One of the reasons that I wrote the Wrand Film Glossary was to record many of the obscure film and entertainment industry terms that get passes down orally but are never recorded.

Art department and set construction lingo is usually not included in the typical film glossary, and “Double dap” is one of those odd terms that you will hear used by Prop Makers* but have probably never had it explained.

The term refers to how the hinges of a door on a stage set are to be installed. Normally the installation of hinges for a door involves creating mortises in the door stile and the jamb that match the thickness of the hinge leaves. That’s referred to as a “single dap” installation. (Note: this is specifically for doors in North America or the UK. Many Continental European doors are half-overlay and don’t use the type of leaf hinges that are standard here.)

A “double dap” installation involves creating a mortise in the door which is twice as deep as usual and not making a mortise in the jamb, as shown below.

The diagram below is a side-by-side plan view showing both types of installation.

So what’s the purpose of this? Well, this is something that is more typical on sets for a broadcast show than on sets for a feature film.

One advantage is speed. We tend to build sets at a pretty brisk pace, sometimes building an entire set over a weekend. For example, if you have a set with six doors, that means you need to install 18 hinges, which means routing 32 mortises. With a double dap installation you cut that number in half.

Another advantage is if you are redressing a set and need to change out the door of an opening for a different door. With a standard installation, you will need to patch and fill and re-rout three mortises. Instead you just need to fill some screw holes.

This is also the case if you need to change the swing direction of a door at the last moment. (Good luck prying off and repositioning that door stop.)

Double dapping has fallen out of favor lately. Production Designers don’t like the look of it for one thing. (Along with Phillips head screws on a period hinge!) They tend to stick out particularly when the hinges are a contrasting color from the jamb or if the wood is painted a light color and the hinges have a dark laquer/black finish. In some instances this condition can either visually hide the extra mortise depth or accentuate it.

Also, notice the round corners on the hinges in the photos. Round corner hinges are a 20th century invention to speed up production. Once machinery, i.e. routers, was being used for mortising, it became a lot faster to create hinges with leaves that didn’t require squaring off the mortise corners as was necessary for period, square hinges. Round corner hinges come in 1/4″ and 5/8″ radius corners, so be aware of what radius size they are if you’re choosing hinges for a door that has already been mortised.

Note: Prop Maker is a designation for a union stage carpenter in Los Angeles to differentiate them from a ‘civilian’ carpenter. They are trained it building theatrical scenery of all types and historical periods and specialize in creating scenery for film productions. They are more similar to cabinet makers than a typical carpenter and are skilled in construction techniques and methods that would baffle most people outside the entertainment industry.