# Masonry Fireplace/Chimney Clearances



## mp25 (Feb 10, 2018)

I'm reading thru chapter 10, 2015 IRC that deals with fireplaces. Section 1001.11 and 1003.18 are the ones that discuss clearances to masonry fireplaces and chimneys. When looking at the diagram of a fireplace/chimney Figure 1001.1 - next to letter R there is a note that states 'thermal clearance 21" min.' but cannot find a reference to this in the text portion of the code.

Exception 2 to 1001.11 states: where masonry fireplaces are part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12" from the inside surface of the nearest firebox lining.

Exception 2 to section 1003.18 states: Where masonry chimneys are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete wall less than 12" from the inside surface of the nearest flue lining.

Looking at the figure 1001.1 is the 21"  thermal clearance measuring from the underside of the lintel to where a combustible wall or floor framing can bear on the masonry? Bearing by chimneys is allowed by section 1003.8 if designed to accommodate the additional load. Does this mean that a wood bearing wall, or a floor joist would be able to bear on this masonry chimney if both conditions are met: the 21" thermal clearance shown in the figure 1001.1 and the 12" from the back of the lining as required by the the other 2 sections?


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## Francis Vineyard (Feb 10, 2018)

The letter R is above isn't a reference to the 21 in. distance to combustible for conventional fireplace and is not applicable to the Rumford illustration to the right. 

Where a conventional fireplace provides a smoke shelf the minimum depth of the smoke chamber is 21 inches for a firebox opening less than 48 inches wide. The top of the smoke chamber is where the bottom of the flue liner is located at the double hash lines illustrated in figure R1001.1

For further details see gobrick.com Technical Notes 19 Table 1


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## mp25 (Feb 13, 2018)

thank you for your response and the additional resources!


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