ChrisJ

Is your balcony proposed to be concrete or wood? Both are possible, personally I’d do concrete for long term. Based on your picture with columns from foundation to underside of roof this will all be quite simple for the engineer to design connection and support details price - you’ll need design first and then go for pricing

https://www.framemax.com Not part of the UK, but a company I have dealt with during my time in the US a long time ago, they have done well with pre fab walls for steel frame construction

Can you post some pics of these corner blocks failing?

Natural Stone for an ICF house is no different then conventional masonry, you can use a Brick Ledge (4.5" sculpted ICF form) form at the bottom to carry the stone, usually placed 150mm above finish grade or use an ICF form 4" wider (i.e. 10" below grade to 150mm above then switch to 6" ICF) the Brick Ledge form with proper rebar stirrups is designed to carry 27' (roughly 8.5m) of standard masonry bricks, I don't know that weight value but if you get that and your stone weight you can sort how high the stone can go There are ways to allow you to go higher, I've done 6 storey buildings all masonry and we used an angle iron every 2nd floor to help break the weight load to the brick ledge form at the bottom Brick Ties can be screwed directly into the ICF webs, most are rated for 450lb pull out depending on the screw fastener used (Sorry don't know the metric conversion for that). There is a 2 part brick tie that you embed part of it prior to placing concrete, it goes thru the polystyrene into the concrete void, probably have to import from North America and if I recall fairly expensive and not sure how well it would work since natural stone is various sizes. I did do a project in Los Gatos, California almost 20 years ago and the owner had very thick tie wire (think what was used for T-bar ceilings) cut in 800mm lengths, folded in half and then pushed though the foam into the cavity prior to concrete placement, this was engineer designed for the stone facade which exceeded 30' (9m+) in many areas

Unless you're planning to purchase the expensive structural screws I would just use 90mm nails in my nail gun to secure the joists down. a little trick it to also use a dap of GripFill or even spray foam between the joist and the ledger, this will help prevent any potential squeaks as the floor will flex and move slightly. May not be a big issue with wood on wood, but if you had joist hangers it makes a huge difference, lets put it this way for the few pence it costs I'd be doing it, same with your filler piece (47x50) that will be used as solid blocking for a fully nailed diaphragm of the floor, don't forget to use GripFill or spray foam when you place your sheathing down either - makes the floor a bit more solid and prevents squeaks

Curious as to why the design calls for a steel beam within the ICF cavity instead of a concrete beam with rebar and stirrups In your detail, you may need to clear out the webs in order for the steel beam to fit, prop it with some timber or acrows, prefer acrows as f any settling occurs from the block during the pour you can adjust the height of the beam, shouldn't be an issue with Nudura tho with solid webs connecting vertically. After the pour is done and acrows removed, use spray foam and attach the polystyrene cap below. Be careful if you have to cut webs out to make beam fit, you may need to do a bit of additional temporary forming to prevent the block from flaring out during the concrete placement as concrete pressures are high and without the webs, nothing to hold it in place

Like I say, maybe not a code requirement in the UK, but keep in mind wood is organic and a sponge it will suck the moisture from the concrete and good potential for rot to occur. This is why I prefer the Simpson ICF hangers for my rim boards, but when doing exposed connections I would use peel & stick membrane on the backside of the rim board to separate the 2 products

Nudura XR35 will run you about £100 per block (Incl VAT) for 1.1 m2, others are slightly less expensive but do not have the accessories available that Nudura provides as well the increased block size reduces on site labour substantially - figure close to 20% savings U value I believe is 0.16

Concrete and wood should not Wood and Concrete should not touch, even once concrete has cured. May not be a code issue or requirement here in the UK, but I have seen wood rot sooner rather then later from touching concrete, even Green Treated lumber will start to fail

Were you advised to put some form of a break/separation between the back of the wood where it touches the concrete, such as peel & stick?

Typically you try and have the ICF bracing system on site prior to start and install as soon as needed, building ICF in vertical stages would typically make the project cost prohibitive just in concrete pump trucks plus the additional .5-1 m3 of concrete needed each time you place concrete. With the exception of tornado style winds, ICF when braced prior to concrete placement holds up quite well, perhaps a bit of adjustment needed after the winds prior to placing concrete

Really look into the steel angle brackets, i'd be a little concerned of rusting and/or bleeding and discolouring the cladding but the theory of it all looks good There is a company that makes profiles for the cladding that would be exposed, non rusting or bleeding and look aesthetically pleasing, I can't remember the name of the manufacturer but I'm sure your supplier would have access to them

Engineer to approve, but your posijoist system will complete the diaphragm of the structure, typically you have straps on top of the posijoist which too will flyover the top of the ICF and need fastening to the top of the ICF wall. Your plywood can simply flyover for a smooth surface for the roofing membrane to be on. I'd suggest leaving the posijoists 5mm higher then the ICF wall, no one gets the concrete perfectly flat or smooth for the plywood to sit accurately on, laydown a nice spread of spray foam before putting each sheet of plywood over and then use some concrete screws to fasten the edge to the concrete, just snug them, don't over tighten to distort or skew the plywood. once the spray foam has cured, trim any extra that has expanded past the face of the exterior ICF wall Looking at your picture, the angle of the ICF cut, embedding a 6x2 to be flush with the top of the ICF will be almost impossible as the webs are in the way in several spots, if you cut them to make proper space, you will need to do additional bracing prior to pour so as the ICF block doesn't flare out from the concrete pressure during the pour

As a regular user of Nudura, what I love best about the block, build the blocks together on the floor, they all lock together, then lay it on it's side, flat on the floor. make sure to oversize it Once laid on the floor, use your truss drawings and layout the cut lines on the block, verify you have done it correctly, the heel height, the peak, double/triple check it all, now you can cut the block, flip it over on the floor, transfer all measurements and cut the other side Depending on the size of your gable you may (with the help of 1-2 people) lift the gable end up on top of the wall and snap it into place, if its to big you might need to dissemble some of it to get it up

Defeating the purpose/point of ICF, just cut the services into the ICF, plasterboard directly onto the ICF for the ceiling, I would use resilient channel, only because wood is typically a mess and RC allows the plasterboard to ‘float’ flat