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I have used this method many times on builds and extensions, as have many. - Reflective thermo breather membrane (external) - 11mm OSB for racking strength and airtight substrate - 140mm timber stud - Full-fill Rockwool NyRock Frame Slab insulation - 25mm or 50mm PIR reflective thermo VCL - Service batten - Internal plasterboard Everything taped to help with air tightness. My opinion, you will always install insulation and take more care carry out the insulation and taping works yourself although it is time consuming

Board with tiler backer, job done

I did 2 undercoat and 2 top coat on mine, primed any bare areas first and produced a lovely finish. You need a depth on MDF or it can show through any imperfections, do it once, do it properly i say

Yes, everything gets a good coat of D4 🙂

I run plywood down in my workshop and doubled up, very strong and remains nice and straight. Certainly not the cheapest method but works well

I completed my own house in December 2025, using a very similar system to yours. For insulation, I selected Rockwool NyRock Frame Slab, combined with a thicker OSB layer to enhance structural performance. The majority of the building is finished with Hardie VL cladding so no external (EWI) system. I used the same construction approach on a house I built three years ago, which has performed faultlessly. Based on that experience, I chose to adopt the same system again for my own home. I stick build this project using kiln dried treated timber, at the point of the build the timber was at 12.8% to minimise movement

Absolutely fine, i use a neoprene coated yoga mat from sport direct only a few pound. Pattern it dry to get a perfect fit, fix it with sticks like turbo, seal all around the edges and joints, never failed me

Has the frame moved slightly compounding the issue, it might be out of plumb

I line them, cures the problem, very little loss in capacity and no more condensation

Fairly common with composites, the slabs bow. I have several replaced by Endurance under warranty due to faulty slabs

As said, clean off if necessary with some white vinegar, then coat with patination oil

I purchased all my c24 treated timbers to carry out my build a year before in required it .4x2, 6x2 8x2 and 9x2 Broke all the packs down and stick stripped every row, when build time come it was all around 12-14% and straight as a die. Not had a single bit of movement in the build. Is it practical, not really, is it time consuming yes, then having thousands of pounds of timber stored, was it worth it 100%

I would say no. 30kw required

Wavin Osma or polypipe hands down. Brett martin, hunter etc are cheaper alternatives, but as everything cheaper for a reason

I have just gone through a similar scenario with ST water. As nickfromwales has said. Follow their guidelines, 750mm deep , sand both sides depending on the ground etc. I used barrier pipe just because I was unsure of the ground , yes it's more expensive but once it's done it's done . They were happy with a series of clear pictures of the installation. Brass stop tap on the inside and proof of insulated ducting where it come into the house

A PRV may help depending on your current water pressure. A shock arrestor will help also on the fees whats causing the problem. Listening to you recording, It sounds like there is a pipe what hasn't been clipped back properly somewhere

Agree , I have worked on several of their builds but never been to their factory , hence the visit to see where it is all made. It was nice to see things from both sides. The visit was very informative and professional until the final section, which was the window and door presentation, this was horrendous and very uncomfortable the way it was presented.

Have a look at MBC, I did a tour of their factory recently and they have a good well made product.

I usually use cls , dry, straight and readily available

What section of timber are you looking for ? . Modern treated timbers are far safer than the old CCA treated timbers.

Painting it will be fine if just standard emulsion I have never had an issue with tiling onto painted walls in a kitchen. Also if you ever decide to change the tiles in the future, there is less chance you will destroy the walls taking the tiles off

Request them to remove them and use them as cuts if possible. They're shouldn't be blocks with large sections missing they should be whole and in good condition

Don't rule out rockwool nyrock frame slab, I have used it several times now and an excellent product

I have installed a large amount, they are both very good . My personal opinion is I prefer Hardie especially the VL plank

If in doubt especially for a sole plate, I would use pressure treated timber