How to Lock an Uneven Pair of Doors
This article discusses why uneven pairs of doors occur and hardware solutions for these unique openings.
What is a pair of doors?
A pair of doors is two doors that occupy the same door frame. Pairs of doors usually occur in commercial, educational and institutional applications because of the need to provide egress for a potentially large group of people in the event of an emergency and/or to move large objects within the building. Doors in a pair of doors are often called "leaves."
Usually both leaves in a pair are of equal width. For example, in a 72 x 84-inch opening each leaf would be 36 inches wide. But sometimes, as in the photo at right, pairs of doors are not equal. For example, a 60 x 84-inch opening might have one 48-inch leaf and one 12-inch leaf, or one 36-inch leaf and one 24-inch leaf. These would be called uneven pairs of doors. This article talks about the challenges that an uneven pair of doors presents to the security and life safety hardware installer.
Uneven pairs of doors often occur in service corridors - that is, corridors primarily used by delivery and service personnel. However, these service corridors are often a key path of egress in the event of a fire or other emergency as shown in the illustration below. Path of egress is one of the chief concerns of architects as they work to build public buildings that provide for safe exit in the event of an emergency.
When a building is designed, the need for life safety sometimes competes with the day to day need for the structure to serve the occupants and owners. The key element is space. Space is a commodity that is leased or sold, and life safety measures also require it.
Service corridors that serve several purposes are sometimes minimized to leave more space available for lease or sale. For example, an architect may design the corridors to have a 72 x 84-inch opening at either end. Looking at the plans, the real estate developer may notice that if the corridors were 12 inches narrower, they could lease another 5,000 or 10,000 square feet without compromising the spaciousness of the public common space. Now instead of a 72 x 84-inch opening, the architect must specify doors for a 60 x 84-inch opening.
A 60-inch door would create special hardware problems. Few door closers are rated for a door that wide, and whereas standard weight hinges may have previously sufficed, now more expensive heavy weight hinges will be needed. Multiply the cost difference by 50 or 100 doors and we quickly see that the idea of the 60-inch door is expensive. Also the big door will be harder to use and its swing will take more space.
The solution is often an uneven pair of doors.
Above you see an uneven pair of doors. At least from this side, this corridor is not a path of egress. We are on the pull side, and anyway there is no EXIT sign as mandated by fire safety code in this location. The handle is an exit device trim, so we know there is some kind of exit device on the push side, though we can't see it from here. On the bottom of the inactive, smaller leaf we can see the heads of through bolts in a pattern that suggests a surface applied vertical slide bolt.
It looks to me like the the leaf on the left, the 'active' leaf, as it's called, is about 36 inches. This is a normal size door and would present no problems to an Authorized Hardware Consultant (AHC) specifying the hardware. Probably the small, inactive leaf once had flush bolts, but the lower one broke for some reason. Perhaps because someone ran something into it, perhaps a pallet or a cart, too many times?
This doorway is representative of the maintenance and usage problems encountered daily with uneven pairs of doors.
If the opening is a public fire exit then the challenges are multiplied. Fire exit doors are closely regulated by local governments and are required to be equipped with hardware approved to meet the needs of public safety. In addition, an opening that is secured by an uneven pair of doors may be fire rated, which further restricts hardware choices. Add the need for access control and choices become even further limited.
Following are some answers to these hardware needs.
In an Ideal Hardware World...
Above is an illustration of a hardware response to the application of a fire rated exit with an uneven pair of doors when it is possible to have the doors made correctly in advance. The left hand leaf is 36 inches wide and the right hand leaf is 18 inches wide. The left hand leaf is outfitted with a fire rated mortise exit device with an open back strike. The right hand leaf is equipped with a fire rated concealed vertical rod exit device. The devices shown are crossbar style exit devices rather than touch-bar style.
Not pictured are door closers that are in this visualization mounted on the pull side.
Following is a Q and A on this application.
- Q. "Why a mortise exit device?"
- A. I chose a mortise exit device so that access control could be easily added later via an electrified mortise lock - not entirely code compliant because this would require an electric through-wire hinge and a wire run through the door. This should technically be done only in a fire rated door shop. Another way to do it would be to use two concealed vertical rod (CVR) devices and, if you want to add access control later, apply an electrified trim. I like the electric mortise lock device better because I think it is more durable.
- Q. "Why the open back strike?"
- A. The open back strike assures that each leaf can be opened independently and that each will close independently. The Authority Having Jurisdiction (AHJ) - usually a building inspector or fire marshal, may require both leaves to provide free egress, as I have seen them do many times.
- Q. "Why crossbar devices?"
- A. As of this writing I know of no touch-bar style exit device that will fit on an 18-inch door. In general I prefer touch-bar style devices. They are generally quieter and more durable. If the smaller leaf is at least 24 inches wide there are touch-bar type devices that fit a door that small (see Fig. 4 at right).
- Q. "Why a concealed vertical rod? Why not a surface vertical rod?"
- A. Typically surface vertical rod (SVR) exit devices are subject to much more abuse than CVR devices. Somebody is always running a push cart or hand truck into the bottom rod and/or latch. Rod and latch guards will help avoid damage, but they are ugly. Top rod only SVR devices can also be used, but single-point locking at the top of the door allows quite a bit of movement due to door flex - not a very aesthetically pleasing or reliable solution. If the doors sag at all over time they may cease to lock.
Usually SVR exit devices are only used in retrofit applications - situations in which there were no exit devices and now there will be exit devices due to changing life safety code regulations or bad planning.
To plan well for door hardware means to think about how any given opening may be used. These are the considerations in order of importance:
- Life Safety
- Accessibility to persons of all abilities
- Access Control
This last item, access control, is often something that is considered later, when daily use shows there is a need for it. Yet is it much better if openings - particularly fire rated openings - are designed to easily accommodate access control if added later. For example, in the uneven pair, both leaves should have a wire raceway built in from the hinge side to the lock side. Then if an electric lock or electric strike is later needed, no fire labels need be voided in the course of the installation.