We have three entry doors in our home: the front door, the back door, and the side door that opens to the basement. Oh, and since the back door leads to a mudroom, our other back door is a wood door. All are pictured below.
At the time that I bought them, I thought these were all decent doors (all three were installed by me around 2002 to 2004). All three are Therma-Tru, with the back door being fiberglass, the side door a composite, and the front door metal.
I chose the fiberglass back door for energy and appearance, the side door was what I could get from the building materials supplier I worked with in a custom size, and the steel front door was what was available at the time for the swing and hand I needed for that location. Again, they are all decent doors with insulated cores. But frankly, I did not take too long to become a bit jaded about my doors.
The back-door gasketing has a 5/8-in. gap at the lockset-side top corner.
The side door has a 5/8-in. gap between the insulated glass lite and its rough opening.
All the doors are bowed away from the stop at the head and foot of the door, on the non-hinge side.
At first, I was pretty angry that the doors were bowed. But then I got to thinking about the physics of expecting a planar surface like a door to resist deformation over more than a 3-ft. span from the door handle to the top free corner of the door. Hey, even for large casement windows, most of which are a lot smaller than any door, we have at least two compression locks.
And in addition to being bowed, I got to wondering about how much force it would take to move the doors even farther off the gasketing? I can pretty easily see plenty of daylight by pushing gently away from the door stop at the lockset-side top corner, as you can see in the videos below.
How easily, you might ask?
Time for a wingnut test
I rigged up a bath scale, looking to convert pounds per square inch (psi) of pressure to Pascals and then miles per hour of wind.
Notes on the pressure test with bath scale:
- I held the scale down from the free top corner of the door—knowing that it would increase the pressure a bit from being right up on the corner—so we could see the deflection in the door and then approximate the amount of deflection for a range of pressure.
- I taped spacers to the door so that each of the four “feet” on the scale was exerting pressure evenly over the scale area.
- I taped a wood spacer to the face of the scale to spread the force I was exerting on the scale.
- The measurements are all approximate; as a wingnut test, I was trying to get a sense of the relationships, not to be strictly quantitative.
- Even though I am only showing one of the wingnut pressure tests in a video—the wood door between the mudroom and kitchen—the results of this pressure test were very similar for all three exterior doors (I did not rig up the bath-scale test rig on the front door; that door is in my wife’s home office, where wingnuts are not allowed).
Here is the math, given that the top free corner of each door deflected from about 1/16 in. to 3/16 in. with forces applied:
- Bath scale force readings: 2 lb. to 7.5 lb.
- Area of bath scale: 9 in. by 9 in. = 81 sq. in.
- Pressure (psi) 2/81 to 7.5/81 = 0.0247 to 0.09259
- Convert psi to Pa (1 psi = 6895 Pa) = 170 Pa to 638 Pa
- Convert Pa to wind speed: 38 mph to 72 mph
Have I ever checked my doors when it is blowing that hard? Nope, those are pretty stiff wind speeds for our neck of the woods. After this work, I certainly will, though!
But all this leaves me pretty convinced: To keep out air, water, dust, insects, and intruders, sure seems as though we need high-low jambs or head-and-foot secure points in addition to the center-of-door lockset.
Multipoint locking hardware options
The stresses that patio doors often face means that we have had multipoint locking hardware for those doors for quite some time.
And certainly European doors have had multipoint locking hardware for quite some time, but Americans often find the operation of European multipoint hardware complex and annoying.
A quick survey of major US door manufacturers turns up some multipoint door-locking hardware home-builder favorites:
I found door manufacturers that use different locking hardware manufacturers (Marvin for example) and door manufacturers that use primarily one locking hardware manufacturer (Sierra Pacific uses primarily Hoppe).
But how do we decide between the two primary types of triple-point locking hardware (shoot-bolt head-and-foot or hook-bolt high-low jamb) and 5-point locking hardware (head-and-foot as well as high-low jamb bolts)?
I spent way too much time trying to figure this out on my own and was having a hard time getting real answers on the phone until I connected with Matt Taylor, director of product development with Hoppe. Taylor very kindly called me during weekend business travel and gave straightforward general guidance on this issue. Here is what he had to offer:
- It’s difficult if not impossible to get the desired or even sometimes code-required Design Pressure (DP) test result for hurricane impact zones without 5-point door locking systems.
- Tall doors—as tall as 14 ft.—often require 5-point locking mechanisms (the example he gave was tall-building residential units with patio doors).
- Jamb tongue-bolts are generally not quite as strong as hook bolts.
- Tongue bolts require less door prep/milling than hook bolts.
- With patio doors in particular, there is a trend toward narrower styles (which decrease door stiffness) and this is translates into a greater need for beefier multipoint door-locking hardware.
- A typical exterior door (3-0/6-8) can probably achieve a DP result of 40 with a single lockset mechanism, but for results greater than that, you probably need at least a triple-point mechanism.
Given what I have observed at my own home and what I learned from Matt, it seems multipoint locking systems are certainly a worthwhile upgrade in certain high-wind areas and with certain types and sizes of door. They may be worthwhile even in the most common doors if you are hoping for a long-lasting weather seal.
—Peter Yost is GBA’s technical director. He is also the founder of a consulting company in Brattleboro, Vt., called Building-Wright. He routinely consults on the design and construction of both new homes and retrofit projects. He has been building, researching, teaching, writing, and consulting on high-performance homes for more than twenty years, and he’s been recognized as NAHB Educator of the Year. Do you have a building science puzzle? Contact Pete here.
—Photos and videos courtesy of the author, except where noted.