Loft Insulation Case Study — Long Loft Insulation Upgrade With Side Wall Detailing, Portsmouth

The problem

James asked us to inspect the loft after the bedrooms at the far end of the house repeatedly felt colder than the rooms nearest the boiler. The roof space ran the full length of the property, but the floor had no consistent insulation.

The extended perimeter and long run of exposed timbers created a substantial route for heat loss. The colder areas downstairs aligned with the sections of loft that had the poorest coverage.

Our assessment

The loft floor measured approximately 47m². We recommended a 300mm Knauf glass mineral wool installation across the full length, using 100mm between the joists and 200mm cross-laid above. Additional care was required along the low brick walls and around the offset hatch.

The installation

The team worked in sections from the furthest end back towards the hatch. A 100mm base layer was fitted between the joists, with close attention to the long edge bays and wall junctions.

The 200mm layer was then cross-laid across the joists to create a continuous blanket. The insulation was trimmed neatly around the hatch and kept clear of the eaves ventilation route. The full depth was checked before completion.

The result

The entire length of the loft was covered with 300mm of insulation. James reported a more even temperature between the front and rear bedrooms and a slower drop in temperature after the heating was turned off.