gambo

I live in a typical estate with a back garden measuring around 10x12m. For some time we were planning to do extension but given today's prices I don't feel it's worth it. On the other hand I always wanted to have a garden room/office which I could use for work, but I don't want the hassle of running to toilet to the house so it needs a proper toilet (ideally) with shower. I would also use it as a guest house when someone visits us. How much hassle is it to get permission for something like this? The plan would be to get it very well insulated and heat using some small ASHP but if it's well insulated anything will probably be good enough even a candle if it's just 10-15m2.

Wouldn't this create a significant thermal bridge (the battens)? I've just removed carpet and underlay and put: 25mm quinn therm (from someone's skip) + 6mm cement board + carpet (but no old underlay). It's just around my desk and chair to see how it feels. I'm a bit worried about thermal bridging of battens so perhaps using thin backer boards + 25mm kingspan would spread the load evenly. I'm a bit worried that that's not well money spent. Based on my research it would cost £10-15k at least. Having a very well insulated floor would force me to start looking at other bits like insulating walls (internally), replacing windows. Now I at least have an excuse that the house is not good for ASHP anyway. Other thing is finding someone who will replace the floor without causing structural damage to the house.

That's the plan but trying to understand what to be prepared for and what to use. Mrs doesn't like when I rip off something in a middle of the house and leave it for couple months I'm thinking about removing plasterboard in window bay to see if there is a cavity gap I could fill, there is one under sill I filled with plastic wool as a temporary solution but can't feel if the bay is filled with bricks.

Why mastic beads instead of some silicone and what do you mean by doing it properly? I removed internal trim around my window some time ago because it was blowing so much air I thought someone installed a micro PIV unit under it. Turned out there were holes I could put my finger in. I filled it initially with soudal foam but haven't done a proper finishing yet because I'm still investigating what the best solution is. Would you in such case remove it and use FM330 inside too?

That's the plan, ie. insulation boards + engineered wood (woodpecker 15mm). Posts above suggest using T&G over insulation boards but it would reduce the insulation by 18mm. I'm thinking if I can just buy wider planks to spread the load even more.

I haven't checked the depth. I most likely stick to insulating the current slab as I think it could be too disturbing to dig it up.

How much could it cost on 80s/90s build very roughly? Just for digging. Im a bit worried it will make a lot of mess.

I will rather move house than reduce height by 10-15cm. So, after more research my options I think are: PIR + T&G or marmox, perhaps PIR + marmox to achieve better U.

50-60mm including wood floor is the maximum I can sacrifice. Adding T&G feels like a waste of space but I know I can't lay floor on top of PIR. Could I lay tile backer boards on PIR instead of T&G, or just backer board of let's say 40mm?

Yes, I meant 5cm. I need to check stairs and building regs. Upstairs there already is 6mm cement board (as sound insulation) + 3-5mm underlay + 15mm floor but the stairs are not finished yet so perhaps I could adjust them accordingly. What would be the best solution if I wanted UFH? btw we can ignore stairs for now, I don't like them tbh so would happily replace them if it opens us to more suitable options.

I'm afraid it's just concrete floor. I can't see any ventilation outside in bricks and when I lifted a piece of carpet I can only see concrete. It feels warmer where laminate floor is (with some sort of insulation underlay) than in living room and garage conversion. The garage conversion is the coldest room but apparently it was done during the build even though LA doesn't know about it.

Any specific expanding foam you would use? I may have a similar issue given how cold it's inside one of the units. When I had similar hole behind skirting I put a piece of xps (leftover) then exp foam around it.

I live in a detached house from late 80s. At the moment the floor downstairs is some cheap carpet with rubber waffle underlay (tog of around 1.3-1.5 based on what i've found). When it's not freezing outside I can live comfortably with temp set to 19.5-20. But after 2-3 days of very low temperatures I need to increase the temp to 20.5-21 because of the cold i get from floor in some rooms. I've already renovated upstairs and am quite glad I didn't start downstairs before the energy crisis because I wouldn't have done it very efficiently. I have lots of different leftovers at home and one of them is some random 9mm sheet of insulation from b&q (insulation board). I put it on top of carpet and can already feel a HUGE difference. I don't think the technical spec of the board actually proves what i feel but perhaps it also thanks to air trapped between carpet and the board. Anyway, downstairs will be renovated and will lay engineered floor. I'm thinking about heat pump in future but I don't want to put 100m boards because the most i feel I can sacrifice in height is 50mm including wood floor. So, maybe HP won't be needed if I insulate the house properly and lower the cost of gas. What would be the best to put as underlay? 25mm eps topped with backer board?