saveasteading

I think some presenters have something to sell, but they can't fill 10 minutes with the facts so exaggerate. The less they understand it the more they exagerate. It's as if those prescious but flighty heat particles were rushing through a piece of timber as if it was a big hole in the wall.

Yes it might be moderately simple but this is SE work. If we are to help further we need photos.

Whatever we build, it is a thermal bridge to greater or lesser degree. BH can sort this And carpentry skills will be of huge benefit to the final product even though the SAP doesn't acknowledge build quality.

I like the word 'just' there. Would it also creep into every corner under the floor and expand to put an upward pressure onto the floor, as in underpinning? But its certainly going to be easier than barrowing in the first 80% So that is a decent shout for the bulk fill.

Not something I'm familiar with.

A coal hole? It would probably be difficult to fill and compact after the first few feet.

He says you've failed but doesnt know why? He put the numbers in. It doesn't sound like an expert, just someone with a licence for a sap spreadsheet. I've come across one such. He wasnt interested in the reality and just wanted to enter conservative defaults. Your construction should pass but tell more. Insulation spec in floor and roof?

Simple can be elegant. The trouble is the method. Imported stone ( a lorryload) has to be placed in the basement and thoroughly compacted. Where would it be stored? That mean breaking out the floor. Would the stone all be barrowed in? Then a new floor. So that does have the advantage of simple support to your floor and added lateral stability. You would have to move out for a month minimum. Another easy solution might be to support the existing beam. A central prop means that the beam only gets 1/4 of the current bending. Or a masonry wall all the width, or a new beam. All needing foundations. Not quite as disruptive but still a month out of the house. Gut feeling £50k including fees and unknowns. Lawyers will take more than the Engineers. 25 leases, £2k each. PS. On second thoughts there will be redecorating, accommodation and likely more that we don't know about. For discussion say £100k = £4k each. Would they all contribute or some not be able to or want to?

@Nickfromwales it's a very big deal as liability extends to the whole block of flats. And might there be other basements? Who owns the basement/ void?

. It needs to be made clear that there will be no blame. Whoever is top of the pile is making the decision. Only that way does the designer bring up the 'crazy' idea from the back of their mind. Or the contractor says... if only we could do x, and the designer says there is a way but hadn't realised it was a practical issue.

Im thinking @zoothorn doesn't need to turn off the water as it is after the taps, before removing this part but it may be prudent? A spanner with a decent long lever?

I don't like the idea. An SE is the best bet. The steel has to be examined. Rust isn't always as bad as first impressions. But there are usually other options such as multiple small beams, additional supports or a wall underneath. It's going to be expensive. Some insurers reject on any excuse. All you can do when getting a quote is answer to the best of your knowledge, so reread what you told them then try again. You are all in this together. Have neighbours been below? Pictures would help.

Stop Press. I replied 'identical' but I was wrong. I've spent the afternoon comparing the Scottish and English reg's because I had a feeling that might be confusing me. The old fashioned way with a printout and a yellow marker. First appearances show the same rules, calculations and options, referring to the same document, and with shared drawings. BUT they are far from the same. I haven't checked out the implications of which is stricter yet but simply warning anybody who is involved at present.

That's interesting , especially for 'too slow'. It may be easier, cheaper and less disruptive to build a drainage mound if the topography allows, and it won't take so much space. Thus ground that has slow percolation may be beneficial.... which is plain silly. I think the documents need more nuance as well as awareness of reality. Does your pipe reach the top of the mound by gravity or do you need a pump? A pump built into a tank appears to cost an extra £500 or so. I've also had a look at digesters that remove a lot more of the chemical which appear to be the main concern. The figures are very impressive. Unfortunately it costs more but still does not allow the reduction of the dispersal area.

The pumped screed we have used is cementitious but has lots of additives so my opinion (no research) curl is not a thing. If using a cement and sand screed by old fashioned tamping and trowelling, the water content is very low so much the same applies. With structural quality concrete I've never seen curl either, in some hundreds of buildings. I guess the mesh or fibres help somewhat but again I've never heard of it being a thing. Anybody's other experiences would be be interesting. Can do no harm and may do a lot of good. Would you mind reporting back on how much condensation is there tomorrow?