Pocster Posted February 17, 2023 Share Posted February 17, 2023 This light well is outside the insulated build . So has zero insulation or ventilation. As you can see it gets condensation on the inside of the glazing . Doesn’t block the light - but looks a bit crap . I’ve no intention of drilling the upstand it sits in for ventilation. Was wondering if a pipe up in the light well and some kind of extractor at the bottom of it would be sufficient to drag the air and moisture down …. 🤔 Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2023 Author Share Posted February 17, 2023 Link to comment Share on other sites More sharing options...
Thorfun Posted February 17, 2023 Share Posted February 17, 2023 50 minutes ago, pocster said: no idea about your condensation issue but I like those tiles. have you got a link to them? we have plans for a textured wall in a couple of places with nice wall lighting to give a cool effect. I keep trying to persuade SWMBO that something like that would look great but she's not so sure about it. Link to comment Share on other sites More sharing options...
Mr Punter Posted February 17, 2023 Share Posted February 17, 2023 Does internal conditioned air get into the light well? Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2023 Author Share Posted February 17, 2023 2 minutes ago, Mr Punter said: Does internal conditioned air get into the light well? Nope . Triple glazed window between build and light well Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2023 Author Share Posted February 17, 2023 14 minutes ago, Thorfun said: no idea about your condensation issue but I like those tiles. have you got a link to them? we have plans for a textured wall in a couple of places with nice wall lighting to give a cool effect. I keep trying to persuade SWMBO that something like that would look great but she's not so sure about it. I bought loads . But I use them in ‘ isolated ‘ places ; otherwise I feel it’s over use . Will dig up the link - they weren’t expensive. No grouting . But will ‘ drift ‘ so need to be careful 1 Link to comment Share on other sites More sharing options...
Radian Posted February 17, 2023 Share Posted February 17, 2023 1 hour ago, pocster said: I’ve no intention of drilling the upstand it sits in for ventilation. As you've already identified, this is the root of the problem - whatever vapor content the trapped air has will condense out once the inside face of the glass drops below the dew point. The delay between the mixing of the internal and external air is what causes this to be a problem so ventilating it to the outside to increase the rate of mixing is the most effective solution. If you're triple glazed below, what's the issue with getting cross-ventilation into the space? Link to comment Share on other sites More sharing options...
Mr Punter Posted February 17, 2023 Share Posted February 17, 2023 I think it needs ventilation. Your pipe and extractor could be good. 1 Link to comment Share on other sites More sharing options...
Radian Posted February 17, 2023 Share Posted February 17, 2023 1 hour ago, pocster said: Was wondering if a pipe up in the light well and some kind of extractor at the bottom of it would be sufficient to drag the air and moisture down But unless hermetically sealed above it will just pull more outside air into the space. If it was hermetically sealed then it would be exchanging inside air which would be even worse in terms of dew point. Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2023 Author Share Posted February 17, 2023 7 minutes ago, Radian said: As you've already identified, this is the root of the problem - whatever vapor content the trapped air has will condense out once the inside face of the glass drops below the dew point. The delay between the mixing of the internal and external air is what causes this to be a problem so ventilating it to the outside to increase the rate of mixing is the most effective solution. If you're triple glazed below, what's the issue with getting cross-ventilation into the space? Well ! I tested that . Build nice and warm ; light well (expletive deleted)ing freezing . I left the ‘window ‘ open thinking mvhr on the build might circulate the air . But no joy . Assume I need an inline extractor - with pipe up to the glass ??? Link to comment Share on other sites More sharing options...
Radian Posted February 17, 2023 Share Posted February 17, 2023 1 minute ago, pocster said: Well ! I tested that . Build nice and warm ; light well (expletive deleted)ing freezing . I left the ‘window ‘ open thinking mvhr on the build might circulate the air . But no joy . Assume I need an inline extractor - with pipe up to the glass ??? No, your light well has a fair volume of air in it. That air needs to be at the same temperature and humidity as the outside air. If you 'extract' it what will take it's place? 1 Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2023 Author Share Posted February 17, 2023 Just now, Radian said: No, your light well has a fair volume of air in it. That air needs to be at the same temperature and humidity as the outside air. If you 'extract' it what will take it's place? Ok - erm . So what should I do to remove the excess moisture?? . Are you suggesting heating the light well ? Link to comment Share on other sites More sharing options...
Radian Posted February 17, 2023 Share Posted February 17, 2023 2 minutes ago, pocster said: Ok - erm . So what should I do to remove the excess moisture?? . Are you suggesting heating the light well ? No. That will probably make it worse. As I said earlier it's outside air that you need in the light well so the same air is on both sides of the walk-on glass. If you could control the temperature and RH of the trapped air to an extent such as to always keep its dew point below the outside temperature you'll be some way to eliminating the condensation but it would take some serious engineering/expense. 1 Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2023 Author Share Posted February 17, 2023 1 minute ago, Radian said: No. That will probably make it worse. As I said earlier it's outside air that you need in the light well so the same air is on both sides of the walk-on glass. If you could control the temperature and RH of the trapped air to an extent such as to always keep its dew point below the outside temperature you'll be some way to eliminating the condensation but it would take some serious engineering/expense. Oh ! There I was thinking a simple fan / vent was the solution 🙄. It ‘ feels’ drafty in the light well ( not sure why / how ) - circulating that air any help ? Link to comment Share on other sites More sharing options...
Radian Posted February 17, 2023 Share Posted February 17, 2023 Think about what we do with sheds to stop condensation wrecking our stuff... We leave big gaps for drafts. Same with cold lofts. Dissimilar air (RH and temperature) is what results in condensation. Having the same conditions on either side of the glass is key. Think about a freestanding sheet of glass outside. You wouldn't expect to see condensation form on it - except for when the weather changes from cold and dry to warm and damp. In this case there will be a short time before the glass warms up when it's below the prevailing dew point and vapour in the air condenses on it. The faster it reaches the same temperature the less condensation risk there is. This is why you need to ventilate the light well to the outside. If your walk-on glazing was triple glazed and your light well insulated then your inside window could be left open and no condensation would form on the underside of the walk on glazing. But you didn't build it like that. 1 Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2023 Author Share Posted February 17, 2023 7 minutes ago, Radian said: Think about what we do with sheds to stop condensation wrecking our stuff... We leave big gaps for drafts. Same with cold lofts. Dissimilar air (RH and temperature) is what results in condensation. Having the same conditions on either side of the glass is key. Think about a freestanding sheet of glass outside. You wouldn't expect to see condensation form on it - except for when the weather changes from cold and dry to warm and damp. In this case there will be a short time before the glass warms up when it's below the prevailing dew point and vapour in the air condenses on it. The faster it reaches the same temperature the less condensation risk there is. This is why you need to ventilate the light well to the outside. If your walk-on glazing was triple glazed and your light well insulated then your inside window could be left open and no condensation would form on the underside of the walk on glazing. But you didn't build it like that. Ok . So I need to get the lighwell temperature to match the outside temperature yes ? Link to comment Share on other sites More sharing options...
jayc89 Posted February 17, 2023 Share Posted February 17, 2023 Can you walk on that? Link to comment Share on other sites More sharing options...
Pocster Posted February 17, 2023 Author Share Posted February 17, 2023 48 minutes ago, jayc89 said: Can you walk on that? Of course !! Link to comment Share on other sites More sharing options...
Radian Posted February 17, 2023 Share Posted February 17, 2023 2 hours ago, pocster said: Ok . So I need to get the lighwell temperature to match the outside temperature yes ? Less than or equal to the outside temperature and for the RH to be less than or equal to the outside air. Equal is your friend because it means all you need is to bring the outside air inside. To lower the RH would mean actively condensing the vapour i.e. a local cold spot sometimes AKA a dehumidifier. Or refrigerate the walls of the lightwell. It's all too complex because it needs power, and equipment, and somewhere to dump the condensate. How much simpler then to bore a bunch of freaking holes in the upstand 😆 Link to comment Share on other sites More sharing options...
Onoff Posted February 17, 2023 Share Posted February 17, 2023 1 hour ago, jayc89 said: Can you walk on that? Does it fit would have been my question! Link to comment Share on other sites More sharing options...
Onoff Posted February 17, 2023 Share Posted February 17, 2023 Call me mad but how about some large, moisture hungry plants in the space below the lightwell? Link to comment Share on other sites More sharing options...
Radian Posted February 17, 2023 Share Posted February 17, 2023 OK, yes, you're obviously mad. But how cool would that look? Tree ferns lit in green at night and with little plastic dinosaurs. Probably just increase the condensation though.😂 Link to comment Share on other sites More sharing options...
Onoff Posted February 17, 2023 Share Posted February 17, 2023 17 minutes ago, Radian said: OK, yes, you're obviously mad. But how cool would that look? Tree ferns lit in green at night and with little plastic dinosaurs. Probably just increase the condensation though.😂 https://www.express.co.uk/life-style/property/1689261/Mould-condensation-how-to-prevent-get-rid-of-best-houseplants Link to comment Share on other sites More sharing options...
Pocster Posted February 18, 2023 Author Share Posted February 18, 2023 10 hours ago, Radian said: OK, yes, you're obviously mad. But how cool would that look? Tree ferns lit in green at night and with little plastic dinosaurs. Probably just increase the condensation though.😂 Did actually think about plants in there and whether they would add / subtract from the moisture . I might be able to stick a hole in the insulation outside the build ( but next to the light well ) . Wouldn’t be at the top though ( assume I really need it as near to the glass as possible ) . Link to comment Share on other sites More sharing options...
Pocster Posted February 18, 2023 Author Share Posted February 18, 2023 Got another one of these light wells to do soon ( ish ) . Going to build it in a similar way but leave a nice hole at the top . Get the glass on and see what happens . A proper comparative test @Radian ! Drilling the other to make a hole of some kind will be a pita ; so want proof of theory . Link to comment Share on other sites More sharing options...
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