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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorRex
    • CommentTimeApr 3rd 2021
    What ho one and all,

    SHMBO has sorta put her foot down and really, really, really wants some kind of solar reflective film on the first floor south facing windows.

    I am not a fan of the reflective unless all windows are done, otherwise, the house looks a bit rinky dinky. So I at least, have to go through the motions of investigating.

    We have 3g glazing and the EN coding reveals that it should be OK for any self adhesive film. But they are argon filled (I think) with the various internal coatings, etc, etc. However, this web site (https://www.purlfrost.com/mirror-and-tinted-window-film/reflective-window-film/srf-50-light-reflective-window-film/) under the ? buttons, indicates that triple glazed with air gaps are not suitable for adhesive film.

    How can this be? Or is it an air gap v. argon issue?

    Certainly mine are supposed to be argon filled, but how would I know and after 10 years, I assume it has seeped out.
    We have a large area of west facing glazing which is triple glazed argon filled with coatings. We had it fitted with solar reflective film (Clearview Vista80X) three years ago which has proved to be very effective. It's not cheap though. I don't have the cost to hand unfortunately.

    • CommentAuthorRex
    • CommentTimeApr 4th 2021
    Thanks for the link, useful to know.

    Did you apply it yourself or had a contractor? Seems the Vista80X is designed for external use; presumably not evidence of pealing around the edges?
    We had it installed as the glazing is over 4m high but I wouldn't try it myself. There's no evidence of pealing but as with all external films you have to just wash the window down to prevent scratching.
    Posted By: PeterStarckas with all external films you have to just wash the window down to prevent scratching.

    What do you mean by this?

    is the reason it's external because you must not install internally with 3g windows?
    • CommentAuthorRex
    • CommentTimeApr 6th 2021
    "because you must not install internally with 3g windows"

    Is this true and if so, why not?

    I have seen that 3g argon filled are not recommended to have film applied but I don't' understand why not.

    I have applied some UV with slight darkening to some 3g argon filled interior windows and no problems, but SHMBO would like something reflective to prevent heat build-up. And who am I to argue?
    Some films are suitable for internal and some for external application. AIUI external films are heat reflective and if used on the inside will cause a heat build up within the glass unit.
    • CommentAuthorEd Davies
    • CommentTimeApr 7th 2021
    Posted By: PeterStarckAIUI external films are heat reflective and if used on the inside will cause a heat build up within the glass unit.
    So what do the non-reflective films do with the energy?

    I've no idea really, but on purely first-thought physics grounds I'd think reflective films would be more likely to be safe on either side whereas ones which absorb the heat would need to go on the outside so they can lose the heat better.
    ? One or more panes may be coated within the gaps of the 3g, to absorb certain IR wavelengths but not others. If the reflective film is on the inside, the waves have to pass through the coating twice on the way in and again on the way out, which might not work the same as reflecting them before they come in ?

    • CommentAuthorRex
    • CommentTimeApr 7th 2021

    Having spoken with two separate reflective film suppliers, you are essentially correct. One suggested that the heat build-up could cause sufficient 'thermal expansion' that the glass could break, although unlikely if toughened but not recommended.

    The other suggested that with toughened glass, there is unlikely to be any problem, but the interior surface can become almost dangerously hot. If that is the case, surely it would not be much use as the heat would be on the inside that that is what I am trying to avoid.

    The best practice is external film and Sun-X (mentioned by Peter) told me they leave a 3mm gap around the edge, then apply a vinyl sealing tape to prevent the film lifting at the edges. Not really happy with that as a long term option but what do I know?

    The good news is that now SWMBO is on the fence and tending towards 'no go' for reflective film.
    • CommentAuthorRex
    • CommentTimeApr 8th 2021
    I guess this is the definitive word.

    Chatting with a neighbour who is a retired architect and used to work in the Middle East. He said that for most buildings, reflective film is specified for the 2g windows, and is applied in the factory, to the inside of the external glass. this not only reduced heat build-up within the 2g unit, but also eliminates any weathering issues. He said that external reflective film does require an edge sealing of some sort, but the general weathering / cleaning of external film will eventually lead to it breaking down in some way; either micro scratching and/or the edge sealing tape giving up.

    His recommendation is that if there is any advice not to apply reflective film to the inside of 3g, argon filled, low-e units, there is a good reason so best practice, don't do it!

    SWMBO seems to have taken that on-board, much to my relief!
    Maybe something like this would work https://www.quarzwerke.com/en/products/high-performance-fillers/acrysmart/ Thinking of using it with translucent insulation on the south (50m2) facade of a house from roof ridge to ground to eliminate the need for a heating system or HRV as there's excess heat in Nov+Jan.
    • CommentAuthorjms452
    • CommentTimeApr 11th 2021 edited
    Posted By: RexSHMBO has sorta put her foot down and really, really, really wants some kind of solar reflective film on the first floor south facing windows.

    Presume the problem you are trying to solve in summer overheating...?
    If so have you thought of an alternative solution...

    solar reflective internal blinds
    shade cloth
    brise soleil
    external shutters
    • CommentAuthorRex
    • CommentTimeApr 11th 2021
    Holy schmoly. That is amazing. Guess is is not dissimilar to photo-reactive glasses. Not sure how I could use in with existing glazing apart from fixing in front of the existing.

    Dread to think of the cost.

    I will bookmark the site as it is an interesting material.

    Toodle pip
    • CommentAuthorRex
    • CommentTimeApr 14th 2021
    Oh dear God. She is like a pit bull!

    Since solar reflective film is off the table, her waking hours are now devoted to trying to find a solution to reduce the interior temp.

    Next idea is a 'solar blind' hanging from the wall and lower end can be swung up to be clipped onto something at the lower end of the skylights. It will look bloody awful but that is not her concern!

    And in my opinion, it will not work as if the interior is already hot due to sunlight passing through the skylights, noting will reduce the internal temperature.

    We have some black-out curtains in one of the front rooms. I really hate the things; the only thing they do is make the room very dark, so why did we pay for large 3g? Certainly the 'shade' makes a psychological cooling experience, but as for the actual interior temp, I don't think it makes much difference.

    But what do I know? She won't be satisfied until the interior looks like rubbish1
    • CommentTimeApr 14th 2021
    Posted By: jms452external shutters

    or external blinds

    plus active ventilation
    Check out Passive Stack Ventilation and Shading. Is there a window or roof-light you can leave open upstairs?
    • CommentAuthorHollyBush
    • CommentTimeApr 14th 2021
    Posted By: jms452solar reflective internal blinds
    shade cloth
    brise soleil
    external shutters

    I have a similar problem and this summer will hopefully build a pergola in front of the windows / patio doors to act as a brise soleil - I should be able to put clear plastic on top to use the patio on more occasions, maybe leaving furniture out and will be looking at blinds or a sail on it if still too hot.
    • CommentAuthorRex
    • CommentTimeMay 13th 2021
    A final update.

    SWMBO has decided that we will have an external blind on an opaque glazed roof window and black-out blinds on the two internal roof windows.

    Reasoning is that the external is one that is accessible from just reaching up. It was installed as a future proof for an additional bathroom.

    The other two are light the entrance area and first floor landing and can be reached with an extension pole which we already have. These can then be opened a closes as desired.

    Personally, I am not in favour of the black-out but then, I would just tolerate the heat, which we have been doing for the past ten years and open a few windows (oh no, you cannot do that, the dust will blow in!)

    My personal belief is that the internal black-out will have little effect on the heat build-up as they are inside the house and it is too late. The external will provide shade to the window and will almost certainly be more effective, but also a greater hassle in opening and closing, let alone cleaning.

    I am sure I will be proven correct but will hold back on the "I told you so" comment.
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