Case study
Loft Insulation Case Study — Full Loft Insulation Upgrade Around a Central Hatch, Bristol
Sarah's first-floor bedrooms warmed up but lost heat quickly once the heating went off. We laid a full 300mm Knauf glass mineral wool upgrade across the 42m² loft floor — 100mm between the joists and 200mm cross-laid — while keeping the central hatch clear and usable.
What we found
- •The loft floor was largely uninsulated, with exposed ceiling joists across most of the space
- •Only small traces of old material remained at the edges and provided no meaningful thermal coverage
- •The central loft hatch had open gaps around the timber frame
- •The large uninterrupted roof space was allowing heat from the bedrooms below to escape quickly
The problem
Sarah contacted us because the first floor felt cold even when the heating had been running for several hours. The bedrooms warmed up initially, but the temperature dropped quickly once the heating switched off. The issue was most noticeable overnight and during cold mornings.
The survey showed that the main cause was the almost complete lack of insulation at ceiling level. With the joists exposed across the loft, there was very little resistance to heat passing into the roof space.
Our assessment
The usable loft floor measured approximately 42m² and had clear access from a centrally positioned hatch. The roof structure and brick gable wall were in serviceable condition, so the most effective solution was a full loft-floor upgrade using 300mm of Knauf glass mineral wool. We specified a 100mm base layer between the ceiling joists, followed by a 200mm cross-laid layer to reduce cold bridging through the timber.
The installation
The loft floor was vacuumed and loose debris was removed before installation began. The first 100mm layer was cut neatly between the joists, with careful detailing around cables, timber trimmers and the hatch opening.
A second 200mm layer was then installed at right angles across the joists, creating a continuous 300mm blanket across the full floor area. The hatch perimeter was kept clear and accessible, and the insulation was finished neatly at the eaves without blocking the ventilation route.
The result
The completed loft had consistent insulation coverage from end to end, with the central hatch remaining fully usable. Sarah reported that the bedrooms retained warmth for longer and felt less affected by cold changes overnight.
The installation helped to
- Reduced heat loss through the loft floor
- Improved heat retention in the upstairs rooms
- Reduced cold spots around the loft hatch
- Provided a consistent 300mm insulation depth
- Improved the overall condition and appearance of the loft
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