Loft & Attic Calculators

Loft conversions are one of the most popular home improvements in the UK, adding valuable living space without extending the building footprint. Whether you are boarding a loft for storage, installing a loft ladder for easier access, or planning a full loft conversion, accurate measurements and calculations are essential for a successful project.

Before starting any loft project, the first step is checking whether your loft has adequate head height. UK Building Regulations (Approved Document K) require a minimum head height of 2.1 metres over at least 50% of the habitable floor area in a loft conversion. Our loft head height calculator uses your ridge height, eaves height, and roof pitch to determine usable floor area and whether a conversion is feasible.

For loft storage projects, boarding the loft is a straightforward improvement that most competent DIYers can tackle. Standard loft boards are 2400 × 600 × 18mm chipboard panels that sit on battens raised above the insulation. The loft boarding calculator works out the number of boards, battens, and screws you need. It is important to raise the boards above the insulation using loft legs or timber battens — compressing insulation reduces its effectiveness and can cause condensation problems.

Safe access is equally important. The loft ladder sizing calculator helps you choose the right ladder type and hatch size for your floor-to-floor height. Two-section, three-section, and concertina ladders each have different hatch requirements, with the minimum hatch opening being 726 × 526mm per Building Regulations. Three-section aluminium ladders from manufacturers like Youngman and Werner are the most popular choice for UK homes.

Structural considerations are critical for any loft project. Existing ceiling joists in most UK houses are designed to carry the weight of a plasterboard ceiling and light loft insulation — not heavy storage or habitable rooms. Eurocode 1 (BS EN 1991-1-1) specifies 0.25 kN/m² for storage-only lofts and 1.5 kN/m² for habitable rooms. Our loft load capacity calculator checks whether your existing joists are adequate, based on their size, spacing, span, and timber grade (C16 or C24). If the joists are not sufficient, you may need to sister new joists alongside the existing ones or install a new structural floor.

Ventilation is a commonly overlooked aspect of loft work. BS 5250 and Approved Document C require adequate ventilation to prevent condensation in cold roof spaces. For pitched roofs over 15°, this means a 10mm continuous gap at the eaves (or equivalent soffit vents) and, ideally, a 5mm continuous gap at the ridge. Our loft ventilation calculator computes the required ventilation areas and gives you the number of soffit vents or tile vents needed as an alternative to continuous strips.

For those planning a dormer loft conversion, the dormer sizing calculator helps determine structural opening width, cheek depth, cladding area, and window size recommendations. Dormers are subject to planning constraints — most local planning authorities permit dormers under Permitted Development rights provided they do not exceed 50% of the original roof plane width and meet other conditions. A full loft conversion will require Building Regulations approval covering structure (Part A), fire safety (Part B), ventilation (Part F), drainage (Part H), thermal performance (Part L), and staircase design (Part K).