Boarshurst Lofts

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Loft Conversion Building Regulations

Guide to structure, fire safety, ventilation, stairs and insulation rules.

UK Building Regulations are prepared by the Department of the Environment and approved by the Secretary of State. They are different from Planning Permission.

Statutory Building Regulations apply to loft conversions where is structural change, even new flooring. "Habitable use" is generally taken to mean a room intended for use as a dwelling that is big enough to stand up and lie down in (excluding bathroom).

The key parts are:

Loft Plans and Regulations

Applying for a Loft Conversion


Full Plans Submission

The finished loft plans are submitted to the Local Authority for examination against minimum requirements. Any amendments (exceptionally rarely with us) are notified and plans modified before Approval. Examination of plans is within 3 weeks, but work can begin 2 days after submission.

Building Notice

Providing 2 days notice to allow the Building Control Surveyor to visit the site and inspect work as it progresses. Plans and structural calculations can be requested and until full Plans Submission there is no Formal approval notice or certification.

Part A - Structure

A roof consists of structural members such as: joists, rafters and purlins. These will be designed only for the current loadings and planned loading changes need checking so there will be no compromise to stability. Large change requiring steel beams require structural calculations.

Architectural plans show proposed structural change and details of materials. The overall house structure is shown to demonstrate how loads are supported by walls down to foundations. Change to the roof covering is also shown and considered, as are proposed notch and hole dimensions.

Part B - Fire Safety

The key elements of fire safety legislation include adequate detection, means of escape, suitable access and prevention of spread.

The loft needs to withstand fire for 30 minutes so occupants and emergency services can evacuate and enter from windows.

Rules on doors have changed over time. Originally, self-closing doors were required, but as they were often left propped open and of little practical use, 30 minute fire doors could be substituted. However, as doors are often left open one options we like to consider is fitting linked, mains powered smoke detectors (with battery back up) throughout a property. This specification is approved for us as it alerts inhabitants at an early stage to the presence of fire/smoke affording valuable time to escape.

Rules on escape windows have been modified and we are rarely required fit these.

The loft floor needs to provide 30 minute fire resistance and in some circumstances the staircase may.

If close to a boundary wall, then dormer cheeks and gable ends might need to meet fire specifications.

Part F - Ventilation

Ventilation provides clean air into a living environment and vents moist or stale air that would otherwise cause condensation.

The required window opening(s) size relates to floor area, and background ventilation (trickle vents) have volume measurements. WC's, en-suites and bathrooms must achieve volume extraction and operating time overrun minimums.

Ventilation is also needed under the roof tiles to prevent condensation that would rot timbers. There is a minimum distance allowed between materials to allow air to flow freely up to and out of ridge vents.


Access to the loft is via a fixed flight of stairs and we always carefully consider the design of stairs as many rules apply because they provide a means safe access and of escape.

The means of escape rules require stairs to 'extend to the final exit' i.e. vent onto the existing landing or hall rather than living areas.

Stairs must meet minimum specifications, with some allowance for small spaces. Pull-down ladders are not acceptable.

A fire door is needed at the top or bottom of the loft stairs.

Enclosed staircases (often built between 2 bedrooms) need walls with 30 minute fire resistance.

Stairs must not exceed a pitch of 42 degrees and have maximum and minimum rules on risers (vertical) and goings (horizontal) elements.

Two metres headroom is needed on stairs - taken from the outermost point of the stair (lip) and lowest parallel point of ceiling above.

Where this is not possible, the rules allow for reduced headroom based on half width of stair having 1.9 metres.

Part L1 - Insulation

Converting a loft often make it the best insulated part of a house. This is due to standards rising over time which cover the U-values for walls, windows and roofs, and emphasis is put on reducing cold-spot potential around insulated areas and eliminating drafts.

Acoustic insulation needs to meet the current house levels.

Other Requirements

Other requirements include Part K - Protection from falling, collision and impact. For example, window heights for dormer windows have a minimum height above ground level. General building regulations also apply, such as those for drainage if a loft en suite is installed.

Local Variations Exist

Building Regulations give practical guidance to comply with performance standards set out in various regulations. They are not mandatory but are used to test satisfactory compliance and performance (i.e. minimum standards). Regulations are subject to change and appropriate professionals, such as our architectural surveyors have the latest standards and information.


Please note that this information is intended only as a summary guide only and not a basis for making decisons on. It is not a substitute for discussing details of an individual loft with a professional surveyor.

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