PeterW

..??? This isn’t a constructional hearth ..??

So it doesn’t need to be non-combustible, you’ve answered your own question. Use the stuff that everyone else uses, move on ..

I would be doing it to flush the pipework rather than the tanks - static body of water that size will be fine (assume the attic tank has a lid ..?) and more about crap settling in the pipes.

why ..?? Point me at the BRegs where it states that a below slab expansion material behind a structural slab required to be non-combustible and I’ll find you the product.

Turn the cylinder stat up to 75°C if you’re worried and then run at least a couple of buckets of water out of the system. If you’re really worried just drop a couple of Milton tablets into the top tank, leave 10 mins and stir it then drain off the couple of buckets.

Why..?? Coefficient of expansion on concrete is around 10x10-6m/°C so if you heated up a 1m concrete slab uniformly from 15°C to 80°C then it would expand around 0.5mm. Expansion foam is there for a number of reasons, usually to de-bond the slab from the structure and also so as it dries and contracts you don’t get gaps. A 15mm expansion foam will also be pretty much covered when you have boarded and skimmed the wall behind - beware that ordinary plasterboard is not suitable for behind a stove - and the remainder of any foam will be below your hearth anyway so is not subject to any sort of temperature that would cause issues.

They are using Zone valves to potentially stop thermosyphoning but with a decent manifold they really aren’t required if you’re going all in on UFH. Where they are needed is between buffer and boiler, and DHW and boiler which is standard S Plan wiring. The variation is where you add the buffer thermostat and the call for heat from the manifold(s) in place of the room stat, and let the UFH control when the boiler fires based on the buffer temperature. The only downside to this is you need to align the timers (or put the buffer zone on constant) as there is no direct interlock between UFH time controls and the boiler controls.

Telehandler will cost you between £350-450 ex VAT a week for hire. Add in £100 or so each way for delivery and £150 for insurance. That’s about £1000 all in and you still have to know what you’re doing which needs skill which isn’t something you need to be learning with attic trusses at 8-10m up. That sort of money will easily pay for a day of an iron fairy or a 3t crane with operator and it will be much much safer.

Ok - any reason for zone valves ..? All of your UFH zones have valves on them. You are making this much more complicated than it needs to be.

a lot if you use Tectite Sprint fittings … but they aren’t cheap

Get it done now. It will both let the ground recover and also won’t be an issue for planning and tree surveys etc in the eyes of the planners …

Heating source on the right is the pair you need to the buffer thermostat then on to the boiler. May need a live feed if the boiler requires power to switch on.

Isn't that before the Banksy got removed from the side ..?

Get one of these .. and decent gloves and a face guard !!! Grinder Wood Carving Disc GRAFF® Speedcutter 115mm, TCT Circular Saw Blade for Angle Grinder - Woodcarving Saw Blade 22.23 mm Arbor, Sculpting, Shaping and Cutting Wheel with 3 Teeth (115 mm) https://www.amazon.co.uk/dp/B07KFJ31G6/ref=cm_sw_r_cp_api_glt_fabc_AMHJZ05K9SSN9A31X1B2?_encoding=UTF8&psc=1

Yep and also use it to mark both sides of the joist and draw the cut lines so you keep the saw parallel and can also see where you need to clean the cuts down.

200kPa is equivalent to 20 tonnes per square metre. 150mm of concrete weighs 345kg… Think you’ll be fine ..!

5x2 will be +/- 2-3mm on dimensions anyway so a 2mm variation on the the seat will be lost in the thickness of the rafters and variation in the wall plate. I would just use a jigsaw to cut the seats after making up a marking template and then crack on.

Built in ..?? Or slot in ..?? Leave 5mm either side and if you can add some nitrile foam pads on the panels on the machine to stop vibration.

I would go for a contrast - or statement - colour or finish. Copper sheet ..?

It depends - what is the grading and what is listed ..??

Right, so first thing is to get digging outside if you can ..!! Get the soil away from the walls, get at least 150mm below internal floor level and then back fill that with coarse clean gravel. That will stop water coming through the wall. Joists can be replaced like for like but you need to sort the sleeper walls they sit on. It sounds like you would be better off replacing the floor with insulation and a concrete slab with a decent DPM lapped up the walls.

11sqm is tiny - you could DIY it. What are the other ground floor rooms like..? Are they suspended or solid ..?

Sod the compression fittings ..! 3/4x15mm Hep2O with some PTFE Tape/ paste in each connection and do up tight then run 15mm Hep2O pipe up to the valves. Nothing needs to be 22mm

Why do they want to use limecrete..? And why the Newton layer on the walls ..? Is that a retaining wall ..?? Damp needs ventilation or non-porous materials. If it is truly damp - and you want to retain a floorboard finish - then consider putting in a suspended floor with insulation between the joists and allow the underfloor to breathe with cross ventilation and air bricks.

Your issue will be the 15% semi matte finish that they use - it will be sprayed and potentially has a binder / flatting agent in the paint which will change the overall finish.