Tony L

I'm just guessing, but I should think people use the other Catnic lintels - the kind with a thermal bridge, because they're cheaper.

May I just check, the tray (blue line above) goes beneath the lintel, as shown - I think it might go above. & I'll just remind you, I know next to nothing.

The Catnic split lintels look good to me. I know next to nothing, by the way, so don't take this as advice. I'm just wondering how these compare, performance wise, with the (presumably cheaper) option of two separate steel reinforced concrete lintels.

Good analogy. @Iceverge talks a lot of sense, as usual. My own experience was that the council didn't take too much notice of the neighbours' objections, so it was just the planning dept I needed to work on. Eventually, I was able to wear them down & achieve PP for something that was worth building. Once I had PP, I was able to bolt on a little extra something, via a non-material amendment application, that I had removed from one of my original designs, as part of the compromise arrangement to achieve PP. The planning dept were more concerned about the ridge height than any of the many other aspects of my design that they didn't want. I chopped the top off my pitched roof design - so I have two ridges, with a long flat roof in between. It will still look like a conventional house when viewed from the street/driveway entrance & the house still has good depth - just an idea you may be able to use. Achieving PP can be a frustrating & lengthy process, but I'm sure you'll have something you're really happy with by the time you finally get there.

I think the recessed full height glass into the double height entrance hall is a really nice feature - the rising sun likely won't get in there as it moves around to the living room side in the morning. I'm no expert, but I think you're going to have too much solar gain from all the south facing glass to the living room side. Perhaps you're planning to spend the extra for solar reflective glass. If your architect is used to working to PH standards, perhaps he can plug your design spec' into the PH software that will tell you about solar gain, cooling requirements, etc.

That's been on my to do list ever since the 'van arrived (ie make a skirt on a lovely warm summer's weekend, to feel the benefit in the winter) - I know that's what you meant.

The situation isn’t clear: it’s her building, but it’s in your garden. How did that happen? It sounds as though you already own it if it's in your garden. You don’t say how much land is included in the building’s sale. I’m assuming this land is adjacent to your garden. Does it share a boundary with any other properties? Might other people want to buy it? How much it’s worth entirely depends on who’d like to buy it & how much these prospective buyers are willing to pay. If it’s in your garden & you’re the only prospective buyer then it’s not worth very much (unless you have let slip that you want this building very much). If the vendor might be selling their house any time in the next decade & the building might form part of that sale then that will make it worth more than “not very much”. I’ve perhaps not been very helpful so far, but it may help you if I explain, I bought a strip of land (approx. 2m x 16m) to increase the size of my very small back garden. This was worth a lot to me, because adding 2m to the length of my small garden has made a big difference. I offered £5,000 for the strip of land to the developers that were building the neighbouring new build + I said I’d pay all the solicitors’ fees. The developers said they’d spoken to the local estate agent (whom the developers & I both know & trust) & the agent said it was worth £10k. I said, it probably is worth £10k, but nobody other than me will want to buy it & I only have £5k to spare, you’re not going to miss a tiny slice off your big back garden & it’s £5k straight onto the margin you’re making on the new build house, which you definitely will notice. He agreed. I did some drawings for my solicitor, who acted for both parties (£400 four years ago). I think there was some small land registration fee to pay as well. The developer built & paid for the new fence on the new boundary. The entire process was very easy – certainly a lot easier than hiring a builder to complete some seemingly straight forward tasks. Hope this helps.

Thanks, @Russell griffiths. My understanding now is: I should build almost all of the dormer by continuing the ground floor cavity wall up to the flat roof on top of the dormer, as suggested by @ETC . I made a mistake with my mark ups on the previous Sketchup & there’s a new one below showing the section that will be in timber, behind the diagonal orange lines. I’m thinking the problem with lateral loads is now solved, because the outer edge of the timber section can be built off the pitched roof rafter, like a normal dormer. The cavity will be closed off with a cavity closer, where the blue line is. My problem now is, how do I attach my first studs to the ends of the 100mm wide blocks on either side of the cavity, where the blue line is. I don’t think I should be drilling into the ends of the blocks, in the same way you could drill into the face of a block wall. Perhaps I should use L-shaped brackets fixing into the centres of the full block faces. & should I put frame sealant on the ends of the blocks before offering up the timber stud or is there a better product to get these to fix together well & allow for the timber to expand & contract? Perhaps this is not worth worrying about so long as I get my airtightness detail right across the masonry-timber junction. Any thoughts on the above would be most welcome.

I don't think that's an option now. For reasons I won't trouble you with (as there are so many), the B&B floor is already built, with the 215mm sleeper wall beneath. Also, I wouldn't really want to waste space with a cavity wall inside the house when I'm sure there will be a solution based on a 100mm wide block wall.

Here's an update of my diagram showing the dormer plan on top of the foundation plan (just so we can see how it all lines up). Any comments on this (positive & negative) will be gratefully received. Are there any colour conventions I’m flouting as I draw my diagrams (eg airtight layer is always shown in red) or does everybody just choose any colour they fancy as they make each drawing? I’m using MS paint, & I can’t figure out how to get the neat S shaped squiggles that usually represent insulation.

Thanks @Russell griffiths. That sounds like a good idea, but it’s going to need some thought to make it work. Although you say “cavity wall coming up against the roof”, my current understanding is it won’t be a cavity, it will just be a continuation of the inner leaf from the cavity at the front of the house, & this single skin block wall will sit on the edge of the 215 wide block wall, so the wall from the hall up to the landing area above will be a nice flat surface, ready for wet plaster. My current front runner for the cladding (Dura Cladding Flush Resist) is designed to fit to 25mm Dura Aluminium bearers (will be 50mm by the time I’ve got them going both ways for vertical cladding). They’re expensive, of course, so I’ll be using wood for the cross battening for the walls other than this awkward cheek. I didn’t know anything about EWI until I started Googling 30 min.s ago. I realise now, I can’t just stick 135mm+ EWI against the single skin block wall then 50mm crossed battens, due to the lateral loads (the cladding needs to be 185mm+ off the wall we’re talking about). I found this diagram in a cladding handbook. There’s some cold bridging, but it’s only a small section of wall, so perhaps I shouldn’t worry about that. I’m assuming wooden battens with EWI in between is not going to work, so perhaps I could source some bigger aluminium brackets/battens to get to 160 off the wall, with 150mm EWI embedded in these then the 25mm Al horizontal battens on here (not sure if the air gap is desirable/necessary behind composite cladding) - I could pack the whole 185mm out with EWI. The heaviest part of the triangle (at the front of the dormer cheek) will be going onto the small section of cavity wall, so the battens won't have to reach out very far here, which is good. Any thoughts on this anyone? Do I need to think about using VCL with EWI in this scenario?

We got ours from O'Leary caravans OX2 9BY. It's a 37 x 12ft. They told me how to prep' the site then they delivered it, moved it into position, levelled it. My partner did all the negotiation & bought it. I didn't see it until it arrived, but I was very pleased when I first saw it, & it's been a good buy. Perhaps it helped that she has Irish roots & an Irish name, but I'm giving these guys 10/10 for customer service & value for money. It looked great on the outside, but very tired on the inside. We removed all the built in furnishings & redecorated. We turned the master bed room en suite into extra storage. We replaced the built in seats with our sofa from the old house + an armchair. Flowery curtains replaced with pale grey roller blinds, no more flower prints on the walls. It now looks very modern inside. If I'd had more time, I'd have crawled underneath to fit insulation, starting with the middle section where all the pipes hang down. I must add that, although it's a great place to be when the weather's right, we both have other places where we can stay, so we're not there all the time. Ours didn't come with a boiler & we're just making do with oil filled radiators. Good luck.

Sorry: on re-reading I see this is ambiguous because I used orange again on the next drawing. It's the dormer cheek marked with diagonal pale orange lines on this drawing, below, I'm struggling with.

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.