“insulation”

The insulation component achieves a percentage reduction in space heating energy demand:

"insulation": {
  "include": true,
  "cost": {
    "gbp": 2500.0,
    "gbp_per_year": 0.0 
  },
  "energy_saving_percent": 20
}

The above example is for adding cavity insulation to a typical 5 bedroom house: initial costs only of £2,500 and achieves a 20% reduction to its space heating energy demand.

Insulation investments should be your first until they result in diminishing returns.

It pays to stop at some point, and your house doesn’t have to be a passive house for adding more not to make sense. For example, after adding a little extra loft insulation to our wall cavity filled 1960s house, there was relatively little we could do to improve it further beyond paying another £30k to clad it, inside or out: far less financially attractive compared to installing solar PV with a heat pump and battery.