lizzie Posted August 3, 2018 Share Posted August 3, 2018 Well thats an end to the window film quest for me. The definitive answer is no window film is suitable for my laminated spec glass. The chances of the glass cracking are near certain. Window film (of any brand) is not suitable for my laminated or for float glass. If you have toughened glass then you will be fine with film as it has been heat treated so the stresses are removed. For me now its back to praying for cooler weather whilst I try to find a blind solution that wil work at a sensible price too. Link to comment Share on other sites More sharing options...
Vijay Posted August 3, 2018 Share Posted August 3, 2018 Just cos I'm nosy, why does a film make the glass crack? Link to comment Share on other sites More sharing options...
lizzie Posted August 3, 2018 Author Share Posted August 3, 2018 it is the stress caused by the heat - laminated and float glass are not heat tempered as toughened is and the heat build up from film causes stress......thats a short version of a very technical answer from 3m an other film supplier and my glazing via Internorm Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 3, 2018 Share Posted August 3, 2018 30 minutes ago, Vijay said: Just cos I'm nosy, why does a film make the glass crack? Not at all sure. I can state with certainty (based on measurements made of the glass surface temperature) that both the inside and outside panes of our glazing now run a great deal cooler with the external heat reflective film than they did without it. In other words, the external long wavelength IR reflective film has reduced the glazing temperature swing by a lot - at least 20 deg C, possibly more, and this, in turn, has significantly reduced the stress in the glazing elements. The opposite would be the case if we had tried to use an internal long wavelength IR reflective film - that would have definitely caused the glazing to run hotter in bright sunshine. It's why it's critical to make sure that the analysis is done with the film on the correct side of the glazing. Link to comment Share on other sites More sharing options...
lizzie Posted August 3, 2018 Author Share Posted August 3, 2018 I can only cite what 4 independent sources have told me...3 film supplier/manufacturers and the glass providers themselves Do you have laminated glass @JSHarris ? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 3, 2018 Share Posted August 3, 2018 Just now, lizzie said: I can only cite what 4 independent sources have told me...3 film supplier/manufacturers and the glass providers themselves Do you have laminated glass @JSHarris ? No, ours is toughened, but that makes no difference, as it runs cooler with the external film fitted and so is subjected to lower thermal stress. The films reflect the heat away before reaching any of the glazing elements, so they all stay cooler - it's pretty simple physics - the external film decreases the long wavelength IR emissivity of the very outer surface, so as a consequence heat is reflected away before it reaches the glass, so the glass stays cooler. Link to comment Share on other sites More sharing options...
Vijay Posted August 3, 2018 Share Posted August 3, 2018 17 minutes ago, lizzie said: I can only cite what 4 independent sources have told me...3 film supplier/manufacturers and the glass providers themselves Do you have laminated glass @JSHarris ? Hi Lizzie, Did any of them give any sort of explanation or reason? Vijay Link to comment Share on other sites More sharing options...
lizzie Posted August 3, 2018 Author Share Posted August 3, 2018 (edited) The reason they wont use it on laminated or float is that is that those types of glass have not been heat treated like toughened. They are very specific about it laminated and float glass are different animals to toughened which has been heat treated and so not vulnerable to the stress in the same way as non heat treated glass, they all say they the same they can’t all be wrong. If you look around you will find this information on glazing federation etc web sites....laminated and float glass are most definately not deemed suitable for any external film Toughened can have any film you like and get the sort of results you get with no risk of cracking. The heat treatment changes the structure of the glass somehow I think and makes it tough and not prone to heat stress. The opinions i have had are for external film, internal was never considered an option. Edited August 3, 2018 by lizzie Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 3, 2018 Share Posted August 3, 2018 17 minutes ago, lizzie said: The reason they wont use it on laminated or float is that is that those types of glass have not been heat treated like toughened. They are very specific about it laminated and float glass are different animals to toughened which has been heat treated and so not vulnerable to the stress in the same way as non heat treated glass, they all say they the same they can’t all be wrong. If you look around you will find this information on glazing federation etc web sites....laminated and float glass are most definately not deemed suitable for any external film Toughened can have any film you like and get the sort of results you get with no risk of cracking. The heat treatment changes the structure of the glass somehow I think and makes it tough and not prone to heat stress. The opinions i have had are for external film, internal was never considered an option. But simple logic suggests that if a film lowers the temperature of the glazing, and reduces the range of temperature that the glazing sees, then the stress must be lower, and hence the risk of cracking must be lower. External low emissivity film MUST reduce the glazing temperature, and hence the stress in the glass, and it makes no difference what the glass is, as the external film has to result in it running cooler. 1 Link to comment Share on other sites More sharing options...
newhome Posted August 3, 2018 Share Posted August 3, 2018 Maybe they just don't want to take the risk of any liability if something were to go wrong? Link to comment Share on other sites More sharing options...
Dreadnaught Posted August 3, 2018 Share Posted August 3, 2018 (edited) I wonder of its to do with ageing. With new film, @JSHarris point would be right. But what about some years hence, with potentially ragged and patchy film. Could the stresses from areas of hotter and cooler glass then cause a problem I wonder? Similarly, what if it was a poor quality installation of film, with areas of hotter and cooler glass, could the stresses be problematic? Edited August 3, 2018 by Dreadnaught Link to comment Share on other sites More sharing options...
lizzie Posted August 3, 2018 Author Share Posted August 3, 2018 Who knows but one of the opinions comes from 3m suppliers of Jeremys film. 3 installers have refused to fit film after initally quoting then checking spec of my glass and saying sorry not on that glass.....one said if pressed they would fit but only if signed all sorts of waivers and disclaimers, who would be mad enough to subject tens of thousands of pounds of intenorm glass to that and void their internorm warranty too. The toughening process changes the glass structure and that makes is less vulnerable to heat stress. Laminated and float are not heated, laminated just has the lamination added to glass...float.....that lamination process gives no heat stress protection and film even external causes heat stress. I have been quizzed not only on the specific glass I have but the aspect, orientation, overangs and shading from trees etc. The questions from different people have essentially been the same which tells me there is some sort of guide. I am given to understand that laminate is more prone to cracking than toughened even without film.....and I had laminated as I wanted the extra security I had no idea it would be such an issue. Link to comment Share on other sites More sharing options...
Mr Punter Posted August 3, 2018 Share Posted August 3, 2018 I am very intrigued by this. I am also looking at heat reflecting film (bet they are all on a bonus, together with air con, ice creams and swimming pools!) for some south west facing glazing. It seemed fairly hot even on cold clear days earlier on. @lizzie why is your glass so "well" engineered? We have some river wall retaining glass and that is only 25.5mm laminated. Is there a consensus on what is the best supplied and fitted option for external film that does not look obvious and anyone know the cost? The development has 13 patio doors - each about 5.5m2. Link to comment Share on other sites More sharing options...
lizzie Posted August 3, 2018 Author Share Posted August 3, 2018 @Mr Punter god knows I just bought what internorm salesman said. I knew nothing about the technicalities he told me laminated was more secure so I had it. Cost more than toughened too. Are your development doors toughened or laminated? my overheating is an issue on south and west elevations, west is worse than south on mine. If you are toughened then the film world is your oyster. I can look out some msq prices I got. The films I have all seem to have a slighly blue/grey tinge, that is the ‘clear’ option. Top price is 3m with other brands about 20% cheaper for pretty much same spec I found. Incidentally I had external condensation on the two major problem windows this morning, first time since about April. Link to comment Share on other sites More sharing options...
Ian Posted August 4, 2018 Share Posted August 4, 2018 Online guide to compatibility of various solar films with various types of glass inc toughened and laminated https://www.windowfilm.co.uk/content/files/1045/The Window Film Company - 2016 Film Compatibility Chart.pdf Link to comment Share on other sites More sharing options...
lizzie Posted August 4, 2018 Author Share Posted August 4, 2018 Thank you @Ian page 1 item 4 in the notes - if your window is triple glazed please avoid fitting window film. 1 Link to comment Share on other sites More sharing options...
dpmiller Posted August 4, 2018 Share Posted August 4, 2018 "please avoid (and call the office for advice)" looks rather different to "you must not". Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 4, 2018 Share Posted August 4, 2018 I'm 100% certain this is just ass covering because they don't understand the science and are reluctant to say yes to something that hasn't been fitted and tested for 10 years or so. The science is pretty obvious - reduce the IR emissivity and the glass runs cooler when it's sunny and the internal stresses are a lot lower, end of. The stresses in any glass, even laminated, will be when the temperature differential across it is at its highest - it's why pouring boiling water onto ordinary glass breaks it - the face subject to the boiling water heats up quickly and expands, the other face is cooler and takes time to heat up, so there is a pretty high shear stress inside the glass, as the heated side tries to rapidly expand whilst the co0ler side expands far more slowly - the glass literally tears itself apart. Lower the emissivity of the outer face of a glass sheet with a film and it will never get as hot in sunlight as a glass sheet of standard emissivity (which will be around 0.8 to 0.9 - glass absorbs long wavelength IR pretty well, much the same as a wall. FWIW, some glass manufacturers now produce glass with an external low emissivity surface, specifically to reduce overheating in buildings. There is a high demand for this in offices, where overheating is often a problem and costly to overcome with air conditioning or chillers. Pilkington Solar -E, for example, behaves just like glass with a low emissivity film on the outside, and it's available as laminated glass. There's no technical difference between coating the outer surface of the glass with a low emissivity coating and applying a low emissivity coating using a film that I can see, other than one is a bit neater, If you're glazing units are Pilkington, then perhaps what they really want it for you to change them for Solar-E, which may well be another reason to say no to a low emissivity film... Link to comment Share on other sites More sharing options...
lizzie Posted August 4, 2018 Author Share Posted August 4, 2018 1 hour ago, dpmiller said: "please avoid (and call the office for advice)" looks rather different to "you must not". and when office is contacted with glass spec the answer comes back no. I dont have pilkington glass I have Internorm supplied glass. They say no too and I am not about to ignore the weight of professional expert opinion and experiment with thousands of pounds of glass and void my Internorm warranty. I may be foolish in lots of ways but not with this - window film is something that I have extensively researched and each time I get the same answer back so I will not ignore it. Link to comment Share on other sites More sharing options...
PeterW Posted August 4, 2018 Share Posted August 4, 2018 Out of interest @lizzie what does the Internorm warranty cover ..?? I’ve never seen one that covers glazing units for 25 years - they normally only get 10 - so would be nice to know that some suppliers are putting trust into their glazing systems ..! Link to comment Share on other sites More sharing options...
lizzie Posted August 4, 2018 Author Share Posted August 4, 2018 Its 10 on the glazing longer on the frames in the warranty book it tells you to avoid attaching ‘foils and paints’ after....this includes films. They suggest shading with blinds or overhangs. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 4, 2018 Share Posted August 4, 2018 AFAIK, Internorm don't make glass or glazing units, they will fit whatever meets the spec they need, so probably either Saint Gobain or Pilkington. Saint Gobain do SGG Planitherm Total + that is very similar to Pilkington Solar E, and is available as a low external emissivity laminated glass. The whole argument being put forward against external films seems based on fake science to me. This is the second summer we've had external low emissivity coatings on our glazing and my contact thermometer always shows that the surface temperature, inside and outside, of the glazing with the low emissivity film is a lot lower than it is for the glazing on the same elevation that doesn't have the film. The temperature differential between the internal and external faces is also always lower for the glazing with the film on, so any thermally-induced stresses in the glass must be lower. I'm convinced that the manufacturers simply haven't conducted long term tests on the specific glazing system you have, and so are just covering their backsides by saying "no", even though they know it's completely illogical. 2 Link to comment Share on other sites More sharing options...
Dreadnaught Posted August 4, 2018 Share Posted August 4, 2018 (edited) 3 minutes ago, lizzie said: they suggest shading with blinds or overhangs. Of course, blinds and overhangs can have the other advantage of allowing passive solar gain in the winter months, when it will be welcome, unlike film. Edited August 4, 2018 by Dreadnaught 1 Link to comment Share on other sites More sharing options...
lizzie Posted August 4, 2018 Author Share Posted August 4, 2018 @JSHarris that may well be true but I’m not prepared to risk it I will find another solution that is compatible with manufacturers guidelines and warranty conditions. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 4, 2018 Share Posted August 4, 2018 On the topic of overhangs, because "normal" glass has a high emissivity, it will absorb a lot of heat when exposed to long wavelength IR from the sun and get very hot. This means that glass external sunscreens can work very well - they will absorb the heat from the sun but let the light through, so as long as the external sunscreen has a gap between it and the house it will work just as well as any other sort of external shade. Glass canopies are an option, perhaps. Not massively expensive, won't reduce light levels, tend to look OK on a fairly contemporary house design and can be easy to fit. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now