Double-cylinder deadbolts and fire safety: what the building code says

Updated November 10, 2026 · KeystoneProGuide editorial team

What is a double-cylinder deadbolt?

A deadbolt that needs a key on both sides. A single-cylinder deadbolt has a keyhole outside and a thumb turn inside, which the King County Sheriff's Office in Washington State describes as the usual arrangement: locked with a key from the outside and a thumb turn on the inside. A double-cylinder model replaces the inside thumb turn with a second keyhole, so the door cannot be unlocked from inside without the key.

The appeal is easy to see. Radnor Township police in Delaware County say to make sure no one can reach through an open window and unlock the door, and a lock with no inside thumb turn is one way to address that. The trade-off is getting out quickly in a fire.

What does the building code say?

That a home's exit door must open without a key. Section R311.2 of the International Residential Code, published by the International Code Council, requires at least one egress door for each dwelling unit and says egress doors shall be readily openable from inside the dwelling "without the use of a key or special knowledge or effort". The sentence is the same in the 2021 edition. A deadbolt that needs a key from inside does not meet that wording on the door that serves as the required exit.

Does that rule apply in Pennsylvania?

Pennsylvania's Uniform Construction Code adopts the International Code Council's codes, known as the I-Codes. The Department of Labor and Industry says the state's regulations adopting the 2018 I-Code series took effect on February 14, 2022, and that a later update of the code took effect on January 1, 2026; its page does not say which edition that update adopts. The R311.2 sentence is identical in both editions.

How it applies to your house is a separate question. The code governs construction and regulated work: the state's regulation leaves repairs and alterations without structural change outside the code unless a local ordinance requires otherwise. No source read for this guide says that an existing double-cylinder deadbolt in a Pennsylvania home is unlawful, so this guide does not say so. Over 90% of Pennsylvania municipalities enforce the code themselves, and your township or borough code official is the person to ask about a specific door. In a rental, ask the landlord and the municipality, since the rules for rental housing were not part of this research.

Why do fire safety groups care?

Because escape time is short. The National Fire Protection Association says a fire can leave as little as one or two minutes to get out safely after the smoke alarm sounds. It advises planning two ways out of every room and, when you walk through the plan, checking that doors and windows can be opened easily. For security bars on doors and windows, it says they need emergency release devices inside so they can be opened immediately, and that such releases do not compromise security.

A door that needs a key from inside depends on that key being at hand when those minutes start. The NFPA advice does not mention deadbolts by name, but it is clear about the goal: doors that open easily from inside.

What do police and locksmiths recommend?

• Police. The King County sheriff recommends single-cylinder deadbolts on all exterior doors, with a bolt that throws at least one inch.
• Local police. Radnor Township police in Delaware County recommend a heavy-duty deadbolt with a 1 inch throw and a knob lockset with a dead-latch on entrance doors. Their checklist does not mention double-cylinder locks at all, and neither does Lower Moreland Township's in Montgomery County.
• The trade association. ALOA, the locksmiths' association, says there are fire and life safety codes that must be followed when choosing locks, and that a locksmith should know which locks give good security while staying code-compliant. That is ALOA's description of its members' role.

What are the alternatives?

If the worry is glass near the lock, the sources suggest working on the door rather than trapping yourself inside. The King County sheriff recommends solid or metal exterior doors and strong frames. Radnor police recommend a solid-core or metal door at every entrance and a wide-angle peephole for seeing visitors. A locksmith or door installer can advise on options for a particular door.

What does each type cost?

HomeGuide says double-cylinder and electronic deadbolts cost more than average, and gives $100 to $350 or more per lock to install a deadbolt including the trip fee, hardware and labor. No survey gives a separate price for converting a double-cylinder deadbolt to a single-cylinder one.

Does Pennsylvania license the people who install them?

No. The Department of Labor and Industry says Pennsylvania has no licensing for most construction contractors, and there is no locksmith license; what Pennsylvania requires of locksmiths explains the registration that does apply. Making an exterior door stronger covers door and frame work, and local businesses are on the locksmiths directory page.

Sources

1. Chapter 3 Building Planning, 2018 International Residential Code, International Code Council
2. Chapter 3 Building Planning, 2021 International Residential Code, International Code Council
3. Uniform Construction Code, Pennsylvania Department of Labor and Industry
4. 34 Pa. Code § 403.1. Scope., Commonwealth of Pennsylvania (Pennsylvania Code)
5. How to make a home fire escape plan, National Fire Protection Association
6. Doors and locks, King County Sheriff's Office
7. Burglary Prevention Tips, Radnor Township Police Department
8. Prevent Burglaries with these tips from Chief Smith!, Lower Moreland Township Police Department
9. How to Hire a Professional Locksmith, ALOA Security Professionals Association
10. How Much Does a Locksmith Cost?, HomeGuide
11. Contractor Licensing, Pennsylvania Department of Labor and Industry