anarres

In my office outbuilding I have a well insulated slab foundation approx 30m2 (200mm XPS under 170mm concrete, with DPM) which is fairly level (up to 10mm dips in 2 places). I have 75mm to make up to final floor level. I was wondering if instead of screeding (which would be a significant PITA), if I could instead do the following: Level the slab with something like Mapei 1210 leveller (for 1mm to 10mm) add DPM (standard 1200 gauge poly, up the sides and taped to existing DPM for slab) add 50mm XPS (e.g. Danopren) add 5mm high density underlay (for sound reduction mainly) finish with floating engineered wooden floor As I understand it the reason to screed is to make the floor level and it it is not a structural layer, so not technically required. I guess my main question is if I can use 50mm XPS and then another underlay on top - because I'm not convinced XPS by itself wouldn't cause significant noise issues as it is so rigid. If I can do this, can/should I glue down the DPM and/or the XPS to make it firmer? Perhaps if I lay the XPS correctly it would not be able to have any movement anyway but I've not found this construction method anywhere so I'm scratching my head a bit...

Thanks for the responses. I'm not sure why I thought there was a restriction on toilets - I'd read that they could not be habitable and I assumed this to mean they could not have everything required to be a dwelling. Instead I just re-read the guidance and it clearly says "NO sleeping accommodation" but that's crazy because it just means don't put a permanent bed in right? In any case there are practical issues about waste pipes... my rainwater goes to a soakaway but proper waste would have to go 45m to reach up to the existing drainage and near some large trees through very heavy clay (or take wide detours). These practical issues make it not worthwhile for now at least. Perhaps when I renovate my house in the next year or two, when I have diggers on site and I am relaying the existing soil pipes in the house. Can anyone answer my questions about A2A heat pump positioning though?

I'm not doubting what you're saying but I've seen a lot of posts about how UFH isn't quick to heat up due to the maximum floor temp of 27 degrees, especially if using laminate/wood? In either case I would use smart controls. I've been looking at a 2 part A2A heat pump and the main downside I can see is noise, but reduced running costs compared to electric UFH.

Hmm what's the issue? I've already constructed this, and to connect underground the waste pipe would have to go through two 90 degree turns and it's possibly not deep enough at the front to accommodate this. Yes, but if it had a toilet it would need planning permission as it would be habitable, and this was done under permitted development. I don't believe they would sign off on building essentially a small house in the garden (also it would need to be signed off on regs - I did in fact do it to regs standard but without notification or anything being signed off). Also, I have many trees in the garden and the route the electrics and water has taken is not a straight line, and it goes to the front (middle) of the build - waste would need to come from one of the sides and the route to the main drainage would really not be simple. If planning rules change in future there is the possibility of adding it in but it's not happening right now.

Thanks for the responses everyone, much appreciated. 😀 I've been down an A2A heat pump rabbit hole the last day or so and it looks very promising. If it's ok I have some follow-up questions... Near the top of the list of requirements for me is noise followed by reliability and then cost - are there any brands which you would recommend or avoid? Are there websites you would recommend or avoid? I read that you should take cubic volume and multiply by 5 for a BTU rating which gives me about 15000BTU. Looking at an 18000BTU unit the max amps are under 10, so I'm guessing running it on a dedicated 16A line would make sense? I also read you must have a split unit professionally installed - is this correct? Is there an actual danger to doing it yourself if you are a competent DIY-er (like refrigerant gas leaks??)? I guess it's going to add a few hundreds to the price to get it professionally done and I've not needed any assistance so far with building the office (other than having to get electricial sign-off). I have a question about placement - my room is a rectangle (approx 8m x 4m), with a standard gable roof (2.4m room height with another 1.6m height on the roof). Half the space has a ceiling and the other half is open to the roof. The door (and 2 windows) are all on one of the long sides. I can either place this unit in the middle of one of the small walls (@2.4m high) - this wouldn't look great TBH but circulating air would probably move around the space better. The other option is to place it in (near?) the middle of one of the long sides, opposite the door, and just on the corner where the half-ceiling ends (so just under 2.4m). I'm guessing in the middle of the short wall where it can blow in to the open roof space as well as down the long room is better, but would the other position not work or is it possibility an acceptable trade off? I've attached a pic of the office with roof removed and the two positions marked.

Hi, I have built an office in the garden (32sqm) and I am looking for advice on how best to heat it in the winter. I'm leaning towards electric UFH but maybe this isn't right. If UFH is the right choice I'm not sure on if my proposed construction would work (and I can't easily find info on this online). There is a concrete slab base with good insulation underneath, and I have 70mm - 75mm to the final floor height. I was looking at levelling the slab base (it's up to 10mm low in a couple of places but generally pretty flat) putting 50mm XPS insulation down, an electric heating mat on top, with floating engineered or laminate floor to finish. The first question - is electric underfloor heating so slow to heat up that I'm better off with wall mounted IR heaters or something else? I'll be using the office for 8 hours a day, 5 days a week so super-reactive heating isn't really required, and I don't mind it a bit chilly in winter as long as it's not totally freezing. The office itself is fairly well insulated (see below). My second question is can I put an electric mat straight on top of 50mm insulation, or do I have to use thinner insulation board with a screed on top? I'd prefer the first option because it's both easier to do (by myself), and more importantly would push more of the heat into the room rather than heating the slab below. If it helps the office construction is: 8m x 4m external size 7.6m x 3.6m internal size Built on concrete slab 170mm thick (reinforced), with 200mm XPS insulation underneath. Wall construction: plinth of 3 courses engineering brick (225mm high), then 100mm timber frame construction with glasswool insulation between and 80mm wood fibre and render externally, and 25mm PIR + plasterboard internally. Roof construction: 125mm rafters with glasswool between and 25mm PIR + plasterboard internally, tiled externally Final note - there is no hot water or gas out here (40m from the main building) so electric is the only option for heating one way or another.

Hi everyone, Over the last couple of years I've built a small (32sqm) outdoor office in my garden, and I'm nearing completion, although I have a number of issues to fix (will be posting these in the appropriate forums). I'm also at the very start of a large renovation/extension of my 2 bed bungalow into a 1.5 storey 5 bed house (had pre-app advice and on the verge of submitting plans). I'm planning to have a single contractor up to ground level, then trades in after that where needed to get watertight. I can do a reasonable amount myself but I guess how much I do will be a question of available time. I also have to live here so some interesting logistics are involved in how I do this. I'm sure I will need a lot of advice on the way! I've learned a lot in the last decade or so but I'm definitely jack of all trades and master of none, so I know my limits and when I need help.