When it comes to sealing a house against weather, doors are always a weak link. To prevent air and water infiltration, especially on hilltop homes, I’ve used every type of threshold imaginable. Years ago, I settled on interlocking water-return thresholds. Interlocking thresholds are touchy, though: The doors have to be cut and rabbeted at precisely the right elevation, and tricky alterations must be made if the house settles.

A new doorsill from Endura Products has hit the market, and it doesn’t require a sophisticated skill set. Almost anyone can install the new Z-Articulating Cap (Z-AC) Sill or retrofit it on a door with an existing Endura Z-Series Adjustable Sill. If you ask, your door supplier can provide the Z-AC already installed on a prehung door.

Endura’s new threshold looks a lot like standard cap profiles on the most common sills—the ones that come with a vinyl sweep attached to the bottom of the door—but under the aluminum surface, there’s a composite substrate that won’t rot or warp. The sill also eliminates adjustment screws. Instead, it has an articulating cap, which is activated by a unique mating door bottom. As the bottom of the door crosses the cap of the threshold, the sill cap rotates up and interlocks with the door bottom, creating a weatherproof seal. The articulating cap has a respectable amount of latitude, too; if the door or the floor settles, even up to 1⁄4 in., the Z-AC still provides a solid seal. The upcharge for adding the Z-AC to a prehung unit is $6 to $12; retrofit kits run from $20 (single opening) to $40 (double opening).