This article complements the Masonry Heater Foundation Details article by providing real-world process examples.
All framing is placed 2″ beyond the heater footprint to meet clearance requirement. Only the subfloor bridges across that clearance (since it is a membrane that can dissipate heat and is necessary practically in construction).
Although pink board was used in this build, we strongly recommend 2″ Foil Faced Rock Wool Bats for that location. The insulation doubles as formwork for the slab. The extra vertical block columns are simply to support the cement board form work for the slab above.
Rebar hooking from the concrete vertical posts in the block work and meeting the 12″ O.C. #4 Rebar Grid on the top slab.
Drop screed creates flat surface for additional layers.
You can see a calcium silicate board product that was used here. We far prefer the Skamol SuperIsol product, if available.
The final layer that is not pictured is the 1/2″ cement board layer to finish the foundation and prepare for the heater.
Please address any questions you have in the forum topic on this article.
