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The Thermotech pipe helped here, it's very robust and doesn't kink. It's Ø17 polyethylene which won't damage from the mesh being trodden on squeezing the pipe.

I did one that had a massively over-engineered slab (I think I talked the buffoon in charge down from nearly 300mm with a screed for the UFH down to 230 with the heating pipes inboard of the raft). Bonkers. This was a 1.5 storey ICF build, timber floors. The client has a 7kW heat-pump running UFH with 120mm c's; the idea of the tighter laid pipe loops is being they can use the additional water volume and additional cross sectional area of pipe > concrete (surface contact area) to quickly chunk heat into the slab during pockets of cheap electricity, but more importantly to allow cooling to be done at a higher temp (to stay WELL away from the dewpoint). Is in and working well, but it's a huge thing to get to a set temp. Once it's there, it's very comfortable, just needs the stat to have the aforementioned tight hysteresis to prevent unwanted under / over shoot. Seriously consider the extra volume of pipe & water as it can reduce or negate the buffer tank

When choosing a lock its worth checking what the Lock Picking Lawyer on YouTube thinks of it. Or your house might be as secure as this...

Yes they are a good personable team. In fact I'm working with them on a project. I also have found Hilliard and his team very approachable and willing to engage to date. My outline SE brief from the Client is to coordinate a Hilliard basement design with a superstructure. In some ways my brief is to act as the overall supervising Engineer for the project. I'll spot check say 10% of Hilliard's calcs and make sure their stuff makes sense in terms of overall stability and performance.. everyone has a boss / someone watching over.. even Tanners! For all .. Nick mentions a " passive raft" this tends to be a structrual concrete slab and by my previous post you would expect that to have no movement joints. But you can also do passive house design with a direct ground bearing slab on insulation and this would often have movement joints. We make these thin as we can with minimal anticrack reinforcement or use concrete with fibres to control the cracking.. @saveasteading has implemented this approach. @Nickfromwales I think we are both singing from the same hymn sheet here.. practical and buildable design!

Nice job. I very much like the idea (simplicity) of installing the mesh atop the UFH pipes, as the UFH goes down very quickly and simply, just it pains me to trust the groundworkers to not damage the pipes during the steel installation.... If one company is doing the lot then it's managed and there should be some quality control and robustness of their procedures, but if left to Tom > Dick > Harry then I'll always prefer leaving the meat get off site and then I install over the top before the concrete goes down.

Hello all. I'm planning a garage upgrade this year and could do with some pointers as I'd like to do a lot of it myself if possible including working out the costs in advance where posible. My existing garage is on a 6x3m slab and I have the space to extend it by 3m or more into my garden and out to 5m wide to the property boundary. For budget reasons, I only want to add to it, not remove and replace it. I have already bought nearly enough concrete pebble dash panels and want to set them on a single course of blocks to give a decent headroom. First question is how do I calculate the correct block to take weight? The blocks I'm looking at have a load rating of either 3.6N/mm2 or 7.3N/mm2. Is it just the actual weight of the walls and the roof plus a bit for safety or something more? Secondly, I have what I can only describe as a brick chimney in the garden which could limit how long the garage can be. It's about 1.8m deep and has an in and out pipe that only ever seems to flow a small amount of water, fortunately not under where I'm planning to build. The manhole cover and surrounding area of about 4x5m is about ½m above the garage floor level. My local water company don't have it on their plans, even though the house was built in the 1960s. Any advice on how close I can put my new slab to it without any issues? Thanks in advance.

Unlikely as an ASHP normally will supply a minimum of 25 Deg in heating mode. Then at deltaT 4, plus restart hysterisis for the heat pump, you need the floor temp to drop below 20. If that's the case your floor would provide zero heat to the house. Tried that with mine (25 Deg flow) it ran fine, but never restarted, floor just never cooled enough to allow ASHP to restart. Thermostat you need a hysterisis of 0.1 or less if you can one. It has to be on/off not TPI. I have 100mm concrete with UFH pipes at the bottom - I am also 300mm pipe centres, response is slow. But if you are prepared it's something you can use to an advantage. But don't expect setbacks to work, they won't. WC works fine. If you use a tou tariff, get a bigger heat pump and batch charge the floor storage heater mode. I am at a out 3kW at -9 and have a 6kW ASHP, will run without stopping buffering into the floor if I want it to. If your heat loss is 2kW, you need 48kWh of heat, if you only have 7 hours to heat you need 7kW of heat input, plus it may need defrost or modulate down to manage dT, so even 8kW would be fine.

Very quick reply as it is past bedtime. It sounds like you have it all covered and well understood. The ASHP with weather compensation handles the temp variance. It will take awhile to dial in the best compensation curve. So in the early days the house might not be at quite the right temp. The heat changes are very gradual, but that is actually its strength. A well insulated, air tight house is nothing like traditional houses. In my build you don’t even think the heating is on, the floor is cool to touch. But somehow the house at 20° does not feel cold, whereas the 90’s built rental house feels freezing even when the room temp is 24°. Remember, even though you have MVHR you can still just open windows to quickly change the room temp. It will have very little impact on the floor or ASHP in the short term. You are not losing control of the heating, you don’t need to worry about the response time. Just one extra thought, 250mm raft sounds very thick, my ring beam is 250mm but the main raft is 150mm. I have a very heavy ICF house, concrete stairs and concrete first floor, I would have thought you only needed 100mm raft for a timber frame house.

Insulated Rafts remain pretty niche in the UK, so you'll not find a standard way of incorporating UFH. They are however quite standard in Sweden, which is where Advanced Foundation Technology originate from. AFT Engineered and supplied my insulated raft including UFH from ThermoTech (Sweden) - Olof even dropped by to help install the UFH. The Swedes do their UFH a little differently to the UK but they take their plumbing very seriously.

I have to say, the Illbruck FM330 stuff is very good, a totally different beast to the regular build-shed foams. I've had the pain benefit of being around some very elongated full new builds from day 1 to day Z (thanks to Covid) and have used this stuff for many different applications, from fixing things, general sealing, through to airtightness work and more; I've used it thick & thin! I've then been around it for anywhere up to a year, sometimes more at the plant rooms etc, after it was first squirted in, and I cannot recall any notable shrinkage with this stuff. I do make a point of spraying a mist of water, if adverse I'll do a 50/50 water/PVA mix, and this does help the curing process no end. It's also massively hardier than regular foam, when poked / scraped / cut into etc. Yup, I install the PIR with angled cuts, so there is friction for fitting, and a gap to get some foam into. Gaps aren't the killer here though, addressing airflow up between the boards is, hence me saying to foil tape over the tops of the joists from PIR board to PIR board (foil backed obvs) as the VCL.

Sketch it for me please what you're thinking. You really need to have the bottom of the membrane quite taut or else you'll end up with baggy droopy bottoms empty voids in the insulation which isn't good. The deeper you go the harder this will be to execute in practice.

Have replied. I do this as a day job but feel free to PM me and will be happy to spend a bit of time having a chat with you on the phone. Have included my tel number in the survey response. Text me first as as I oten filter my calls. All the best. I know that geting hard info / evidence for a PHD is challenging to say the least.

Great, IF it's a 1 bedroom house yes? Factor in some redundant space for one, install cables and plumbing in abeyance, then add it later if needed?

Of all the foam products, EPS is my favourite. Not great in a fire, but then I don't suppose any foams are. Form personal "laboratory" fire testing it seems to give the least funky gasses too.

If you do this as meticulously as you can, and get a score of <1.0 ACH, then that is absolutelt going to be the best tine and money you have spent of the job. You can have 1000mm of insulation in a draughty house, and still be sat there with the heating on full and be cold. Airtightness is where the rewards are really reaped; then you'll need MVHR and THEN the MVHR (HR) will look after you for life. Spend on 'fabric first', and enjoy the benefits long term. Quality doors and glazing next, then bags of solar PV after that. Prob after that will be a nice kitchen for the other half so you don't get murdered before the ROI is calculable, lol .

To add: 100mm, and with only 1x layer of reinforcing steel mesh too Thicker at intermediate junctions and ring beams etc, obvs.

We are due to build a small very well insulated 1.5 storey timber frame house later this summer. Using the Jeremy Harris spreadsheet, the house will have a thermal demand of under under 2kw when it is -10c outside . U values of 0.09, 0.13 and 0.10 for the roof, walls and floor respectively. The house has passed Part O for overheating and will have MVHR. We are now definitely going to have an85m2 insulated reinforced raft. I want to have ufh in the raft and in line with what others have done on this site it will have 3-4 loops, a singe zone and one thermostat. We will have a small ashp perhaps 3.5-5kw. I expect water temperatures in the ufh will be under 25c. The ashp will also provide our hot water - a 250l unvented cylinder. I keep on being given the advice that a 250mm slab will be very slow to heat or cool e.g. from my designer "My concern with a heated slab of 250mm thick is that the response times will be so slow that you will find that you are unable to adjust internal temperatures when the house heats up to the required temperature and then continues to heat when you don't want it because of the thermal mass." I am aware that the raft will be slow to warm up and cool down but am I right to believe that with the weather compensation a single thermostat and a low water temperature I am unlikely to have the issues suggested re overshoot? It would be great to hear from those on the forum that have thick rafts, ufh in raft and a well insulated house . Thanks in advance

Not IMHO, and even more so as it's the North elevation. In my opinion, you've been lucky elsewhere. Vapour is supposed to be arrested at the fabric connections, to seal the room, then the cosmetic layers get applied afterwards and decorated. You cannot compare this to a DPC as the DPC is at the foot of a wall only with the remainder of the surface left to 'breathe', so "no" . Next steps are: Go and scream loudly into a pillow so as to not frighten the kids, Take everything off and do it again properly. Drink beer when done. I genuinely think I should have worked as a therapist

Exactly where I want us to be. I investigated these units more for cooling than heating, and I was dissuaded on the grounds that they won’t have a significant effect on our internal air temperature because of the low relative volume of air going through the MVHR system. We are, however, aiming at a long way short of PH standard insulation, not much better than building regs in fact, (though we are putting great efforts into being airtight). I can understand that if part O means we see fewer ‘glazed cathedrals’ type grand designs, or at least lots of high spec anti solar glazing, that the cooling needed would be moderate in a very well insulated house. But ours, despite the modest of glazing, might need more cooling. Won’t know till we’re there. We’re going for an ASHP that can be converted to cooling, so we can gently (above dew point) cool the downstairs UFH, with a fan coil in our bedroom all on a single zone. I still wonder about cooling the MVHR airstream too though….

@Nick Laslett HAS got this, and it's doing great, is what he's saying. Not sure if you're confused there, sorry. FYI @zzPaulzz, I have done a number of MBC PH TF M&E installations, (I got recommended directly by MBC or otherwise got awarded the project after MBC engaged), and there has been UFH in a 100mm constructional slab on EVERY SINGLE ONE . I have worked with many SE's to date, and found Hilliard Tanners to be the most approachable and pragmatic by far (including myself designing foundations for ICF builds with insulated rafts + UFH etc) and they accommodated my methodology; only once they had suitably scrutinised everything I had sent them and they were then 100% satisfied to produce a design that we could then use on site to instruct the groundworkers to build the foundation from. I've NEVER fitted expansion gaps on a 'passsive raft', NEVER cut expansion gaps in anything other than much thinner and non-constructional screeds, and most were tiled over. Zero cracks / other evidence of cracking etc whatsoever. I always leave it a full 6-9 months to allow the slab to cure before applying the tiles, other floor coverings can go down much sooner, but the builds normally progress sympathetically to that timeframe being acceptable / possible. The running temps of the UFH in the raft are just so low the damn things don't move much at all, if anything! The MBC PH TF I have just moved clients into has a flow temp into the raft of 26oC, and I'll bet that gets dropped back 1-2oC by next winter, once they've got the house bone dry and properly acclimatised. 140m2 L-shape slab.

Hope this helps a bit. The following is general but this is the way I do it... the following is simplistic and I mess about later on technically..to value Engineer where I can.. but roughly.. If you want to cast your UF into the structural slab (think of a structural slab like a wide reinforced concrete beam.. you don't put movement joints in a beam). By definition this would be a continuous slab with no crack /movement joints. To design a structural slab for strength, shear and deflection etc I would take the effective structural depth as being to the underside of the UF pipes. The bit above that is neglected... just like a screed. But in this case you just cast the slab to the full depth. If you have say a ground bearing slab with movement joints then each bay gets it's own UF loop that does not cross the joints. UFH design is much based on common sense and past experience. To my mind there are too many folk that are trying to make wet UF seem like an exact science. This I can tell you from forty years experience.. it is NOT!.. well it may be for the first year or on a calculation sheet (if you get really lucky) but after that when the controls start playing up and no one has a clue about the design philosophy / how to operate and maintain it. Then you actually need to look at how the stuff gets installed on site which can blow any theory out the water any way! In the heat of battle on site I would challenge most folk to stick to drawings! Cut yourself some slack. There is no point in paying for a UF design you can't deliver practically on site. I see this all the time... folk just waste their money. I'm a massive fan of UFH and have put these systems into my own self builds and renovations. But I always go for the simple stupid.. like they do often in Nordic Countries. Now simple stupid does not mean the system is uncontrollable. But it needs the home owner to be aware of how their house warms and cools,that is you weather compensation! @zzPaulzz Go back and have another chat with your SE. It seems like you are working at cross purposes.

It's not done with a membrane because obviously a membrane outside of plasterboard wouldn't work. In principle it should work with a painted/ coated layer. There are examples of this that you can find (it's not an ideal comparable, but think of a liquid dpm - this does the same job as polythene for example). We've used a similar technique elsewhere in the house with no issues... The problem here seems to be the plasterboard sandwich behind it (at least I'm assuming). Do you think perforating with drill holes and then filling and decorating after allowing some time for the moisture to escape could work?

@zzPaulzz I went down a rabbit hole on the different types of UFH pipe, because I wanted the pipe embedded in the concrete, but it was hard to find details from suppliers if they endorsed this use case for their product. Optimum underfloor were one of the few at the time that had a technical drawing showing their pipe embedded in concrete slab. https://www.optimumunderfloor.co.uk/s/Optimum-Installation-Guide.pdf @garrymartin provided details of the Warmup specification for UFH pipe embedded in concrete in this post. I have the generic Kore Technical Drawings from my foundation design that show the UFH in the raft. In the NSAI certificate for their system it states tha UFH can be in the raft. They have a recent blog post that elaborates; “When fitting underfloor heating pipes, the pipes can be clipped to the steel mesh or to the KORE Floor Insulation.”

We're in Suffolk...the firm we're thinking of employ their own installers/surveyors etc as well as make windows....has the attraction of it being in their hands and if the worst happens they have capability to fix pretty quickly.....or that's the theory 🤞

Yes that's right, timber frame walls are original. We basically added the insulated plasterboard over the top (made a sandwich like you said). Yeah I checked the buildup and the software was happy so I assumed low risk. Wondering if the plaster wasn't fully dry, seems funny that it could have accumulated significant moisture so quickly but either way unless the smell is caused by something else that seems to have happened