Iceverge

A primer is the correct choice. Tapes need a dry and very importantly dust free surface to stick to. Masonry is rarely this without a primer.

On the side you can get to you could slot 25mm X 200 wide PIR above the membrane and between the slating battens. Then run a strip of membrane down over them. Otherwise parge coat taped to your airtightness layer inside and internally insulate with insulated plasterboard like @PeterW says. By the way full fill rafters with mineral wool would give the same u value. And be much easier and cheaper to do.

Personal preference. So the concrete doesn't seep into the insulation when it's poured and so the EPS isn't sitting in a swimming pool of water before the concrete is poured. I don't like the idea of 2 layers of impermeable material anywhere in a building as water can't escape from between. The EPS won't be wet underneath if you take care to ensure the water table never gets above its base. No, the main purpose here is to ensure water from outside doesn't get in. The blocks are somewhat porus anyway and any moisture will drain away through them over time. I did drill some larger holes to allow rain water escape during construction. I put many iterations through Therm to see what performed best. I did try a third block below but the gain was tiny. Ideally they would be directly in line with the insulation but in the real world blocks only come in certain sizes. It's vital the aerated concrete blocks are kept dry. Hence keeping them away from the bottom of the cavity. The one below is a strip of membrane and the one above is an extension of the whole DMP barrier extending over and down the cavity. The 100mm block above it is to give a level surface to screed the floor from. You don't want to screed on top of a DPC as it'll tear. Mislabeled This is not the detail we built but rather an improved one I would have preferred. Our actual foundation is stepped twice so various levels of fully filled wall were raised to give a level platform to work from. It's called deadwork in Ireland. Not sure about the UK. Also begining a cavity wall directly from the foundations will be difficult as it'll be too uneven and rough. I will direct you towards our as built design if I can find it. 100mm to save concrete. A production builder near us uses this with reinforcing fibers and no mesh. We used 150mm with mesh. Total overkill in my opinion but our builder wanted it and didn't charge extra so hey ho. One thing that is vital with no subfloor is to compact the substrate thoroughly. Otherwise it may sink and you will get cracked tiles etc.

The EPS beads are easier to install tight to the wall and cheaper. Like @cwr says mortar droppings are your enemy. I would prefer to have them at the bottom of the cavity rather than sitting on top of my XPS insulation. Golcar used mineral wool batts to avoid this but this also requires conscientious blocklayers to make sure batts are installed in the proper way. I did spend 2 days with a homemade brush and long shovel cleaning all the cavity ties and collecting all the mortar droppings. I had very skinned knuckles by the end. It may not be an option in a narrower cavity. Below would be my preferred arrangement should I do it again and I would insist the block layers used boards to catch any droppings.

Our Foundation With perimeter insulation internal U value 0.1689 And without the PIR 25mm upstand. It's a small improvement but worth it I think.

Ditch the XPS and just put EPS beads right down to the foundation. French drain outside. We didn't have any cavity tray either. If you can't have any French drain I would consider a perforated pipe at the base of the cavity draining out and down to a soakaway. I would add perimeter insulation to the slab too.

@Adsibob What are you taping the windows to? Brick?

What U value do you need? How deep are your rafters?

We have a 250mm cavity. 215/250/100 downstairs and 100/250/100 block cavity block upstairs. Structural engineer will have the final say on this.

Batt insulation, sprayfoam or blown up in. Followed by a membrane and insulated service cavity Life is too short.

I think any plastic insulation will be just fine so long as it's not sitting in a pool of water. That sill looks A1 so long as it won't break from someone standing on it.

I'd be tempted to put an aluminium sill dripping into an channel drain to deal with this with insulation behind.

@Hanksy What thermal camera are you using. I am planning on asking Santa!

I did an experiment with PIR and Graphite EPS 70 by weighing them and submerging them both is water for a month. Towel drying them both and weighting them. I can't find the details now but the EPS had absorbed some water and the PIR almost nothing. I think this comes from the EPS being more porous . However this is an extreme case as if your insulation should never be saturated for long periods of time. I would always look at EPS first as it's the cheapest and "dumbest" material. However in this case I would consider PIR as you have very little thickness to play with to prevent quite a bad cold bridge. More important is how you'll deal with rain and possible pooling of water by the window. What level do you hope to put the paving slabs?

It was a suggestion but I imagine OP will want an outside ground level higher than the void.

What a lovely project. It's nice to see old buildings being looked after. I would probably stick at 400mm centers as it is much easier to fix. Just set your sole plate. Cut your verticals roughly to length. Tie a string in the right place, nail the top horizontally to the rafter, get a mate with a level to toe nail the bottom. Job done. To save cost, drop from 140*45 studs to 88*38 CLS. Doing anything too clever with 600mm centres will probably only increase labour I suspect. I have potentially a similar project somewhere in my distant future. I would like to set my stud wall at least 50mm back from the outside stone wall, put a an airtight layer inboard of the studs and blow eps beads between the studs and between the studs the wall. Then counterbatten 45*45 with 50mm batt insulation and plasterboard. Can anyone see any issue with this?

I was suggesting installing the periscope vent through the wall below the level of the block and beam floor. Letting the riser come up the outside to be above ground level. It would need to be backfilled carefully to avoid damaging the riser.

Groan, I should have though you had quite enough holes in the house as is. "Thermal Mass" is promoted by the concrete industry. Can't think why ? https://www.irishconcrete.ie/concretes-multiple-benefits/thermal-mass/

Americans. https://www.jlconline.com/how-to/foundations/a-frost-protected-shallow-foundation_o Your builder needs to do more reading, it'll make him happier. EPS can be used in lieu of ballast in supporting railway lines.

Of course I'm not a structural engineer so beware internet advice! The way I look at is if you were to make an arch, entirely in compression over the hole, would it be self supporting within the remaining brickwork? All that the lintel does in this situation is support the semi circle of material directly above the hole as well as reducing sideways thrust from the "arch".

Putting the vertical riser inside the blockwork isn't going to gain you anything. The easiest solution if you have a ground level that is below the red line is put vent straight through the blocks. Assuming your ground level is higher just mark an outline of the vent at the top of the bottom line of blocks as shown below. I'd use a diamond blade to cut the mortar and the blocks and remove a place for the vent. The blocks above will be fine as a "lintil". You will need to run your telescopic vents outside the foundation walls.

That's good. I would contact the company at the highest level you can (in writing) and give them an opportunity to fix it. It may only have been a rogue operator and they may be terribly embarrassed about it all. If they fight you or don't offer a prompt and satisfactory resolution certainly don't pay them. If you are confident to undertake the works yourself I'd remedy it and deduct your labour from any final settlement payments. If not, engage a tradesman who you trust to fix it and likewise withhold the difference of any payments from the installers. It doesn't need to be a ventilation specialist but someone who is willing to take on the recommendations of the forum and is well handed. It's important to give the installers the benefit of the doubt to begin with though.

Am I correct in assuming the red line I've drawn is the top of the ventilated void? If so I can't see how you'll be able to put the telescopic vent in the "side" as the telescopic vent will be obstructed by the beam inside it. Can you post a picture like the first one but showing a corner of the building so we can see how far back the first beam is set from the 140mm wall? If it is hard against it you will have to have your vents outside the wall or else in the "end" walls.

@Nickw1982 How are the noise levels?

I've not heard of anyone having trouble with these slumping. I think @ProDave used something similar. Apparently the better insulating ones (Slab 32) are better to work with. Rockwool would be better acoustically and maybe nicer to work with but it's expensive. Blown in cellulose is my favourite however. It is how a wall or roof delays the suns heat passing through it in the summer. It's also called decrement delay or phase shift. Don't confuse it with overheating caused by poor glazing/shading choices. It's well explained here. https://www.greenspec.co.uk/building-design/decrement-delay/ You're right to ask. I make tons of mistakes and often think I know more than I do!. It's here to create a service cavity which allows you to run pipes and wires through the walls around the house without puncturing the vapour membrane ( in most cases also the airtight layer).https://foursevenfive.com/blog/the-service-cavity-making-airtight-construction-easy-2/ This membrane is important, it stops air moving through the walls taking moisture into the structure where it will get cold enough to condensate rot the timber. It prevents cold drafts blowing into the house. It must be carefully installed, taped with airtight tape to all windows and doors, floors and ceiling membrane. All penetrations the same. You should aim to have no holes at all anywhere. Effectively hermetically sealing your house. Contrary to cranky old chippies opinions, combined with proper ventilation, you will have a much more durable, healthier building. Normally clipped to the service cavity batten AFAIK. I won't pretend to know this. Maybe an electrician will be along to help.