Ian79 Posted June 30, 2022 Share Posted June 30, 2022 Here for some advice. Have a brand new flat roof going on single storey extension, with lantern. The electrician has just drilled holes in the new roof timbers which seem very near the bottom of the joists. Can anyone advise whether this is acceptable, and what the solution is if not? Guess should get BC back to inspect before they are covered up - they should have a view, right? for context, the tripled joist shown is approx 4m long, 2x 6. The hole is maybe half an inch from bottom edge… thoughts welcome - don’t want to confront builders unnecessarily, if a non-issue - but equally an expensive project that want done correctly / to last! Link to comment Share on other sites More sharing options...
Russell griffiths Posted June 30, 2022 Share Posted June 30, 2022 Should be 50mm up to protect it from screws. One hole in that location is not going to affect anything. But it is good practice to put it central of the joist. 1 Link to comment Share on other sites More sharing options...
Onoff Posted June 30, 2022 Share Posted June 30, 2022 https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists Link to comment Share on other sites More sharing options...
saveasteading Posted June 30, 2022 Share Posted June 30, 2022 A notch or hole near top or bottom will greatly affect the strength and bounce, unless near the end. Just being a single hole isn't the point. Joiners and plumbers don't usually appreciate/understand this and can be dismissive. However in this case it is reasonably far up plus the additional timbers are adding to the strength. Link to comment Share on other sites More sharing options...
SuperPav Posted June 30, 2022 Share Posted June 30, 2022 It's bad practice and technically not following the guidance, but no real risk of anything happening there unless there's going to be an elephant playing a grand piano on the roof. I wouldn't lose sleep over it. Link to comment Share on other sites More sharing options...
Ian79 Posted June 30, 2022 Author Share Posted June 30, 2022 Funny you should mention a a grand piano as that is what is going in the room - but no elephant and definitely not up top….! Thanks for useful and generally reassuring thoughts. In summary, I take the consensus view to be “not ideal / fully following the guidance but not a disaster” Some concerns over insulation too: The main kingspan insulation is above the joists / OSB - I.e a warm deck. Though I do have concerns that there should be some insulation around the lantern opening where it protrudes above the deck as this looks a potential cold spot (yellow highlight). Similarly, in the eaves there are voids all along one side where there is nothing but fascia board between the plasterboard ceiling to be and the outside world (orange highlight shows the white inside of the fascia board at the lhs of this photo)….is kingspan appropriate here (as used on the main deck) - or would wool insulation be better? Will be raising these issues with the builders next week…. Link to comment Share on other sites More sharing options...
Marvin Posted July 1, 2022 Share Posted July 1, 2022 Hi @Ian79 Yes lantern walls needs insulating. Yes fascia area needs insulating. You need to achieve a thermal resistance all around your habital space. If you can find a route where you can go from the inside to the outside without going through the appropriate amount of thermal resistance, that route will become warmer in the summer and colder in the winter. As you say, these will become cold spots and some can cause condensation issues, espically high up areas where warmer and potentially moister air can hit a cold surface. (Have seen this with uninsulated loft hatches) As to what type of insulation, it depends what standard of thermal resistance is supposed to be achieved. Remember that 200mm of wool has about the same resistance as 100mm of rigid PIR. Good luck. M Link to comment Share on other sites More sharing options...
Ian79 Posted July 1, 2022 Author Share Posted July 1, 2022 Thanks for that. Just raised this with builders who seem surprised - said in their view it needed ventilation in eaves - but they have agreed to put in some kingspan…will be watching how much… building control seem unconcerned / relaxed about such details, which i find surprising. Also, having done some reading have concluded they have missed out the vapour control layer that seems to be required as part of the warm deck roof - fairly sure the kingspan went straight on the roof deck. Again, should this have been flagged by building control? (they have had plenty of chance, on more than 1 visit) How big an issue is this / should I be raising / demanding they put right? Very late in day as rubber membrane is on and roof all sealed - though joists still exposed… Link to comment Share on other sites More sharing options...
Big Jimbo Posted July 1, 2022 Share Posted July 1, 2022 Your builder seems to have very little idea about warm roof, or insulation. Hate to think of how many extensions / builds he has done. Link to comment Share on other sites More sharing options...
Ian79 Posted July 1, 2022 Author Share Posted July 1, 2022 31 minutes ago, Big Jimbo said: Your builder seems to have very little idea about warm roof, or insulation. Hate to think of how many extensions / builds he has done. I’m not impressed so far. Though equally, maybe naively, I expected a bit more rigour from the council building control officers… I at least am lucky enough in a position to watch them / technical enough to understand how things should be done (with help of Google and forums like this!). Should I be insisting that they dismantle the roof to install a vapour barrier below the insulation (would be a big battle, and very inconvenient for us as well as them!) ? Or is there any other vapour control mitigation that could be done from inside before plasterboard goes on? Or is do we just live with it and assume / hope ok…! Advice gratefully received… Link to comment Share on other sites More sharing options...
Miek Posted July 1, 2022 Share Posted July 1, 2022 You could install a VCL between the joists and the plaster board. Might be worth filling the void with insulation wool as it's so cheap and easy yo do. If you do just take care to uprate any electrical cables, or at least think about that side of it. Link to comment Share on other sites More sharing options...
ADLIan Posted July 1, 2022 Share Posted July 1, 2022 Do not install further insulation between the roof joists. Creates a hybrid roof that is not recommended by industry or BSs and greater risk from condensation. Link to comment Share on other sites More sharing options...
saveasteading Posted July 1, 2022 Share Posted July 1, 2022 Building inspectors do some spot checks but are not expert on everything, and don't work for you. So please continue to check up yourself. Link to comment Share on other sites More sharing options...
Roger440 Posted July 1, 2022 Share Posted July 1, 2022 5 hours ago, saveasteading said: Building inspectors do some spot checks but are not expert on everything, and don't work for you. So please continue to check up yourself. This^^^^ For the most part the whole building control process is a joke, a bad one at that. They are only there to ensure that minumum requirements are met. In reality they dont even manage that. System is broken. Needs fixing. Wont get fixed. Link to comment Share on other sites More sharing options...
Dave Jones Posted July 2, 2022 Share Posted July 2, 2022 On 30/06/2022 at 20:43, Ian79 said: Funny you should mention a a grand piano as that is what is going in the room - but no elephant and definitely not up top….! Thanks for useful and generally reassuring thoughts. In summary, I take the consensus view to be “not ideal / fully following the guidance but not a disaster” Some concerns over insulation too: The main kingspan insulation is above the joists / OSB - I.e a warm deck. Though I do have concerns that there should be some insulation around the lantern opening where it protrudes above the deck as this looks a potential cold spot (yellow highlight). Similarly, in the eaves there are voids all along one side where there is nothing but fascia board between the plasterboard ceiling to be and the outside world (orange highlight shows the white inside of the fascia board at the lhs of this photo)….is kingspan appropriate here (as used on the main deck) - or would wool insulation be better? Will be raising these issues with the builders next week…. holes are nothing to worry about. cant see any evidence of how the room below is going to be air sealed from the roof makeup to prevent the transition of moisture into the insulation and becoming trapped. the same level of insulation should be applied externally to the roof light upstand. Link to comment Share on other sites More sharing options...
Temp Posted July 2, 2022 Share Posted July 2, 2022 (edited) On 01/07/2022 at 10:20, Ian79 said: Thanks for that. Just raised this with builders who seem surprised - said in their view it needed ventilation in eaves - but they have agreed to put in some kingspan…will be watching how much… Have them read this.. https://www.cncbuildingcontrol.gov.uk/wp-content/uploads/2019/07/CNCD-053-Warm-Roofs-Easy-Guide.pdf Quote Warm Deck/Roof A warm deck/roof is where the insulation is placed on top of the rafters/joists and the roof covering is then placed over the insulation. No ventilation is required for these types of roofs. Cold Deck /Roof A cold deck roof is where the insulation is placed between the joists/rafters or in between the ceiling joists in the case of a pitch roof. Ventilation is required for these roofs Edited July 2, 2022 by Temp Link to comment Share on other sites More sharing options...
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