Insulation and Airflow
The 2000 Loft Conversion Building Regulations set down insulation standards for all new loft conversions and also minimum airflow standards to avoid problems like sweating.
Although your existing property may not comply with new insulation standards, any new rooms must. In simple terms, the walls, roof slopes and ceilings around the new rooms are required to have achieve a certain standard of heat loss (known in the Building Regulations as a 'U' Value).
Your loft conversion must also be constructed to ensure avoidance of any 'cold spots'. Cold spots are where heat escapes, and as heat will seek out the weakest points in any construction special care needs to be taken around areas like doors, windows and joists.
The introduction of a room such as a divided loft into a previously open roof space will restrict the flow of condensation, which in turn prevents a roof's natural ventilation. Often in a loft conversion, the existing eaves ventilation will need to be increased and roof vents added to ensure adequate airflow.
