Sounds easy to DIY , foam on 200 thick sheets, plastic or nylon insulation fixings through mesh and thin breathable high tech render 4 to 6mm thick,

Mass concrete will be a cold bridge down into the ground, I would EWI down as far as you can, definitely below ground level.

If the house is warmer than the ground moisture will be trying to go from the house into the ground!

I would put my damp course on top of the new concrete slab and it will then act as a vapour barrier too. I put insulation under slabs, 200 mm of it is nice with floating floor or screed on top

If you have mass concrete walls I don't really see the point of breathable lime plaster 'cos the concrete isn't going to breath enough to make it worthwhile. The EWI is going to protect the outside from driving rain. You don't mention ventilation - worth considering MVHR. If this was installed it would (IMO) make the lime plaster even less useful. What is the existing internal plaster / render? If it is acceptable or just needing some repairs I don't see the point of hacking it all off. A recent thread here discussed 2 small MVHR units rather than 1 bigger unit and more ducting. Two small units worked out significantly cheaper and retro-fitting ducting can be a pain.

As Tony said take the EWI below ground level, easy to do if you are putting in french drains around the building.

A quick dip into a U value calculator gave a U value for the walls (20mm plaster, 400mm concrete, 200mm EPS) as 0.18 with no condensation issue flagged.

DIY EWI is perfectly feasible. Over here the adhesive is cheaper than foam and quite easy to use. It is worth buying a stick mixer from one of the DIY sheds rather than using a mixer/stirrer on an electric drill. Doing the render coat DIY is no big deal if the EPS goes on flat. A 10mm notched float to gauge the render going on, lay on the mesh and then float over with a normal float. For the top coat the particles in the acrylic render gauge the thickness so no problem there either. If there is an unobtrusive bit of wall to test your skills then try it out and if you don't like the result get the professionals.

EWIstore do a tool to recess the fixing heads into the EPS, and sell dowel caps to cover the recess. Reduces thermal bridging from the fixings and provides a much more even surface for the basecoat to go over.

https://ewistore.co.uk/shop/eps-router/
https://ewistore.co.uk/shop/thermo-dowel-cap-for-eps-polystyrene/

Posted By: bhommelsEWIstore do a tool to recess the fixing heads into the EPS, and sell dowel caps to cover the recess. Reduces thermal bridging from the fixings and provides a much more even surface for the basecoat to go over.

https://ewistore.co.uk/shop/eps-router/" rel="nofollow" >https://ewistore.co.uk/shop/eps-router/
https://ewistore.co.uk/shop/thermo-dowel-cap-for-eps-polystyrene/" rel="nofollow" >https://ewistore.co.uk/shop/thermo-dowel-cap-for-eps-polystyrene/

The router and caps are designed for use with metal mechanical fixings. I have always used plastic mechanical fixings which have a minimal cold bridge which IMO would make the router and caps redundant.
https://ewistore.co.uk/shop/plastic-mechanical-fixing-180mm/

@hhommels, it's not just me then! I found the same problem even with 210mm fixings, for 150 EPS. I think it may be a question of getting what you pay for. I have never had a problem with Ejot fixings, but have had with cheaper 'un-branded' ones. I think our failure rate was worse than 1 in 6! Snipping the ned off helped a bit without seeming to affect pull-out resistance, but it was very annoying.

Infinitely preferable to not need to use mech fixings!

Thanks so much for all the replies, plenty of food for thought Especially re the help with DIY EWI, thats great news, it will be a substantial saving for me.

Posted By: Peter_in_HungaryIf you have mass concrete walls I don't really see the point of breathable lime plaster 'cos the concrete isn't going to breath enough to make it worthwhile. The EWI is going to protect the outside from driving rain. You don't mention ventilation - worth considering MVHR. If this was installed it would (IMO) make the lime plaster even less useful. What is the existing internal plaster / render? If it is acceptable or just needing some repairs I don't see the point of hacking it all off. A recent thread here discussed 2 small MVHR units rather than 1 bigger unit and more ducting. Two small units worked out significantly cheaper and retro-fitting ducting can be a pain.

Thanks so much for looking at the figures regarding my wall, very helpful. Its just plaster on the inside (not in great condition). Are you assuming the French drains will solve the rising damp inside the house completely? What happens to any damp issues that remain if using standard plaster inside?
Yes I am considering a heat recovery system that includes a de-humidifier, I understood this approach would cause any latent dampness to be evaporated from the walls (if they are breathable)?

Posted By: fostertom
What floor does the house have already? With 'coffer dam' of perimeter insulation, the need for underfloor insulation is at least reduced if not eliminated, if the present floor is otherwise serviceable and/or to avoid more disruption.

Almost no floor! very thin concrete on dirt! I will definitely be removing it and digging down

Posted By: fostertomAgree - all your ideas plus tony's comments - ideal.

If the existing paint on the concrete is really well adhered, you can fix the EWI with cementitious adhesive,

If the paint is a bit flakey I guess it would need to be stripped off and/or fixings used?

If it were my EWI I would do rounded corners everywhere 75 or100mm radius to all external reveals to make it look different from run of the mill homes. I would make a “rasp” out of a load of old saw blades that runs up and down the face of the corners leaving a pile of polystyrene shavings and a perfect rounded corner.

I fixed my windows -3g- to the outside of the reveals overlapping by 60mm on the sides and slightly less on the head and sill. Angle brackets or drilled through the frames.

Head needs a positive drip . ie head slopes up hill towards the house unless well under the eaves.

Sills from Europe with end caps.

Lime plaster is fine inside, no downside.

Is ground level below floor level all round outside?

Posted By: tonyIf it were my EWI I would do rounded corners everywhere 75 or100mm radius to all external reveals to make it look different from run of the mill homes. I would make a “rasp” out of a load of old saw blades that runs up and down the face of the corners leaving a pile of polystyrene shavings and a perfect rounded corner.

I fixed my windows -3g- to the to the outside of the reveals overlapping by 60mm on the sides and slightly less on the head and sill. Angle brackets or drilled through the frames.

Head needs a positive drip . ie head slopes up hill towards the house unless well under the eaves.

Sills from Europe with end caps.

Lime plaster is fine inside, no downside.

Is ground level below floor level all round outside?

Cheers Tony, just looking at your website,great resource, I may do something similar for my house

Thanks for the idea about rounding the corners, never would have thought of that. Regarding the windows, what do you mean "to the mm on the sides and slightly less on the head and sil"?

Yes ground level is about 50-80mm lower outside, but can be improved when laying new slab (we have high ceilings).

Sorry about the odd bit, now edited, basically my window frames are larger than the openings and sit outside the reveals in my insulation layer.

You should wrap insulation round the outside of the frame onto the face of the window a bit, mine did more outside than inside as they opened in.