Garage conversion building regulations

If you are planning a garage conversion you will need to find out if any building regulations apply to your property and any work that you intend to carry out on it. Following are examples of works that may require adherence to building regulations. Please note: this is not an exhaustive list and for precise information about your individual garage and project, you will need to contact your local authority;

  • General garage conversions: The conversion of a garage into a living area or space is deemed as changing the purpose and/or internal structure of a building. To this end, an application for approval under the building regulations must be made prior to the commencement of any work. Individual circumstances will vary.
  • Wall thickness: If the existing walls of a garage are of a single brick construction they must be checked for stability and also that they are free from defects. If the condition of the walls is deemed to be satisfactory, it is likely that they will be considered suitable for a conversion product, pending assessment of their resistance to weather and insulation.
  • Foundations: If additional masonry loads are required for a conversion project, such as new external wall inner leafs or a garage door infill, a new foundation may be required. The condition and suitability of the existing foundation and flooring will be assessed on removal of the door area. Generally speaking, there are three acceptable ways to replace a garage door with a wall;
    • The building of a new foundation – the depth of which will be dependent on ground conditions.
    • The installation of two pre-stressed concrete lintels from the footings of each pillar.
    • The installation of a steel cavity lintel with a minimum bearing of 150mm either side onto the brickwork.
  • Floors: During a garage conversion, it is often a desirable option to increase the existing garage floor to fit into alignment with the ground floor of a property. To do this, concrete or timber can be used to increase the thickness of the garage floor. Concrete can generally be applied onto an existing slab, on a damp proof membrane and bed of insulation.

If timber battens are used, they should be tantalised and fitted over rigid floor insulation - on the existing slab and on a damp proof membrane. Additionally, a vapour barrier may then be laid under the boarding. A damp proof membrane will need to be aligned with any damp proof course to existing or new walls.

  • Weather resistance: Single leaf walls will need to be treated in order to provide a satisfactory resistance level to the passage of moisture. To achieve this, a waterproofing compound can be applied to the internal face and incorporated into the floor membrane. If a new inner leaf wall is installed, it will require a cavity tray at the base of the walls and covering any openings. Both existing and new floors will require the fitting of a suitable damp proof membrane.
  • Insulation: When you are planning a garage conversion, it may be necessary to insulate any external walls, roof and flooring for the area to be deemed as fit for habitable standards. Here are a few guidelines on insulation methods;
    • New windows need to achieve a U Value of at least 2.0W/m2K for PVC or timber frames and 2.2W/m2K for metal frames. Usually, this can be achieved using a sealed double glazed unit and incorporating a 16mm air gap and inner pane of low-E type glass.
    • Walls need to achieve a U Value of approximately 0.35W/m2K. This can normally be achieved by dry lining the wall. However, the performance of individual insulation methods will differ.
    • Floors need to achieve a U Value of approximately 0.25W/m2K. This can normally be achieved using 100mm of polystyrene floor insulation.
    • The roof will need to achieve a U Value of approximately 0.25W/m2K for a flat roof or 0.16W/m2K where a loft space is apparent.
  • Ventilation: Windows in a garage conversion must incorporate an area that can be opened that is the equivalent of 1/20th of the entire floor area of the space. Trickle vents must be used to provide background ventilation of 8000mm2 for any habitable room or 4000mm2 for any other room. In cases where a kitchen, utility room, bathroom or toilet is being created, mechanical ventilation may also be required.
  • Safety/escape: Generally speaking, a clear opening of around 0.33m2 with an opening width and height of at least 450mm s must be provided in scenarios where a garage conversion can only be accessed via a second room i.e. using the kitchen. Additionally, the bottom of the opening should be below 1100mm above floor level.

The above points will give you a better idea when you are creating your garage conversion plans – allowing for the alterations to be included in the work at various stages. By taking into account any additional materials and labour required, you can also factor these aspects into your overall project budget, therefore avoiding any costly surprises further down the line.

It is important to note that every garage conversion will differ – depending on the type of garage that you have (i.e. single, detached, double, tandem etc.) its size, condition and suitability for conversion. To this end, it's vitally important to check with your local authority if you are unsure as to any aspects of building regulations or how they apply to your specific garage or conversion project.

The practice of adhering to building regulations is generally an ongoing task. It is standard practice for a building control officer to check your building work at regular intervals. The purpose of this is to check on any progress and confirm adherence to any applicable building regulations. During this time, if you are unsure about any aspects of government building regulations he/she should be able to provide you with further advice. Additionally, you may need to obtain planning permission for a garage conversion, so investigate both options fully.

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