Thorfun

been through these discussions on this thread recently common consensus seems to be that 8mm expansion strip is all that's needed and it is what our screed company has asked for (just bought 125m of the 8mm x 150mm stuff from eBay). I thought the 25mm or thicker insulation upstand was to reduce thermal bridges? but you've got ICF, right? so there shouldn't be any of those. @Nickfromwales has also mentioned in the past (iirc) that even with the insulation upstand you'd still need the expansion strip. I do have a thousand things going around in my head though and so can't retain everything I read so I might be wrong. plus I'd hope the screed company know what they're doing!

We did very similar to @Bitpipe, he was, in fact, inspiration for a lot of my decisions. Our basement has cost us approx £1100/m2 and that has got us a large area for 'fun' rooms where our teenagers can go and be out of the way with their friends. that cost is just to build it though and doesn't include the fitting out costs. when you consider that in the SE England finished houses can go for approx £4000/m2 there is a massive uplift in value of the property by building underground when planning won't let you build above ground. it was quite an easy decision for us as our ground conditions meant that any foundations would've needed to go down 2m to the bedrock (we're on clay surrounded by ancient woodland) and so, although more cost, as we were going down 2m anyway I thought let's just dig it all out and build a basement that I've always wanted. Also, as has been said previously, you could reduce the size and bulk of the above ground structure and make it fit within the plot a bit more as you could put snug/cinema/study/gym etc all underground. I really like @ETC's sketches and look forward to seeing what @Iceverge comes up with. But, in saying all of that, I fully understand that you're very far down the line with this design and get that the thought of basically starting over again, when considering the time and costs you've already put in to it, is not very appealing. but read the comments above again. it's not just one person mentioning these things. you've got architects, architectural designers and other professionals and serial self-builders all saying the same thing. can they all be wrong? I remember watching an episode of 'Building the Dream' where Charlie went in and said the plans were all wrong and suggested they go back and redo the design and planning approval etc. the family were reluctant but they did in the end and said it was the best decision they'd made. sometimes we get so caught up in it all it takes someone on the sidelines to point things out and to help make those tough decisions. whatever you choose I wish you the best of luck and will follow your progress with interest.

but passivhaus principles are all about reducing heat loss through airtightness and insulation, those renewables you've listed are gravy on the top and the UFH is a byproduct of having a well insulated and airtight house. I think that what we'd really like to know is how you plan to build the superstructure and what details you're planning to achieve the passivhaus levels of build? you've already stated that it's going to be timber frame but are you planning passive house walls (300mm blown cellulose) or a standard closed-panel system, or an open-panel timber frame and fitting the insulation yourselves, which is what we've done, or even a SIPS build. knowing this will allow you to focus in on who to approach for quotes as some TF manufacturers don't offer some solutions. we chose the open-panel TF due to costs but if I hadn't built the basement then the money I would've saved would've gone on a 300mm blown cellulose wall structure but we couldn't afford that with the house that we designed with the basement included. also adding insulation yourself is not something to be taken lightly! I have saved thousands doing it ourselves but I am already pretty sick of the sight of insulation and I haven't even started on the internal PIR boards over the studs. For windows/doors we bought Norrsken and the fitters they got for me were excellent. Windows are very good quality 3g and were delivered on time and I couldn't fault the lads installing them. I can very highly recommend Norrsken and am a very happy customer. this is the approach we took and it has worked well so far. don't underestimate the time and energy project managing takes though. your brain will be swirling with the 100s of decisions you have to make and sourcing materials to ensure they're on-site at the right time for the trades to do the work etc. There are many blogs on here which will give you great insight in to the whole process. I highly recommend you read through them. mere babies. ? best of luck with it all, looks like a great project and we look forward to reading about your progress.

no, it's really not that bad at all down there. and it won't get wet again as all our windows and doors are in now so if we get any more water in the basement then we've got big problems!

thanks. so that makes me feel a bit better about running heater and dehumidifier on one extension during work hours. will turn the heater off overnight though.

definitely not groundwater! it's more just a case of rain getting in to the building and through the block and beam before we put the windows and doors in. and it's cold down there (about 6°C) and so I just wanted to warm it up and get it dry. I looked at the dehumidifier sticker and they're a bit cheeky with their 20l/day. that's at 30°C/80% humidity! it's 10l/day at 27°C/60%. so at 6°/90% I'm probably not getting much water out at all. which is confirmed by how little I'm having to empty the tray. ? I'll stick with my current plan though and I will get it dry.

that is a damn good idea! I will speak to my sparky about this. I think we're still about 4 - 6 weeks away from starting 1st fix, the bloody insulating is taking me bloody ages. ?

yeah. I saw this thread. devastating. we live on site in the existing property so there is always a sense of over-confidence as we're always here if things go wrong. but even living on-site wouldn't really help if a fire like that breaks out.

I didn't know this. how is that calculated? so with one heater AND the dehumidifier on one extension I'll be over the 10A continuous load? why do they say a 13A plug then if it will only take 10A? isn't that dangerous and confusing?

thanks Temp. looks like I'll do that. sticker on the dehumidifier does say 420W and I can plug both extensions in sockets in the main house that are on different rings which is fortunate! with the formulas correct I'm thinking that one heater and dehumidifier on one extension (2420/230=10.53A and even if the voltage drop is to 220V then that's still 11A) and the other heater on the other extension and things will be ok.

yep. I have fully unwound it and run it out along and through the basement so it is unwound and not just off the reel in a heap on the floor!

I looked at hiring an industrial dehumidifier and the specs on it just weren't very good! said it removed 20l/day and so I bought a dehumidifier that removed the same quantity and it is running but the trouble is I can't seal the basement very well as there's a massive void where the stairs will eventually go. so I thought heat the room and dehumidify it at the same time. I thought the heat would allow the air to hold more moisture that the dehumidifier could then remove.

oh dear. so I should stop using the one heater on the 40m lead then? I also have the dehumidifier running on the same 40m extension. out of interest, how does the length of the extension make a difference? would the 25m extension be better? I don't have electrics in the new house yet so I'm running everything off extension leads from the existing house.

I'm trying to put some heat in to our basement to dry it out and I have the following products to assist me. 2 x PTC 2kW heaters (https://www.screwfix.com/p/ptc-2000-freestanding-ptc-heater-2kw/9158t) 1 x dehumidifier (https://www.amazon.co.uk/gp/product/B0839M7VQT/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1) 1 x plug-in oil radiator (it's the wife's and I don't have any specification on it although I could climb down the ladder to the basement to find some details out if required!) I'm wanting to run both 2kW heaters from the same extension cable (I have this https://www.mad4tools.com/masterplug-open-drum-40-metre-cable-extension-reel-240v-13a and this https://www.mad4tools.com/masterplug-open-drum-25-metre-cable-extension-reel-240v available to use) and the dehumidifier and radiator of the other extension cable. I'm looking for some smart people to tell me if running the items off of those reels is an issue. I did A-level physics 30-odd years ago but spent more time mucking around that I did learning which would probably account for the 'E' grade I got. I do remember V=IR and P=IV but I'm not sure how that relates to running this stuff on a 13amp extension reel!

I had read that EPS was a nightmare with ufh staples. so I decided to go with 25mm PIR in the end. still worked out cheaper than having that space done in liquid screed and using click-strips or the like. I'm hoping that the ufh staples will hold fine in 25mm PIR!

I understand this but I had no issues using it. Fully PPE’d up and was cautious. I still have all my limbs intact. I bought specific shot fire fixings from my local fixings store.

A Paslode SPIT will do the trick. https://www.jewson.co.uk/p/nail-gun-JTH03300 I hired one through Jewson and it nailed some 4x2 into our steels. they're very loud though so I highly recommend using ear defenders!

it's definitely expansion that I need. stated on the prep document from the liquid screeders. I have no need for perimeter insulation in the other sense of the phrase. this screed is going in our basement on top of 25mm PIR and ufh pipes. below that is 250mm reinforced slab with 200mm EPS300 underneath that. the walls are 250mm reinforced concrete with 200mm EPS100 externally. so there are no thermal bridges to rectify and no need for perimeter insulation. to quote from our pre-install prep instructions: "Expansion Edging and Crack reduction You should install a minimum 8mm perimeter edging strip around the perimeter of EVERY area to be screeded including in and around door thresholds." so, I'm just going to go for the yellow stuff from eBay that I linked to in the first post.

sorry. didn't see you'd edited this post. it's for expansion only. I have 200mm EPS outside my basement walls that wraps underneath the slab.

Jewsons quoted me 4 - 6 weeks when I looked for 25mm EPS100 for insulation under the screed.

lead times and ripping to width put me off this route.

I've done a search on the forum and couldn't find much detail about recommendations for what to use here. I found this post from @Nickfromwales back in 2017 but the links aren't working any more so it's hard to know what products they relate to our liquid screeders have suggest the JG product (https://www.screwfix.com/p/jg-speedfit-jgufhedge-edge-insulation-roll-150mm-x-25m/87019) but this is 4x the price of something like this (https://www.ebay.co.uk/itm/350335173377?hash=item51919a8301:g:XzYAAOSw6dteOuEt&_trksid=p5731.m3795) and twice the price of this (https://www.underfloorshop.co.uk/product/underfloor-heating-edge-insulation-roll-50m-150mm-x-8mm/?gclid=EAIaIQobChMIltDoleCu9QIVy-3tCh1UkgK9EAQYBCABEgJjg_D_BwE). I would assume that this stuff is pretty much the same (apart from colour) as it's all 8mm x 150mm and so why would anyone buy the JG stuff? is this a case that paying more is not actually a better product?

I wonder if it helps that the Architect and Architectural Technologist that did the work at the practise we used are both relatively young?

our [A|a]rchitect gave us a SketchUp file of the CAD drawings. that way I could zoom in, measure, check, adapt etc to my hearts content without affecting the CAD drawings. seemed like a perfect solution to me.

that's a good price. the quote for ours comes in at about £19/m². but we are in SE England where prices are inflated!