Inside The Insulated Building Envelope
For maximum effectiveness, thermal mass should
be insulated from external temperatures, i.e. it should
be located within insulated walls. The benefits of
thermal mass are considerably reduced if the
external envelope is not insulated.
For this reason brick veneer walls offer little
thermal mass benefit, as the brick is on the outside
of the insulated cavity.
Concrete Slab on Ground
A concrete floor slab directly on the ground will
take advantage of the huge thermal mass of the
Inside North-Facing Rooms
Using thermal mass in north-facing rooms should
be a priority, particularly on those walls which
receive direct winter sun. As the area of northfacing
window increases, the more internal thermal
mass is required to maintain a stable temperature
Hot Rooms During Summer
Locate thermal mass throughout the dwelling for
summer comfort, but particularly in north, east and
west-facing rooms. Shading of the
windows to these rooms is also important.
Amount of Thermal Mass
High levels of thermal mass are beneficial
with the exception of alpine
areas and some situations where solar access is
poor. While technical studies often recommend
certain percentages of thermal mass for different
construction types and climate zones, in practice
most homes have thermal mass provided in only
the following few locations.
- Floor: concrete slab or timber floor.
- External walls: double brick/masonry or brick
- Internal walls: masonry or stud walls.
Of all the material choices, the wall selection
accounts for about 60–70% of the thermal mass of
the building, with the floor area accounting for
Generally, the more thermal mass the better. A
double brick or masonry home on a concrete slab
offers the highest comfort benefits and energy
savings. However, the cost of heavyweight
materials can outweigh the value of energy
savings. For this reason, use as much thermal
mass as you can afford to achieve comfortable
In most cases, give first priority to provision of a
concrete slab (substantially less cost than masonry
walls) and supplement this with heavyweight walls
where the building budget permits.