Fireplace Mantel Clearances

A discussion of national codes and local variations concerning the clearance from a fireplace opening to nearby combustible surfaces. January 12, 2009

It's been about a year or so since I've done a mantel and am experiencing a senior moment. I am in NJ and need to know the firebox setback requirements for a mantel surround. I believe it is 8" on the sides and 12" on top, but I am not sure.

Forum Responses
(Architectural Woodworking Forum)
From contributor P:
That's my understanding also.

From contributor K:
I also agree.

From contributor D:
I'll be the odd one (I'm used to it) and say it depends. Two reasons... Code differs from area to area, although there is an effort to standardize. Your code may be different than the next guy's. And there is a projection limitation/calculation on the upper side that covers the projection of the shelf or other elements beyond the setback.

From contributor C:
Most fireplaces require 12" vertical of noncombustible material, then allow 1" projection per 1" of rise (45 degree) to a maximum depth of 12" above the top of the firebox (12" depth at 24" above).

From contributor R:
I have to agree with contributor D. Better check the local codes.

From Gary Katz, forum technical advisor:
I agree with the code check! I got caught once using LA requirements on a home in Thousand Oaks (Ventura County, CA), which is right next door. Ventura requires 12 in. on the top and 10 in. on the sides. That code requirement is not at all universal, which is pretty silly.

From contributor C:
Well... It is common knowledge that the flammability of wood changes as you cross county lines.

From contributor D:
Type of fireplace may also come into play with codes. Gas may differ from wood.

From contributor N:
We have done a lot of mantels and have always deferred to the manufacturer's specs in the owner's manual. For a fireplace, you go with local building specs.

From Gary Katz, forum technical advisor:
I used to defer to the manufacturer's specs, too... until I learned that many municipalities have more stringent requirements. For instance, according to some manufacturers, 8-10 inches is all that's required for mantel clearance from the top of the firebox (depending on one inch of clearance for every one inch in projection). But codes around me (Ventura County) require 12" clearance no matter what, whereas codes in other areas where I've designed mantels (like some cities in Oregon), go by the manufacturer's specs. I'm telling you, this hodgepodge of requirements is really ridiculous and often ends up confusing building inspectors and occasionally feeding the authoritarian needs of others.

From contributor N:
Sounds like good advice to do more research.

From contributor H:
As a qualified fire inspector, I can assure you that in Manitoba, Canada, there is only the National Building Code and the National Fire Code. These Codes are then recognized by the Provincial (state) Government as Manitoba Building/Fire Code. Municipalities (county) then enforce (?) these codes locally. How many fatalities have occurred over time to develop and implement these codes is a guess. Think White Shark/Rhode Island. Wonder how the authority having jurisdiction made out there? Who, by the way, can/will/may change the codes any way that they see fit. Which may explain differences from one area to another.

From contributor L:
Check out the NFPA website at You can get the codebook online or borrow it from your local brick mason. I'm pretty sure it has the requirements in it. I've misplaced or lent out my copy, so I couldn't tell you. I've heard that soon, or maybe even now, this will override any local codes, which will be good.

From contributor S:
I am also researching clearance requirements. I found a diagram at I am in Baton Rouge Louisiana and will be calling the city inspector soon to verify.

From Gary Katz, forum technical advisor:

Unless I'm not understanding that drawing - which is very likely - it makes no sense at all. According to that drawing, at 12 in. from the "top edge" you would only be able to install a 1 1/2 in. projection. Not until you were 18 in. above the "top edge of fireplace" would you be able to have a 12 in. projection. I haven't seen that code requirement anywhere.

From contributor N:
There are some gas stoves we have seen with clearances of 21" above edge for any protrusion over 3\4". Have also had a customer in tears after we told her with her stove and the fact that they wanted a raised hearth, that would put the top of her mantel 24" below the ceiling. Stove was already installed to accommodate the raised hearth. She went without a mantel. It was a very efficient stove that put out a ton of heat.

From Gary Katz, forum technical advisor:
Another good reason to check the manufacturer's instructions and the building code. I'm not familiar with wood stoves at all!

From contributor D:
Gary, I just had one a while back, in a commercial project, that had the wood mantel shelf drawn at 6" above, with a 6" projection. I inquired about the code, and it came back as 1-1/2" projection, 12" above the box, as you mention, to comply.

It went back for redesign, and it changed to concrete so as to be non-combustible. Last I heard the designers were trying to verify that the concrete was, in fact, non-combustible.

The proportions get really odd with the regulations and the fact that these metal box things are 6"-10"- 14" off the floor. Nobody wants the "funny looking" mantel we designed, and they think it is our fault for not designing right. Since inspectors don't know, or don't care, or don't even inspect, about half the mantels I see now are non-compliant.