Tony L

Thanks for that. Building almost everything in block cavity walls sounds nice & straight forward. It would be good to get some opinions from others on which of these options (blocks vs timber) might be best for the wall with the orange lines drawn on, where "best" means a compromise between expense & a solution that will make it difficult for the builders to get wrong. My concerns are: If it's blocks: the outside wall becomes the inside wall & there's a significant cold bridge (perhaps I have stepped Marmox Thermoblocks along the line of the sloped roof). If it's timber, the junction with the pitched roof is easy because it's like any other dormer, but I don't know how the timber joins the block cavity wall across the front (where the longest blue line is in the Sketchup image above). Also, I was imagining wet plaster on the interior wall next to the stairs, going all the way from the ground floor to the top of the interior wall where it meets the high point of the vaulted ceiling, & if the top part is timber, there’s another problem to solve. Thinking about this has made me realise things don’t quite line up in the way I imagined. I’ve drawn the bedroom dormer & the edges of the pitched roof on top of the SE’s foundation plan. I’ve drawn the inner wall of the dormer in orange & the squiggles represent insulation against the dormer block wall that sits on top of the 215 wide blocks laid flat wall that the stairs might hang on. Have I got this right? Ideally, I’d draw all this up in 3D so I could understand it better, but I don’t have time to improve my very basic Sketch up skills (I paid someone to produce the images at the top of the thread). I can see I’m going to have to reposition the windows in the pitched roof, so they’re centred between the dormers, rather than the walls either side of the hall – I wonder if it will look odd from the inside. Alternatively, I could build out the cladding on the small dormer (ie more substantial battens), but then it won’t match the approved planning drawings, & it may make the pitched roof section between the dormers too narrow.

Thanks for explaining. I wouldn't want to trouble the mods with something so trivial, when it might divert your attention from the important business of house construction.

Thanks, @ETC. Are you suggesting I continue my block cavity wall up behind the areas marked in red, then I suppose, in timber in the parts marked yellow & orange (as I guess this will be cheaper/easier than strong lintels & blocks above the corner window) - please correct me if I'm wrong. If timber, what happens at the interfaces marked with the blue lines? I could continue the blocks behind the orange lines (2nd picture, below) -there’s a wall underneath that would support them, but then I have to deal with the problem of the block exterior wall becoming a block interior wall, as it passes through the sloped roof.

Thanks for pointing this out, but there's ample space in this dormer, so it will be drawn as a warm roof, once I have taught the arch tec what BH has taught me about roof systems.

That's good to know, thanks @Russell griffiths. I will paste that sentence into my drawing notes. & I must also compliment you on your wonderful view.

I'd be happy with that, if that's what everybody recommends - that's the way I designed it, then the arch tec "improved" my design. Yes, I accept my fantasy spec' glass meets glass cantilever lintel idea is out of the window, due to budgetary constraints. Maybe an internal post, so it still looks a bit special, is achievable, but more likely we'll end up with a big black post on the external corner where two windows meet.

[edit] there'd be a fancy staircase... Why can't I edit my post? I can see there's an argument for fixing historic posts, but this was less than an hour ago.

Just in case it’s relevant, here’s a drawing of the GF corner immediately below the dormer bedroom. The wall in the red ellipse is to be built from high density blocks laid flat, the idea being that if I have any money left as the end of the build is in sight, there’d be a fancy staircase hanging off this wall.

This design makes the bedroom 250mm wider than I’d envisaged in both directions, which would be great. However, problems I see include: 1) outside wall becomes the inside wall, with no cold bridge mitigation (perhaps a few Marmox Thermoblocks could help here) 2) no VCL or airtight membranes shown 3) Posi joists butting up to outside wall – I prefer the idea of hanging the joists from a ledger board that’s bolted to the inner leaf block work (or structural outer external stud walls). 4) incredibly skinny flat roof section, with parapets, but let’s ignore the roof for now; I may come back to that in a separate post. I should just add that these are supposed to be building reg. drawings & more detailed construction drawings will follow on, so perhaps I’m expecting too much from these drawings – am I? Q1) The first thing I need to understand is: would it be better to build most of the dormer in block & block, & if so, where does the block work end & how will the junctions from blocks to the sloping roof work? Q2) If it’s going to be better to build the whole dormer from timber, how will the vertical junction to the block work on the side of the house work (where the chimney used to be)? This junction could be hidden behind the cladding, so I’m not concerned about my cladding cracking, but I’m concerned about timber shrinking & pulling away from the masonry. & is it OK to build the whole thing off the outer leaf of the blocks?

The main building construction will be block & block, 150 cavity with blown beads. I’m aiming for high airtightness & heating on GF only (UFH). The outer blocks will be rendered, so it makes sense to go right up to the flat roof, at the highest point, in blocks, rather than build the first floor gable end in timber. Here’s the arch tec’s first attempt at the dormer.

I’m hoping you can help me steer my architectural technician in the right direction with these drawings he’s done for me. It seems the arch tec wants to build the 1990s way, with concessions to the latest building regs. I want to build the Build Hub way. I don’t have an architect (although I have recently looked into bringing one on board). I drew the house myself to achieve PP & now I’m relying on an arch tec to get my design through full plans BR approval & then do the construction drawings & notes, so I can continue building (we’ve already built up to the B&B floor). This Sketchup shows a very early draft design for my house (the chimney has since been deleted & other improvements have been made, including reducing glazing). I’m seeking advice on the detail for the big dormer that hangs over the edges of the first floor.

Thanks, @Iceverge & @Roger440. I've spent some more time on this this evening, including looking at some of your older posts, Iceverge, & I am convinced. Is Warmcel my only option or are there other suppliers I should consider?

I agree with your point re cavity walls, & having learnt so much from your other posts (thank you again @Iceverge ), I was able to tell my arch tech why he needed to change his drawings/notes to show blown EPS beads in my block cavity walls. I was thinking I'd be putting PIR boards between my rafters, with Gapotape around the sides. I'm planning to do this myself, to ensure good attention to detail & also save paying somebody else to do something that looks like it would be easy to do & also probably save money over blown cellulose (I haven't priced these two alternative methods yet). The rafters will be a mix of 150 x 50 & 200 x 50 C24 & there are no valleys, so there won't be any awkward compound cuts. Will PIR + Gapotape be a good solution for me, or should I specify blown cellulose? Video here, for anyone who hasn't seen Gapotape:

Our gutters will send the rain water into the same 110mm pipes that will take foul water away. Our builder built the drains without gulley traps. The BCO told him to fit gulley traps for the downpipes to feed into. My understanding is, this is to prevent smells coming up the drain pipes, rather than to trap debris that's washed off the roof. I could be wrong on the purpose of the traps, but they were a BC requirement.

Welcome to the forum, @mads. I'm doing the same as you - the bungalow has gone & the new build is just out of the ground. Have you got planning permission, yet? If not, you really don't want to be racking up architect fees on the design of every last detail of your new home, until you know the planners are going to let you have a house that's the size, shape & ridge height you're hoping for. Looking forward to hearing more from you, in future.

Congratulations. & I'm looking forward to hearing more in the coming months.

If you're in London, you could get this guy round to do a survey & quote. I've learned quite a lot from his Youtube channel. He puts a lot of thought into his work. londonflatroofing.co.uk

I'm no expert, but floor joists on ledger boards & hangers seems like an easier way of achieving airtightness. Perhaps the Tony trays are a good idea if you're going to be doing the work yourself, but I wouldn't want to leave Tony tray drawings with a team of builders to let them get on with it while I was off site. Some learned person, please enlighten me: why are Tony trays often the preferred solution over ledger boards? Is TF too flimsy for ledger boards? That can't be the whole answer, because I know TTs are used in blocks.

Hey @saveasteading. You misquoted me there. I am happy to blame the not terribly good forum software, rather than you, but I will still set the record straight: I was quoting @sb1202 & saying I disagree with his/her ludicrous ideas about debt collection companies.

I disagree.

That's right. They wouldn't be allowed to charge 8% a day, even if their T&Cs tell you that's what they will do. I received a letter from my builder's solicitor within the past couple of days that says, "This may include interest at 8% per annum above the base rate, a fixed sum for compensation for late payment and the costs of recovery.", so I'm guessing 8%pa above base is the max. they're allowed to charge.