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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    We're getting a local joiner to make replacement oak framed windows for our entire house.

    The house itself is old and is never going to be super energy-efficient.

    So I'm trying to work out how far it is worth going with the double glazed units in terms of cost to benefit.

    The joiners are quoting for SGG Planitherm low-e glazing. Does that sound like it will be adequate, or would we benefit - even if the rest of our house has uninsulated walls - from another product like SGG Planitherm Futur N or SGG Swissspacer for warm-edge spacers? Its a minefield of poor manufacturer websites and potential over-specification.

    Not to mention tints... I don't want any tints affecting the views from our house!

    Any input welcome.
    •  
      CommentAuthornigel
    • CommentTimeJul 16th 2007
     
    The most important thing with dg is to get a decent air gap - 16mm minimum.

    Also make sure he uses good quality window seals to prevent draughts especially as oak will move about a bit.

    Low E glass is little extra cost and worthwhile.

    None of this however will make much difference if you have uninsulated walls but if you are replacing the windows anyway its worth doing them properly.
  2.  
    Warmedge spaces are not worth using in my opinion.
    • CommentAuthorken davis
    • CommentTimeJul 16th 2007
     
    why can't an old building be super enery efficient?
    double glazing is really hard to justify before insulating, draught stripping and efficient heating system unless the windows are useless . even then because it is the gap thats of greatest import rather than edge seals etc two frames are a better solution in order to create the biggest possible gap between panes. the inner frame can be very simple and therefor cheap and can be put in after the expensive outers as each room is decorated. remember sealed units do not last forever. also, do not know your house, but any chance of infilling any windows especially on north side?
    • CommentAuthorbiffvernon
    • CommentTimeJul 16th 2007
     
    Oooo, there is a lot of confusion about, isn't there :)

    Cost/benefit is fraught with problems as it depends on whether you are replacing the windows anyway, how warm you keep the house, and the price of heating the house in the future (anyone care to speculate on the cost of energy in ten years time?).

    Planitherm? Both Pilkingtons and St Gobain make low-e glass. And they both make 'hard coat' and 'soft coat'. Soft coat gives slightly better insulation but is more difficult to handle so some igu manufactures don't supply it. Hard coat does have a slight tint but is virtually unnoticeable. With bright sunshine at an oblique angle it can just be detected if you know what you are looking for. Hardly a deal breaker.

    A gap of 16mm is, indeed the best with argon filled units. With krypton fill you get the same performance with a narrower gap but it is more expensive, and not all suppliers offer it as an option. Forget it unless a narrow unit is essential.

    To meat Part-L of the Building Regs you almost certainly will need to have 4-16-4mm units with low-e glass and argon fill. That gets centre pane U-value well under 2, maybe about 1.6

    The importance of insulated spacers increases with decreasing pane size as there will be proportionately more edge. Significant thermal bridging occurs through edges on windows that are divided with real glazing bars. I always use insulated spacers but they are not the branded 'warmedge' variety, which, as Mike says, may not be worth it. I would not use the old-fashioned standard aluminium spacers.

    I'm afraid Ken is wrong to say that the biggest gap between panes is best. A gap of more than around 18mm allows convection cells to develop within the gap, transferring heat from the inner to the outer pane and removing the insulating properties of the gas. If sound insulation is important then a bigger gap is, indeed, preferable, but you lose the thermal insulation. Ken is right to remind us that sealed units don't last forever, but there are various strategies for optimising their longevity. I have some in my house that are now 20 years old and I would expect a well made unit fitted in a sensible way to last rather a long time.

    Remember that you will have to get Building Regs approval for your new windows, and that's mostly about the insulation performance.

    Congratulations on finding a local joiner willing to use oak. It's good to know I'm not alone :)
    • CommentAuthorTerry
    • CommentTimeJul 17th 2007
     
    Can anybody recommend suppliers of hi performance double glasing units (argon fill and thermal break around edges) as our local joiners and glazing suppliers seem a bit lost on this?
    • CommentAuthorbiffvernon
    • CommentTimeJul 17th 2007
     
    There should be one not too far from wherever you are as 'hi performance' is pretty standard these days. I don't think the firm I use, Spire Window Systems of Louth are so very exceptional.
  3.  
    Re warmedge spacers, not much point at all if the window frames are full of air, such as upvc.
    • CommentAuthorbiffvernon
    • CommentTimeJul 17th 2007
     
    Does anybody still use uPVC? So last season.
  4.  
    Posted By: biffvernonDoes anybody still use uPVC? So last season.
    Me I'm afraid. My customers cannot afford timber window, certainly not oak :bigsmile:
    • CommentAuthorbiffvernon
    • CommentTimeJul 18th 2007
     
    But oak is cheaper.
  5.  
    Cheaper than upvc! not in South Wales in my experience.
  6.  
    Lets think a little more holistic here, as I understand it, warm edge spacers do help to reduce condensation and thus help to preserve window frames and they give the glazing unit a greater lifespan (due to reduced damage sealant being damaged by condensation ingress between the sealant and the glazing.)

    Mike,
    Have you considered insulated extruded window frames such as those by Pultec? Supposedly they don't cost to much more....

    Mark
    • CommentAuthorbiffvernon
    • CommentTimeJul 18th 2007
     
    Oh Mike, you'e not just considering the up front price are you? A much better measure of cost is to divide the price by the number of years the window frame lasts and then quote the cost as so much per year. The holistcally thinkng Mark would want to include externalities of oil refineries, illmenite mines and the noise nuisance of birds singing in oak trees. To the nearest order of magnitude, I'd put uPVC windows at ten times the cost of oak.
  7.  
    Oooooooooo, the trouble is that in the real world people just won't stay in the same place long enough to recover their outlay, so given this aren't really interested in the arguments you put forward.
  8.  
    Extruded glass fibre frames are "more" environmentally sound than UPVC (hope I don't sound like a rep!). For what it's worth I' sure that I read that they get a BRE Green Guide "A" rating (can't lay may hands on the documentation to confirm...sorry). As far as I know the only other window to do that is timber.

    Mark
    • CommentAuthorbiffvernon
    • CommentTimeJul 18th 2007 edited
     
    Posted By: Mike George...in the real world people...aren't really interested in the arguments you put forward.
    That's why I make the case on the Green Building Forum, rather than diy.com. We need to get real world people interested in such arguements.
    • CommentAuthorbiffvernon
    • CommentTimeJul 18th 2007
     
    Posted By: Mark SiddallExtruded glass fibre frames are "more" environmentally sound than UPVC
    Maybe but they still look rubbish :)
  9.  
    Can't argue with that one Biff. Not the most aesthetic of beasts but the better evil of two.

    Mark
    • CommentAuthorMike George
    • CommentTimeJul 19th 2007 edited
     
    Posted By: biffvernon
    Posted By: Mike George...in the real world people...aren't really interested in the arguments you put forward.
    That's why I make the case on the Green Building Forum, rather than diy.com. We need to get real world people interested in such arguements.


    Fair enough, but you can explain this to people till you are blue in the face - most simply cannot afford oak windows, sorry but that's reality. Just because people cannot afford optimum solutions doesn't mean they cannot try their best with what they can afford to be green.
    • CommentAuthordavid
    • CommentTimeJul 19th 2007
     
    Why the emphasis on Oak for windows?
    I use "home grown" Sweet Chestnut.
    It's cheaper and there's less waste because there's negligible sapwood.
    Its' almost as durable as Oak with much better stability .
    A lot lighter in weight and most people can't see the difference.
  10.  
    We had softwood windows made by a local joiner, and good quality low-e units from a local glazier. Painted the frames up myself before installation & afterwards too. Still looking great 5 years later, and only a fraction of the price of U-PVC.
    Don't forget the U in U-PVC stands for UN-maintainable.
    When these start to look a bit tired I can rub them down and give them a quick coat of paint so they look brand new again.
  11.  
    Posted By: Dominic CooneyDon't forget the U in U-PVC stands for UN-maintainable.


    Nah-not true. I fitted Upvc windows for my mother-in-law nearly 20years ago. Gasgets have shrunk and some of the sealed units have broken down. They were the cheapest on the market at the time as she could not afford better. She is about to have them overhauled. No problem getting replacement glazed units or gasgets. :bigsmile:

    Love to hear from a joiner in S Wales who can supply timber windows cheaper than they can be supplied in Upvc -not holding my breath though:bigsmile:
    • CommentAuthorEthics-Man
    • CommentTimeJul 20th 2007
     
    OK. We're not comparing like with like here, are we?

    Upvc windows are a travesty - they form a scourge on the face of the otherwise rather attractive town I live in. What's more, anyone concerning themselves with green issues should have no part in facilitating the sale or use of Upvc- the manufacturing process thereof is one of the most toxic of all industrial activities.
  12.  
    Ethics-man,

    Thanks for the advice about what I should be 'facilitating' but like I said before - Just because people cannot afford optimum solutions doesn't mean they cannot try their best with what they can afford to be green. My mother in law cannot afford new windows, replacement glazing units with new draught seals is a green thing to do.

    Regarding comparisons I'm not trying to compare anything, this thread is about warmedge spacers, which I beleive to be a gimmick. However, if you want me to compare frames then for a start you should know that in terms of energy conservation it is the glazing which reduces the lion's share of heat loss though a window, not the frame.

    Whether a frame is timber or UPVC is irrelavant in terms of maintenance, both can be maintained or even painted if dealt with in the correct way.

    Regarding upvs being a 'scourge' on the face of housing, UPVC frames can also be made to resemble timber sections. I agree that they should not be used where Architectural conservation is concerned but elsewhere people still have a choice in this country.

    Please tell me more about the toxicity of the upvc manufacturing process. Is it akin to petrochemically derived insulation? Should we also not facilitate the use of this?
    • CommentAuthorJohan
    • CommentTimeJul 20th 2007
     
    Marc,

    It's difficult to say if you will gain anything by using warm edge spacers. It very much depends on what U-value you're aiming for. If you're already at 1.2-1.3 W/m2K for the whole window then a warm edge won't improve it that much, but if you're looking at a window with a over all U-value of 1.5-1.6W/m2K then using warm edge technology should knock off roughly ~0.1W/m2K.

    - PVC windows are easier to break into then timber ones even though most sales reps will tell you it's the other way round...
    - Normally they have worse thermal performance with the same glass as the frames tends to be hollow...
    - Only reason I can see they are cheaper is because the quality is a bit so, so on some of them...
    - My parents have their original softwood (all beit slow grown) timber windows, fitted in 1921! Needs a bit of painting every now and then, but I'd like to see a PVC window 86 years down the line...
    - Personally I don't think they go particularly well on a >100 year old house either, but that's just a preference I guess...

    Why are even PCV windows discussed here?? Nobody can ever argue they are 'green'...
    • CommentAuthorMike George
    • CommentTimeJul 20th 2007 edited
     
    Posted By: Johan
    Why are even PCV windows discussed here?? Nobody can ever argue they are 'green'...


    Reality in my street is that 90% of the houses have upvc windows. It is greener to keep them maintained with replacement glass and seals than to rip them out and take them to landfil. Why can't upvc last a 100 years?

    Oh and by the way, isn't there a shortage of timber? prices are only going one way, as is the associated embodied energy of transportation etc.

    Last question, How many advocates of timber windows here have something to do with selling them?
    • CommentAuthorJohan
    • CommentTimeJul 20th 2007 edited
     
    Posted By: Mike George
    Reality in my street is that 90% of the houses have upvc windows. It is greener to keep them maintained with replacement glass and seals than to rip them out and take them to landfil. Why can't upvc last a 100 years?

    It's possible they could last for a hundread years I guess, as long as you make sure you protect them from UV. As I understand it the UV stabalising agents used in uPVC does decay over time eventually making the PVC brittle. Please correct me if my understand is incorrect.


    Oh and by the way, isn't there a shortage of timber? prices are only going one way, as is the associated embodied energy of transportation etc.

    Isn't there a shortage of oil as well?

    Last question, How many advocates of timber windows here have something to do with selling them?

    I don't sell any building material, not do I work in the building industry. I hope it's alright to have a preference even if you're just a private individual? :wink:
  13.  
    Here's an interesting article on the ills of PVC(uPVC) - and this is from a big business web-site, not some whacko environment group:

    http://www.fujifilmsericol.co.uk/NewsArticles/PioneerOK2.htm

    Perhaps this should be a new thread, but for now everyone seems to be interested in discussing it here, so I'll have me pennyworth.

    Timber is becoming expensive, but windows don't use a lot, do they?

    I don't have anything to do with selling timber windows, but I am about to make all the replacement windows for my own house using a friend's workshop - in oak or chestnut or probably.
  14.  
    Should have read "in oak or chestnut or probably". How can I edit once posted?
   
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