Garage Conversion Floor Insulation and construction - which system should you be
Part of most garage conversion works will involve upgrading the existing garage floor
construction. Most house extension designers or architects will want to retain the existing garage floor
construction unless it is so poor it needs removing and replacing. That means in order to comply with the Building
regulations the existing garage floor construction will need to be thermally improved.
Depending upon the difference in floor levels there is a design solution for each type of floor level
difference. Most garages have a lower floor level than the main ground floor of the dwelling. In order for a garage
conversion to comply with the floor insulation requirements under the Building Regulations usually requires an
insulation thickness of around 75mm for Celotex. Covered with a 75mm reinforced screed allows an ideal floor level
make up of around 150mm. For lesser floor level differences an insulation board can be covered directly with a
vapour barrier and boarding. This is great for when a garage floor level difference is between 80 and 100mm.
Greater floor level distances of over 150mm usually require a new treated timber floor joisted system with new
insulation between. Regretfully this system has knock on technicalities such as sub-floor cross venting which can
be difficult to achieve or add significantly to the garage conversion floor upgrade costs.
Whichever solution is selected by your house extension designer or architect, it should be matched to the floor
level difference for the best application and budget cost. Sometimes the difference in floor level is less than
80mm or non-existent. In these cases some form of agreed dispensation will be required from the Building Inspector
and provided they are satisfied that the cost / benefit is non recoverable over a 15 years period they will agree
to the less U value standard.