Heat pumps and solar panels get the attention. The insulation and airtightness behind the plasterboard do most of the actual work.
Clients frequently arrive with a technology list: air source heat pump, solar array, battery storage, mechanical ventilation. All good things. But installed into a leaky building envelope, they are an expensive way to heat the outside.
What fabric first means in practice
Reduce the demand before you specify the supply. Insulate well, detail the junctions to eliminate thermal bridging, and make the building genuinely airtight. Only then size the heating system - which will be smaller, cheaper and cheaper to run.
On our Meadowbrook project we used 300mm of wall insulation and triple glazing, and achieved airtightness results of 1.8 and 2.0 m³/h·m². Both units reached EPC A with a modest air source heat pump rather than an elaborate technology package.
Airtightness is a detailing problem, not a product
You cannot buy airtightness. It is achieved at the junctions: wall to floor, wall to roof, around every window, and at every service penetration. It requires the whole site team to understand where the airtight line runs and to protect it.
Test at first fix, not at completion
This is the single most useful thing we do on low-energy builds. An air test before plasterboard goes on means any failure can be found with a smoke pencil and fixed in an afternoon. The same failure discovered at completion means taking finished surfaces apart.
Ventilation is not optional in an airtight house
Build a tight envelope without mechanical ventilation with heat recovery and you will have condensation and poor indoor air quality. The two must be specified together. An airtight house with trickle vents in the windows is the worst of both approaches.
