Insulation under custom orb roof brisbane

Hi all,

I have a question. I have some general knowledge on insulation, what I am looking for is specific recommendations for my specific problem.

I live in a tiny 45 sqm house built in the late 1800's. I'd put a bulldozer through it but unfortunately it's heritage listed. I'm west of brisbane on the west side of a mountain and the place is VERY hot. In summer I can achieve a small amount of thermal lag by keeping the place closed up in the morning, but by late morning inside temperatures are as high as outside.

The house has a high pitched single pitch/belcon roof. The block faces north east so the front pitch gets the morning sun and the rear pitch cops the afternoon sun. Currently it is clad in rusty gal custom orb which is very second hand.

Now I don't need another job on my list, which is already infinitely long. At this rate I won't be allowed to die until I'm well over 200 years old. I thought however that re cladding in a lighter colorbond colour and laying some foil insulation under it might help drop my temps.

Understand that cold is NOT a problem. It hardly ever gets cold enough to warrant a jumper let alone anything else. The problem is excluding heat from the house.

The problem is I am a bit baffled by the array of foil insulation products and don't really know what I can expect in terms of temperature reductions.

So can anyone enlighten me?

Thank you very much for reading.

I have no quantitative answers but my story might give you some qualitative idea. Our current house, facing pretty much due north, has a low pitch roof. It was originally Decramastic Titles (those horrid tin things covered in bitumen and small gravel, [looks away and spits]). Anyway the last owner painted the house for sale a sort of ochre yellow colour with a black roof. The black painted tin roof turned the whole place into a quite efficient solar oven.

I attempted to put some insulation in the ceiling space after we moved in. Two problems, it was summer and the with the low pitch I didn't have enough room to move around in the ceiling space to place insulation batts. I did get some packs of batts through the manhole but after being there for a few minutes (I never put a thermometer in there so don't know the actual temp it got to) I just about passed out. I managed to crawl out of the roof space and fall into the pool fully clothed and must stayed there for a very long time until my core temp dropped to something reasonable.

Following that aborted attempt to insulate we engaged professional roof replacement. We went with cream colourbond metal decking and since I already had the batts for ceiling insulation asked for just plain sarking under the decking. The installers spread around my batts on the ceilings while doing the decking. You could monitor what part of the roof they were working on by simply walking in the rooms underneath. The indoor temp drop was instant.

I had the option of getting foil blanket rather than simply sarking at the time of installation, but because I already had the batts and I was low on funds at the time, I saved only a few $ by using simple sarking foil.

I can now get into the roof space in summer and it is still a reasonable temp. Hot but reasonable, it wouldn't kill me anymore. If I did it again I would get the all in one sarking and insulation blanket installed under the decking. After seeing the water damage done to houses simply after whirlybird roof vents blew off during a cyclone, I wouldn't put one on my roof in an attempt to ventilate the roof space.

When I'm driving around new housing areas in SEQ these days I only wonder about the vagueries of decorator fashion and why people put dark coloured colourbond roofs on their houses. It''s like cars, why anybody in Qld would buy a black car is beyond me. Go light colour with insulated blanket foil.

Hope this helps.

Consider solar fans to change the air in the roof space.

Quote:

---

Originally Posted by Fuzzie

When I'm driving around new housing areas in SEQ these days I only wonder about the vagueries of decorator fashion and why people put dark coloured colourbond roofs on their houses. It''s like cars, why anybody in Qld would buy a black car is beyond me. Go light colour with insulated blanket foil.

Hope this helps.

---

Thank you for the reply.

I actually bought a black car brand new in 09 but I do see your point. I too have wondered about people doing dark colour schemes in qld. I understand the victorians doing it but up here it's madness.

I expect the light roof and foil insulation will do something I was rather hoping for some independent advice/experience on how big a difference it will make.

I happen to have a brand new whirlybird I bought years ago for the house but never installed it. I put 2 on the shed and it made a measurable difference but not the sort of difference I'd hope for spending $1600 re roofing. Some of the ebay sellers claim about 7 or 8 degrees, that would make me very happy but I'm not sure it's realistic. Combining it with venting the roof is another can of worms. I'm inclined to do either or not both.

Anyway suffering 36 degrees today. The heat up here is entirely different to down south. When I lived in sydney it could be 45 outside and I'd be mowing, walking etc no bother at all. Up here at 30 I'm like a goldfish out of water, gasping for air.

Argh. I've spent much of today reading forums. Religious wars everywhere. Sigh.

Is there a particular reason you only want to do foil and not an insulated blanket which is the standard practice for housing and then batts on top of the ceiling
The foil is more the cheap option for sheds where it also helps for condensation but is not as good as an insulated blanket

Quote:

---

Originally Posted by Beardy

Is there a particular reason you only want to do foil and not an insulated blanket which is the standard practice for housing and then batts on top of the ceiling
The foil is more the cheap option for sheds where it also helps for condensation but is not as good as an insulated blanket

---

I think that's a question for me not the OP :rolleyes:

I did it because of the budget available at the time. I was recounting my experience that the combination of light coloured colourbond plus sarking alone was still quite effective.

Use a product called anticon. It is reflective foil on insulation blanket. It goes imediately under the corrugated iron and over the top of the purlin. The foil side is on the underside thus it supports the insulation from deteriorating. The anticon also helps eliminate the bang of the corrugated iron due to the expansion and contraction (heating and cooling) of the corrugated iron. Then lay thick insulation batts inbetween the ceiling rafters. You will notice a dramatic difference.

Good question. I wasn't ruling out anything but because of the way my house is built I can't lay batts on the ceiling. I can explain if you care, house was built in the 1800's...

I wasn't planning to use plain foil. I've looked at the earthwool space blanket, anticon, ametalin and the kingspan product and others. Prices vary a lot and it is not at all clear to me how their performance compares. I've ruled out the ebay bubble stuff. It is probably chinese and may not be approved for use in australian homes. It may even present a fire risk in queensland temperatures. The problem with foil blanket products is it's not just R values, you have to factor emissivity and installation.

I am amazed at the religious wars around roof ventilation and paints. Most of it is ignorant rants and trawling through the rubbish to find useful information was exhausting. It has however got me thinking about refinishing the existing roof. Once I've mulled everything over I'll post here what I have found in case someone in future has a similar issue but I'm still digesting it all. Reading other forums really makes you appreciate they happy friendly places like this one.

If anyone has any actual qualitative experience I would love to hear about it.

Damian,

I installed air cell in two houses in lismore. Same problem and Similar climate to you - pre 1900 houses, tin roofs, no insulation, with crazy hot and wet air in summer.
Installing on NY day stapling to the underside of the rafters my family could tell which room I’d done within minutes. Went from oven to bearable with a fan on.

Worth every cent.

The only downside was in winter the houses took a while to warm up. There were massive losses of heat out of the ceilings and floors and no heat load from the roof anymore to warm it up.

I trialed sarking alone. It was about half as effective as the air cell, and harder to install as retrofit.

If I was re installing the roof sheets I’d use anticon like I did in my shed, but for retrofit aircell is great. Just make sure you don’t electrocute yourself like those poor backpackers.

Forgot to add - aircell is good to retrofit because it’s a bit stiff. Makes installing by one person ok, and tapping joins and seams do able

On my current house I installed foam backed silver stuff on one veranda and air cell on the other. Both installed to spec when putting tin sheets on. The aircell is considerably cooler - far less radiant heat on my balding head!

Thank you so very much for that, exactly the sort of first hand information I've been looking for.

I have a plan.

The custom orb I found cheap is listed as white/beige. It should be highly reflective. My ridge runs left to right so the neighbours won't see it at all and there are no houses above me. I'm planning to call them monday confirm availability and go pick it up. About $750 will do the main pitch.

I've ordered a couple of indoor outdoor thermometers on ebay. When they arrive I'll get some base measurements, then fit new roof with insulation under and remeasure.

Because I'm fitting new steel I'll have options due to improved access to the cavities. I can't get at any of it from underneath.

Cold is not a problem, it basically never gets cold at my place. We would get maybe 7 days a year when I put on a jumper.

Thank you for the recommendation on insulation. My neighbour is a builder and he uses glass blanket with foil backing. I'll decind on the insulation when I get closer to the installation.

Today I got up there with the waterblaster and cleaned the roof and gutters. The sheets are pretty shot so I might as well replace them no matter what.

Damian, a word of caution. You say the property is Heritage Listed. It would probably be advisable to make some enquiries about what if any restrictions may exist regarding colour schemes allowed for renovation/repair before you commit $s.

Cheers,

Quote:

---

Originally Posted by Fuzzie

Damian, a word of caution. You say the property is Heritage Listed. It would probably be advisable to make some enquiries about what if any restrictions may exist regarding colour schemes allowed for renovation/repair before you commit $s.

Cheers,

---

A valid point, be careful not to draw undue attention to your property or you might find council with their heritage architect on your doorstep
If it currently has galv sheeting I would be sticking with that and maintaining its character

Another point to consider is if you have lead flashing on your existing roof it is not compatible with colourbond

No lead.

I read over the heritage regs and I don't think it will be a problem. They say tek screws are ok and colour schemes should be in keeping. House is white with cottage green trim so white corro and I'm considering a cottage green ridge.

You would think they would be grateful I'm replacing the rusty and shot old roof but of course the idiots minds don't work like that.

I have been spending sometime probing. I've never looked inside the roof so decided to lift a couple of sheets and measure the structure. It was a lot better than I expected. Rafter 100x50, perlin 35x75, ceiling batten 25x50. There is more structure in the cavity section than I thought as well.

I've had another thought. I've been thinking about teh structure of the roof and I reckon getting foil blanket to drape as it needs to is going to be a huge problem.

Being me I built a spreadsheet and the cost differences are surprising. Kingspan glareshield is $11 sqm. Ametalin thermalbreak 8 and 7 are $10 and $9 respectively. Earthwool foil blanket 75mm (1.8) is $6.66 and 55mm 1.3 is $4.72.

I can get earthwool 2.5 batts and ametalin silversark for $5.60sqm. The 2.5's are 125 thick so will fill the whole space between the ceilings and the steel. Lay the foil on top of that hard against the steel and you could have up to the equivalent of R4 depending on how the actual installation functions. It'll cost me about $300 plus 500 tek screws to try it and refit the old sheets.

I'm thinking of doing that, seeing how it goes and maybe resheeting later. It also eliminates the possibility of the hysterical mob objecting.

In the cavity section in the middle of the house I'll run the sarking under the steel over the pitch and lay batts on the ceiling.

It will be a bit of work, but a lot less money,and I can always change it later.

Waiting on my temperature gauges. If they arrive soon enough I'll get some measurements before I do anything. I was in the roof this morning, hotter than below but not appalling. What I did notice though is tremendous radiation from the pitched ceilings at the front and back of the house. I think insulation batts will help a lot.

This is an interim update.I did 3 hard days on the roof but then storms wind and heat have stopped me. I've got about 2/3rds done and I estimate another day and I'll have it finished.

Because of the raked ceilings for and aft I opted for R2.5 batts, earthwool, the thickest I could fit in the 145mm gap without compressing them. I fitted sarking hard against the steel. I couldn't have an air gap above and below so I opted for teh air gap below, between sarking and batts.

I've finished the back of the roof up to the ridge board. The forward pitch faces north east, the rear is exposed to the west.

I ordered some thermometers on ebay but they only arrived after I'd done some of the work so the experiment is not as systematic as I would like but I made some measurements before hand and did a rough calibration of the new units.

Here is what I have observed so far, I think.

In the morning the steel heats up quickly. The roof cavity is 20 degrees hotter than the living space by 9am. By 1pm it's started to cool. I believe this is due to the sarking on the rear pitch and when I fit it to the front the cavity will remain cooler all day. Temperatures drop quickly as the sun goes down.

I believe my living space was 2C hotter than ambient before. It's now consistently 2C cooler. Sometimes more. Again temperatures rise in the morning but as the middle of the day comes they stop rising. Overnight the living space always remained warm and this does not seem to have shifted much.

Pulling the roof nails was a nightmare. I bought a hart brand nailpuller from bunnings. $15.Worth it's weight in gold although a claw hammer is still vital. The roof steel is shot and I will have to resheet sometime, I can do further measurements when that happens.

The batts are the best bang for buck and the earthwool was wonderful to work with. I used no ppe and had no irritation at all. Nothing like the old bradford fiberglass batts.

If I had been able to vent the roof properly installing either a mushroom vent or solar exhaust fan would have aided cooling significantly, but my house is both clad and lined with asbestos fibro so cutting vent holes is problematic. It is useless to fit a whirlybird etc unless you can cut inlet vents to draw air into your roof cavity. And obviously none of that is an option in the areas with raked ceilings, which in my case is 2/3 of the building.

I believe the sarking definitely helps. I'm thinking of unrolling it over the top of the steel at the front and fixing it down as a temporary measure until I can rebuild the front pitch. Unfortunately while the sarking is waterproof it isn't sunproof so if it remained on top of the roof for some time it wold probably degrade.

The house is already a lot more livable.

More later.

Just another really quick update.

Ambient 38C. Lounge room 33C. Bedroom with air con 25C. Before the insulation the lounge would have been the same as ambient or even higher. My bedroom with air was usually 7C below ambient.

I'm hoping Wednesday will be cool dry and calm enough to finish the job but the difference is already remarkable.

Well about time I got back to this. I've delayed because, ironically, we have been having some milder and variable weather so my data points have not been what I wanted.

So today for example temperature peaked at 35 ambient. My air conditioned bedroom held at 22C. The unairconditioned lounge held at 30C. Roof did go over 50C but for a much shorter time. I think the insulation has taken a good 6C out of the living spaces and made air con more effective into the bargain.

Now this is what I THINK I know about roof insulation. I am typing it up to save others the epic learning curve I had to go through. Advice as always worth what you paid for it.

Your first option is shading the roof. The obvious option is trees but people installing solar panels have reported measurable improvements. Decades ago landrover came out with the safari roof. It was a double roof with an air gap open at the sides. The upper roof shaded the roof proper, convection circulated the air in the gap and the car stayed cooler. Same thing can work with your house although unless you are installing solar panels or similar items it's probably not practical.

As a side issue if you are considering solar hot water plain old 12mm irrigation hose is not that much less efficient than the expensive SHW systems. Just arrange it over your roof,put in a small pump and circulate it to a reservoir of some sort.

Anyway..

Your next option is coating the roof. Anti heat paints seems to be one of those areas that attract snake oil salesmen. Be careful. From what I could glean some do really work. They either use reflective elements in the pain so though it looks dark it actually reflects the light and heat,or they are thick and use insulating materials within the paint to stop it reaching the roof material itself. They are not cheap and do your homework. Even dulux seems to have copped a fine for misleading claims.

Be aware that you get more bang for buck preventing heat getting into the house structure. Once in it has to be radiated back out, so the earlier you get it the more effective it is in reducing the living space temps. That's why sarking with an R value of maybe 0.4 can have a real effect beyond what that number indicates.

So the next level is the roof material itself.

I guess this is where we have to talk about reflection, emission and thermal mass. Light colours usually reflect light well but radiate heat poorly. Conversely dark colours usually radiate well but reflect poorly. Massive materials like bricks and concrete have signifigant thermal mass. They absorb heat when the surrounding temps are higher and emit it as they drop. My parents built a house in 1980.I remember well it being quite comfortable until they put in insulation. It would stay freezing in winter until about 11am then stay hot as hell in summer until late night. Get your insulation wrong and it can make life miserable.

Zincalume is rated at 0.3 as is surfmist colorbond. There is a special white colour that is 0.22. These sorts of colours will definitely help keep your home cooler. Unfortunately dark colours are in fashion lately.

Tile roofs have a higher thermal mass than steel and all too often come in darker colours. Not only will they transfer more heat to your roof cavity they will keep doing it into the evening.

The next option is sarking. Some of these come with a layer of insulation, glass wool, foam etc. I went with plain sarking because of the particular situation with my roof. If the roof material is shot then replacement with light coloured colorbond or zincalume is cheap and easy. If you can access the cavity sarking can not only help with heat but it will channel drips down to the roof edge and away if it's installed with that in mind. If like me you choose not to renew the roof itself. It cost me about $1.50 a sqm. In combination with the rood cavity it is rated as an effective R value of 1.5. Good bang for buck.

Next is venting the roof cavity. As mentioned mine gets up 15 -20C above ambient on hotter days. Getting this down to ambient would really help. Plenty of people on other forums yell at each other about venting. It's because they don't understand that for a vent to work there needs to be a point of inflow. It's no use putting on a whirlybird unless you also install large vents in the eves or somewhere similar. Personally I would use a whirlybird anymore. They were never much good and there are now very cheap mushroom vents and solar extraction fans at bunnings. Those fans are cheaper at bunnings than anywhere else I could find them. Unusual, because cheaper prices are not normally the beginning...

Now we come to the best bang for buck. If your roof is watertight ceiling insulation is cheap, fairly easy to install and will really impact on living space temperatures. I used the earthwool from bunnings. It was cheaper than bradford batts and areal pleasure to work with. Very little irritation, nothing like the old glass batts. I like glass because it's vermin proof and fire retardant. Go for R4 if you can fit them. If you have the opportunity do the walls aswell. I could only get R2.5's in my place. Previously you could touch the ceiling on a hot day and feel the heat radiating off it. Now it's the same temperature as the air in the living space.

If your problem is cold I'm not sure what to suggest. Insulation will retain heat, but there needs to be heat to retain. Putting irrigation pipe on the roof and circulating it through inside radiators could probably help. It would be a cheap experiment. Use 12mm as you want the best ratio of surface area to volume. Bigger bores are less efficient.

Anyway I hope all that is some use to someone.

Here are some links to colorbond pages.

The coolest steel roof is called coolmax, the color is whitehaven and it's part of the commercial range, although you may be able to use it on a domestic home.

COLORBOND® Coolmax® steel - BlueScope Steel

Here are the ratings for different colours:

Commercial Colours - BlueScope Steel