts to minimize disruption of cavity insulation. Water pipes should be insulated to R-3 (2012 IECC) even when they are installed in interior walls, to conserve the heat in hot water and to minimize the potential for condensation.

2. For larger holes in the top or bottom plate, use a rubber gasket. Use of a flexible gasket allows some movement of the vent stack without loosening the air seal (Lstiburek 2009).

1. Cut a hole in the gasket to just fit the width of the pipe.
2. Apply caulk to the top plate. 
3. Fit the gasket over the pipe and press down to adhere the gasket to the caulk.
4. Staple the gasket in place. 
5. Apply more caulk around the pipe.

3. Use caulk or canned spray foam to seal the holes made in rim joists for plumbing pipes. Keep the pipe runs close to the floor joists to avoid compressing the insulation.

4. Use caulk or pre-fabricated gaskets to seal around the plumbing pipe penetrations in exterior walls. Make sure the gasket is properly integrated with the house wrap and that cuts in the house wrap around the gasket are taped or caulked.

5. For bath tubs on outside walls, avoid running the water pipes along the exterior walls, if possible. Install piping, then air seal any holes in the exterior wall framing or subfloor.

1. If the tub or shower is installed on an exterior wall, insulate and air seal the exterior wall behind the tub with sheet goods before the tub is installed. [See Walls behind Showers and Tubs for insulating and air sealing exterior walls behind showers and tubs.]
2. After the drain is installed, seal the hole around the tub drain pipe with canned spray foam. For larger holes, seal the hole with pieces of water-resistant sheet goods such as rigid foam or cement backer board that is cut to fit around the pipe and caulked or foamed in place.