Mulberry View

I have had a spec for wall-plate fixing from me SE, that's all cool. I was immediately concerned about the amount of steps to install the wall-plates as I was planning to do these during the concrete pour. I have abandoned this thought process and will now wet-set the fixing studs (using a jig that I'll make to ensure accurate placement/straightness). This way, I can do the wall-plates with a bit less urgency and hopefully once the concrete has hardened. By which time hopefully I'll have taken a balanced view of all the great input I've had here as to how this will be detailed.

Thanks @SimonD. Our VM Zinc installer will, I'm sure, follow the prescribed build-up to protect our warranty, I just want to make sure I'm right up to there. It is my responsibility to install the roof structure (Posi Joists) and the deck (Plywood). So, you're saying 18mm if fine? My Architect 'specified' Class 3 Plywood, is this what I need to order? Does it need any other preparation or treatment by me before I hand over to the Zinc installer? Yes, I'm a chronic overthinker, but hopefully for the right reasons.

As above, our Architect is no longer involved with the project, so I cannot get it redrawn. We have already made the decision to beef the insulation up to 200mm. I am trying to ascertain a better detail for the Zinc roof, in conjunction with the actual contractor, but am open to ideas on that. This, of course needs to take into account the increased insulation thickness. 22mm Plywood or 22mm OSB for the roof deck? I'm erring towards OSB. The service void was drawn because the Architect had no inclination to learn about the ICF system. I am having to be fluid on these details and re-think everything. What type of sealant to bed the wall-plate onto please? Any suggestions? I'm concerned about the mix of materials at the face of the wall and the risk of cracking. I have built the building as drawn so far, so the only workaround I can come to is to add a further layer of EPS to the whole portion of the building that will be rendered. This improves another poorly designed detail as was discussed here The above drawing is only of only 2 short walls that will have gutters (probably only about 10% of the total wall length, the rest has no gutter at all. The Zinc Roofer has proposed something a little different to that drawn for those walls... All help here is greatly appreciated.

I agree about the detail being poor, it's like many aspects of our design. We only paid 16 grand for our Architectural design, we can't expect proper details can we? *jokes* I'm installing the wall-plates with the 5° tilt on them to match the roof pitch. I cannot fathom why they were drawn like this, but my Architect has left the project after being paid and I have to try to figure out the details. I'm also not a fan of the eaves detail arrangement and am trying to figure that out a bit better since we are upgrading the roof from 120mm insulation to 200mm.

Can anyone tell me the purpose of the DPM under the wallplate? Does this present an opportunity to somehow add a membrane layer over the Posis, under the deck for air-tightness? Or that not the best way? I had otherwise planned to implement an airtight layer under the Posis with a deeper service void for downlights etc. Finally, 22mm OSB or Plywood for roof deck? I'm erring towards OSB.

You mean the problems with the fabricator? Not with Reynaers? Keep in mind I'm still looking at Reynaers for a few positions that are better in Aluminium, so if there's an issue with a Norfolk or Suffolk based fabricator (we're talking to one in each county), I would really appreciate a heads-up. Privately of course.

Thanks for your reply Gary. So you have Reynaers issues outstanding? That's not good to hear, I do hope you get sorted. It looks like we'll be going for Timber Aluclad Windows as they absolutely eclipse the u-Values of anything else. I've managed to get past the notion of extremely narrow site-lines and now think that even the chunky frames of Timber windows won't look chunky once they're in context in their large openings.

Hadn't really thought of that, what's the concern from BC point of view?

I'll be very interested to see your scenario, do you have render over brick like us?

I would presume the renders will install a drip bead at the bottom of their work? If that protruded beyond the brick slip layer, would that be sufficient? Though, with that said, I wouldn't want to 'see' the EPS on the underside of the ledge (albeit tiny) created by the added EPS

Yes, these look good, but expensive. I'm pretty happy with how my Ledgers went in for the lower level, I'm hoping to do the same for the upper deck (roof), with the learnings from the first time.

Our external finish schedule is brick slips at low level, with render on the upper level, as per this detail. A local K-Rend applicator has told me that their build-up is likely to be no more than 8mm for thin-coat render. The slips are like to be in excess of 30mm, resulting in a more pronounced version of what our Architect drew. It feels strange to have the upper finish not overhang, or at least level, with the lower finish. Would you agree? What would the process be for adding, say, 30mm of EPS to the areas that will be rendered in order to create this effect? Would get rid of the need for the Aluminium flashing, would it not?

Would OSB3 be a good choice for a sacrificial floor? I'm expecting it to be exposed from now until about June/July. If so, could/should I apply an additional sealer to it to give it a better chance? I can get it for about £16+VAT/sheet for 18mm, so it's not wildly expensive. I'll need about 30 sheets.

OK, fair enough, but these fixings will penetrate the vapour barrier, will they not? Is this an issue?

As I said, the Zinc guy has offered to help me with detail drawings. In all honesty, he is awaiting our decision on colour, one we should have made weeks ago. If he's as good as he sounds, I think he'll be a goldmine of info once I get to that point. I haven't furthered to detail conversations with him yet, I will do that soon as we need to bump the date with him once more. The roof joists are not fitted yet, why do you ask?

@Russell griffiths I completely agree. Another of the mysterious unknowns that was apparently 'out of scope' for a £20k Architectural design package. I have good Zinc guy lined up. It's early days yet, but he's also a self-builder and has offered me lots of help with the details, so I'm going to sound him out on it as a first port-of-call. So many woolly details though, people have paid a quarter of what we did for their design and came out clearer than we are. If I had the headspace for it, I would like to employ someone to inspect our plans and critique the details to form the basis of a case against the Architect, but also as a way to know what needs sorting out.

@Russell griffiths, What is the build-up on top of the joists? Presumably you have a deck under the metal? Although I haven't looked at it in great detail at this stage, I have planned for a 6x2 wall-plate on top of the Nudura core, the concrete is 2" lower than the top of the EPS. The wall-plate will be bolted down and the top will be level with the top of the Posis. From there, the Plywood deck will sit on top of the Posi and extend out and onto the wall-plate. The Architect drew a timber upstand to the edge (4x2 timbers?). Though the mix of materials at the outer face does appear to be an issue (EPS, Plywood and Timber all reaching the outer edge under the render). I think this was not considered by the Architect. I am minded to pull that timber and the Plywood inboard by 50mm and add an EPS infill to the outside edge. Although there will be a join in the EPS, there won't be a mix of materials. The real-world implementation of that detail or a variation of it with the 5° roof angle translated to the timberwork is a little confusing. As is the fixing down of the timbers, these will evidently go through the vapour barrier. Am I overthinking this?! As an aside, I plan to amend the roof service void to 50mm as mentioned earlier and may/may not implement the service zone in the wall. That is to be decided on the basis of whether it adds to the u-value or might be better detailed with an additional internal layer of insulation?

I will not use Aerobarrier to allow me to be lazy on the air-tight details. I just need to know more about what is needed, I have the time and attention to detail. There is some great info in this post, for which I am very grateful. Reverting to an earlier point I had. How concerned should I be about the standard Nudura blocks and their u-value? What are Nudura doing now if the standard block achieves 0.24 yet current regs require 0.18? I am thinking of adding EWI, but this will screw up all my planned brick coursing and sub floor vent placement which I carefully considered at foundation stage.

I don't think that's a bad price really.

My architect specified an air gap, which I had suspected was to add to the thermal performance (as well as for services). Some on here said that it was not necessary from a service standpoint because services can of course be cut into the EPS layer. I do not intend to have the service void on the ground floor ceiling because it seems pointless with the Posis, but as I said, will aim for a 50mm void above the top floor ceiling. It's already been mentioned on here that the roof detailing is not ideal as it shows a mix of materials at the outer layer. My building is currently committed from an ICF standpoint, so I can't change that, but I'll be exploring ways to give me an EPS layer all the way up to the top of the outer skin. I think I'll be setting the outer roof timber and the edge of the Plywood deck 50mm back from the outer edge and adding an layer of EPS at the top. It's ironic because this could have been done with the Nudura but I built the ICF as drawn so that ship has sailed unfortunately.

Similar insulation levels to what I'm proposing then. The quoted u-value for the Nudura standard blocks is, I believe, 0.24, though I am told that things aren't this simple and that the individual components of the wall should be calculated and that the concrete brings its own advantage. In fact it was the relatively poor u-value that came to my realisation when Total Home Environment pointed it out as being probably the sole reason for my 'C' as designed SAP score. With that said, the as-designed SAP has window, insulation and air-tightness values that are easy to exceed.

I had presumed we'd fit 200mm of PIR. Keep in mind I haven't costed this up yet, so that might be where that decision changes. Budget is a whole other conversation, we're winging it in that regard too, though think we're doing OK so far. No spreadsheet!

Yes, I've seen Aerobarrier. Luckily my 'kid' is all grown up and not biting at our ankles. Well, actually that's a lie. At 29 years old, she's more dependent that ever, but that's how it goes! Did you do Airtesting after the wet trades? I'd love to know what Aerobarrier costs. I feel as though the cost will be linked to the result it brings and not to the amount of work in applying it. I'm shocked to hear of your unexpected air 'leaks', particularly the windows.

Yes UFH. One of the major appeals to us wanting to build a house is to have warmth underfoot (and no condensation! something we lived with for years).

My Posi Joists sit within the ICF walls as opposed to on top of them and the Plywood layer oversails onto the wallplates, in my head this feels like a good start with being able to airtight the roof junction, though I'm not certain how that will occur. Ultimately, I do have it in my head to place a 50mm service void under the roof to enable me to get most of my electrics etc inside the the airtight envelope, which I also gather is a good idea. I have first floor structure in the works, as can be seen here. The penetration to the inner skin for this is minimal. You'll also see in that thread that I have passed Zehnder Comfopipe lengths through and cast them in concrete so they ought to be fully airtight already?