Getting out of the ground was easier than anticipated. A refreshing and novel change to the stress of getting the land, and issues dealing with planning. Four years of nothing but bills and hassle vs. three weeks from ‘waste ground’ to foundations. Karma perhaps, or another reason to be grateful for my great-great-grandfather’s shrewd investment.
The majority of UK houses are built around the concept of a cavity wall. Two four inch block walls separated by an insulation-filled cavity. Timber framed houses are also gathering momentum thanks to their speed to build, and lower cost of development. Combining a heatpump and living in Cornwall’s, slightly less extreme temperatures, we are gambling there is a more energy efficient way to construct our house. Building single six-inch block walls externally clad in insulation, creating a cave-like effect. In summer months the insulation reflects higher outside temperatures, helping the block stay cool. In winter months the heatpump and underfloor’s heat soak into the block. The external insulation then helps retain the heat and protects from the outside elements. Creating our very own heat store.
Low-intensity heat required to maintain core temperature, ideal conditions for a heatpump and underfloor heating.
The six-inch block provides a larger thermal mass to store heat.
Insulating the outside, not being limited for space by a cavity or framework, allows for significantly more insulation.
Twice as expensive to build.
Complex to build, especially where we’ve used stone cladding.
Slow to finish.
Even slower to initially heat (or change temperature).
In our case, where we are not building for profit, the upsides far outweigh the down. The concept of the heat store and easier to maintain temperature should require a lot less energy to keep the house warm. As long as we avoid completely losing the core temperature in the house. Getting heat into the floor and block is no small task, and can take over 24 hours to heat.
In theory (hopefully to be proven in practice) by heating the block work and floor of our house, using it as a heat store with extra insulation on the outside, means for less energy we’re warm in winter, and cooler in summer.
Credit goes to our structural engineer, and my Father-in-law, for pioneering the approach in our current house.
Initially, our heat store approach is far quicker to build. Thanks to only building single six-inch block walls. The extra cost and complexity creep into the latter stages of the build. Two layers of 50mm insulation are battened horizontally and vertically to the exterior of the block. This is then clad in 9mm marine ply, a damp proofing layer, mesh, and finished with render.
Complicating things nicely, where we are using stone to finish the house doesn’t work with our chosen construction technique. To get around this we’ve attached 75mm of insulation to the outside of the block work and combined it with Surecav damp proofing. The stone has ended up costing us fourteen inches of interior space, a fair bit of head scratching and a few headaches. Here’s hoping it looks good when done. Local Cornish stone at least.