Passive… From the Ground Up

We had a productive week at Kingston Passive House.  There were a number of tasks which had to be completed before the “prior to back-fill” inspection. First on the list was a basement floor; a SIP foundation requires both the basement slab and the main floor be installed before back-fill.  Of course, very little of this house can be considered typical, so pouring a concrete slab is a multistage process.

Basement under-slab insulation.

Basement under-slab insulation.

We started by rolling the 3/4″ gravel; this isn’t normally necessary, but it helps with leveling and flattening out the more pointy stones before laying down the vapour barrier and subsequent insulation. The vapour barrier was cut or stretched around protrusions and subsequently taped.  This picture shows how the poly is sealed to the rim of the sump-pump tank.  Once the lid is sealed to the tank, it becomes part of the barrier.  There is 10-inches of EPS insulation below the slab.  It was installed in two layers with offset joints for improved stability and reduction of convection currents.  It is a lot of insulation, but this floor will be high and dry.  We were fortunate to source recycled insulation for this job.  It was formerly installed on a flat roof and is in remarkably good shape. The staircase was already onsite, and supporting the bottom from chains meant there was clearance for installing the poly, insulation, concrete and just enough room to pass the power-trowel underneath.  We had to pump in the concrete because the window is located on the South corner for solar gains – not accessible by truck without destroying the neighbors lawn.

SHX PEX tubes on the bedrock

SHX PEX tubes on the bedrock

Another task  was the placement of the subsoil heat exchanger (SHX) PEX tubing. There are three continuous (no joints or fittings) lengths around the perimeter of the foundation.  They are filled with water and pressurized to 30 psi.  We wound have liked these to have been a bit deeper for a more constant temperature, but bedrock is the next best thing.  We’ll pack dense clay above these tubes to ensure there is effective thermal conductance with the rock.  The landscape cloth will help keep that clay out of the gravel and drainage ports through the footings.  We were very pleased to learn that our SHX design (and overall HVAC strategy) was signed-off by an HVAC engineer.  He had never seen anything like it, and is also very curious to see the true (measured)  performance numbers of this house.

The photo below shows the “in” and “out”  manifolds connected to the PEX loops.

SHX manifolds and gauges

SHX manifolds and gauges

We still have a 2×4 service partition to build along the walls, so these manifolds will be permanently mounted at a later time.  The picture quality isn’t great, but in addition to a pressure gauge there is a thermometer on each manifold so we can monitor the ground temperature and observe the temperature drop (or rise) caused by the liquid-to-air heat exchangers (coils) in the HRV ducting.

The building department requested that our SIP foundation installation be inspected by the manufacturer prior to back-fill.  We were happy to get a vote of confidence from the manufacturer yesterday, and even more happy to see the positive reaction of the building inspectors that came out to join the party.


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