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Best polycarbonate sheet colour for an Adelaide pergola?

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  1. #1
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    Default Best polycarbonate sheet colour for an Adelaide pergola?

    Hi Folks,

    I know that there has already been a long discussion here about polycarbonate roofing but it's a few years old now so I thought it OK to propose a few more specific questions.

    I'm in Adelaide - hot summers! I've built a new pergola attached to an existing 1.5m deep veranda (see pic below), replacing a previous dodgy effort that I covered about 20 years ago with what I think were Suntuf grey sheets. The pergola measures about 3.6x7m and faces north, oriented east-west. We're about 200m from the beach and the pergola fascia is 2.4m high so I reckon we'll get plenty of air flow underneath (when there's a breeze).

    My main concerns are creating some decent shade and keeping the sun off the enormous concrete slab the pergola is built over, while still letting enough light into the rear of the house (rear door is 1.8m wide with a wide window above it. Actually, I'm not too worried about the light - minimising heat transfer to the slab and double brick rear wall while having somewhere nice to sit are the main objectives.

    I recall that the previous polycarbonate would occasionally get a bit hot to sit under so I'd certainly like something a bit cooler. Funds are somewhat limited but I reckon I can afford the current Suntuf Solarsmart product. I'd like to get something a bit cheerier than the previous grey sheets. Does anyone have any experience with the current Suntuf Solarsmart Sand Dune sheets in a context similar to mine?

    Suntuf state a light transfer of 15% for Sand Dune - which I reckon would be plenty of light. Solar transference (which I presume means 'heat transfer') is also advertised as 15% which I find remarkable. Is this to be believed?

    I'm also going to build a shallow-height deck over the existing slab and have considered 3-4 sheets of Colorbond over the central part of the patio where we are most likely to have our table. But if Sand Dune really does transmit so little heat then the steel sheets hardly seem worth the deeper shade they'd offer. Thoughts?

    I also hope to train some vines and climbing plants along the west and northern-facing eaves of the pergola to try to get a bit more shade, particularly in late afternoon when the Adelaide sun can get really punishing...

    thanks,

    Sam.

    Attached Thumbnails Attached Thumbnails pergola-2.jpeg   pergola-3.jpeg  

  2. #2
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    For what you've descibed you certainly want a very light colour, as it will reflect more heat, (rather than soak it up and transfer to underneath like dark colours do). Some polycarb products contain reflective particles too, but not sure they are worth the extra, or are within your budget. Steel sheets will also transfer heat, the darker, the more heat, but the complete shadow helps - sometimes it's nice to have a shady spot, but it seems that garden of yours has plenty of that

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    Heat comes from the sun in the form of infrared light (IR), visible light (VL) and ultraviolet light (UV). The latter is the long wavelength UV near the VL spectrum ('near UV') not the cancer causing short wavelength UVA and UVB so much (far UV). All sheets will block the far UV wavelengths.

    All of the near visible and visible light wavelengths contain significant heat, not just the IR. If the polycarbonate is not spectrally selective, then the transmission loss for near IR and near UV will be pretty similar to that of the VL transmission of the sheets. If the sheeting gets hot, it will also radiate long wavelength IR or 'far IR'. Far IR radiation is what makes it hot under iron cladding.

    The heat gain of polycarbonate sheeting is the sum of near IR, VL, near UV transmission and far IR re-radiation. A spectrically selective sheet will ideally reflect the unwanted wavelengths, so the sheet does not heat up, whereas a tinted sheet will absorb the energy, heat up, and re-radiate more heat as far IR.

    Rule number 1: get spectrally selective polycarbonate sheets, which are usually made with nanoparticles of reflective material in the polycarbonate. These sheets have much lower heat gain than standard sheets.

    If you plan to spend time working or partying under the pergola in the daytime, you might want to think about colour rendition. Some people (me, for example) find it tiring to work when colours are not easily discernible. Also people's faces can look sickly in light that doesn't reproduce all colours. Some sheets that are nominally white transmit light that is very biased to the yellow end of the spectrum. Of course the light transmitted by coloured sheets cannot render colours properly. Gunmetal and grey sheets are probably more neutral spectrally.

    I personally like Laserlite 3000 colour Ice, which gives as near white light as you can get. On the outside it looks silver, almost like new corrugated iron. It has the biggest ratio of light transmission to heat gain. Suntuff has a similar sheet.

    Be aware that any sheeting that is dark will be hotter underneath because the sheets themselves heat up and re-radiate far IR. Also 15% light transmission is much darker than it sounds. YMMV.

    https://laserlite.com.au/wp-content/...-DataSheet.pdf
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  4. #4
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    What John said (and r3nov8tor) is spot on.
    However ... the idea that you can build a roof that lets the light through and not the heat and that you can be there in the heat of summer and be cool is an illusion. Not possible. It's like saying you want to build a cool greenhouse. You either reflect the sun or you wear it.

    So what's the solution? Forget all the semi/nano/reflecting/cooling gobbledigook gimmicks and build a solid insulated roof like this one here, with sheets that have colorbond on the top, a panel of insulation and the ceiling all in one.
    https://atsawnings.com.au/services/i...RoCQWQQAvD_BwE

    You will have plenty of light coming from the sides. I just finished one like it and the loss of light due to a solid roof is negligible. If you are really wanting more light all you need to do is build a couple of gaps between your solid roof for the nano-mumbo-jumbo sheets. You will get plenty more light with hopefully not much heat gain.
    The times of the magic translucent sheet for our climate are over. Build proper roof to stop the heat, and if you must let a slither of light come in here and there. do it in minimal proportion.
    Or start sweating and go indoors with aircon.
    Alternatively, have outdoor aircon. Not that hard and rather cheap with fans and micropumps and spray.

    https://www.mydeal.com.au/mist-fan-w...RoCgKcQAvD_BwE

    https://www.ebay.com.au/itm/15264400...RoCesYQAvD_BwE

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    I think I also said a lot of what John did, haha I tend to stick to John's signature advice

    I thought about suggesting insulated panel, but for the OP's budget concern

    See, I'm done

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    If you haven't used heat discriminating polycarbonate sheet you should not knock it. I've been using Laserlite 3000 for decades since I stood under a comparison display on a summer's day, and was stunned at how much difference it made.

    My electronics workshop has about 50% Laserlite Ice sheeting interleaved with insulated Colorbond iron sheets. Under the polycarbonate sheets is a layer of bubblewrap and a second layer of clear polycarbonate. The bubblewrap (AKA "bubble glazing") and clear sheet separated by about 6cm provide insulation in both hot and cold weather, and I have plenty of diffused light in all seasons for the detailed work I do.

    I also have this sheeting over parts of the verandas and some skylights and it makes a huge difference compared to veranda sections and skylights where there is just clear polycarbonate.

    Attached Thumbnails Attached Thumbnails img_0470.jpg  
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    Quote Originally Posted by r3nov8or View Post
    I think I also said a lot of what John did, haha I tend to stick to John's signature advice
    Yes you said it in a nutshell. I put the science for those who think cool polycarbonate is too good to be true, although explaining how and why it works was obviously a waste of time in retrospect.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

  8. #8
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    Growing vines over is going to be the coolest option I'd say.

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    Quote Originally Posted by John2b View Post
    Yes you said it in a nutshell. I put the science for those who think cool polycarbonate is too good to be true, although explaining how and why it works was obviously a waste of time in retrospect.
    I do appreciate the science, thanks. Just being a little cheeky

  10. #10
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    My electronics workshop has about 50% Laserlite Ice sheeting interleaved with insulated Colorbond iron sheets. Under the polycarbonate sheets is a layer of bubblewrap and a second layer of clear polycarbonate. The bubblewrap (AKA "bubble glazing") and clear sheet separated by about 6cm provide insulation in both hot and cold weather, and I have plenty of diffused light in all seasons for the detailed work I do.
    Thank you for confirming what I know. Polycarbonate sheeting, be it magic, sophisticated or polished, does not perform well in our sun on it's own.
    You need to build something under it to stop the heat to a reasonable level.
    Your solution with the bubble wrap and second layer of clear under it is brilliant. Never done that,must try it. Alternating with solid insulated roofing is also the way to go ... hum, didn't I say that? Oh well never mind.

  11. #11
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    Quote Originally Posted by Marc View Post
    Thank you for confirming what I know. Polycarbonate sheeting, be it magic, sophisticated or polished, does not perform well in our sun on it's own.
    You need to build something under it to stop the heat to a reasonable level.
    Er, no, the bubble glazing and clear polycarbonate second layer do not alter the mechanism of radiant heat transfer from sunlight. Clear transparent materials can not and do not reduce radiative heat transfer.* That is done by the magic of the spectrally selective concoctions in the polycarbonate sheets. You really should try it.

    * The purpose of the extra layers is to reduce conductive heat transfer, particularly heat loss in winter.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

  12. #12
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    Oh come on John, cut your losses. Of course it stops conductive heat, it does stop all that heat that is not stopped by the magic polished tu ... I mean bit of plastic on top.
    It is good in winter too? Magic! Would you remove it in summer since it only stops conductive heat? Of course not. It all works in conjunction.
    Good stuff, yes of course I will try it.

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    Quote Originally Posted by Marc View Post
    Oh come on John, cut your losses.
    I've no losses to cut, Marc. I've had the magic polycarbonate roofing like this for a few years. I put the bubble glazing and extra polycarbonate sheet just last winter to keep winter warmth in, nothing more, and that's what it does.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

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    I know polycarbonate is UV resistant but I had corflute under polycarbonate roofing and the sun ate it all up. I would have expected the same with bubblewrap too!

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    Yep, I expect the bubble wrap will die doing its duty. But it cost me nothing and I kept it out of landfill a little bit longer.

    I had bubble wrap as secondary glazing on a frosted bathroom window at the last house. No one ever commented on it so I assume they never noticed, and in ten years it showed no sign of deterioration. But if it had, so what, it cost nothing and nor would replacing it.
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    I brought a economy bubble wrap pool blanket. Two months later I was removing it with the pool scoop and filter. Definitely one of those cases that you get what you pay for and another case of don't believe anything the seller states. UV proof.. pfft.

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    Quote Originally Posted by Uncle Bob View Post
    UV proof.. pfft.
    Most flexible plastics that have useful properties are not 'UV proof' unless they are black. The black comes from added carbon, which absorbs the UV energy and turns it into heat before the UV energy breaks the molecular bonds that hold the polymer together. I would be dubious about any flexible plastic that is not black being resistant to UV.

    The polycarbonate that is used for transparent roof sheets is not UV resistant either. However a UV blocking film is bonded to one side of the polycarbonate sheet, and this side must face the sun or the polycarbonate will quickly deteriorate.

    When using bubble wrap as bubble glazing, it is important to put the bubble wrap behind a UV blocking material, to ensure the plastic isn't quickly destroyed by UV. I have bubble glazing that is 10 years old with no signs of visible deterioration yet. It will will happen eventually, but it didn't cost me anything, and nor will its replacement. I keep the bubble wrap from deliveries, which otherwise goes to landfill.
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    Quote Originally Posted by John2b View Post
    I keep the bubble wrap from deliveries, which otherwise goes to landfill.
    I just ran around on it like Ace Ventura

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    Thanks everyone for the comprehensive and well informed advice - I really appreciate it - both the explanations of the principles involved ('the science') and the practical experiences!

    I have thought a bit more about my specific situation and needs. To be realistic, as anyone who has lived through an Adelaide summer will know, you stay inside on 'hot' days anyway! I think I'm just hoping for an outcome that allows us to use the pergola and deck area as flexibly as possible, especially in the afternoon and evening when things start to cool down a little. Given the pergola is open on 3 sides and its east-west orientation, I now doubt that getting sufficient light into the house will be a problem and I reckon it'll be high enough to take advantage of natural air circulation.

    Everything is a compromise and everyone obviously has to deal with a specific set of needs. In my case managing the 'heat soak' of the large concrete slab under the pergola (and the deck I'm building over part of it) is a key factor as is wet weather protection. I think I'll probably end up with a simple combination of colorbond and 'reflective' poly sheets, especially if I can get them in matching light colours - white or the 'sand dune' colour. I plan to grow vines around the periphery of the pergola, especially on the western side where we get a lot of hot, late-afternoon sunlight. I'm also considering a role for lattice sun-screens and maybe movable shade cloth curtains and covers or blinds which I can take down for the cooler months.

    I would love to try colorbond sheets with insulation underneath if it could be achieved relatively cheaply - I'll have to give that some thought, especially with regard to a suitably lightweight ceiling lining. But I suspect that I now need to stop theorising over this and find someone with an outdoor display structure of poly sheet material which I can go and stand under. Thanks again everyone for your help and thoughts on this enterprise! ;-) Sam.

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    Hi Savvas - John mentioned some good points. Personally, the "dune" color you mention is all that Ive used over the last 20 years. Its a good compromise with light transmission and heat reduction. Definitely don't go clear or grey smoke color if your concerned with heat

    I'm also not sure I'd cover the entire roof with poly carb although I must admit I've never done this before.

    The last big pergola with a 22deg pitch, 10m x 8 m, I'd covered in colorbond and placed 2 rows of poly carb for the light. Heat wasnt really a problem due to the height and opened end.

    The Verandah around the entire house I've recently built, ...a lot lower than the pergola, I covered in colorbond with polycarb "windows on the north side over our living areas to get extra light inside. Used the Dune color once again and standing under it on a 40deg day isn't an issue.
    • but I'd also put insulation blanket under the colorbond on the north living side and Sisialation foil/paper under the rest
    • And placed batons underneath the rafters with cement sheeting lining....mainly to have a better finish but also to stop to constant buildup of spider webs which would drive me nuts.....there is lots of them here


    If you want a few photo's let me know.

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    You can always double up and put a white shade sail over the top of the poly roofing. Put the sail at an angle and you also get a small airflow boost. Deciduous vines are possible the coolest solution for Adelaide tho, especially Big Muscat grapes so you can make your own port over winter
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