Below is a list of general requirements that XTREND adheres to strictly for every garage conversion:


Support will be needed for any new walls constructed to infill the former door opening. If the original foundations do not continue below the door opening, either:

  • A new foundation should be provided, the depth of this foundation will depend on the ground conditions on the site and that of the existing foundation (generally between 750mm – 1000mm).
  • Two No. 100 x 150 deep concrete lintels or 2 No. 100 x 110 pre-stressed lintels may be used to span the opening of a single garage door. The ends of the lintels should be cut into the existing brickwork to ensure a minimum end bearing of 150mm,
  • If the existing floor slab was thickened at the door opening and a lightweight form of construction is proposed for the infill, it may be possible to carry this infill on the existing floor. It will be necessary to expose the edge of the slab to ascertain its acceptability.


Any new wall constructed to fill in the former door opening should be constructed to achieve a U value not exceeding 0.30W/m2k

A typical wall construction to achieve this would be 100mm blockwork 75/85mm insulation (depending on blockwork type). If the existing external wall is un-insulated, then upgrading will be required to ensure a reasonable thickness of insulation. The work necessary will depend on the construction of the external wall.

If the existing external garage wall is only 105mm thick, then an insulated cavity should be provided with a new inner skin of blockwork or timber studwork. If the new inner skin is blockwork, this should only be supported off the slab if extra lightweight blocks are used.

If the existing external garage wall is 215mm solid brickwork or an un-insulated cavity, it may be possible to upgrade the thermal resistances of the wall via insulated drylining. Where the garage is semi-detached, sound insulation may be required to the party wall. Construction as for the external walls above should, in most cases, be sufficient.

If only part of a garage is being converted, both thermal insulation and 30 minutes fire separation must be provided to any new separating walls.


The existing floor will need upgrading to ensure adequate damp protection and to prevent heat loss.

Damp protection can be provided by either a liquid or sheet membrane. This should link with the damp proof course in the wall. The floor should be insulated to achieve a U value not exceeding 0.22w/m2k.

The thickness of insulation needed to achieve this will depend on the type used.

The floor finish can be 18mm T & G chipboard or 65mm reinforced screed.


A traditional pitched roof should be insulated to achieve a U value not exceeding 0.16w/m2k.

This can be achieved by providing 100mm fibreglass between the joists, with a further 150mm layer laid across the joists.

The roof should be ventilated at the eaves equivalent to an area of not less than a continuous strip 10mm wide and if the roof is a mono-pitch at high level with an equivalent area of not less than a continuous strip 5mm wide.


Flat roofs are likely to need upgrading to provide adequate thermal insulation and roof Ventilation.


Windows and doors should be draught proofed and be double glazed to achieve a U value not exceeding 2.0mw/m2K (e.g. Low E glass).

Should the new room not lead directly to the hall approaching the front door, the new window should be sized to allow escape. This will require an unobstructed area of 0.33m2 with a minimum dimension of 450mm high/wide and be positioned between 800-1100mm above ground level. If the new door/window is installed within a cavity wall, then insulated damp proof courses should be provided around the opening. Should the new door/window be installed within a solid wall, then insulated dry lining will be required around the opening to prevent thermal bridging/heat loss.


Ventilation openings should be provided to each room, there is no minimum size for kitchens, utility rooms or bathrooms, but other rooms require a ventilation opening of at least 1/20th of their floor area. Background ventilation is required to habitable rooms at a rate of 5000mm2 and to kitchens, bathrooms, WCs and utility rooms at a rate of 2500mm2. Suitably sized mechanical ventilation ducted to external air or passive stack ventilation is required to bathrooms, kitchens, utility rooms and some WCs.


All electrical work must be carried out by a contractor certified under one of the “Part P” approved installer schemes.