DIY guide · From our staff training manual
DIY insulation batts: how to install them like a pro.
Installing roof batts is a difficult and dangerous job. This is the real safe-site method from our staff training (safety, tools, roof-walking, choosing 430 vs 580, spreading and getting the itch out) not an endorsement that you should do it yourself.
I’m Peter Johnson. I’ve personally insulated more than 6,000 roofs, and as a family business we’ve done more than 12,000 since 1986. I’d strongly recommend you only use trained professionals, but the insulation industry isn’t regulated and a lot of new installers get no training at all, so here’s the honest manual. (And by the way: Earthwool doesn’t come from a sheep.)
Proper PPE, every time
respirator + ear protection, not the paper mask
Before you climb the ladder
A must-read, and an honest warning.
Installing roof insulation batts is a difficult and dangerous job, and the tricks and tips below should not be taken as an endorsement or a recommendation that you should install your own insulation. I’d strongly recommend that you only use trained professionals to install your insulation batts.
That said, I do understand that some people starting out in the insulation industry get no training at all from the companies hiring them, so this is written for the people who want to be professionals and are looking for safe, honest advice in an unregulated industry. It’s lifted straight out of the safe-site procedures in my own staff training manual. Read all ten sections before you start. And read section nine twice. It’s the one that tells you how hard this really is.
The honest reason this page exists: most people who read the whole thing decide it’s not worth it, and just get a quality cellulose fibre insulation pumped in instead, no roof-walking, no itch, no gaps. I’ll make that case at the bottom. But first, if you’re going to do it, do it safely.
Section 1 · The most important one
Health and safety is number one.
This is a physical job. If you're not fit and healthy, don't attempt it. It's just too demanding, and if you faint in a roof you'll fall through the ceiling and you could have a fatal injury. I've measured 83°C in a roof while installing insulation and burned the skin under my shirt from baking in the heat. So before anything else, get this list right.
Weather: pick a cool day and start early
Pick a cool day and start early, but because you left this job until the middle of summer to start doing it, the best time to start might be at 3am in your roof when it has just cooled off from the day before. I recommend putting the batts into the roof on one day and then tossing them out before laying them the next. If the day temperature is forecast to be more than 30°, don't even attempt it, because by 8am it could be as hot as 60° Celsius. (I assume all the people with cool homes in summer aren't wanting insulation.)
Safety clothing: fibreglass batts are itchy
Fibreglass batts are itchy! Don't believe the packet… lol. Wear disposable painter's overalls during the job, and you may need to buy two or three of them because they rip and tear easily. They're also hot, which is why starting early is important. I recommend good shoes in the style of joggers. Dunlop Volleys are good on the roof, but inside a ceiling the dust quickly fills the tread and they become slippery. I always wear a shirt in the roof to keep spiders off my back and stop me getting bad splinters. I don't recommend jeans, they restrict movement and they're hot. A set of soft leather gloves might be a good idea, but they get hot, so I never wear them.
Respirator: buy a proper $30–50 one, not the paper mask
Buy yourself a proper $30–$50 breathing respirator (silicone ones are better: I use a Sundström SR100) and wear it the whole time you're in the roof. Yes, the actor in the photo on the pack of batts has one of those crappy paper masks on, but they're useless if you actually want to protect yourself from harm. It's worth the extra money. Maybe in 20 years you won't have to worry whether the lead dust in your roof or the glass particles from the batts have hurt your lungs. At the end of the job, look at the front of your mask: you'll see it caked with glass fibres that would have gone into your lungs. The dust in your roof cavity is dangerous.
An LED head lamp is your number-one best friend
These are a great advancement. I've used Energizer LED head lamps for years now, and they're the best for making sure you can see properly while you're in the roof. I use the hard-case rugged version.
Electrical precautions: turn the power off and pad-lock the board
I recommend turning off all the power circuits at the power board to your home while anyone is on or in your roof. Put a padlock on the box and the key in your pocket so nobody can turn it back on while you're in the roof space. In Queensland in 2009, four people died working in roof spaces during the home-insulation program; a documented danger is contact with live or poorly-installed wiring (see WorkSafe Queensland on electrical safety). It happens because ordinary people aren't trained to watch for live wires in a roof.
Always have one person on the ground
Always have one person on the ground who can call for help if need be, and who can call out to you through the plaster downstairs to check on you from time to time. They should be able to track you downstairs as you move through the roof, but don't stand underneath the person in the roof. It's a good idea to have two people in the roof too: they can help spread the batts, and it's an extra set of eyes to spot dangerous timbers or nails as you move.
You can become physically stuck
It's possible to become physically stuck in tight corners. Just because you can climb in does not mean you can turn around or climb out again. I've had to have roof sheets and tiles removed on a number of occasions to get people out of tight areas in the roof space.
Have someone hold the ladder
Have someone hold the ladder for you as you climb in and out, and have them pass you the tools you need. The golden rule is one hand for the job and one for the ladder: a lazy man climbs a ladder with both hands full. Please follow the safety instructions for setting your ladder up properly; many a person has fallen off a step ladder in this industry and never walked again.
Wear a hat in the roof, and move slowly
Wear a hat in the roof: it softens the blow every time you hit your head. The other trick is to move slowly, so it won't hurt as much when you do hit your head. It also stops some of the timber splinters getting into you as you move around.
Stay hydrated, but mind the salt
Stay hydrated, and don't worry about energy drinks, because you lose too much water for that. Just drink about a litre for every 30 minutes you're in the roof on a hot day; I'd often drink 20 to 30 litres in a day during a Queensland summer. But too much water without salt is dangerous and can cause problems, so eat some regular salt if your muscles start to cramp up. Leg cramps are a sure sign you need to get out of the roof, cool down and eat something salty. And remember: a bad leg cramp in a roof can start you falling, so the best thing is to grab anything you can on the way down. If you can't grab anything, stiffen up and spread out as much as you can. I've fainted in a roof and fallen flat on my back, but because I stiffened up as I fell I didn't even break the plaster. Then I got up and kicked myself for not following Rule 3 of the next section.
Keep your eyes open for dangers: snakes, possums, redbacks
Keep your eyes open for dangers at all times. You'll find snakes, possums, redback spiders, and even porno magazines, in the roof. The last one isn't so dangerous, but it could still have your eye out.
Never cover a heat source
Do not cover any heat source with insulation batts: that includes downlights, transformers and exhaust fans. Read your local regulations for installation standards, but in Australia there must be a 50mm gap around any heat source like a light or transformer, and a 300mm gap around heater flues or chimneys.
Know when to leave it to the professionals
If your roof is low-pitched, fibro, metal-tile, or has any raked, exposed-beam or split-level sections, leave the job to the professionals. You won't get it right, because 90% of the professionals don't even get it right. And if it's a steel-frame home, don't waste your time with batts at all. Here's why fibreglass batts just don't work on steel-frame homes.
The 2009 deaths are a matter of public record. See WorkSafe Queensland on electrical safety in roof spaces. I’m not quoting a statistic at you; I’m telling you to turn the power off and pad-lock the board.
Section 2
Basic tools you need in the roof.
You don’t need much, but each item earns its place. Notice there’s a knife on the list and a warning right beside it. The rule is tear your batts, don’t cut them. A knife in a hot, cramped roof over live wiring is how people get hurt.
- Disposable overalls
- Soft leather gloves
- A retractable-blade knife, but don't try to cut batts in the roof; tear them into shape if need be. Never cut on a surface that may have a power lead under it.
- A step ladder, locked into position
- A stick or PVC pipe with a screw through the end of it, to poke batts out to the edge and into corners
- An LED head lamp
- Lots of water ready for when you get out: room-temperature water is actually better than cold
- A good pair of joggers with good tread and flexible soles
- A garbage bag to put the rubbish plastic in as you open the packs in the roof
A trained installer in a proper respirator inside a roof cavity: the gear matters more than the speed.
Section 3 · This is the life-saving one
Rules for walking in a roof cavity that might save your life.
Read these like your life depends on them, because it might. The number-one cause of damaged ceilings, and a lot of serious falls, is people getting these wrong.
- 1
The plaster is deceptive
When you're in a roof the plaster is deceptive. It's very brittle and weak. Keep in mind that if you fall through, it may not just be a matter of falling on the floor. You might fall on an office desk with one of those receipt-holder spikes that goes right through you, or you could fall down a stairwell below you.
- 2
Never rest anything on the plaster
Never rest anything on the plaster. It will break. That includes the packs of batts: make sure they're laid across the joists and not in the bays on the plaster ceiling. Don't sit on the packs in the roof either; the extra weight pushes down on the plaster.
- 3
Always have 3 points of contact
Always have three points of contact in a roof when you move through, or even when you're working with two hands. Lean a knee against something to make the third point of contact. Your life may well depend on it. This is the number-one cause of damaged ceilings by people walking in your roof space. This one rule could save your life.
- 4
Never twist or slide your foot on a joist
You can't slip off if you are sure-footed and don't twist or slide your feet while you're in the roof. I think this is the number-two reason people put their feet through ceilings.
- 5
Never stand on the batten timbers
They're not made to handle your weight. If your joist spacings are more than 900mm wide, bring a timber board into the roof to lay across them as you move through. It should be at least 2m long.
- 6
Always be sure-footed
Never just step like you do on the ground. In a roof you might be stepping on rotten timber. I once went to step on a timber that looked perfect and strong, but it was fully eaten by termites on the inside and just cracked to bits when I put weight on it. I've also had timbers that were plain not bolted on at one end, or actually cut in half by other trades getting access. Avoid a costly fall by having three points of contact at all times and testing every step before you put weight on it.
- 7
Don't stand on anything other than the joists
Many newbies to roof work will stand on timbers left in the roof, or on plastic bags laying on a joist, and those can be super slippery. Even timbers that look like they're meant to be a path: always stand above the joist on that timber, and only if it's properly attached to the joist.
- 8
You will cut yourself on nails, screws and gang plates
When you do, just remember there's only 16mm of plaster between you and the kids downstairs, and although you can't hear them very well, they will hear you. Don't teach them any words you don't want them repeating to mum…
Three points of contact at all times. If you take one thing from this whole page, take that.
Section 4
Choosing the right batts: 430s or 580s?
Roof insulation batts come in two standard widths. If you get the wrong ones delivered, you’ll be in a world of pain trying to fill all the gaps for them to work properly. The right thing to do is lift your manhole and measure the distance from the start of one joist to the start of the next. It should be roughly 1200mm, 900mm, 600mm or 450mm. That includes the timber, so once you take off the 50mm joist you normally land on a 580mm-wide batt or a 430mm-wide batt.
Now there’s a trick that works about 95% of the time without even looking in the roof, and it’s exactly why we don’t need to inspect your roof to do a quote. A corrugated iron or Colorbond roof is usually 900mm between the joists and takes two 430mm batts side by side to fill the bay. A tile roof of any kind is usually 600mm between centres and takes a 580mm batt. The exception is old Queenslander iron roofs, which often have 600mm centres, or on odd occasions 1200mm centres, normally the small, low-pitched iron roofs.
430mm batts
Iron / Colorbond
~900mm joist centres: two 430mm batts side by side fill the bay.
580mm batts
Tile roofs
~600mm joist centres: one 580mm batt fills the bay.
Section 5
How to get the batts into your roof.
Getting batts in through the manhole is the safest way for the DIY person. For a professional, you should definitely learn how to handle lifting roof sheets and tiles to gain access to put packs of batts into a roof. There’s a lot of safety to consider when you’re up on the roof itself, so I’m not going to cover that here. Lifting the roof does let in more light and let out a lot of heat, and it’s far easier to physically get the packs in.
On a tile roof you’ll need to cut the batten timber on one row and lift out at least six tiles. I normally create one entry point for every 100m² of roof, unless it’s one big open cavity that’s easy to move packs around inside.
Assuming you’re using the manhole, make sure it’s big enough for your average pack. Generally you’ll need a 550mm-square opening, with at least 1.2m of clear space above it in the roof to pull the pack into. (I assume you did all this before you ordered the packs delivered to your house?) Much smaller than 550mm and you’ll be passing them in two batts at a time, which turns a one-day job into a week-long nightmare.
If you’re pulling them up, one person on the ground passes the pack opening-first (it’s easier to grab in the roof). The person in the roof grabs the top and pulls it straight up in one movement while the person below keeps applying upward pressure. If you let the pack fall back and pull it up again, that action very often breaks out the skirt that holds the manhole cover in place, so just keep constant upward pressure on it, and pull it over when it’s nearly all the way up.
Once a pack is in the roof, move it up as far as you can while leaving it in the middle area of the rafters. Don’t split a pack and start laying batts until most of the packs are in the roof. I normally leave about 10% of the packs on the ground just in case I don’t need them. I always bring a few extra to my measurement.
On the amount you’ll need: the coverage is printed on the bag, and that figure normally allows about 6% for the timber joists in your roof. It’s better to have one pack left over than to drag a pack of itchy wool home in your car because they didn’t deliver enough. We measure every customer’s house from the aerial drone photos and it’s very accurate. You’ll need that measurement before you place your order if you’re doing it yourself. (Wondering whether to just buy the material and lay it yourself, or have us supply and install? Here’s the honest answer.)
Section 6
A plan of attack for spreading them out quickly.
Ideally this is a two-person job, and this is the basic system I follow in every roof. First, get the packs in. Then spread them out while they’re still in the packs. The batts are hard to get into the roof in one go, but if you can it saves climbing out and back in. Once you’ve climbed out of the heat a few times to cool down, you’ll realise every time you get back in it gets harder to climb the ladder… so fewer trips up and down is better.
Each pack has about 8–14 batts in it (you’ll know after the first one). Start cutting packs open one at a time and toss two batts out to the edge in each bay around the outside of the roof. If the house is very wide, put two groups of two. The idea is to get enough batts out to cover each bay while you’re still standing in the middle section of the roof. Work all the way around while the other person heads out to the edge with the stick and pushes the batts into place.
Work around the edges in one direction until all the batts are tossed out, then climb into the edge and lay them back to meet the other worker as they follow you around. You should be able to toss them out at about twice the speed the other person lays them, so they should be about two-and-a-half corners in by the time you work back to them. Then repeat for the middle of the roof and you’re done. Sounds easy, right…
Section 7
Key points to installing batts that actually work.
You can do everything else right and still ruin the job in the last hour. These are the points that decide whether the R-value on the bag is the R-value in your roof.
Fill every gap and every corner
Make sure every gap is filled and all the corners are done. Even small gaps badly hurt how well batts work. CHOICE puts it at roughly a 30% loss from just 1% of gaps, and the Australian Government's own guide says "even a small gap can greatly reduce the insulating value." That's the whole reason gaps matter so much, and the whole reason a pumped-in product wins.
Don't cover a heat source
Don't cover any heat source, and keep all batts away from chimneys: 50mm clearance around a light or transformer, 300mm around a flue or chimney.
Don't bury the wiring
Do not install insulation batts over wiring. Where possible, lift the wires and slide the batt under them, or tear the batt around the wire.
Don't forget the manhole, in-ceiling walls and garage
Put a batt over the manhole cover, and do any in-ceiling walls and attached garages. These are the spots people skip, and they're exactly where the heat sneaks back in.
Keep following the roof-walking rules
Follow the safety recommendations for walking in a roof: three points of contact at all times, and so on. They matter just as much on hour six as they did on hour one.
Watch out for danger signs
If you get cramps or taste blood in your mouth, you need to hop out, cool down and rest. Don't push through it.
CHOICE puts the cost of just 1% of gaps at around a 30% loss in a batt’s ability to stop the heat, and the Australian Government’s Your Home guide warns that “even a small gap can greatly reduce the insulating value.” That’s the figure that haunts every batt job, and the reason I keep coming back to pumped-in cellulose vs cut-to-fit batts: you can’t leave a gap in something you pump in.
Section 8
Cleaning up and getting the itch out.
You will be itchy if you install fibreglass batts. Just how itchy depends on the person. If you’re so itchy you want to scratch your eyeballs out, these suggestions might help.
- 1Wash with cold soapy water. I never do this myself, but I've been told a hot shower opens your skin's pores and lets the glass in deeper, while a cold shower closes them and pushes the glass out. I'm not certain, but a cold shower might be good if you're still really hot.
- 2Take a couple of pain killers.
- 3For a really bad itch, rub baby oil into your skin (rub it in good) and then have a hot soapy shower to wash it off again. This one really works, and it's my go-to solution if I get a fibreglass itch.
I’ve been told some people itch for as much as five days. For me it gets less and less over about three days, unless I use the baby-oil trick, which knocks it down by about 90% on the first night.
“If all this sounds hard, it’s because it is very hard. As hard as you think it is, it’s a lot harder! I’ve had grown men in tears trying to keep up with me on their first day. I describe the job to new staff as running on a treadmill in the dark while in a sauna, with people hitting you in the sides with baseball bats.”
And here’s the other point: after all that work, you’ll have a cheap, crappy batt insulation in your roof that’s prone to rats and mice living in it and will most likely need replacing in about ten years. Why bother? Just get a quality cellulose fibre insulation pumped into your roof.
Section 9
How long should it take?
With my trained teams, I estimate about 1 to 1.5 hours per 100m² of batts that need laying, and that’s my total site time, from when we drive up to when we leave. To be honest, it’s hard to find installers who want to work that fast, but that’s what a good team does all day, every day.
The truth behind the speed: most big batt companies only pay about $1.50 per square metre for subcontract batt installation, so if a subbie can’t hit that speed they’re losing money. That’s exactly why batt installers so often cut corners and do dodgy jobs. The economics push them to rush.
Following my method
~3 hours / 100m²
Two people, tossing and tearing batts (not cutting).
Not following it
~5 hours / 100m²
…and they’ll probably give up, in fact.
Section 10
Hot-tip bonus information.
The few extra things that separate a job that works from one that doesn’t, straight from the back of the training manual.
- 1
Tear batts, don't try to cut them. A knife is dangerous in the roof, and batts don't cut well anyway. Polyester batts don't cut at all. They only tear in one direction, across the width of the batt.
- 2
If you've got 430mm bays but only 580mm batts (or the other way around), tear them to size from the middle of the roof, where you have room to work, then toss them into the offending bay. It's much easier than fighting to tear batts to size out in the edge. Tear, never cut a batt, ever!
- 3
Lying down in the roof is fine, and in tight places it can help to use your foot to push batts into a small area (legs are longer than arms). Just make sure your hip is always sitting on a joist, and never rest anything on the plaster.
I’ve personally insulated more than 6,000 roofs (over 12,000 as a family business) so this is the best advice from my experience if you’re going to attempt the very dangerous job of installing insulation without proper training. I do not recommend you do this job. This information comes straight from the safe-site procedures in my professional staff’s training manual. If you’d rather we did it, get a quote on your home insulation here.
From our staff training
Watch: doing batts properly
A few clips from how we train it — laying batts with no gaps, fixing the battens you cut, and a reminder of just how itchy the things are.
Filmed on real jobs over the years — our methods, safety standards and products have moved on since. Subscribe to the channel for more.
Now that you’ve read the whole thing…
Or, just get cellulose pumped in instead.
Here’s the honest truth after more than 6,000 roofs of my own: almost everyone who reads this manual the whole way through decides batts aren’t worth the heat, the itch, the danger and the gaps. Pumped-in cellulose is blown in as one seamless blanket: no roof-walking for you, no cutting, no 430-vs-580 guessing, and no gaps for the heat to pour through. The rig stays in the truck and a trained installer does the hot, dangerous part.
It’s the only product I’d put in my own home: borate-treated so pests won’t live in it, shown to slow fire spread, and backed by a transferable Life-of-House guarantee. If you came here to install batts and you’re now having second thoughts, that’s the manual doing its job.
Found this useful? You might also want why batts don’t work on steel-frame homes or the full cellulose vs fibreglass comparison.
Did we do your roof? Leave us a review.
A quick honest review genuinely helps a small family business, and helps the next person decide. Thank you.
Skip the itch. Let us do it.
Get a home insulation quote today by filling in our simple online form and receive a detailed quote within 48 hours for most houses. No roof-walking, no itch, no gaps, and no deposit. Servicing Brisbane & SE QLD.
Peter Johnson
Owner / installer · Comfort Zone Insulation Team® · Since 1986
In the trade and want to install it yourself the right way? We make cellulose in Tiaro and run exclusive territories: franchise with the family.