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I am getting ready to do the floor for a small outbuilding/office with a small toilet/shower room. It is an old barn with solid walls and the floor build up so far is an insulated limecrete slab (expanded glass sub base and 100mm limecrete). For the shower room I was thinking of laying some 50mm battens down and infilling with some 50mm EPS i have spare. Then gluing and screwing 18mm ply to the battens, then PVA the ply and finally ceramic or cork tiles on top. One sheet of ply will be big enough for the whole room. Does this sound sensible? Could I get away with not fixing the battens to the limecrete floor?

How far is the neighbours house from the building/workshop? If you are making noise then sound proofing might be a consideration. My instinct is that rather than reroof I would start again. Permitted development limit on outbuilding size is 30m2 so this is larger already. I wonder when it was built and if there has been any planning discussion about it.

Nobody beats Thames Water for incompetence in my view!

I think it was a few things. I had a few architects come around at the beginning and one who had some experience of renovations of this type suggested a concrete floor for cost reasons and after a general assessment of the house not being too damp as it was. He also pointed me in the direction of cheaper woodfibre boards than I was considering. (he was Charlie Luxton from a programe called 'Building the dream' if that means anything). I think it is undeniably cheaper to use a concrete floor as it uses more conventional materials (I was comparing limecrete and expanded glass sub base against concrete slab and type 1). Also I had quite a large area to do so used a pump for the pour which might be possible with limecrete but not as straightforward. It did also leave the floor finish more open as you don't have to think about permeability of tile/floor finish. In fact for a new extension to the house I ground the concrete slab down for a polished finish which wouldn't have been possible with a limecrete slab. I also read up on some issues with UFH and limecrete floors. I would say that my place isn't in an exposed situation so that is to my advantage. I ended up with 60mm steico woodfibre board and 20mm on window reveals. In theory the 60mm of woodfibre board doesn't meet building regs but my thinking is that the more insulation the higher the risk of interstital condensation. I suspect this wall buildup performs much better in practice than theory might suggest. Room size is also a consideration when using IWI. MVHR is another thing that I wasn't 100% I was going to install but the more I read the more I decided to go with it. Also I think the architect had the assumption that it would be necessary. I did go pretty overboard with airtightness detailing in the end and got a reading of 1 ACH/hour so I am glad I went with MVHR. Overall I have been very happy with the results - house temperature remains very stable without much heating needed and we have barely used the radiators upstairs.

I don't think this is true. My stone walls have lime render (as flattening layer and airtight layer), wood fibre board, lime render, limewash. Breathable both ways and airtight. I also went for a concrete floor with 200mm EPS below with a DPM under this. Also some French Drains around the perimeter. Initially I had looked at limecrete floor (and in fact did install a small limecrete floor in a small outbuilding) but was persuaded not to. Seems to have worked well.

I would cut the foam back a little and fill with lime. It is what I have done on my house with wooden windows and stone walls and it has been fine. Looks like pretty large gaps in places so you would use a lot of mastic if you go that route.

Zoot yes I did mean using 10 or 20mm insulation instead of the 50mm. I didn't mean going back to the bco to try and get the OK for that. Just when you rip up the floor after he has visited you could easily put the thinner insulation down before the wood. The only cost would be what it costs to buy as it will take minutes to install as the floor is coming up anyway. It will still make a worthwhile difference. Remember that with insulation there are diminishing returns for greater thicknesses of it meaning the first milimetres provide the most benefit. Not sure if this is clear but make sure when the flooring goes down for the final time that you glue all the joints.

You can get 20mm and even 10mm sheets of xps insulation if the ceiling height is really important. Something like this. https://www.thefloorheatingwarehouse.co.uk/acatalog/Warm-Pro-XPS-Insulation-Board-XPS_Pro.htm And I have to say that this thread has provided some vintage back and forth between you and Peter!

yes that all makes sense - i've only used a simple tube without a bucket so this isn't an issue.

i can't say I managed to watch the whole video but I am struggling to see what is going to lead him to have an wonky pool!

Is this the expansion gap you are talking about? (As in rather than the 5mm suggested earlier in thread). Presumably it is dependent on the overall size of flooring?

Have you done a search on this forum for acoustic insulation or soundproofing? I would have thought that would be the place to start.

I suspect it will still be warm. Think how quickly a lagged hot water pipe cools down (surprisingly quick I think). Also, what happens in summer if the pipe is near the top of the insulation?

you'll have warmer water from the cold tap?

If it was mine I would use membrane around the whole French drain if the ground is sandy. If clay I wouldn't bother with the membrane as it will clog up. Line up the perforated pipe so that there is a smooth (no perforations) channel right at the bottom. What size pipe are you thinking of using?

Just noticed it is a retrofit so that may constrain you.

200mm minimum of EPS (polystyrene) under slab. Why not attach UFH pipes to mesh in slab then no need for screed on top? This seems very little insulation. Does it even meet building regs? Also 50mm screed with pipes in it seems very thin but I don't know quite what liquid screeds are capable of. I would have thought 70mm minimum screed.

do you have a plan for the ducting? are you using radial/manifolds? have you allowed room for a silencer on the supply side? easy access to filters? I think you might be underestimating how much space a typical MVHR setup takes.

I'm planning on running some of my ducting in my barn conversion at the apex like prodave has suggested and then between the rafters and to the edges of the room. I have a extra insulation on top of the rafters making it easier to use the rafters for ducting (still within insulation envelope). What is happening at rafter level for you?

I believe from looking at other threads on this that some have been happy with multipanel. I was planning on using them.

I got BC approval as well for mine.

As I understand it if you get a passport through grandparents then your children won't get one.

Does the chimney have a liner?

True. But what is the value of a whole brick/block/stone compared with a crushed brick/block?

Every day is a good day to use lime! Well maybe not if it is really freezing, but then not so good for cement either. How about for starters - at the end of the building's life cycle you will be able to reuse materials you couldn't with cement.