- Grade 1 survives ten hammer strikes and 250,000 cycles. Grade 3 survives two and 100,000.
- A deadbolt needs a one inch throw to reach meaningful material in the frame.
- Four three inch screws through the jamb into the stud beat a lock upgrade for stopping a kick.
- Double cylinder deadbolts trap people in fires. Check code and offer alternatives first.
ANSI and BHMA grades
The American National Standards Institute and the Builders Hardware Manufacturers Association publish a three tier grading standard. Grade 3 is basic residential. Grade 2 is heavy residential or light commercial. Grade 1 is commercial and the highest of the three.
The grades are earned on measured tests. A Grade 1 deadbolt survives ten strikes from a hammer test and two hundred and fifty thousand operating cycles. Grade 2 survives five strikes and one hundred and fifty thousand cycles. Grade 3 survives two strikes and one hundred thousand cycles. Those are the numbers behind the marketing.
Most homes ship with Grade 3. Moving a front door to Grade 1 is a real improvement and costs less than most customers assume. Say the numbers out loud. A customer choosing between a forty dollar lock and a ninety dollar lock deserves to know that one takes five times the beating.
Throw, strike and the three inch screw
A deadbolt should have a one inch throw. Anything less does not reach far enough into the frame to matter. Check it by extending the bolt and measuring from the face of the door.
The strike plate is where most residential doors fail. A standard strike is a thin plate held by two three quarter inch screws that bite only into the door jamb, which is a thin board nailed to the framing. A kick transfers straight through it and splits the jamb.
A reinforced strike box with four three inch screws driven through the jamb and into the structural stud behind it changes the failure mode entirely. The lock is no longer holding a decorative board. It is holding the house. This single upgrade costs a few dollars in parts and does more for a door than upgrading two grades of lock.
Single cylinder against double cylinder
A single cylinder deadbolt takes a key outside and a thumbturn inside. A double cylinder takes a key on both sides. Customers with glass beside the door often ask for a double cylinder so an intruder cannot reach through and turn the thumbturn.
The trade is escape. In a fire, in smoke, in the dark, a double cylinder deadbolt requires a key to get out. Many jurisdictions restrict them on residential exits for exactly that reason and building codes should always be checked before fitting one.
There are better answers to glass beside a door. Security film on the glazing, a laminated glass panel, or a thumbturn that can be locked with a key when the house is empty and left free when it is occupied. Offer those first, explain the escape risk plainly, and put the customer's decision in writing.
Common Questions
What does ANSI Grade 1 actually promise?
That the lock survived a million cycles and the highest force in the standard. Grade 2 is residential heavy duty and Grade 3 is the basic level most builder locks meet.
Is a double cylinder deadbolt a good idea?
It stops somebody breaking the glass and reaching the thumb turn, and it also stops your family getting out in a fire without hunting for a key. Many codes ban it on a main exit, so check before fitting one.
What is the cheapest thing that makes a door harder to kick in?
Three inch screws through the strike plate into the wall stud. The bolt is rarely what fails. The frame is.