Mr Punter

Looks tiny. How much concrete? I haven't really been paying attention and imagined at least a couple of lorry loads and 900 deep trench fill foundations.

Should be but ask the people doing the doors. You need this to the entrance floor WC as well and that needs to open out. All the escape windows should be min clear opening of 450mm x 450mm and the bottom less than 1100mm from the floor.

Blimey! Like we said, shut up about the rain on the concrete already!

There are differing opinions on insulating old solid wall buildings. If the walls are damp it is worth trying to find out how the damp is getting in. Originally the solid wall would be ventilated to the inside and out. The inside air would be slightly warmer and have lots of ventilation / drafts from chimneys and ill fitting windows. This may have allowed the wall to remain fairly dry but the cold and drafts make it uncomfortable to live in. I would not want to use organic material against a damp wall and would choose Celotex / Kingspan type with a VCL on the warm side. I have used silane / siloxane cream on the outside of a solid brick wall and it is claimed that this prevents rainwater saturation while still allowing evaporation, helping the wall to dry.

If it is trench fill the rain won't hurt. The rain water will be displaced by the concrete. More harm will be done by leaving the trenches open. If it was a floor slab I may want to delay, especially if I was after a polished finish.

You mentioned Passivhaus. EnerPHit is aimed more at existing buildings. https://europhit.eu/ There was someone over a greenbuildingforum (shevek?) who did this on a terrace house. If you are insulating the walls internally you could have the insulation directly against the wall. If is rigid boards you could secure them with battens which would also form a service void. Do not introduce a cavity between the wall and the insulation. The inner face of the insulation should be as vapour impermeable as practicable, so tape the joins and use a decent VCL. The permeable materials are best introduced on the cold side of the insulation, so repointing externally should be lime etc. Join the wall insulation to the ground floor insulation. Regarding air permeability you could aim to achieve 5 m³ / (h.m²) and MVHR will be fine with this. Forget the log burner and the open fireplaces. Regarding build method for the extension, perhaps get a price for blockwork and ICF. See how they compare in cost, wall thickness, ease to finish etc. Most builders are familiar with blockwork. I would not suggest timber frame against an existing stone building.

Off topic but if it not too late, consider having a larger door to the airing cupboard as if the cylinder fails you would need to demolish a section of wall. I don't think the clear space at the head of stair matters as this is a cupboard. You could have a bifold type door. The plumber will thank you, or rather, the plumber will not curse you as much.

But you could find it with a metal detector!

I use an impact driver for these. Makes the job easy and does not strain your wrist with the torque.

That is quite an imbalance between land cost and build cost, which at less than £1000 per metre is very low. You should be able to borrow 4 times your income up to a max of 75% of the finished house value. If you borrow on your current house this will be factored in. With a self build mortgage this will be released in stages, often n arrears. If you can't comfortably make the mortgage payments from your employment income you will run into financial problems.

I can understand the timber at the bottom to take the weight but I would fix metal strap to the sides and the head and fix this to the brickwork. I am not sure what look you are going for but I would prefer to have, say, 30mm of frame in the brick reveal and the remainder in the insulation. This leaves you with a reasonable cill inside and out. A section detail for windows is really useful. How do you fix timber cladding to 120mm EPS? 200mm screws through battens? Can you post pics of your progress and let us know what to look out for?

Be aware if they price for the CAT 5 or 6 per point as it can get really expensive. The cable is v. cheap and you could always run it yourself. Run all to one point, same with TV. Don't bother with phone sockets - you can just use the CAT 5 / 6 and use an adaptor. Have a light near the barbecue, switched from indoors. For under counter kitchen appliances, have a socket under the plinth on flexible cable as most appliances have a plug fitted.

I have the same recip saw. That is a good price. I often use mine to shorten scaffold poles.

The epitome of a first world problem...

If you are using standard lintels for openings and don't have cantilever floors or no wall returns you should not need one.

I have an old en-bloc garage that had a damp concrete floor. I covered with DPM and 18mm flooring chipboard and it works surprisingly well and was v. cheap.

I am not keen on the inverted roof with the waterproofing under the insulation as the insulation can be compromised by water under it. I prefer a layer of OSB or cement board over the insulation to carry the EPDM.

Yes and it is a crazy price once you have a special mix. Even more if you want it signed off by Sika or whoever. I would say voids and honeycombing are more of a risk as normal concrete, especially if it has a low water:cement ratio, is fairly waterproof anyway. For quality concrete, specify correctly, don't let the pump guy or concrete lorry driver bully you into adding water and let the batching plant know you will be doing cube tests.

I just looked up what these mean. The top 2 are about 1mm out and class 1 allows +-0.9mm over 8m, so they may be OK. The third one is way out but may be kept for [other reasons]

Leave it until the rest of the work is done, then take a view as it may get damaged or it may be OK as is.

If you are doing polished concrete, don't bother with a mat well. Just use the thin rubber backed mats - they are less than 4mm. You will not need to cut them to fit the well either.

A bit like fixing into Weetabix. I like Fischer fixings. They might work well if you drill a nice clean hole the same diameter as the shaft of the fixing. What do the wood fibre manufs suggest?

There are lots of ways to approach this and as it is a garden room, not a Passivhaus, there should not be any issue with what you have done. You can just lap the VCL over the DPM. Staple in place. I like to leave plasterboard 15mm off the floor, so if you get spills they don't get wicked up. I like the Screwfix pink fire rated gun foam.

I like to tape around the outside as well with the foil tape.

I think some aluminium, zinc or lead flashing round the bottom would work well. You could fix this to the Durisol. It will finish the base off nicely. You could have it run behind the bottom batten.