Thorfun

ha ha....I've paid the deposit for my solar PV and powerwall 2. just need to get the house built to a stage we can install. should be about 6 months or so I hope.

thank you @jack. puts my mind at ease. I also asked for them to just make it all one zone after reading on here. I think with a slab this thick the response times will be so slow there's no point of having individual zones and we'll just keep the whole basement at a constant temperature, assuming we even need to turn it on for most of the year that is!

if I may carry on with this thread and ask another question somewhat related... the A393 rebar that the SE has specified in our slab has a 200mm spacing between the 10mm wires. if I'm not mistaken I've read on here that the UFH pipes are better off being supported by following the runs of rebar so I'd be looking at 200mm spacing for the UFH pipes. I've spoken to Wunda and their response was: "As you will be having a heat pump, I would advise against taking the pipe spacings to 200mm. Having a heat pump would mean the heat outputs are naturally less than they would be with a boiler and by spacing the pipe further apart would make it less again, meaning you would most likely need a supplementary form of heating alongside the underfloor heating." obviously, Wunda are not aware of our planned insulation or airtightness levels as they don't have the SAP calculations (nor did they ask for them), so this could be a stock response from them. This isn't a financial decision for me as the extra cost for 150mm spacing would be negligible in the grand scheme of things it's more about 200mm centres will be better protected during the slab pour. Anyone able to comment or advise on this? I have posed the question to the suppliers/designers of our ASHP system but while I wait for that response I thought I'd ask the collective mind on here.

maybe. tbh I don't really have a clue. I have done lots of reading on this whole thing but I don't seem to be able to retain as much information as I used to (mis-spent youth probably) so I keep having to go over it all again and again.

the dig depth from ground level is approx 4m and with the stone at between 2 - 2.4m it's going around 2m of stone that has to come out. We have a certain type of stone that's local to our area and there is a company that deals with it so I will be speaking to them about either selling it or converting it in to paving slabs etc. so we've already thought of that. ? Don't worry, I'll be taking lots of photos and boring everyone on here with blog posts.

our 'normal' trench foundations for the non-basement areas of the build are designed to be dug down to the sandstone. this is required because of the clay we're on. for the basement though, the sandstone is not deep enough at between 2m - 2.4m from ground level and our basement dig is much deeper than that. so, it's either dig through the sandstone or not have a basement. I think we all know which one won on that decision. ? I don't think you put a spanner in the works. I appreciate a different view on it all. and in fact the way the basement guys have come back saying it'll cost more to take the care around the pipes actually gives me more confidence in them that they do actually know what they're doing! everything I've done with regards to the basement and foundations has been run by the structural engineers (TSD). they have been amazing throughout and I'm very grateful for the assistance and quick responses they've given me to my numerous questions. I also phoned Wunda today about the pipes they use and their technical team said no issues with attaching direct to the rebar using cable ties. so I've got the sign off from them if I decide to go this route and to use them. I'm really not worried about abrasion though as there are so many people on here with pipes attached to rebar and we have friends that have just finished an MBC build with their passive foundations and have the same thing so I just don't think it's an issue if you use the right pipe. this has been an interesting thread and I'm very glad I started it. definitely lots of food for thought!

sure, that link to another post above has a document that will explain it for you. but basically it boils down to for every metre below ground level you are you add 14mm of 0.04W/mK of insulation due to the effect of the earth below it. I'm 99% sure the perimeter/area ratio does apply. pretty sure other posters with more knowledge than me on the subject have said as much.

Hi Gus, thanks for the good advice. I have spoken to the SE and they're ok with the proposal with a few caveats as follows: "Firstly, you should check with the UFH pipe supplier that they are okay with the pipes being tied to the rebar, as some manufacturers are okay with this and some are not due to possible wear in the pipe wall (I’m guessing it has to do with the wall build-up of the pipe). Secondly, just make sure there are no big bunches of pipes together, as these can cause a weakness in the concrete, and can easily happen in the vicinity of the manifold. We usually look for bunches that are no more than 150mm across with a min. gap of 100mm to the next bunch of pipes (hopefully this is clear)." I have also had a response from the basement contractors who have said there will be an extra cost for power floating and protecting / minding the heating strips while the concrete is being placed, so you're spot on there! I have asked what the extra cost will be and am awaiting a response. your advice is wise and it makes a lot of sense and gives a nicely different perspective. The problem at the moment is they've already dug 2.4m down and hit the sandstone and there isn't any surface water so, even if I did take a break and see if the water comes in, I doubt there'd be any to come in especially as we head further in to summer! But I will sleep on it and ponder some more in the morning.

comes out to 0.103W/m2K when adding the 3.5m below ground insulated effect (14mm x 3.5m of 0.04W/mK insulation) which will do me just fine. increasing it to 250mm EPS300 gives 0.089W/m2K which, when you consider the extra cost of dig out and muck away over the area and the cost of the extra EPS300 and labour to lay it, I'm not sure it's worth it.

yep. it is EPS300 under the basement and other parts of the house. I had confirmation from the SE that the thickness of the EPS300 had no bearing on the structural calculations so could increase or decrease as desired.

I was....then dinner was on the table so I had to take a break.....back on it now. ?

but at a depth of 3.5m under ground that U-value is much reduced.

well insulated and airtight is the name of the game around here. ?

200mm EPS. I've done the calculations using previously supplied document that @A_L linked here taking in to consideration the depth below ground. although it's just occurred to me that the recent change I've made to the insulation levels at ground level has removed 30mm PIR from the slab. s**t. think I need to do some more quick calculations to make sure what I've done hasn't completely messed up my desired U-values. ?‍♂️

I know a large number of folks on here have insulated slabs where generally the slab is 100mm thick and the UFH pipes are cable tied to the rebar. We're going this route now for our basement UFH but our slab is 250mm thick with 200mm EPS underneath. I was just wondering if a slab ever got to a thickness where putting the pipe within the slab became the wrong thing to do?

<goes hunting for a photo of @Dreadnaught's toilet>

that could just be the camera angle. ? but I'm not normally known for being very tidy so I whole heartedly accept the compliment. thank you. ?

I'm having one of those enthalpy exchangers jobbies on my Zehnder unit. apparently that doesn't need a condensate drain thingy-ma-jig.

it's been a bit quiet on our blog so I thought I should update it. While we've been waiting for the groundworks to start we've been busy getting the site ready. This has included getting the new entrance to the plot created, getting the sub-base for the driveway in place and then topping it off with a layer of 6F5 as a hardstanding for the construction vehicles (after the build I can then remove the top layer to reveal the, hopefully, still in good condition sub-base to put the final layer on top of. well that's the plan at least!) and putting up the site toilet. Obviously the last job was the most important. Our new entrance to the plot is over a culvert and as it's connecting to an adopted road it had to be done by an insured contractor and so I had to fork out the cash to get it done. but they did a very good job and we're very happy with it. the culvert in situ with enough concrete on top to take the lorries and cranes for the build a nice base layer of tarmac finished, which will see us through the build when they will come back and put a nicely finished top layer on. nice sand-bagging. ? once, they'd finished the entrance we moved on to the driveway and hardstanding but, first, an observation....it's funny how things don't look as big on paper as they do in real life. that's exactly the conclusion I came to after I looked at the plans and thought "that driveway isn't that big I'll just dig it out myself and save myself a fair chunk of cash" and then went on to dig it out. it was only after I'd finished the 120m2 area did I realise how big the driveway is going to be (I swear it doesn't look that big on paper!). oh well, it's done now, at least we'll have plenty of parking. maybe I can rent it out and do a 'Park and Ride' in to the local town to recoup some of the costs. ? a big hole dug and covered in Terram (or an equivalent to be exact) 100 tonnes of beautiful primary Type-3 granite aggregate all compacted by that beast of a roller. Don't really care what everyone else thinks but I think I did a darn good job for my first driveway sub-base. Sadly it all got covered by another layer of Terram and then a load of 6F5 got dumped on top and it now looks like a building site hardstanding area (which is what it is!). here's a photo of the lovely lady of the house helping out on the roller. it was a bit cold out that day. And finally we get to the most important job, the building of the site toilet. Friends of ours got it from a local freebie site and used it for their self-build, we then dismantled it, transported it to our site, erected it, put a new roof on it and plumbed in the toilet and sink to our existing STP. we think it's a very luxurious WC for site use. it's even got a couple of windows so you can watch the work progress while you're doing your business. and that's it for this blog post. we are extremely excited as tomorrow is the day we've been waiting for and the groundworks starts in earnest. They'll be on site to set up and start digging out the big hole for the basement as the basement contractors are due to start on the 3rd May so we should start to see some real progress now! finally!! thanks for reading. ?

I think we need to take a leaf out of your book. we're getting about 3 or 4 mice a day at the moment being brought in.

is that a good thing? ?

just realised my post sounded like I was planning on two of the passive house flaps! but when I mentioned 2 x flaps I was talking normal flaps that cost £30 from the local pet shop. unless you were just making an obscure reference to this of course. https://en.wikipedia.org/wiki/Filthy_Rich_%26_Catflap

whoops! sorry. I hadn't got to that part of the forum yet in my research. my apologies! but how to the cat(s) get from the main house to the sun room? I guess they just stand at the doors and shout loudly at you to open them? that's what our cats do whenever they want something

I'm waiting for them to integrate a video camera to check for mice/birds in our cat's mouths and deny/allow entrance accordingly. then I'll be all-in for one!

how are you planning on maintaining air tightness with the cat flap? I see airtight flaps are crazy money (https://www.petwalk.at/shop/doors) available also from @craig @ Ecowin (https://www.ecowin.co.uk/products/petwalk/) (although I have to say they do look pretty darn cool!). I was planning on having one flap on a door into the garage and then another flap on an external door from the garage outside. the other option is to build a deep tunnel through the wall so that there are 2 x flaps through the tunnel, one at the start and one at the end so that only one flap is open at a time.