Adding Locks to Antique French Door

Question

I have a set of 1927 french doors that are 18" wide and have a built-in astragal -- measuring ~7/8" wide and ~1/4" deep -- on both doors. The astragal narrows to about a 1/4" where the locks used to be, allowing room for the former lock.
I'm restoring the doors and I'd like to add a lockset to the active door (passive door is secured with slide bolts). I'm wondering if I should try and add a modern mortise lock to the door by removing whatever filler is in the old hole or attempt to add a modern deadbolt and knob in.
My concerns with using a modern deadblot/knob is that the distance between the base plate and the strike plate will be too great and the knob's latch won't be long enough to securely catch.
Here's a picture of the door edges. The original strike plate is still there, but the hole where the mortise lock used to be has been filled.
How would you proceed?
As a side note, I've considered replacing the doors with a new set, but no one stocks french doors in this size. When installers come out, they all suggest adding a full size entry door, but a full size door would open too far into the room and be awkward in the space. Also, I just like the look of the smaller doors. The only other replacement option I've thought of would be to use a pair of 18" sidelights and turn them into french doors.

Jack · Accepted Answer

Those types of latches for had specific shapes to follow the door edge profiles. You may be able to find a new latch that will work, but I would suggest shopping for an antique latchset that will suit your needs and have it reconditioned by a locksmith.
After that is accomplished, then cut out what is needed to get the new or reconditioned latchset to work. Don't just remove what was filled in, although it may be needed anyway, but some filler may be able to remain, since the new lock may have different cutouts needed. Then again, in making the new mortices (cutouts) the filler may fall out anyway. Just as well, if it does, it can be reset properly and more permanently.

ThreePhaseEel · Answer

You'll want a pair of automatic flush bolts if you want this opening to have any semblance of Code-compliance
The problem you have here is that not only does the French door setup you have require funny latchset hardware to fit the existing door, it doesn't provide enough clear opening width (equivalent of a 24" leaf is necessary) to meet Code requirements unless both leaves are operable.  As a result, you'll need to have something more sophisticated than a simple set of surface bolts on the inactive leaf; in particular, you need a pair of automatic flush bolts that latch the inactive leaf when the active leaf is closed and unlatch it when the active leaf is open.  Since this hardware is designed for fire door service, it's not a common or cheap item, but versions for 1¾" minimum solid wood doors are available, such as the Ives FB41P or the Rockwood 2942.
Also, may also have difficulty with the latchbolt setup depending on what you use; it'll need to spring-in if closed into so the inactive leaf doesn't hang on the latchbolt if closed into a closed active leaf.  If you didn't do that, you'd wind up needing a coordinator to hold the inactive leaf open while the active leaf closed, which is an added expense (and thing that can break).
The other alternative would be to make these both active leaves with vertical rod latching hardware, but that would require some hackery as most vertical rods are found on panic hardware (crash bars), which are far wider than this application calls for, and can't reasonably be shortened atop going on the push side of the door, while not being lockable from that side.  A pushpad type of device could be used here, but I'm not sure if surface vertical rod versions of those are made.

Adding Locks to Antique French Door

2 Answers

You'll want a pair of automatic flush bolts if you want this opening to have any semblance of Code-compliance

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