Insulating single brick utility room

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Hi. Somewhat confused Newby looking for advice re insulating walls and ceiling of a single skin brick utility room at the back of a garage, adjacent to kitchen.
I assume that this would be classed as a non habitable space so won't have to comply with the U values.
We also plan to add either a radiator or a an electric panel heater. Probably the first.
We've had a couple of quotes from people and don't have the budget for the quotes are asking, so planning to do most of the work ourselves.
Read a fair bit and still a little unclear as the best way forward.

As I said it's single brick and has a flat roof.
Previously there was a large concrete "step over and down" step in the doorway between the kitchen and utility room, which has been removed so we need to bring the solid floor up to the same height as kitchen floor. Planning to create a floating floor.

2 of the walls have a 30 mm layer of ?plaster on them, which is loose in some places, especially on the wall between the garage and util'.

There is a damp proof course in the walls, but when we ripped off the 70's style wood wall panelling, some of it was damp at the bottom where it had been below the DPC level, and also round the external door, but this seems to have been because the door frame wasn't well sealed, plus before we had it recovered, water from the garage roof was dripping down between the edge and the guttering and soaking the concrete step and water was running in via the gap. That's dry now, but the block paving running up the North facing side of the house has no drainage and water tends to pool slightly against the wall, so although we haven't yet pulled up the carpet tiles and ancient vinyl flooring, suspect the wall at the bottom, below the DPM may still be slightly damp.

We're planning to take the BP bricks that are up against the wall (they're all laid at right angles) out and probably relay them length ways to leave a gap between the block and the wall ,create a channel and fill with fine gravel. Will this be adequate? The BP height isn't above the DP course. We had thought about an Arco drain, but the path is narrow (only about 150 mm wider than the wheelie bin) and there's nowhere handy for it to drain to.

Q Above the UPVC window and door there's a 100 mm piece of horizontal PVC filler on the inside and the same on the outside. There doesn't appear to be much between the two, so essentially a gap between the top of the window and the underside of the garage roof. Not sure how to deal with this?

Doubt there's any damp proofing in the floor, but having said that we're not sure if the utility room is original to the house or was added later. There is a step up from the garage into it. Don't know if that gives any clues to anything, but the garage floor is poor in places. It has largish pieces of gravel in it and seems to have denatured in places.

PREP
1. hack off any loose plaster/cement
2. seal any gaps (some of the battons that the panelling was fixed to is still in place round the windows ATM) round windows and doors
3. remove plaster board from ceiling
4. pull up carpet tiles and vinyl and check condition of floor
Q1- how smooth does the floor need to be for using Kingspan or similar?
Q2- is it best to bring the new wall structure down to the new floor or vice -versa?


FLOOR

Q3- what would you recommend minimum thickness of ply/OSB to use, bearing in mind weight of washing machine?
1. Lay DP membrane as per instructions from Kingspan here, ie bringing it up the walls past the height of the DPC, battoning under doorways etc https://www.kingspan.com/gb/en-gb/p...ice/why-and-how-to-construct-a-floating-floor
2. lay insulation as per above
3. lay OSB/ply over the top

WALLS
1. Batton walls with treated softwood backed with DPM, at 600 mm centreS and round windows/doors
2. use a tapered edge combination insulation/membrane,plasterboard product fixed to the battons
3. tape and use a drylining technique, or get a plasterer to skim
3. skirting boards

Q4. a couple of people have said best to use separate products because you can't tape the insulation boards at joints when using these combi products.We realise they're considerably more expensive than separate products, but chose them for ease as we're DIY'ers. Any opinions please?

Q5. If we used separate products, then is it best to fix batons to wall, place insulation between the batons flush against the wall, and then pb fixed to batons?
Q6. or place the insulation between the batons, but with a small air gap between the wall and the insulation, which is what you'd end up with if you used the combi' product?
planning on having surface mounted electrics running in metal conduit. so socket back boxes not an issue.
Q7. In both Q5 and 6, what about thermal bridging where the batons have no insulation over them?
Q8, could place insulation between and across , and then PB, or OSB, but we'll lose more space doing this. Is it worth it?

was planning on talking through plans for the ceiling, but kind of run out of steam!
 
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I suspect that your n̶o̶v̶e̶l̶ post is too long.
It might be best to search the plethora of "garage conversion" threads, and then if you still have questions come back, but bullet point them.
 
I suspect that your n̶o̶v̶e̶l̶ post is too long.
It might be best to search the plethora of "garage conversion" threads, and then if you still have questions come back, but bullet point them.
why did you write novel and then cross it through? I have read "the plethora" of garage conversion posts and do still have questions, which I thought I'd listed and numbered quite clearly?
Thanks for your help anyway.:)
 
Ok. Maybe I can try again?
There is actually a DPM under the concrete floor. Looks like the stuff used on flat roofs-some sort of mineral covered material
As I said the floor is 10 mm below the level of the DPC, and the DPM doesn't appear (there's still a batten round the bottom of the walls where the wood panelling was fixed ATM) to connect with the DPC. We can see that the 10 mm of wall is damp in some places at least.
We thought that as there was a DPM in place we could put foiled insulation down then the subfloor over that, but now think we should put a DPM down first.
The other issue I'd like advice on is where the builder who did kitchen work removed the concrete step in the kitchen/utility doorway. The door sat up above kitchen and utility room floor level on the step, if that makes sense.
Anyway, he removed it. We have a gap in the cavity wall between the suspended timber floor and the (70 mm lower) utility solid floor and we can see down into the foundations.
We can see the straight edge of the DPM on the Utility side, then an approx' 50mm gap, and then another straight edge of DPM just showing under the edge of the kitchen floor.
So my question is how to deal with this gap?
Would it be better to ditch the floating floor idea and instead build a suspended floor (of sorts) that joins up with the kitchen floor? I guess we would need to use joist hangers attached to one of the walls in the cavity to bridge the gap there?
Sorry if I'm asking stupid questions.
 
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