CADjockey Posted March 9, 2023 Share Posted March 9, 2023 Afternoon, I could do with some help if you brains out there might be willing. I've got a newbuild underway, there are a raft of windows and a couple of bifolds, all in aluminium. and have just been informed that the whole house windos U value is calculating at 1.7. I gather the 2023 Part L requires 1.6 min ( or max if you like) but I don't know what the previous part L required to know if I'm in regs or not, I just can't find the prior documentation. We commenced building May 2022. Add to this picture the fact we are currently installing an MVHR system so will have no holes in the windows for the heat to leak out unfettered (trickle vents). Do I need to meet 1.6 legally or can you offset against the whole fabric of the building with the additional insulation under the floor screed or in the loft for example? Help! Link to comment Share on other sites More sharing options...
Conor Posted March 9, 2023 Share Posted March 9, 2023 Spend a bit more and get triple glazed or a better window system, if not too late. You really don't want to be scraping minimum standards. What's your overall building heatloss? Estimated EPC? We have a LOT of glass and the worst unit is 0.9 (bi-folds) and it's noticeably chillier in this room than other parts of the house. Windows are the weakest thermal element in a building and need the most attention. Link to comment Share on other sites More sharing options...
CADjockey Posted March 9, 2023 Author Share Posted March 9, 2023 (edited) I've put the order on hold until I get some sense. It seems slightly incomprehensible how they can potentially manufacture and sell something that is not to the required legal spec. Projected EPC is a high level B, but that was with windows that only the Scandanavians can make as far as I can tell. Edited March 9, 2023 by CADjockey update Link to comment Share on other sites More sharing options...
Conor Posted March 9, 2023 Share Posted March 9, 2023 Just now, CADjockey said: I've put the order on hold until I get some sense. It seems slightly incomprehensible how they can potentially manufacture and sell something that is not to the required legal spec. The size of the window makes a HUGE difference as it's usually the frame that's the weakest part. While the glass we had has a centre pane u value of 0.6, most windows average out at 0.8-0.9. Out of interest, who are you going with? Link to comment Share on other sites More sharing options...
CADjockey Posted March 9, 2023 Author Share Posted March 9, 2023 They are frame profiles from ALUK, local supplier. I may change the tiny window to a fixed unit and reduce the frame profile by half. MVHR will mean we don't need to open the window really anyway. Link to comment Share on other sites More sharing options...
saveasteading Posted March 9, 2023 Share Posted March 9, 2023 2 minutes ago, CADjockey said: not to the required legal spec. Nothing illegal about it. These are ok for a garage or gaden shed. Surprising though that these have been suggested. Even if they achieved 1.6, you would lose a lot of heat and they would be a bad idea. Link to comment Share on other sites More sharing options...
CADjockey Posted March 9, 2023 Author Share Posted March 9, 2023 Yeah, point taken. But they don't advertise them as shed windows do they? Link to comment Share on other sites More sharing options...
Mr Punter Posted March 9, 2023 Share Posted March 9, 2023 I am very surprised you got the SAP calcs to work. It should have been flagged as a fail at the design stage. Aluminium frames need to be very high spec to get a decent u value. The alu clad and composite ones are far more energy efficient. Even if you got the windows at the minimum spec I doubt you could compensate elsewhere sufficiently to get this to work. Get back to your SAP person and get them to re-run this. Link to comment Share on other sites More sharing options...
Conor Posted March 9, 2023 Share Posted March 9, 2023 How many openings do you have and how big are they? Drawings would help as well as screenshot of window spec, e.g. Link to comment Share on other sites More sharing options...
Kelvin Posted March 9, 2023 Share Posted March 9, 2023 1.7 is poor even if you could mitigate it with more insulation elsewhere it wouldn’t be advisable. As others have suggested you need to fit better windows. We compromised elsewhere in our design to fit triple glazed units. Our average U value is 0.78. Link to comment Share on other sites More sharing options...
CADjockey Posted March 9, 2023 Author Share Posted March 9, 2023 I might add at this point that we are replacing a house that was entirely of wooden construction (1950s), 150mm thick (empty) walls with no insulation, single glazing and even cedar shingle roof tiles. So in some ways, what we are building will be at least twice+ as insulated. If the GSHP, UFH and MVHR do their jobs we will be more likely to be complaining about solar gain from the south facing bifolds 😅 That said I am looking into better as I type... Link to comment Share on other sites More sharing options...
Conor Posted March 9, 2023 Share Posted March 9, 2023 2 minutes ago, CADjockey said: I might add at this point that we are replacing a house that was entirely of wooden construction (1950s), 150mm thick (empty) walls with no insulation, single glazing and even cedar shingle roof tiles. So in some ways, what we are building will be at least twice+ as insulated. If the GSHP, UFH and MVHR do their jobs we will be more likely to be complaining about solar gain from the south facing bifolds 😅 That said I am looking into better as I type... I feel cold just reading that! Yeah, but you should be comparing to the average modern standard. You want to be better than that. Re bi-folds... Be very wary of these esp the weather and air ingress ratings. We spent a lot getting a good spec model from solarlux. How big are they? You should have solar gain modelled. Oh, and a good quality triple glazed units will reduce solar gain compared to standard double glazed unit. Link to comment Share on other sites More sharing options...
Dave Jones Posted March 9, 2023 Share Posted March 9, 2023 1 hour ago, CADjockey said: They are frame profiles from ALUK, local supplier. I may change the tiny window to a fixed unit and reduce the frame profile by half. MVHR will mean we don't need to open the window really anyway. post the whole frame U value datasheet for the windows. Link to comment Share on other sites More sharing options...
JohnMo Posted March 9, 2023 Share Posted March 9, 2023 5 hours ago, CADjockey said: frame profiles from ALUK Have you reviewed all their profiles on the aluk website, some are good other are rubbish. Could you just change the profile to fix the issue. 6 hours ago, CADjockey said: MVHR will mean we don't need to open the window really anyway. Not sure where you get that idea. Windows still need to be opened to help shift the heat out in the summer. 5 hours ago, Conor said: might add at this point that we are replacing a house that was entirely of wooden construction (1950s), 150mm thick (empty) walls with no insulation, single glazing and even cedar shingle roof tiles. We moved out of 1830s house its just not relevant to your new build. A modern new build house with today's energy prices needs to be well insulated, cheap to run etc... Big difference with windows is the comfort factor sitting by the window, and general heat loss. The window will typically loose heat 10 to 15 times of an external wall. Sitting next to a window when it's -5 outside (this morning) can be comfortable or not. Triple glazing is comfortable, however the frames you suggest would be sucking the heat from you and feel quite uncomfortable. Link to comment Share on other sites More sharing options...
CADjockey Posted March 9, 2023 Author Share Posted March 9, 2023 27 minutes ago, JohnMo said: Not sure where you get that idea. Windows still need to be opened to help shift the heat out in the summer. In this room specifically, north facing and tree shaded, never gets overheated on this side of the house. Apart from that we are adding in a 'reverse' function to the GSHP to push excess heat back into the ground in the summer months if required, especially if the summers are going to get warmer in future! Link to comment Share on other sites More sharing options...
JohnMo Posted March 9, 2023 Share Posted March 9, 2023 It's great have other cooling means, for the summer but there will times when you need to cool house as well as heat the house during the same 24 hour period, so cooling the slab is not appropriate. Real example the other day, we had a low of -5 and high of +1, but the sun was out all day. So by 3pm the house was starting to get hot, so I opened the windows for an hour or so. If you need to cool a house naturally you do it by cross ventilation i.e you open windows and front of the property to wash air through the building. MVHR does little or no cooling due to flow rates being low. 1 Link to comment Share on other sites More sharing options...
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