Insulation under custom orb roof brisbane

[damian]

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.

[damian]

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.

[damian]

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.

[damian]

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.

[damian]

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