Tony L

Thanks, @torre. I think attaching my gutter solution to the plumb cut rafter feet will be less costly than cutting all the rafters. I may end up with something like this.

Thanks @torre. I don't follow what you're saying, but your comment makes me think I could have aluminium bits made up to match the roof & conceal the gutter, which would be attached to the plumb cut on the rafter feet & look something like this.

I'd like something like this:

To me they're very different, because with my design I have a neat sloped roof panel that's at 42 degrees from the highest point to where it ends, with a gutter concealed in the 42 degrees slope. With the arch tec's first draft drawing, the gutter is tacked on to a projection from the roof edge. So the drawings show this:

I think I've seen rafter ends (feet) being extended on a YT video, which I'm unable to find. Like the light coloured rafter extensions in this drawing, below, only they'd be twice as deep. Then I could end up with something like the 2nd drawing below, where the orange outline shows the added rafter end & the pale blue shows my hidden gutter. The roof is overhanging my porch in this detail drawing, by the way - just in case you were wondering where the wall is that supports everything.

Yes, I'm far more concerned about airtightness than insulation (I learnt that here on BH), but should I really not worry about the cold bridge highlighted by the red line in the drawing below - so there's a direct route from the cold outside air, through some steel & plaster, to the inside of the house? + thanks for the "not doubling up on the K118" tip. I could put 60mm or so of PIR, or some other type of insulation, behind the insulated board - it would be easy to do & this in one of the few areas of the house where I don't care about losing a small amount of interior space. Would that be OK or is that a bad idea because the K118 insulated board is airtight?

Thanks for that, @DevilDamo. He's made many sloppy errors all over these drawings. I'll also ask for the 72.5mm insulated plaster board, which is the only insulation running along the length of the top edge of the (over 4m long) steel beam, to be doubled up (if not tripled or replaced with something better), as think this would be sucking heat out of the house all winter long, if it were left as it is. 72.5mm Kooltherm K118 is only 60mm of phenolic + 12.5mm plaster. I don't think 60mm insulation is enough here, is it? & my brief said, "hidden gutter". What he's drawn is something that pokes out half a mile from the roof edge & is very obviously a wide gutter.

I'll ask the arch tec, although I think @Nickfromwales is probably right - thanks Nick. Strange though, that there's no other lighting shown anywhere else. I asked here first, because I my list of requests for change & questions is already so long, I wanted to slim it down a little, & also do my best to understand what's going in these drawings before I go back to the arch tec to ask for changes.

Another TAFKAP. Could be. The Andrew Formerly Known As Prince. My new name for him is Andy Battenberg. Being a clever chap, you will already know, @SteamyTea: his ancestors anglicised the Battenberg name because they no longer wanted to be associated with Mr Kipling's best selling cake.

I'm checking through the drawings my architectural technician has done for me. Can somebody let me know what this architectural symbol means please? It's used in the detail drawing, below.

Thanks for the reminder - same probably goes for GRP, which I may end up with. I understand GRP can be very noisy as it expands & shrinks, although expansion ridges can be built in to mitigate this. My arch tec has specified phenolic insulation for the sloped roof, which I suspect is almost as bad at providing noise insulation as PIR. He's specified PIR under the GRP flat roof.

What improvements could I suggest? One solution would be to put the steels lower down, so their tops are where their bottoms have been drawn. This eats into my narrow vaulted ceiling space, but it could be a price worth paying. Another solution would be to have them lower by half the height of the steel & the sloped roof joists could then have a cut in to accommodate the steel, which the joists would rest on. I don’t think we could maintain the height of the steels & move them closer to one another (even just 100mm, to allow 100mm of insulation to be added), could we? I don’t know how we’d deal with the connection of the sloping roof joist ends if we did that – perhaps just by adding blocks of C24 where we already have C24 bolted into the steel I-beam, to make the connection to each joist end. I wish I had time to draw all these ideas. Perhaps I should be aiming for a warm flat roof with up to 200mm of PIR on top of the rafters.

The detail picture shows the vent at the top of the standing seam is open to the rain – not just the odd raindrop - another drawing shows that all the rain from the flat roof will drains off both long edges (14m along the front of the house, 14m along the back of the house) onto the sloped roof. Surely this detail should show the flat roof edge overhanging the top of the standing seam (perhaps right on top of the seams) – so air just vents out where the standing seam finishes & rainwater from the flat roof drips onto the standing seam 80-100mm beyond the end of the standing seam?

Here's what my arch tec has come up with...

There’s another aspect of the roof design I would also like to receive advice on. Due to the LA planning dept. limiting the ridge height, my roof design has two conventional sloping sides meeting at a flat roof running the full width of the house. The flat roof is 14200 x 1800mm. I am happy that the arch tec hasn’t drawn a parapet flat roof, but I don’t like the flat roof design he’s come up with, especially the way it interfaces with the sloping roof sections & the way the two steel ridge beams run the entire width of the house, with next to zero insulation on the outside edge & only 72mm insulated plasterboards across the whole of the bottom of 102mm wide steel beams. This looks like 28+ metres of unnecessary cold bridge to me. Am I right to be concerned about this? Maybe I shouldn’t worry about it & I should just focus on building something I can afford, & making sure it’s super air tight. What does everybody think? Here’s an early draft roof plan from my SE, showing steel beams, in dark blue.

Thanks, @Russell griffiths & @Nick Laslett. I've watched quite a few of Steve Roofer's YT videos, but I hadn't seen that one. He's very good. This is so difficult - even an expert like Steve Roofer doesn't have all the answers. He's got tons of good ideas & he explains things very well, but rather than say, "Do it exactly like this.", he's saying (in this video), "Talk to the manufacturers.", to choose a suitable membrane. Very interesting that he recommends sandwiching the outer membrane between the battens & cross battens - so it's in the middle of the 50mm vent cavity under the tiles, standing seam or whatever - that idea wouldn't have occurred to me.

Sorry, I'm too busy to dig that information out for you. I engaged him quite some time ago, although I have only recently received the full set of draft drawings that I was supposed to receive early in July. He came highly recommended by a prominent BH forum member.

Thanks, @Russell griffiths & @saveasteading. Pagurek offer this make up, below, as one of their suggested options. I will perhaps choose to upgrade from OSB to wood. I'm not keen on ply as it warps so much when it dries out after becoming damp. I'm happy enough with the standing seam above the 50mm air gap. It's the other aspects of the roof build up I need help with, please.

Well, yes, if you're not going to do it yourself, then you'll have to pay somebody to do it. You could get an M&E consultant, such as @Nickfromwales, who posts here a lot, to do the whole lot, or you might get one company to deal with CH & hot water, & a separate company to deal with MVHR, if that's what you're having. & if you're not having MVHR, I should think you just need to mention the trickle vents in the windows & give the spec' of the extractors in the bathrooms & kitchen. Somebody who knows a lot more than me will be along to help you out tomorrow.

If I increase to a 300mm I-joist, the U-value comes down to around 0.129 W/m2K. The arch tec’s roof is just 290mm thick, which is useful. The notes say it has a U-value of 0.11W/m2K. Actually, it says “0.11/m2K”, because he missed the “W” (Watts). Another thing he’s done, just to confuse us all, is he’s used label numbers that don’t correspond to the positions of the materials within the roof make up – so number 1 is the standing seam layer, on the outside, but number 5 (50mm air cavity) sits on top of the rafters (number 4) & the insulation between the rafters (number 6). Confused? I am. I think he’s drawn the Tyvek membrane on top of the 50mm cavity, rather than beneath it, & he hasn’t spec’d the battens for the 50mm cavity; should he have? Perhaps, 50 x 50mm C24 battens should be specified? I don’t know. I can’t find K107 & K118 in Ubakus, so I haven’t checked the arch tec’s 0.11W/m2K U-value for his roof design. I don’t like the look of the arch tec’s design. I don’t like the idea of cutting boards in between the rafters (ie relying on somebody else to do it properly) & I suspect the K118 might be off-gassing more poison than my design too. I think the arch tec’s roof may be more expensive (just on materials) than the design I proposed, & it will be significantly more expensive once the labour is factored in. Have I got that right? So far, I haven’t found time to get all the prices & work it all out. What do you think I should be saying to the arch tec about the roof make up?

I’ve had a go at plugging my I-joist based design into Ubakus. I couldn’t find most of the materials I wanted to use & Ubakus won’t let me have my battens for the interior plaster board running the other way from the joists, unless I pay a subscription, but this gives me a rough idea of how my 240mm I-joist roof option might perform:

I’d very much appreciate some opinions on this roof design please: I’ve designed a house myself (with no prior knowledge). I have planning permission. An architectural technician has recently prepared a full set of building regulations & construction drawings for me - ie one set of drawings will go to the SE for his input, then to BC for approval, then to builders. Now I’m working through the draft drawings, to make sure I’m happy with all the decisions the arch tec has made. My brief for the sloping roof sections was: standing seam on special SS membrane, then OSB, then 50mm air gap, more OSB, I-joists at 600 centres & Warmcel blown cellulose in between. I suggested 300mm deep I-joists or next size down (240mm), if we’re struggling to make everything fit (there’s a PP ridge height restriction). Also, I’d seen some of the arch tec’s drawings for another project (with phenolic everywhere) so I told him, to keep costs down, we should only use phenolic in one very small area where we need to avoid bulky insulation. He’s specified two layers of phenolic, over the entire sloping roof. My own (240mm I-joist based) roof design would be about 354mm thick – so, compared to the arch tec’s roof design, my design significantly reduces the space in two of my in-roof bedrooms, which don’t have dormers. The extra depth of the I-joist solution will be why he’s done drawn something that doesn’t fit with my brief. Here’s the arch tec’s design:

Here's Gordon, talking about his work, for anyone that's interested:

The prospect of a Section 75 claim, if your contract allows for payments to be made by credit card. Has anybody here ever made a Section75 claim? How did it go?

Thank you @saveasteading & @Mike. I got about half way through the video. You're right - it's not at all exciting. I'll watch the rest tomorrow. It hadn't occurred to me that a QS might help me evaluate the builders' quotes. There's a lot to think about here. Asking about the BoQ & cost estimate has raised more questions than I expected. I probably ought to leave this for now & focus on getting my drawings completed.