Air-Core Floor

An air-core floor is a passive solar heat storage feature. Solar heat from the south-facing windows and skylight is stored and distributed by circulating air through many channels below the floor slab. Click for a description of the way the air-core floor contributes to the performance of the house.

We're following the basic concepts presented by James Kachadorian in his book "The Passive Solar House". Whereas Kachadorian uses concrete blocks and slabs to create his floors, we wanted our floor to be earth, constructed over a base of bricks. Our 4" (10 cm) thick base layer of earthen floor mix contains a high proportion of gravel, for enhanced heat storage capacity.

installing many rows of bricks
Above: Jeremy lays row after row of bricks and pavers.

edge view

Left: Bricks in a slush coat of clay plaster over the compacted gravel sub-base. The plaster will cap off the dust in the gravel, to avoid circulating it throughout the house.







concrete cores next to brick cores

Left: A portion of the air-core floor is made of concrete blocks, at the Mudroom rear entry, because we wanted the extra durability and water resistance of a concrete floor. The earth slab will be placed over the bricks, flush with the top of the concrete.





the exhaust manifold

Left: The opening for the duct into the exhaust manifold. A small fan will pull air through the cores. The grey pipe will carry sensor wires; the black tube is a hot water supply to the baseboard radiator.





step 1: forming the manifiold

step 2: covering the manifold

step 3: placing the earth slab

Above: The intake plenum is created below the South windows, using bricks to form an open channel. The tube at right will supply hot water to a cast-iron baseboard radiator. Above: The plenum is covered with plywood subflooring, with wooden openings formed for the registers. Salvaged antique registers (grilles) will fit over the openings. Above: The first layer of earth slab has been placed, with a geo-technical mesh embedded to minimize potential cracking at the edge of the plywood. The smaller openings will be under cabinets

half-completed earth floor nailing tubing down to the gravel
Above: Photo taken from the same angle as above, with the first layer of earth slab placed and tamped. This view is into the kitchen, under the 'garden balcony'. Click here to see a diagram of the air-core channels and the temperature sensor locations. Above: We installed water tubes for a hydronically heated earth slab floor at the bedroom. Because of the placement of the neighbors' house and trees, this portion of the house will never receive much heat from the sun. Click here for more on the hydronic heating system.


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