Zero International 366 Sill Protection Automatic Door Bottom with Solid Neoprene Insert - Semi Mortised - Heavy Duty

That's what the 366AA is built for. A plunger at the hinge jamb is compressed as the door closes, releasing a concealed flat spring that drops the solid neoprene seal out of the aluminum housing in a scissor motion, so it conforms to an uneven floor or saddle instead of bridging the high spots. Maximum effective drop is 1 inch, so measure the worst gap between the door bottom and the finished floor across the swing: anything over an inch needs a threshold to make up the difference rather than a bigger drop.

Semi mortised means the housing sits partly recessed into a shallow routed pocket in the bottom of the door with a mounting flange left exposed on the face, rather than fully buried like a mortised unit or simply screwed flat like a surface applied one. You need to be able to machine the door bottom to take it, so it suits wood and hollow metal doors that can be routed or factory prepped. If the door cannot be cut, or it is already installed and hung, a surface applied automatic door bottom is the version to order instead.

Fire rated, and rated to UL10c. It is also smoke seal rated and sound rated, so one part covers the fire, smoke, and acoustic line items on a labeled opening rather than stacking three separate seals. The neoprene insert is self-extinguishing and meets MIL R6855 Type II Class 40 for oil resistance.

No, and that is the difference between this and a fixed sweep. The seal stays up inside the housing while the door is in motion and only drops when the door reaches the closed position, with the spring mechanism activating on the hinge side first so the insert does not scrub along the floor and cause door hang-up or a closing delay. A fixed brush or vinyl sweep is in contact for the full swing, which is why sweeps wear out on carpet and automatic bottoms do not.

The 366AA comes in a 36 inch length, in clear anodized aluminum or black. The 36 inch size is cut to suit standard 3-0 door leaves. Order clear anodized where the seal is visible against aluminum storefront or mill finish frames, black where it needs to disappear against a dark door bottom or dark threshold.

Rated for 5 million cycles, in an aluminum housing with a solid neoprene insert, and classified for commercial use. That cycle count is the reason to spend on this rather than a light duty automatic bottom on an entry, stairwell, or corridor door that gets used hundreds of times a day. The neoprene is solid rather than hollow bulb, so it holds its shape under repeated compression.

A sweep rides on the floor all the time and seals only as well as its contact pressure allows, which is why it is fine for weather and drafts but weak on sound and smoke. An automatic door bottom like the 366AA drops under spring pressure once the door is closed, compressing a solid neoprene seal tight against the floor or saddle, and it carries fire, smoke seal, and sound ratings that a plain sweep does not. Use the automatic bottom on rated openings, conference rooms, and demising doors; use a sweep where there is no rating to meet and no machining allowed on the door.

Handing is not something you specify on the order, but it does matter on the job. The plunger end has to sit at the hinge jamb, because the mechanism is designed to activate on the hinge side first so the seal does not drag. Install the unit with the plunger toward the hinges regardless of which way the door swings.

The neoprene extrusion is supplied under MIL R6855 Type II Class 40, which is the oil resistant classification, and it is self-extinguishing. That makes it workable on mechanical rooms, loading areas, and maintenance shops where a standard vinyl insert would swell or go soft.