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Elroy Jetson said..
You're proposing installing the insulated sheets in the same direction as the rafters! With the sheet joins unsupported and running parallel to the rafters. That scenario isn't covered in the company data sheet.

As I explained, so long as the span from the rafter blocking at the top of the roof section to the blocking at the bottom of the roof is within the permissible span in the tables, there is no problem. Blocking can act as the battens but in plane with the roof. The fact that the sheet joins are unsupported is irrelevant so long as the maximum span is respected.

In fact this scenario provides additional support to an otherwise free spanning system.

It's not covered in the data sheets because it's so obvious it works.

You are correct Adriano.

Shifu I think you owe Adriano a carton for his technical advice. You can in fact install 200mm thick insulated panels to a section of your house on top of the rafters. It says so in the span tables.

There's a few real world details to work out. Lets presume the existing timber rafters are not bowed or warped and the sheets will fit over your fascia after the battens have been removed. Unlikely but lets go with it.

You will need to rework your existing guttering systems and get custom flashings made up over most of your roof to marry up the difference in roof width.

Excluding modifying nearly every other aspect of the roofing system, Adriano's idea will work. Easy as.

And it would be an excellent talking point.

The house could be the first house in Australia retrofitted with 200mm insulated sheets to a part of its roof.

The cost of this would be similar to having solar panels installed on top of your existing roof.

But with the added bonus of making energy while providing shade to the roof.

Luxaflex make a solar panel roof sheet for awanings that would span the same .
I think they might be insulated as well i dont really know anymore about them I only saw a billboard & haven't looked nto it.
But maybe you could kill too birds with one stone.

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Elroy Jetson said..


The cost of this would be similar to having solar panels installed on top of your existing roof.

Realistically one of the best solutions. Block a lot of direct sunlight, air flow underneath, cheaper power. Paint the roof first, or if sheets are not in good condition redo (seriously cheap if you diy).

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Elroy Jetson said..
You are correct Adriano.

Aha.

Cheaper still would be to put a shade sail or tensioned membrane over the whole lot, if that's the look you're after. Even so, this doesn't solve the insulation shortfall. If it's 35 outside, solar panels actually heat the space between the roof and panel even more, so that space you say is "ventilating" might actually be 50-60 degrees.

Gee great idea.

More like no idea.

A lot of research and test casing has been done on creating shaded roof spaces, but the distance PV panels are set above a roof is no where near optimal and in fact can make matters worse or lower pitches.

And no, it would not be the first house retrofitted with insulated roof panels. Just because one is not aware of examples doesn't mean they don't exist. It's the best way to re-roof and insulate cathedral ceilings quickly and efficiently -especially if the roof is rectangular in format!

BTW none of the above solves the problem of releasing the built-up heat from the ceiling space. Still need something operable up high or mechanical air extraction.

How many solar panels would be required I wonder? How many inverters? Any more than 24 panels and you usually need two inverters by law, depending on the state, even though a good inverter can easily handle more than 24 panels on spec.

Let's say 30 panels minimum and two inverters. McLovin how cheap can you do that one, labour free of course with beers at the end of job?

microinverter?

Expensive and unreliable I understand. Slightly more efficient potentially. Hard to make battery storage ready. Still need another inverter to talk to the control module/s connected to the batteries and grid.

And having actually been on a roof, reroofed, insulated, etc etc. The section under a solar panel is much cooler than the roofing in the sun. I'll take my laser thermometer next time.

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Adriano said..
Expensive and unreliable I understand. Slightly more efficient potentially. Hard to make battery storage ready. Still need another inverter to talk to the control module connected to the batteries and grid.

well my 3w outperforms my parents 5kw system. Can handle shade, split roof directions, expandable. Batteries are available already fairly comparable pricing.

Of course the roof surface is going to be lower temp, but infra-red from the air temperature goes through the lot. You're mixing up infra-red radiation with surface temperature. Sure make sure you are measuring the heat of the airspace after it's been in the sun for a few hours and compare it to the ambient air temp.

With a sandwich panel, that 0.42BMT thick Colorbond is no match for 200mm of insulation.

no one is going to put 200mm on their roof. Full Stop.

Why not? If one was to use traditional blanket and batten and roofing to meet current standards it would end up being about 200mm anyway.

There aren't many options then, unless you're prepared to insulate with bulk between the rafters or put blankets above battens.

I'm not aware of any magic tricks available to get around this scenario.

Out of interest, this is how roof shading can work well in architecture. The air gap needs to be significant. Certainly more than 100mm.

2017 QLD Residential Architecture Award Winner.

sparksarchitects.com/verrierdale-2

Or this: www.lindsayjohnston.net.au

Adriano, you are definitely a theoretical thinker. Its been interesting to hear some new insights. Your proposal was food for thought while I was working away on a white coloured tin roof yesterday. But I can see so many real world problems to overcome that you haven't considered.

It's hard to imagine the problems that need to be overcome when it's not your area of expertise. You find creative solutions for designs. You are not involved in the end process, troubleshooting leaking house roofs.

Solar panels shade the roof from direct sunlight and the roof underneath is much cooler. I sometimes put my tools under the existing solar panels so they can cool down. Forget about your graphs and links to architectural websites. It wouldn't matter if there was a 1mm gap or a metre gap. The underlying roof is significantly cooler.

A 200mm thick insulated sheet is a creative idea but not practical to retrofit on an existing house and very expensive. Great talking point for the neighbours though. "Why does that part of the house have a massive bulge on the roof? And wow, look at those odd looking massive patchwork custom flashings? I wonder, how many cartons of silicone tube the installers had to use?"

Actually you could trim the bottom of the 200mm to fit in between rafters & use the outer face like normal roof sheets .
Ive done very similar .
Just fit angle around rafter to trim off & support the bottom sheet .

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Elroy Jetson said..

It's hard to imagine the problems that need to be overcome when it's not your area of expertise. You find creative solutions for designs. You are not involved in the end process, troubleshooting leaking house roofs.

Roofs (rooves?) suck. Mine is terracotta tile and its a great sound as a 100KG lardy bloke walks on them as they go snappity snap. Fun stuff! I don't have any fondness of tracing leaks.

For years I toyed with installed a solar hot water system on my roof but the idea of brittle tiles put me off it and its a fairly steep roofline. It was only about a year ago that I realised that it was far smarter to install a system on the cliplok extension of the house and build a frame for the solar collectors. The bonus is that you can tilt the collectors at whatever angle you decide is optimum and even tilt them further east or west than the roofline otherwise dictates. So far it works perfectly and there are no leaks. I was proud of the way I made up a mounting system through the cliplok. No leaks! I don't know how the pros do it, but this works well. I swear that the extension under the solar collectors is now cooler because of them shading the roof.

The other drama I had was installing a Velux window. From day one it leaked, but the leak was hidden unless it was extreme rain at which point it came down the lightwell. It turned out that the velux mastic sealant had dried out, so it leaked between the glass panel and the seals, and the flashing kit that came with it was from a different pitch roof. The rain was actually bouncing off the glass panel and then up under the flashing to come in through the gap that is there. A DIY folded metal flashing that is longer fixed that problem.

Then of course there is the problem where the gutters are starting to come away from the eaves, so water runs between the gutter and then runs across the eaves and into the ceiling. It only becomes obvious after the plaster is already destroyed. What fun.

Despite this, I am quite happy to install a colorbond roof at a pitch that is lower than the minimum. It wasn't my house

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Despite this, I am quite happy to install a colorbond roof at a pitch that is lower than the minimum. It wasn't my house

A tradie?

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Adriano said..
Out of interest, this is how roof shading can work well in architecture. The air gap needs to be significant. Certainly more than 100mm.

2017 QLD Residential Architecture Award Winner.

sparksarchitects.com/verrierdale-2

Or this: www.lindsayjohnston.net.au

Jeez the Tent House looks the goods doesn't it !

Just adding my 2 cents worth to this...My trade background is in the ceiling industry with over 26 years behind me, so I have seen a few different styles of ceiling from commercial to domestic, pre1900's through to brand new installs.
I also have a house with the same said exposed raking beam ceiling as in the original posters picture.
My first question is about the main house construction as I see that the author hails from QLD, so there could be a possibility that the house might be of full timber frame construction. If so, then this will contribute in my opinion to the heat generated in the house if the walls and flooring are not insulated, as we all know how hot air rises and if it has no where to go it will generate heat.
My practical example to this is with the last two homes that I have owned.
1st was an old timber frame home with high ceilings, that were insulated with r3.5 bats, but the timber floors were up on stumps with a cavity under the floor and plaster lined wall's with no insulation at all. this was by far the hottest house that I have ever lived in EVER. When I would come home in the arvo after work and take of my boots to walk inside I could feel the heat in the floor. It was like an electric blanket. Air con made little if no difference on most days.
2nd house, and current one has concrete slab, double brick walls and high, UN insulated ceilings...This is by far the coolest house that I have lived in. We hardly use the air con at all now.
My point is that an insulated ceiling is not the only factor to a cooler house and this comes from my own personal experience's.
The original poster might want to consider these factors.
If his house is concrete floor and double brick then forget anything I've said

PS the older timber frame house was coastal(doubleview/scarborough) and current house further inland so the seabreeze factor has nothing to take into account for my findings.

I have the same style roof that is the topic of conversation. Just got our summer electricity bill which is $300 over the average for the rest of the year. Most of that would have been running the airconditioning and pool pump. But I'd say its a lot cheaper than most of the alternatives being suggested. I like having an internal 5 metre ceiling height, gives a spacious feel to the house.

I got the same ruf in qld and I open the doors and windows problem fiksed

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OK Big Chief hehehhehe

Bono " big chief" deleting his crappy posts again

Retired custom home builder here, good discussion here, some ideas are good, some not so much.
I don't know if your cathedral ceiling ends at the ridge of your roof or not, but if it does, and you want the least expensive solution possible, I'd suggest painting the roof a very light color and add a ridge vent along the portion of the roof ridge that has the cathedral ceiling underneath it. Even w/o much space between the roofing and the ceiling, you will still get some heat release thru it. Also it will help avoid any condensation that may build up at the top of the ceiling which can lead to a mold issue.

If the cathedral ceiling ends at a vertical wall, at the highest point, like a second story (no ridge) it can still be vented at the top of the roofing with a running vent adjacent to the vertical exterior wall. It's corrugated hard plastic about 30cm wide, and about 2cm thick, that comes in rolls which is installed under the finish roofing at the very top only, venting out on the lower side of it.

Yeah that may help venting the roof space a bit, but how does it help with venting the room or improving insulation in roof and walls?

If your even remotely considering the double-sided insulated panels (which are crazy expensive!!), another option where you can re-use existing roof sheeting is Roof Razors insulation.com.au/product/roof-razor-insulation-spacer/ ,which raises the sheeting 75mm or whatever height you choose, you still have all the associated problems with the roof being raised of cappings etc & having to have a gutter flashing.
Mostly used on new commercial works, but no reason could be used on resi, except cost of course.
Easiest, cheapest & giving the best result imo, would be to plasterboard under the rafters, adding insulation batts as you go.
And as mentioned before, a couple of Velux opening skylights near the top end of the ceiling would also help heat escape, and look at wall & floor insulation.

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Adriano said..
Yeah that may help venting the roof space a bit, but how does it help with venting the room or improving insulation in roof and walls?

Radiant heating is greatly reduced, and the OP didn't seem to be concerned with his walls.