When homeowners upgrade their insulation, they tend to focus on the loft, but older properties may be losing heat through the ground floor. This month Bradley Hirst, Technical Services Manager at Knauf Insulation, provides his top tips for insulating a suspended timber floor.
Comply with building regulations
Approved Document L of the building regulations was updated in June 2022. There’s a one year transition period, which means that projects granted planning permission before that date can still be built to the existing standard providing work starts before 15th June 23. After this date all projects must meet the new minimum thermal performance standards. This means if you are installing insulation into an existing floor, then you will need to achieve a U-value of 0.25 W/m²K. This is typically achieved using 150mm of insulation between joists, but check with the manufacturer’s technical team to ensure the correct specification for your project.
Use Mineral Wool insulation
As well as providing thermal performance, Mineral Wool insulation for suspended timber floors is non-combustible. This means you can reassure your customers that it will not add to the development or spread of fire should it occur.
Choose a slab or roll based on the installation method
There are two methods for insulating a suspended timber floor: from above by removing the floorboards, or from below if there’s a crawl space. When installing insulation from above, use a Glass Mineral Wool roll, such as Knauf Insulation’s OmniFit Roll 40, because it’s quicker. But when working below the floor, use a Glass or Rock Mineral Wool slab, such as Knauf Insulation’s OmniFit Slab 35 or Rocksilk Flexible Slab, because slabs are easier to manoeuvre in a confined space.
Always support Mineral Wool insulation with netting stapled to the joists to stop it from becoming loose, due to vibration from people walking across the floor above over time.
Ensure the quality of installation
Unlike rigid board insulation, Mineral Wool is flexible, so it is easier to install correctly. It friction fits between the joists and knits together at joints, preventing gaps that can reduce thermal performance and fire safety.