Synopsis: Keeping a house warm in winter and cool in summer can be a tough job. Losing conditioned air under ill-fitting doors is a problem that can be remedied with contractor Jay B. Lane’s technique for installing a drop-down door seal. This mechanism hidden in the door’s bottom retracts when the door is open and eliminates the need to install a bulky threshold. Lane’s process includes the use of a Pemko automatic door bottom. A series of photos illustrates the installation process. This article includes a companion video showing Lane installing weatherstripping in a door opening.

Magazine extra: Watch carpenter Jay B. Lane use a specialty weatherstripping tool to seal a door.

As a custom-door and window installer, I always include weathersealing as part of the job. This final step not only improves comfort and energy performance, but it also shields the home’s interior from wind-driven water, insects, and street noise.

While the weathersealing around the sides and at the top of a door is straightforward, I find that sealing an exterior door at the threshold can be tricky. In most cases, I use an interlocking threshold with a water pan underneath and a rubber silicone bead kerfed into the bottom of the door. However, this approach still leaves a visible metal threshold.

For a seamless transition between interior and exterior spaces, I use an auto-drop threshold seal. It’s an adjustable device with a neoprene seal that retracts when the door is opened to allow for a hidden weatherseal. When the door closes, the door jamb depresses a pin on the hinge side of the door. This action engages a leaf spring inside the mechanism, allowing the neoprene seal to drop into place. I use a Pemko automatic door bottom (www.pemko.com) because of its reasonable price ($35) and its solid assembly.

A hidden auto-drop seal won’t work for every door configuration. The stiff aluminum bar crimped to the neoprene bumper needs a fairly flat surface to seal against. Large gouges or dips and undulations in the floor or threshold below the door cause a gap in the seal. Also, the bottom of the door must be within 1⁄2 in. of the threshold. If the door needs to pass over a thick rug, the threshold can be built up to allow the bottom of the door to be higher. This seal is not recommended for high-exposure areas, but for a clean, seamless look, nothing works as well.

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Dial In The Drop

When the door closes, a spring-loaded pin compresses against the hinge-side door jamb to drop the seal. Depressing the pin releases tension on the spring and allows the seal to drop into place. Turning the pin with a screwdriver adjusts the seal up or down. A screw driven flush to the door jamb contacts the pin and prevents it from creating a depression in the wooden jamb. When the door opens, the seal retracts.

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A Groove Hides The Mechanism

1. Trim the door bottom. For the weatherseal to operate correctly, the bottom of the door must be no more than 1⁄2 in. above the top of the threshold. After marking this dimension on both the hinge and latch sides of the door bottom, I trim the door using a circular saw and a straightedge guide.	2.  Cut the groove with multiple router passes. The Pemko mechanism requires a groove 9⁄16 in. wide and 19⁄16 in. deep. After fitting a 1⁄2-in.-dia. bit (www.freud.com) in my router, I attach and adjust a fence to center the groove in the door’s bottom edge. Then I rout the groove in multiple passes, increasing the cutting depth 1⁄4 in. to 3⁄8 in. each time. I widen the groove to 9⁄16 in. by adjusting the router fence on the final pass.
3.  Cut the seal and housing in one step. After I’ve checked the mechanism’s fit in the groove and scribed it to match the width of the door, I move the scribe line clear of the door’s edge and cut the entire mechanism to length with an abrasive grinding blade (a fine-toothed hacksaw will work as well). Note: The neoprene bumper can move laterally inside the housing, so before you cut, make sure its opposite end is flush with the end of the housing.	4.  Secure with screws glued in place. After sealing the inside of the groove and the door bottom with polyurethane sealant, I position the mechanism, drill pilot holes, and attach it with screws. I squeeze a small amount of wood glue into each hole before securing each fastener. I secure the bumper by crimping the aluminum bar at one end.

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