What is a sub-frame for?
A sub-frame is a supporting framework built underneath your loft boards to elevate the storage floor safely above your home's insulation layer while providing enhanced structural support and strength.
Because modern building standards require deep insulation layers (typically 270mm) that protrude well above standard ceiling joists, any loft with insulation higher than the joists requires a professional sub-frame before boarding can take place.
Our Professional Sub-Frame Systems
To create a safe, robust storage floor tailored to your home, UK Loft Boarding utilizes two primary types of sub-frames:
- LOFT-E® System: Designed for modern trussed roof properties built from the 1960s onwards, providing high load capacity and height adjustment.
- LBNW Timber Raised Sub-Frame: Built for older, traditional purlin-style roofs (circa 1960s and earlier), offering independent self-supporting strength without putting strain on existing ceiling joists.
Why Boarding Directly on Joists Is Bad Practice
Attempting to board directly onto joists by removing, flattening, or squashing insulation is strongly discouraged. Compressing insulation squeezes out the tiny trapped air pockets that provide its thermal resistance, drastically cutting your home's energy efficiency and driving up heating bills.
Maintaining Essential Loft Airflow
A proper sub-frame also plays a vital role in protecting your roof's health:
- Unrestricted Air Circulation: Your insulation and loft space need continuous airflow. Boarding out an entire loft incorrectly or completely blocking eaves, roof vents, or soffit vents can trap warm air and moisture.
- Preventing Condensation: Trapped humidity leads to condensation build-up, which can cause damp ceilings and rot roof timbers.
- Open-End Design: When using a raised sub-frame above your insulation, the ends must never be boxed in completely. This allows air to pass freely underneath your storage floor and through the insulation so it can function efficiently.
If you are planning a DIY project or evaluating options from another company, make sure proper sub-frame raising and ventilation practices are followed. Unsure about a proposed setup? Contact our expert team for free advice.
