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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorbardo
    • CommentTimeJan 21st 2020
     
    The verandah on our new build home is part green roof and part glazed in front of the large sliding doors. I'm wondering whether to use laminated glass or 6mm solid polycarbonate. What's best? Would welcome thoughts of anyone experienced with these materials in external roof use.
      IMG_4560.jpg
    •  
      CommentAuthordjh
    • CommentTimeJan 21st 2020 edited
     
    The house looks good :bigsmile:

    Clear polycarbonate is very strong and unlikely to break, but it will get scratch marks. It's possible to get 'abrasion resistant' coatings but I don't know anything about them. The same goes for acrylic sheet but that generally has better weather resistance.

    edit: what kind of a slope does the verandah have? It's not clear in the photo.
    • CommentAuthorbardo
    • CommentTimeJan 21st 2020
     
    Posted By: djhThe house looks good:bigsmile:" alt=":bigsmile:" src="http:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" >

    Clear polycarbonate is very strong and unlikely to break, but it will get scratch marks. It's possible to get 'abrasion resistant' coatings but I don't know anything about them. The same goes for acrylic sheet but that generally has better weather resistance.


    Thanks DJH.
  1.  
    I agree with DJH with regard to the strength of polycarbonate .

    Acrylic cracks very easily. I wouldn't even consider this material personally. it can be surprising what birds will carry aloft and then decide to drop from height. We frequently get bits of detritus that birds have picked up from the nearby garage business turning up on our alleyway roof after they decide that they are too heavy to continue on with.

    All plastics scratch VERY easily. Even if you take care to use non-abrasive cleaning materials there is always some kind of grit hanging about so it will be very difficult to avoid it getting scratched up over time.

    You mention 6mm thick solid polycarbonate. Be aware that this is likely to sag eventually.

    I have personal very good experience of the multilayer polycarbonate product. I have approximately 15 sq. m. of the 1,000mm wide triple layer 'Ariel Clear' product installed in 1m x 1.5m sections with side edge support only and it is stilling showing no sign whatsoever of sagging since installation in 1992.

    I got mine from B&Q, although I notice that they do not appear to carry the 1 metre Ariel triple layer product any more (well, it is well over a quarter of a century ago now from when I bought it! :bigsmile:):

    https://www.google.com/search?q=polycarbonate+roofing+sheets

    I have never attempted to clean it (access restrictions make this impossible anyway, as it in-fills over an alleyway between our house and the next property) but my experience tells me that it is a racing certainty that it would get scratched if I tried.

    The only downside to this is that after more than a quarter of a century lichen colonies have slowly established themselves and the lean-to (as we refer to it) is slowly but surely becoming dimmer over time. But then this is simply a utility and access area through to the rear of the property for us so this does not bother us too much. it certainly would if it was a conservatory or a verandah. And of course glass that went uncleaned for that length of time would suffer similarly of course. interestingly, we do not get the dirty streaks that uncleaned glass often suffers from. Just the (very very) slowly growing lichen colonies.

    The impact resistance of this material is truly impressive BTW. Mine has survived at least two corner on impacts over the years from concrete roof tiles falling over 10 metres off the adjacent roof with nothing more than a very minor dent mark left at the impact site.

    Despite the above eulogy in praise of polycarbonate my recommendation would be to go for glass - mostly purely and simply because of the ease with which polycarbonate scratches when being cleaned, but also because solid material sags and also, finally, because glass will always look just that bit classier.

    I would certainly use polycarbonate again in the right context, just not perhaps if I had a feature verandah such as yours.
    • CommentAuthorbardo
    • CommentTimeJan 21st 2020
     
    Posted By: ealingbadgerI agree with DJH with regard to the strength of polycarbonate .

    Acrylic cracks very easily. I wouldn't even consider this material personally. it can be surprising what birds will carry aloft and then decide to drop from height. We frequently get bits of detritus that birds have picked up from the nearby garage business turning up on our alleyway roof after they decide that they are too heavy to continue on with.

    All plastics scratch VERY easily. Even if you take care to use non-abrasive cleaning materials there is always some kind of grit hanging about so it will be very difficult to avoid it getting scratched up over time.

    You mention 6mm thick solid polycarbonate. Be aware that this is likely to sag eventually.

    I have personal very good experience of the multilayer polycarbonate product. I have approximately 15 sq. m. of the 1,000mm wide triple layer 'Ariel Clear' product installed in 1m x 1.5m sections with side edge support only and it is stilling showing no sign whatsoever of sagging since installation in 1992.

    I got mine from B&Q, although I notice that they do not appear to carry the 1 metre Ariel triple layer product any more (well, it is well over a quarter of a century ago now from when I bought it!:bigsmile:" alt=":bigsmile:" src="http:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" >):

    https://www.google.com/search?q=polycarbonate+roofing+sheets

    I have never attempted to clean it (access restrictions make this impossible anyway, as it in-fills over an alleyway between our house and the next property) but my experience tells me that it is a racing certainty that it would get scratched if I tried.

    The only downside to this is that after more than a quarter of a century lichen colonies have slowly established themselves and the lean-to (as we refer to it) is slowly but surely becoming dimmer over time. But then this is simply a utility and access area through to the rear of the property for us so this does not bother us too much. it certainly would if it was a conservatory or a verandah. And of course glass that went uncleaned for that length of time would suffer similarly of course. interestingly, we do not get the dirty streaks that uncleaned glass often suffers from. Just the (very very) slowly growing lichen colonies.

    The impact resistance of this material is truly impressive BTW. Mine has survived at least two corner on impacts over the years from concrete roof tiles falling over 10 metres off the adjacent roof with nothing more than a very minor dent mark left at the impact site.

    Despite the above eulogy in praise of polycarbonate my recommendation would be to go for glass - mostly purely and simply because of the ease with which polycarbonate scratches when being cleaned, but also because solid material sags and also, finally, because glass will always look just that bit classier.

    I would certainly use polycarbonate again in the right context, just not perhaps if I had a feature verandah such as yours.


    Ealingbadger. You've helped confirm my concerns about polycarb. Glass seems the way to go. Cheers!
    • CommentAuthorbardo
    • CommentTimeJan 21st 2020
     
    edit: what kind of a slope does the verandah have? It's not clear in the photo.


    Approx 12%. The joist centres are 400mm apart and the glazing panels need to be 2675mm long. I was planning to clamp each of the panels to the joists using glazing bars. With glass and bars it all starts to get pretty pricey though the alternatives don't seem to be up to the job.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 21st 2020
     
    You can get Pilks self cleaning glass, at a price - the coating uses natural UV to catalyse organic deposits breakdown so they wash away.
  2.  
    Posted By: fostertomYou can get Pilks self cleaning glass, at a price - the coating uses natural UV to catalyse organic deposits breakdown so they wash away.


    Needs a decent fall to work well - we were advised our roof glazing didn't have enough.

    " It can be installed vertically or at an angle of 10 degrees or more, although most efficient at an angle of 30 degrees." based on a quick google
    • CommentAuthorGreenPaddy
    • CommentTimeJan 22nd 2020
     
    AFAIK glass will also sag, so fall is just as important to avoid ponding.
    • CommentAuthorrevor
    • CommentTimeJan 22nd 2020
     
    I have a veranda and conservatory roof done in glass. It is double glazed. I have used triple layer polycarbonate on a green house roof in the past and it discoloured, also does not let as much light through as glass. If you price up double glazed panels v's single pane there won't be much difference as you will probably end up with 2 x 4mm in DG and 6 mm in single plus the glazing suppliers are all geared up to do DG. The roofing bars are also likely to be designed for DG and if you put in a single pane you will be paying extra for spacer bars to make up the thickness.

    I spent ages looking for suitable bars and eventually bought from here.

    https://www.patent-glazing.com/index.html

    The website has load of information and I had extremely good service from them. Part of my consignment was damaged by the carrier and they sent one of their employees in the MD's car to replace the items. They are only a small company and I was very impressed by how everyone I dealt with would take ownership of the solution to the query.

    What size are your rafters, glazing bars are often wider than the nominal 2"
    • CommentAuthorbardo
    • CommentTimeJan 23rd 2020
     
    Posted By: revorI have a veranda and conservatory roof done in glass. It is double glazed. I have used triple layer polycarbonate on a green house roof in the past and it discoloured, also does not let as much light through as glass. If you price up double glazed panels v's single pane there won't be much difference as you will probably end up with 2 x 4mm in DG and 6 mm in single plus the glazing suppliers are all geared up to do DG. The roofing bars are also likely to be designed for DG and if you put in a single pane you will be paying extra for spacer bars to make up the thickness.

    I spent ages looking for suitable bars and eventually bought from here.

    https://www.patent-glazing.com/index.html" rel="nofollow" >https://www.patent-glazing.com/index.html

    The website has load of information and I had extremely good service from them. Part of my consignment was damaged by the carrier and they sent one of their employees in the MD's car to replace the items. They are only a small company and I was very impressed by how everyone I dealt with would take ownership of the solution to the query.

    What size are your rafters, glazing bars are often wider than the nominal 2"


    Thanks Revor. Really helpful. I shall follow up...
  3.  
    Posted By: GreenPaddyAFAIK glass will also sag, so fall is just as important to avoid ponding.


    Yes, but that is being a little over-pedantic for the purposes of this discussion.

    To all intents and purposes glass may be considered no-sag in this context.
    • CommentAuthorMike1
    • CommentTimeFeb 10th 2020 edited
     
    Yes, glass is undoubtedly best, but it must be properly specified (toughened and laminated, I imagine) to ensure it is strong enough to be classed as 'non-fragile'. Of course that also applies to polycarbonate.

    It's not just a matter of providing weather protection. As you may well already know, under the CDM Regulations there is a legal obligation to eliminate, reduce, or control foreseeable risks in the design, including providing safe access for maintenance and repair. And from the photo it looks as though the verandah is 'in the way of' maintaining the main roof, so safe access would need to be considered.

    See also
    https://www.housingtoday.co.uk/cpd/cpd-4-2019-performance-characteristics-of-glazing-in-rooflights-/5099832.article
    https://selfbuildportal.org.uk/healthandsafety/
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 12th 2020 edited
     
    Posted By: ealingbadger
    Posted By: GreenPaddyAFAIK glass will also sag, so fall is just as important to avoid ponding.


    Yes, but that is being a little over-pedantic for the purposes of this discussion.

    To all intents and purposes glass may be considered no-sag in this context.


    Thanks for that update. I guess I needn't have worried about the 1200m2 of glazed roof we installed a on a previous project, and the suppliers stressing the importance of sag on edge supported glazing. And the chap on a recent thread whose DG panels had a considerable glass centre sag, causing cold bridging mid pane.

    Pedantry has it's place, but usually only valued in hindsight, when something's gone tits-up :bigsmile:
    • CommentAuthorbardo
    • CommentTimeFeb 14th 2020 edited
     
    Hi all, in the end we went with 6mm toughened glass. After looking at various roofing bars we decided to make our own using seasoned oak combined with expanded foam tape.
    • CommentAuthorrevor
    • CommentTimeFeb 15th 2020
     
    Oak will be problematic long term. It is too open grained and whatever finish you put on it will not last. You will be up and down like a YO YO cleaning and recoating. Vertical surfaces are easily ruined yours in an almost horizontal position will look a mess in no time at all. If you must use timber go for a closer grained timber like Sapele or Iroko. They are also cheaper.They tend to have little or no knots and you will need to buy premium grade oak for it to be knot free. The expansion and contraction of the timber will cause no ends of issues with leaks regardless of using expanding foam tape.

    Exp tape does not like being in a pool of water and from my painful experience some of what is on the market does not match up to the claims they make for it, particularly it's resistance to driving rain. Before you commit yourself to the method you propose I would build a trial rig and experiment with that.

    Have you costed the job the tape is very expensive you would be better routing a groove in the rafters and the timber capping and using a proprietary EPDM gasket both sides of the glazing.

    But bottom line is aluminium bars and capping.

    Good luck
    •  
      CommentAuthordjh
    • CommentTimeFeb 15th 2020
     
    • CommentAuthorbardo
    • CommentTimeFeb 15th 2020
     
    Posted By: revorOak will be problematic long term. It is too open grained and whatever finish you put on it will not last. You will be up and down like a YO YO cleaning and recoating. Vertical surfaces are easily ruined yours in an almost horizontal position will look a mess in no time at all. If you must use timber go for a closer grained timber like Sapele or Iroko. They are also cheaper.They tend to have little or no knots and you will need to buy premium grade oak for it to be knot free. The expansion and contraction of the timber will cause no ends of issues with leaks regardless of using expanding foam tape.

    Exp tape does not like being in a pool of water and from my painful experience some of what is on the market does not match up to the claims they make for it, particularly it's resistance to driving rain. Before you commit yourself to the method you propose I would build a trial rig and experiment with that.

    Have you costed the job the tape is very expensive you would be better routing a groove in the rafters and the timber capping and using a proprietary EPDM gasket both sides of the glazing.

    But bottom line is aluminium bars and capping.

    Good luck


    Thanks revor. That's really helpful experience shared. It has given me pause to rethink.
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