Reflective foil batts kill and they are close to useless. Your roof is a dangerous area and the foil makes it worse, a problem that was common knowledge 25 years ago. The foil is hopeless as it only works in weird circumstances. Why was the Australian federal government subsidising something that is useless and fatal?
First a little terminology. When I talk about a roof, I am talking generically about several bits that sit over your head. First there is the ceiling material, usually plaster or gyprock. That layer is supported by ceiling joists, the wooden beams holding up the plaster. Then there is the truss space, the big mostly empty bit with wood bits sticking up at funny angles. Next you have the roof rafters holding up the final bit of the roof, the sheathing.
The rafters and joists are connected by the funny bits of wood to form the roof trusses. Trusses form triangles because triangles are strong and rigid. When you climb up in your roof, you walk or crawl over the joists through the trusses formed by the joists, rafters, and bits at funny angles.
That air space provides some insulation and allows some air movement in the roof space to keep the trusses and plaster dry.
Now look at insulating your home to keep you warm in winter and cool in summer. The roof sheathing, tiles, or tin. or wooden shingles, provide almost no insulation. Plaster provides a little bit of insulation. You need something else. The Australian federal Government was supposed to subsidise something safe and effective.
Your ceiling is covered in electrical wires feeding your lights. Those wires are dangerous no matter how you handle them. You should use only qualified electricians to work on the wiring in your roof and when they begin work, they should test the existing wiring because a fault can be caused by a minor leak in your roof or an insect crawling into a join.
Standard lights are safe. Downlights are dangerous because they put a lot of heat up through the plaster into the roof. Deaths occur because insulation is placed over downlights then the roof bursts into flames. If you have downlights and do not feel like replacing them, make sure the insulation installers place approved protective plates over the downlights and do not place insulation over the downlights.
Your insulation should be non flammable, which rules out the popular polyester and the now banned (I think) ((I hope!)) cellulose insulation. You are left with the choice between glass wool and metal foil.
Glass wool is effective and remains effective for almost ever. Metal foil is tested when is is brand new and shiny but quickly looses the shine. Your metal foil might start with a slightly higher insulation rating but in a few years, especially near the ocean or anywhere where it rains, or anywhere there is dust, the metal foil loses the advantage and becomes second rate.
The foil that beats glass wool in special artificial tests is a triple layer batt but your do-it-on-the-cheap-for-the-subsidy installer will use a double layer batt that is only as good as glass wool at the start before it deteriorates. Some of the news broadcasts show people installing a single layer foil that provides almost zero insulation. People are being ripped of big time and the Federal Government did nothing to stop it and refuse to replace the fake/faulty material in the 47,000 existing cases.
Look at the instructions for installing foil batts. You have to put them over the ceiling joists to make them effective because that creates a big insulation gap between the plaster and the foil. If you install the foil that way, you can never work in your roof again because you will crush the batts every time you move. A small job will have to start with you moving dozens of batts then, on your way out, you will have to replace them all exactly where they were. Even if you spend the ridiculous hours doing everything right, the first trades person in your roof will crush a path through the batts.
Did I talk about lifting and moving the batts before working in the ceiling? You cannot. The media says the installers are stapling the foil batts in place. There goes the option to protect the fragile batts from collapse.
What happens when condensation drips from the roof onto the ceiling? With fibre glass batts, the small amount of heat slowly seeping through the batts evaporates the water then the slight ventilation through the roof space wafts the moisture away. Now rerun that with foil. The drops build up on the foil then trickle down to the plaster. Heat from your room turns the water into steam. The steam is trapped by the foil and starts to rot your ceiling joists plus the plaster.
Metal foil insulation is used between the rafters and the rood sheathing to stop condensation and to stop leaves blowing under the tiles. That layer is called sarking and is two layers of aluminium with a thin layer of fibre glass or some cheap rubbish in between. Sarking goes over the rafters where there is no electrical wiring.
Placing the foil on the joists places the foil in contact with wires. Some stupid installers went one step further and fired staples through the foil into wires. Several people died during installation. More people were electrocuted when working in the roof space after the installation of foil. How many more have to die before all foil is removed form all ceilings?
Now for a list of advantages for foil:
Ok, that is the complete list.
Wind the clock back 25 years to when foil was banned, or supposed to be banned, from ceilings. You could use it over the roof rafters but not on the joists. People in the building trade knew it kills and demanded that the power be turned off before placing the foil over rafters. In new homes the power is not yet connected. Turning off the power in existing homes was super important because the fuses back then were solid wire instead of earth core balance safety switches. When safety switches were made compulsory, it was normal to use them on the power circuits but not the lighting circuit, leaving the roof the one place you could be systematically killed then grilled by the same shock.
Back then I went up into the roof of an old house with one of those off peak water heaters in the roof. Metal pipes crossed electrical wires. I touched a pipe and felt the tingle that told me the electricity was starting to leak into the roof. My hand jerked back from shock. If that roof space was filled with foil instead of fibre glass, I would be still up there cooking away unable to escape because all the ceiling area would be conductive.
I do not recommender foil on the ceiling. If someone suggests it as insulation, ask them for a written lifetime guarantee against electrocution and make them sign it in person so they are liable, not some company that will shut down and disappear at the first hint of liability.
Will the minister in charge of subsidising the electrocutions help? On television he announced all home in danger would be inspected but did not offer to remove the danger. Plus he used the wrong terms. I think he has never looked in a roof to see what we are talking about. He called the metal foil batts
sarking. If he bans sarking, house contruction will go seriously downhill without actually removing the deadly foil batts.
Perhaps the current Australian federal government should hire someone competent.