Building the Cob and Green Roof Garden Wall- Part 3: The Wall Fireplace


Early in the cobbing phase of building our wall, we decided to incorporate a fireplace in to it. We had so much fun building our first fireplace, and enjoyed using it so much, that this seemed like a perfect fit for our wall build. We placed it midspan on the soft curved wall, facing the original fireplace which allows us to have double fire place nights when our friends come over.

The wall is 20″ thick and we made the fireplace 10″ deep, 2″ shallower than the original. Its front face is 29″ wide and the sides angle inward to make for an 18″ back wall. We started by building a trough in the wall the size of the firebox’s foot print and filling it with woodash.


The wood ash fire under base of the wall fireplace.


We then covered the ash in dry sand and began laying down the firebricks. We used an angle grinder with a stone cutting wheel to cut the front base bricks in to a curve that conformed to the curve of the wall. We used this same tool to cut the angles to the get the wall bricks to sit nicely.




We built up the cob around the bricks to support them. And then continued to build the sides up along with the wall until we got to a height of 41″ above the base of the firebox. Recall from the Cob and Tadelakt Fireplace blog that the height of the smoke shelf works out to be 1′ above the height of the top of the fireplace arch. Our fireplace arch was going to be 29″ high, the same as the width of the front opening.



Once the surrounding cob was to height, we began to make the firecob backwall. As with the first fireplace, this was constructed to slope forward and ultimately end in a smoke shelf that is 3.5″ thick.



Once the smoke shelf was in place it was time to install the arch form and begin cobbing the front wall. This arch was constructed to be a perfect semi circle to match the circular openings. The throat of this fireplace is 3.5″.




Once the front wall got to the height of the smoke shelf, we plastered the inside faces of the fireplace in firecob plaster as with the first one. We continued to build the whole wall up another foot so that the smoke shelf was a foot below the top surface of the wall. At this point it was time to start tapering in to form the chimney opening which we did in the same way as described in our first fireplace.


After a couple of weeks we removed the arch form and tidied up the interior of the firebox with firecob plaster. We sculpted a cob edging around the arch opening to add some simple detail and definition.


Since the chimney of this fireplace would sit above the roof on the wall, we decided to make a metal chimney so that it could better tolerate rain and weather. We made the chimney out of sheet metal which Jen welded together to form a rectangular tube 24″ tall. Short sections of square bar were welded to the inside of the corners at the top and bottom of the chimney so as to provide an attachment point for the cap on top and an anchor mechanism for the chimney within the cob chimney. Pieces of sheet metal were also welded along the lower edge of the chimney, perpendicular to and facing outward from the sides which allowed us to easily set the chimney in place over the cob chimney opening.



  • Front face.
  • West face.
  • North face.
  • East face.

Jen cut out Starlings in the chimney sides so as to have the perched under them eve of the chimney cap. Starlings are a big part of our backyard menagerie and so found their way in to our metal art.

Jen installs the chimney
It sits nicely on its sheet metal lip and is cobbed in to place.


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