Insulating an Existing Home: Ceilings, Walls and Floors
Insulation is one of the simplest ways to make an older home more comfortable. It slows the flow of heat in and out, so rooms stay warmer in winter and cooler in summer. Many older Australian homes were built with little or no insulation. Others have insulation that has settled or broken down over the years.
Adding insulation to an existing home is often easier than people expect. Some areas can be done in a day, while others are best left for a larger renovation. This guide covers ceilings, walls and floors, plus the safety checks that matter. It also explains what an R value means.
Where heat goes in a typical home
Heat moves through every part of the building shell. The Residential Efficiency Scorecard explains where most of it goes. Between 25 and 35 per cent of heat loss or gain happens through the ceiling. Walls account for 15 to 25 per cent of heat loss and 25 to 35 per cent of heat gain.
Floors are responsible for 10 to 20 per cent of heat loss or gain. Gaps and cracks add another 5 to 25 per cent. Windows lose 10 to 20 per cent of heat in winter and gain 25 to 35 per cent in summer. These figures show why the ceiling is usually the best place to start.
What an R value means
An R value measures how well insulation resists heat flow. A higher number means more resistance and better insulation. The right R value depends on your climate and the part of the house. A qualified installer can tell you which rating suits your home.
Insulation does not last forever. The South Australian Government notes that it deteriorates over time. If your home is older, it may be worth topping up or replacing what is there. A quick look in the roof space will often tell you a lot.
Insulating the ceiling
The ceiling is the most common place to add insulation in an existing home. If the ceiling space is easy to reach, the Scorecard suggests adding or topping up to at least R3.5. Batts can be laid between the ceiling joists from inside the roof space. It is often the quickest upgrade with the most noticeable result.
Some homes have no easy access to the ceiling space. Raked ceilings and flat roofs are common examples. In these cases you can insulate when the roof is replaced. Another option is an insulated false ceiling below the existing one.
Insulating walls
Walls are harder to insulate once a house is built. The best time is during a renovation when wall linings or cladding come off. Most stud walls have a 90 mm stud, which allows insulation up to R2.5. That makes a kitchen or bathroom renovation a good moment to fill the gaps.
Retrofit insulated cladding is another choice for walls. It can be fitted on the inside or the outside of the house. This works well when you already plan to reclad or reline. Ask your builder which method suits your wall type.
Insulating floors
Raised timber floors can be insulated from underneath. Batts or insulating boards are fitted between the floor joists. This works best when there is plenty of room under the house to work. It can make a big difference to cold floors in winter.
Concrete slab floors are different. The Scorecard notes that a slab on ground cannot be insulated after construction. For these homes, rugs and carpet help with comfort. Effort is better spent on the ceiling, walls and draughts.
Seal draughts at the same time
Insulation works best when the house is also well sealed. Rattling windows, dust around frames and light showing around doors are all signs of draughts. Door seals, window seals and flexible caulking around skirting boards can fix many gaps. A door snake is a cheap fix for the gap under a door.
Some vents are there for good reason. Wet areas often need ventilation to prevent mould, so keep exhaust fans working. Seek advice before blocking any fixed vent. Keeping bathrooms dry also makes eco friendly cleaning easier because there is less mould to scrub.
Never use a portable gas heater in a sealed room. Older wall or ceiling vents can often be sealed, unless you plan to use a portable unflued gas heater. Old halogen downlights can also leak air. Replacing them with sealed LED fittings helps.
Safety checks before installation
Insulation must keep a safe distance from some items in the roof space. The South Australian Government lists halogen and extra low voltage downlights, electrical wiring installed before 1986 and flued gas heaters. High intensity heating lamps, exhaust fans, security alarms and water heaters are also on the list. Tell your installer about any of these before work begins.
Your installer should hold the right licence for insulation work in your state. They need to make any safety adjustments and check if an electrician is required. Any electrical work should come with a certificate of compliance. If you are worried about existing insulation, a licensed builder or electrician can check it.
The Scorecard says insulation should be installed in line with AS 3999:2015 and the wiring rules in AS/NZS 3000:2007. Ask your installer to confirm they follow these standards. Licensing rules differ between states, so check with your state authority. Renters can ask their landlord to install or top up insulation.
Insulation and the rest of the home
Insulation is only one part of a comfortable, efficient home. Shade from trees and plants can cut summer heat before it reaches the walls. Ideas from waterwise landscaping help keep the garden alive in the hottest months. Sustainable landscaping can also place trees where they shade the hottest walls.
A renovation is a good time to look at everything together. If walls are open for insulation, plumbers can reach pipes more easily too. That makes it a sensible time to fit water wise plumbing fixtures. Doing the work at once saves time and reduces mess.
Frequently asked questions
Where should I add insulation first?
The ceiling is usually the best place to start. Between 25 and 35 per cent of heat loss or gain happens through the ceiling. It is also the easiest area to reach in most homes.
Can I insulate the walls of an existing house?
Yes, but it is easiest during a renovation when linings or cladding are removed. Retrofit insulated cladding is another option. Ask a builder which method suits your walls.
Can a concrete slab floor be insulated later?
No. A slab on ground cannot be insulated after construction. Rugs, carpet and good draught sealing help with comfort instead.
Is it safe to put insulation near downlights?
Insulation must be kept a safe distance from halogen and extra low voltage downlights. Tell your installer about all downlights before work starts. Replacing old fittings with sealed LED fittings can also help.
Building, licensing and safety rules differ between states and territories, and they change over time. Speak with a licensed installer or your state building authority before starting work.