MAN Magazine Summer 2019



wall: either the cavity can be injected

with insulation, or a lining board can be

fixed to the inner face of the wall prior to


If the existing external wall is only

105mm thick, then an insulated cavity

must be provided with a new inner skin

of blockwork or timber studwork. If the

garage has good conditioned 225mm

thick solid brick walls, it will require a

damp-proof course, as well as insulation

board lining.

Pitched Roofs: Upgrade to new

house standards of 0.16 U-value by

stapling in place multi-foil insulation under

the rafters and putting PIR insulation

between the rafters. Please check with the

manufacturers for advice on the thickness

of PIR required.

Floor: The garage floor’s thermal

performance U-value requirement is

0.25 W/m2K. This can be achieved by

either covering the floor with rigid PIR foil

insulation, and by then laying 19mm or

22mm tongue and groove flooring grade

chipboard on top of the insulation to create

a floating floor. Or if the floor has to be

raised to a higher level to correspond with

the existing floor height, then a greater

thickness of PIR foil board can be used.

Windows: Adequate ventilation is

required, with window openings needing

to be equal to 1/20th of the room’s

floor area, and trickle-vents providing

background ventilation of between

4000mm2 and 8000mm2, depending

on room type. All windows and doors

must be draft proof, and double-glazed

with a maximum U-value of 2 W/m2/K.

If the room does not have direct external

access, then an escape window needs to

be fitted between 800-1100mm above

ground level, with an area of 0.33m2, and

minimum dimension of 450mm squared.

Doors and windows require an insulated

damp proof course if installed in a cavity

wall, and if installed in a solid wall then

insulated dry lining around the opening

must be fitted in order to prevent thermal


Get the insulation right and you’ll have

a great foundation for the perfect energy

and cash efficient workspace for clients, or

an extra space for your ideal den, as well as

add value to your home if you ever wish to

sell up at some point.

For more information on insulation,

including videos and drawings,




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