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Garage Conversions: Planning and Building Regulations

Before we delve into this topic, just know that in many cases a garage conversion does not involve a change of use. This means that UK Building Regulations should only apply to any structural changes involved and/or to any other building controlled works such as drainage.

Many times, a garage conversion will require nothing more than simply infilling the existing garage doors or doorways with a suitable construction (such as a window). This process may be easy, but because any infill will need to be supported by either foundations or suitable lintels, it is classified as a structural alteration and hence requires building regulation approval. During garage conversions, one should make sure that damp proof courses are incorporated, as these help to prevent water ingress where the new infill abuts the existing walls. In many cases where the garage may already have a cavity walling, this process is much easier. On the other hand, if the garage has single leaf masonry walls with piers, the job becomes tougher and more expensive as additional work will be needed to try to improve both thermal insulation and weather resistance.

Improving thermal insulation and weather resistance can be achieved by simply constructing new internal block work walls; however these walls will need a lot of extra support as in most cases, the existing floor support will not be enough to account for the added weight of these walls. Hence, sometimes it is necessary to excavate new foundations and this can get very tedious and costly. Just to be on a safe side, it is recommended that one provides an internal insulated stud wall to help avoid any extra problems that may arise. If you cannot provide an internal insulated stud wall, it is recommended that you prefabricate the stud walls in panels that will create a vapour barrier which will help increase the durability of the walls.

Other points that need consideration reference building regulations are:

  • If the room is an inner room, any windows installed must be suitable for means of escape.
  • One should make sure that there are reasonable levels of ventilation
  • Any drainage that may be involved will need to be considered
  • If cases where the roof is being insulated consideration should be given to venting the roof void.

For those of you who are a bit more technical-minded, here are some of the specifications for insulation, windows and ventilation:


In many cases, it will often be necessary to insulate the walls and roof to better living conditions. According to the UK Building Regulations, “The wall insulation thermal performance ‘U’ value should be equal to 0.35 W/m2K, flat roofs to 0.25 W/m2K and pitched roof to 0.2 W/m2K. The ground floor should achieve a thermal performance ‘U’ value of 0.25 W/m2K. Examples of the types of construction that satisfy the standards can be found in the guidance notes on complying with Part L of the Building Regulations.”

Windows and ventilation

Consideration should also be given to the thermal performance and ventilation of windows. “Windows must achieve a thermal performance ‘U’ value of 2 W/m2K and should incorporate openable vents of an area equal to 1/20th of the floor area of the room. In addition, background ‘trickle’ vents, having a free vent area of 8,000mm2 are required.”

Disclaimer: The above is just a general guide so that you have an idea of what to expect. The building Control Department (or appropriate organisation if you don’t live in the UK) should be consulted by the homeowner or their agent / contractor for more specific local information