Tony L
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Everything posted by Tony L
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& here’s a detail for where the 3 degrees centre section meets the 42 degrees section. I’ve added in some L shaped plates (green) to prevent rain being blown up the roof & into the vent void. This same detail could be used where the the 42 degrees sections meet the backs of the 3 degrees flat roof sections over the dormers.
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I’ve added to a drawing I found online to show how the ventilation & drip edges will work at the apex of a standing seam roof, at 3 degrees .
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I’m sorry to make the task of resolving these problems more difficult but, there is no way I’m going back for a new planning permission. I don’t want to spend time explaining the long history of how I eventually achieved PP for something that I actually wanted to build: I need to focus on what’s ahead. That's not far off what happened, yes. I don't know anything about site poured lintels. I think I ought to minimise the number of technologies I must learn about to get this house built - I'd really want to learn about it because I wouldn't trust a builder to do it properly, if he thought I didn't understand the process. My learnings about works up to DPC (mostly from BH) saved me at least £7,000 after the builder took advantage of BC's requests for changes & tried to rip me off. I like glulams too. Are these OK to stick through the inner block leaf, so they're flush with the cavity (wrapped in VCL, of course)? Sorry, I can't visualise this. Are you talking about the long inner walls that the rafter ends sit on or the gable end walls (that will have ladders going over them, for some roof overhang)?
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Thanks again for this, @Iceverge. I like what you’ve drawn. Sorry, the roof can’t be at 45 degrees because this would stretch the flat roof section at the top & make the building look very different from the approved plans. 400mm EPS in the walls is appealing, but it would make the inside too small & it can’t happen because [I’ll be in big trouble with you when you read this] the substructure is already built. For the benefit of anybody reading this whilst researching your possible self build, & to save @Gus Potter & @Iceverge the trouble, l will just explain: building the substructure before your superstructure drawings have been finalised is a very bad idea.
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@Iceverge. Thank you again for your work on this. I'm pleased you support the idea of "flat roofs" being standing seam at 3 degrees. Let's hope the planners consider this a reasonable fall for my approved flat roof sections (I'm not intending to ask them). I've been working on some detail drawings for the roof intersections this morning. I have to go out now, so I'll aim to I'll finish these off & post them this evening, along with responses to the other points from your post above.
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Thanks for all this, @Gus Potter. I've designed all my metal web floor joists so they're inside the inner block leaf; those that meet the outer wall will be hung on ledger boards. I've done this to make air tightness easier to achieve, & there's a thermal break benefit too. With the ideas @Iceverge has provided, the tops of the rafters will all be insulated, but at the bottom they'll run from inside to outside over the wall plate, of course. The SE has specified UB19 for the beam in the section picture you posted. This is a fair bit chunkier than I was expecting - only because I can lift the mild steel box section back bone chassis of an old Lotus with ease, & they're very strong. These UB19s (there are 6 of them) are in lengths of max. 4.55m, so that's 86KG to lift into place. I think the top of a UB19 will be 7.9mm thick & the web will be 4.8mm, so it will be good to have insulation along the edges of these UBs, & it's worth considering what's going on at the beam ends too. My plan was to wrap the beam ends that penetrate the inner cavity block leaf with VCL membrane, bring the membrane inside & fix it to the wall (I've got notes on how to affix). The cavity between the block inner & rendered block outer leaf is only 150mm & will be filled with EPS beads. I was thinking it may be worth sticking a rectangle of super insulating something or other inside the cavity on the beam ends. If anyone has any suggestions please let me know. & is it worth sticking a block of high R-value something on the top flanges? There's not much gable end wall going on top of these UB ends. I looked for high R-value padstones, but I gave up this search & decided to rest the beam ends on regular padstones.
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Stairs have more headroom than building regs require - so no problem bringing the roof at the front back towards the centre of the house. Ventilation - I'm aiming for good airtightness & MVHR - you have possibly been misled by the MEVs the AT drew in, despite my clear brief, "air tight, + MVHR". Fire: I read the building regs document. I think my design is compliant. My only concern is BC may demand doors across my kitchen, that opens up into the hallway & stairs. No big problem if the doors have to go in here - it will just be an unwelcome expense. Also, most of the steels will have to have intumescent paint, rather than be boxed in, because they have joists attached.
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@Gus Potter& dealing with your previous post: I am grateful to you for taking the time to explain your thoughts on this - including those I don't like & those I disagree with. I don’t have time to explain the history of how I got to this point, because I have big demands on my time at the moment, in addition to the self build project, but just taking a few of your points in order, from above. The SE has been impressive, so far. He seems completely undaunted by this project. My architectural technician (& he’s not the first one I’ve had on this project) is a huge disappointment. If I start to explain why, I’ll be here all night. Agree: his designed insulation envelope is not good enough. I am having to work to fix this – not something I expected to have to do. Rain will fall straight into the cavity behind my cladding (will be composite or Millboard type, so the top of the cladding is OK getting wet) – some advice says a 6mm gap above the ventilation void (which will be 50-100mm, depending on how much building out we do to get the cladding to where we want it to be, will be enough to vent & will not let much rain in. I could easily have the drip edge from the flat roof running over the top of the cladding, whilst allowing 50mm vented space all the way out of the top of the vent cavity then under the drip edge. It’s not the look I wanted, but if it’s necessary, that’s what I’ll put on the drawings. I’ve got draft drawings from the SE, so I know where all the steels go & this is how I know my rafter depths are different for the two pitched roof sections. Re: “can I get someone to build & at what cost”. I don’t see how I can stop & do that now. I need to get the drawings done properly then I can get a BoQ/build cost. “blindly” I don’t agree with this characterisation of my approach to this project, although I don't mind you telling me this is what you think. “If I go back to the beginning, how much will that cost me?” – difficult to say in financial terms & I'm not going to waste time thinking about this right now, but “going back to the beginning” would cost me the relationship I have with the person who’s paying for the other half of all this. Due to a looming planning permission deadline, the old house was demolished 2024. Self building was her idea, fortunately.
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Thanks, @Gus Potter. Dealing with your most recent post first: I know how I want the vent at the top of the standing seam to work (& be drawn). Just to remind you, I didn't do the drawing; an architectural technician drew it for me. I was quite alarmed when I saw this detail in his draft drawings. It's completely rubbish. I thought he'd know how to do all this stuff. To be fair, although his connection between sloped section & flat section had been given no thought at all, his detail drawing for this corner did actually show vents, but the system he'd designed was preposterous, ugly, expensive & funnelled rain in under the standing seam. I have lost confidence in him, but I think if I put in the required effort, he will produce good drawings in the end. I gave him my PP drawings (which I did draw myself) & my draft SE drawings (fortunately I have full confidence in my SE). I also gave the him a load of notes & had a long meeting with him & he assured me he could do the work to a high standard. So I know how the flat roof drip edge & standing seam vent will work together. What I'm concerned about is the cold bridge created by the steel. In the AT's drawing there's no insulation all along the top corner. With the adjustments @Iceverge has suggested, there'll now be 100mm PIR insulation at this steel's top outer edge. I wonder if this is enough. I could drop the steel down 100mm & have a 50mm birdsmouth cut in near the end of the joist so 100mm of the joist would sit on top of the steel & this would add 100mm mineral wool over the steel too; the only thing lost is ceiling height from the very high ceiling over the landing, but that's not a big problem.
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@Iceverge. This is really good. Thank you so much. I may have to come back with a few more questions as I continue the work of preparing my document that will instruct the arch tec' how to draw my house properly, but I think your explanations may give me enough to get me most of the way there with this task.
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Does aerobarrier negate need for airtightness detailing?
Tony L replied to SBMS's topic in Ventilation
Here's an excerpt from the email that came with a quote I received in August 2025, if that's any help: "Pleased to provide a quotation for the airtightness works in your project - to view in full, please click the Quotation link above. For the supply and installation of the AeroBarrier system in your 190m2 project in [my postcode], your installation would be £2,538.40 (ex VAT but zero rated on new builds). This price is inclusive of travel, labour and materials and we do not charge a premium or any added fees for you end airtightness target (even to high performance levels)." -
@Iceverge, I’m really grateful for your help on this. I like the idea of all the structural elements being within the VCL. Thank you for showing the build-up stages, rather than one diagram of the finished make up. Although your roof build up is thicker than I’d like, I think I can slim it down a little by replacing your 100 x 50 timbers under the standing seam with 18mm OSB/ply then, if I use the 150mm rafters my SE specified for the roof across the back, rather than the 200mm rafters the arch tec’ drew, the sloping roof at the back is only 29mm thicker than what’s been drawn, which should be easy enough to accommodate in the updated version of the BC/construction drawings. Others may not like the 100mm mineral wall inside the VCL – I’m OK with this if you are. I have two questions about this 100mm mineral wool: 1) Does the mineral wool sit on top of the plasterboard (which is where my arch tec’ has it in his flat roof build ups) or should it be pushed up against the 11mm OSB that’s sitting on top of the rafters? 2) Could I full fill between my rafters with mineral wool? The SE has spec’d 150mm rafters at the back of the house & 200mm rafters at the front. I don’t need a service void above the sloped ceiling sections. I may have got this wrong, but when you say, “cover the entire roof & dormers with a layer of 100mm PIR”, I think you’re suggesting this should include the front dormer wall & cheeks as well, so the build-up is much the same as the roof you’ve drawn, but with the stud walls fully filled with insulation – is that right? If so, I don’t much like the idea of my cross battens that will support my vertical cladding, hanging off 100mm of PIR - that would make the PIR a structural element. I have seen C-shaped structural GRP channels, around 100mm deep, so I could investigate the cost of using these, vertically, against the outside of the dormer stud walls. I could then cover the outside of the studs with PIR, tucked into the C-channels, cover all this structure in breather membrane, then affix my cross battens & cladding. If all of the above is feasible then I could delete my arch tec’s dormer wall spec’ element, “140mm PIR cut in between studs at 400 centres”, & replace this with 140mm mineral wool, which would be much easier to fit between studs & noggins than PIR, leaving no air gaps & providing the added benefit of sound insulation. I realise there’d still be some cutting of PIR to do around the outside, but there’d be no noggins & we could fit the first GRP channel, then the first board, then fit the next channel, pushing it up against the previous board – sounds easy.
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The point @SBMS & I are trying to make is: if you fill in No 6, so you're asking Ubakus about a roof, rather than just the lower part of a roof, Ubakus will say it's not OK.
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I'm not. The current plan is to have standing seam on the pitched roof sections only. The flat roof covering has been specified as GRP, although I'm not convinced this is my best option. I do wonder, whether having a 3 degrees standing seam roof over these 55m2 of flat roof areas might be no more expensive than GRP, because the standing seam team will be on site, anyway & it will be one less trade to worry about, one less thing to have to learn about & SS would likely be more robust than GRP. My concern about anything other than metal, is birds pecking through it.
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You need to fill in No. 6 with a roof covering - you can't leave OSB as your top layer.
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It should be, but I don't think it will be very warm in the middle of this make-up. The section I'm talking about is above the Rockwool, & in winter, cold air will be flowing through the void behind the cladding (a wide void due to cross battening for vertical cladding) then there's nothing but a sheet of OSB between this flow of air & the void made up from the firings & the empty space between the joists. I will ask the arch tec' to swap the fall around anyway, so rain drains towards the front rather than towards the back.
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All good points from your post, above, thank you, @ADLIan. Yes, the arch tec's design with extra insulation beneath the warm roof was an alarm bell for me, which is one of the reasons I've asked about these roofs. But, I've seen at least one builder here, who seems to know what he's doing, saying he's done almost exactly what my arch tec' has proposed.
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I must explain: the ridge height absolutely cannot go any higher. I could get away with adding 100mm to the height of the dormers if I have to, although I think reducing ceiling heights by 100mm, or more, is probably a better strategy (due to PP restrictions). There’s plenty of spare space inside my vaulted ceiling, in the section under the long flat roof, so this could be used to make this roof section deeper. The eaves across the front of the house is higher than PP allows, & I will ask my arch tec' for the wall plate height across the front to be reduced by 140mm to bring the eaves height down to where it should be, at around GL+2700mm. This will have the effect of pushing the 42 degrees front roof towards the middle of the house, making the flat roof across the ridge narrower by about 150mm. Rather than have the flat dormer roofs sloping backwards to drain onto the standing seam, as drawn, my plan is to ask for these to be changed to drain into a front corner, into a downpipe concealed behind the cladding then straight into the hidden gutter (from the 5450 wide dormer in bottom left) & onto the standing seam for the other two dormer flat roofs. The drip edges on the long flat roof that spans the house have not been properly drawn. I’ll get these changed so the drip edges overhang the standing seam ends by 100mm+, then the 50mm void under the standing seam will vent between the seams, under the long drip edge, which will protrude from the flat roof & lay on the seams. I realise there are many bad things going on in this section drawing. My plan was to ask about the spec’ for the make up under the flat dormer roofs first, then ask for help with some of the other details once the flat roof make ups have been resolved. I’m very grateful for your interest in my project. Thank you, @Iceverge & anyone else that's able to help.
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Here's an early Sketchup image, to help you understand what's going on with the galleried landing & porch. The front of the house faces north - the north pointers on the arch tec's drawings are all incorrect.
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Here's a section drawing. I’ll also upload 3x pdfs so you can see this more clearly. TonyL 300-04 - Section AA.pdf TonyL 300-08 - NB 1st RT03 is RT02 Proposed Build-ups.pdf TonyL 300-03 - Proposed First Floor Plan.pdf
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The sloping roofs will be standing seam. & I plan to get the roof make up below the standing seam changed to this, although with deeper Rockwool & insulated PB. There are small rooms under the sloping ceilings at the back, so I don’t want to make the roof much thicker than the 296mm drawn; this might include 200mm Rockwool + 72.5 Kingspan K118 (only 60mm of the 72.5 is phenolic insulation). More insulation would be better, I know.
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Thank you @Iceverge & @ADLlan. I'm having a horribly busy day at work. I'll try to get back to you within a couple of hours. Anyone: why aren't my @nametags working as they usually do?
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If you're lucky, one of the mods will do it for you. This looks really nice & I look forward to hearing more as the work progresses. I'd cut back on some of that glass. I'm guessing you have lovely views to the south, so all those windows will stay, but I'd say you should consider deleting some of the windows down the long sides & making some of the windows that are retained smaller. It will make your house cheaper to build & cheaper to heat/cool. I'm envious of your integral garage.
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I don’t like this because: 1) There’s a big wedge of cold, damp air in the middle 2) Even if we fix 1) above, I’m concerned the 120mm Rockwool above the ceiling may insulate well enough to make the OSB supporting the PIR cold enough for condensation to form (& the VCL is above this OSB, so it will have a significant supply of moisture to it). 3) It’s a bathroom – even if we swap out the KNAUF Soundshield plasterboard for a water resistant plaster board, we may still need something else to stop moisture rising into the structure . Would we? I don’t know – I’m a novice. The same roof make up is specified over the bedrooms too. I need to ensure these rooms will be quiet. I’d be happy to hear the rain as I drift off to sleep, but rest of the household demands absolute silence. I’m thinking I should change the design so we have, from top down: 1. roof covering – which may or may not be not be GRP (let’s not get into that now) 2. 18mm OSB (can I get away with 11mm to save £330 over approx. 55m2)? 3. 200mm PIR with top layer Kingspan TR47, which has built in falls, meaning firings will not be required lower down (I haven’t priced TR47 yet). Taped at joins & in two layers with offset joins . 3b & is it worth the expense of Gapotape (or perhaps cheaper alternative) all around the perimeter, which will mostly be OBB3? 4. VCL – If somebody could tell me which one to go for or what the spec ‘should be (in terms of SD value? – I don’t know) that would be helpful. 5. 18mm OSB 6. 170mm C24 joists, or perhaps fatter 150mm joists, if SE allows 7. unvented air between the joists 7b. For outside walls, do I stuff 100mm (or more) rockwool against the sides, (along the joists on the long side & between the joists on the cheeks), so the roof insulation is “tucked in”? 8. 100mm Rockwool fitting tight between the rafters – this is for sound insulation, really, but it’s making the void cold. This sits directly on top of 9) 9. 12.5mm plaster board (water resistant type if it’s a bathroom) 10. resilient bars 11. another 12.5mm plaster board (water resistant type if it’s a bathroom) Once I’ve settled on a make-up, I can start worrying about the edges/interfaces.
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& here’s part of the detail drawing for the bathroom roof.
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