Yes. At least 15% of heat loss is through gaps and draughts. This can rise to over 30% in houses with badly warped or poorly fitted windows and doors. We do not fit or allow letter boxes in doors to increase airtightness.
Houses which have an air tightness below 5 at 50Pa, q50(M³/h.M²) will require a demand control ventilation system (DCV) or a heat recovery ventilation (MHRV) to be fitted to ensure good quality fresh air in the house.
We regularly deliver retrofit houses of below 3 50Pa, q50(M³/h.M²) which is considered very very airtight for a retrofit.