Retrofitting insulation can be difficult in some areas and for some types of construction. However, any improvement in insulation in an existing home is likely to be worthwhile.

Roofs – timber framed

Because most heat is lost through the roof, ceiling insulation is highly effective. For retrofits of insulation, ceiling insulation should generally be the top priority.

If the ceiling space is fully accessible, bulk fill segmental insulation can be fitted between and over ceiling joists. This provides very effective insulation at moderate cost. If the ceiling space is partially accessible, loose fill insulation can be blown in.

If the home has a closed skillion roof, options include:

• fitting battens under the existing ceiling, and installing insulation and new ceiling lining – this is expensive and will provide improved insulation, but will not give the performance of the options below
• installing insulation in a suspended or dropped ceiling – this is expensive but will provide very effective insulation
• removing the existing ceiling lining and installing insulation – this will give the opportunity to maximise the level of insulation but it is expensive; the most cost-effective time to do it is when the interior linings or external cladding have to be replaced
• removing the roofing and installing the insulation, then replacing or reinstalling the roofing –  for metal roofing that is screw fixed this may be the easiest option.

When a skillion roof cladding material is in need of replacement owners should be advised to upgrade the levels of insulation when the roof is removed.

  

Ground floors – timber framed

Provided the subfloor is accessible, insulation options for existing homes are:

• adding foil stapled to the underside of the joists
• fitting polystyrene board insulation between the joists (see insulation options for new homes)
• fitting blanket or matt insulation between the joist and having lining fixed to the underside.

Ground floors – concrete slab

Improving the thermal resistance of an existing concrete slab on the ground is not usually a practical option. Where renovations are major an option (provided there is sufficient ceiling height within the space) is to cover the existing slab with a polyphone damp proof membrane, 25 mm thick polystyrene board and then a new 75 mm (minimum) thick topping slab. The new concrete must be isolated from any existing timber framing by a damp proof membrane to prevent moisture from the concrete being absorbed.

Adding carpet and underlay will reduce the heat loss through an existing floor (although this cannot be used to meet minimum requirements of Clause H1.

Exterior walls – timber framed

Options include:

• battening existing interior linings, insulating, and fitting new interior linings – this option is expensive but will provide effective insulation (but not to the same level as the next two options)
• removing external cladding or internal lining, insulating, and fitting new cladding or lining – this option is very expensive but will provide very effective insulation
• installing an EIFS cladding system over the existing cladding which significantly increases the thermal performance but is expensive to do.

While walls account for a significant proportion of total heat loss from a home, it is usually too difficult and expensive to retrofit insulation. The most cost-effective option is to wait until wall linings or claddings need to be replaced and fit insulation then. Otherwise, it is more cost-effective to further reduce heat loss through the roof by fitting roll-type insulation over the top of insulation segments between the joists.

Exterior walls – steel framed

With steel-framed walls, exterior cladding can be removed, and new external foam battens and plastered foam board cladding fitted. This will reduce the high heat loss through the thermal bridges of the steel framing. It is an expensive option but will provide effective insulation.

Exterior walls – concrete masonry or cast walls

Options include direct application of an insulating plaster or an EIFS cladding system externally, or battens, insulation and new plasterboard linings internally. Both options are expensive but will provide increased levels of thermal insulation. Concrete has very low thermal resistance so additional insulation will reduce heat loss and condensation.

Applying the insulation externally maintains the benefits of the thermal mass of the walls.

Glazing

For aluminium frames, insulating glazing units (IGUs) can be retrofitted. This is a high-cost option but provides improve the level of insulation provided. For example the R-value of a single pane of clear glass is approximately 0.18 while and IGU with two panes of clear glass is 0.33 (replacing the inner clear glass with a pane of low E glass will give 0.53).

Another option, for both aluminium and timber frames, is to install a secondary window frame within the reveal.

Interior designs that incorporate curtains and blinds will assist in reducing night-time heat loss.