Masonry Fireplace Design

By Steve Litchfield on Mar 19, 2015 at 12:04 PM in Feature Articles
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In Santa Barbara, we are fortunate enough to enjoy year-round mild temperatures.  There really is no need to have a fireplace in your home as the main source of heat, though it is  fun to build a slow-burning wood fire for ambiance on those overcast days when the temperature plunges below 60 degrees (brrr!).  My wife and I are one of the few who enjoy a traditional, wood-fueled fire in an open fireplace when the fog moves in over the Mesa.

If you are now thinking of adding a fireplace to your Santa Barbara home, let’s get down to the basics of a properly constructed fireplace.

Even if the logs are arranged properly and the flue is heated, a fireplace will not draw unless three very important elements are constructed properly:  the firebox, which serves as the  combustion chamber, the smoke chamber, and the flue.  They all must be proportionate to each other; otherwise, you risk sitting in a room full of smoke staring at a pile of smouldering logs.

The fireplace starts with the firebox opening, which is typically designed using the size of the room that the fireplace will be built.  With that firebox opening dimension, the rest of the fireplace’s elements can then be determined using the guidelines in the Brick Industry Association (BIA) charts shown in this link to Residential Fireplace Design:

Unfortunately, not all fireboxes are constructed with the same care.  Recently, we had the opportunity to perform repairs on two different brick masonry fireplaces with two very serious flaws in the firebox construction.

Case Study #1.The Smoking Fireplace:

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A client of ours called to say that one night, while enjoying a roaring fire, the marble tile surround popped off the face of the firebox, and the interior plaster wall adjacent to the fireplace cracked and buckled outwards.  A quick review of the fireplace opening showed that the marble tiles were applied over the original brick surround as both an aesthetic improvement and as a way to solve a problem; the fireplace was smoking into the Living Room, as evidenced by the black soot staining on the sides of the firebox shown in the photo below.

The original fireplace did not have an 8” minimum height difference from the firebox opening to the smoke shelf.  So the old owners had applied marble tiles to the surround, hanging them down past the firebox opening about 6”.  This was done  to stop smoke from pouring into the room.  It worked for a while, until smoke and heat were drawn up behind the marble tiles (which were installed using sporadic dabs of mortar, creating an 1/8” air space between the tiles and the firebox), up inside the wood mantle, and into the wall cavity.  During a long fire on an unusually cold night, smoke and heat had been drawn inside the cool wall cavity, expanding the organic materials and causing the wall plaster and tiles to pop off.  Our clients were very lucky that a fire hadn’t started inside the wall cavity or the wood mantle.

Litchfield Builders’ solution was to lower the firebox head down to give the necessary 8” separation between firebox and smoke shelf and to make the firebox opening more proportional  to the size of the firebox, smoke chamber, and flue so that the fireplace could draw heat and smoke properly.

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The first step was to remove the mantle, all the brick at the head, the steel support lintel, and three of the bricks on either side of the firebox opening.  The steel support lintel was reinstalled, and the firebricks were put back in place at the new lower level.  Then the wood mantle had to be cut down and reinstalled up to the brick surround.  Our clients loved the look of the original whitewashed brick surround, so we struck clean joints between all the bricks and applied a light wash over all the brick with white mortar.

Our clients are now able to safely enjoy a wood-burning fire in their traditional brick fireplace that will properly draw the smoke up the chimney flue!

Case Study #2.  The Hidden Fire Hazard:

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During a kitchen remodel of our client’s beach house, we were asked about turning her fireplace , which opened into her Living Room, into a see-through firebox so that the fire could be enjoyed in the kitchen, where she and her family spent most of their time.  Using the BIA tables, along with the size of the existing flue and firebox, we determined that a small opening could be cut in into the back of the firebox without compromising the way the fireplace drew smoke and heat out the flue.  To guard against any risk of “smoking” into the kitchen, we proposed installing glass doors over the new opening.

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After removing the wood cladding at the backside of the fireplace wall so that we could layout the opening cuts, it was evident that there was a more serious problem to solve;the non-combustible fireplace surround was non-existent!  Fully-combustible wood siding had been installed directly onto the backside of the firebrick wall of the firebox.  That means there was wood siding planks only 3.5” away from a roaring fire!  To compound the issue, the firebrick that made up the back of the firebox had a large crack wide enough to see through it) so that flames were licking at the wood siding planks which were badly charred in some places.  It’s a miracle that this house didn’t burn down a long time ago.

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Another issue was that the original fireplace was constructed using a preformed steel damper and smoke chamber with little to no insulation, which meant most of the heat was escaping out the chimney structure instead of warming the inside of the home.

Litchfield Builders’ masonry crew went to work building a proper masonry brick surround, just like what was constructed at the front and sides of the structure.   This afforded us the opportunity to build the Kitchen firebox opening from scratch rather than sawcutting into an existing surround and reinforcing it with steel.  Roxul insulation, special non-combustible dense insulation,was applied to the steel smoke chamber/damper and then padded with mortar and brick filler for added insulation.  The new bricks were primed and painted white to match the rest of the exposed brickwork in the home.

Now, on those chilly summer days living on the coast, our client can safely enjoy a wood-burning fire from both her Kitchen and Living Room!