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This is what's left of the pile + some thicker 40mm sticks that I left (not on the picture). I reduced it by 10 times. I bought it used from a guy. The blade on it was gone according to BOSCH but angle grinder has made it sharper than Japanese katanas. I would not call it an industrial unit but a recreational shredder. I was thinking about hiring a proper shredder but then I would have to do a whole lot more at one go and I simply have no time so I do it piece by piece instead. As long as the blade is sharp it chews sticks even the thick ones in no time. It only struggles with leafy stuff at times. The pile was there for at least a month. I know it was a rainy and damp time but the machine was still doing OK. When I red the manual it said that material should be shredded pretty immediately. I understand it dries quicker in the summer time.

I'd be ( as the contractor ) more worried about why my client couldn't or wouldn't pay monthly, in advance, or agree to stage payments in advance per increment. No way will I ever, again, give a client any form of credit. Been there, got the T-shirt, but not the circa £50-60k ( estimated ) that I'm still owed to date. These disingenuous scrotes of clients are currently using and enjoying the items I purchased, installed personally or worse paid to install, paid hotels and expenses to the subbies etc, fuel and more out of my back pocket. Clients and contractors are equal, IMO, and if an amicable agreement can't be made with my potential ( new ) clients, then it's "adios amigo". There is a huge amount of work out there, and I don't need or want to take the risk, again. Clients can make up any bollocks to sue a contractor but it is very different the other way around, as the courts favour the "poor victims" vs the professional ( who is assumed to have every T crossed and every I dotted ). There can be, the client just needs to recognise this and then justify to themselves that a representative needs appointing to this accordingly, and to whatever else they or the typical general builder won't know, understand or execute with any competency. It's one discipline that keeps me very busy, but clients often either don't see the value of appointing an M&E consultant, or get one in at the 11th hour ( more like 5 mins to bloody midnight ) and then expect miracles. This level of detail and the involvement of somebody appointed to take ownership / responsibility for delivering it needs to be in place well in advance of breaking ground, and then the client can insert this into tenders for the builder to be able to make costs and time allowances for the "additional" work, eg you've then turned an unkown into a known so it can be addressed and quantified, and monitored. Either that, or the self builder needs to get out of the way and go turnkey, a-la MBC's foundation > frame > airtight guaranteed package, which is newbie / idiot proof, but also very safe and simple.

when you supply materials and they don’t turn up you are still paying for a wasted day, and this excuse will be used to get ‘extras’ onto the final build. it then knocks onto other trades, who with the builder would maybe be willing to let it go for you a one off they are charging for the time wasted too. specify the product you want and let the builder get it.

Use a proper spirit level and both ways round as laser levels can be notorious for being out unless they are decent (ie expensive) brands.

Hi all. The new standard deals with everything from convertng a little Victorian cellar to a 4+ storey deep basement structure beneath a new nuclear power station. Therefore some sifting out what suits you is required. Basement waterproofing has suffered from every tradesman seeing 'internal drainage, sump and pump' on the drawings and they instantly know that if their work leaks it will have been covered over and they won't get blamed. That's how someone above paid for all the work then paid more for fixing problems. Internal drainage systems made the preceding structure workmanship worse and worse and worse. The new emphasis is on keeping water out. Yes, the tradesmen are gong to get a shock when they are dragged back a few months later to fix all their leaks before they get their final payment. A new-build, single storey deep basement for a new dwelling or new extension should be built from waterproof reinforced concrete all poured and compacted with care. The concrete will be waterproof. Any cracks and voids need to be repaired. The Standard says that one form of waterproofing should be continuous from the base of the basement floor slab to 150mm above outside ground level or DPC, so a narrow upstand in the waterproof reinforced concrete replacing the first course of blocks achieves that. Neither beam and block, steel beams, precast planks or composite steel floors work with the upstand, so they are out. ICF and twin wall (like Glatthaar Keller) are specifically mentioned in the Standard as risky because you might have to partly destroy either to find and stop leaks. (Why would you insulate both sides of a wall anyway?) Sticky-back membrane on the outside seems to be assumed to not work very well either, but what it says is that a bit of membrane might cover a crack and protect that crack from leaking. The term that describes concrete self healing cracks is called autogenous healing. You can look that up. Essentially, retaining walls need extra horizontal steel to restrict crack widths to what will self heal. The extra steel makes the concrete crack a lot more often but each crack is much thinner. Some unused cement grain exposed by the crack finds some unused water and they react and fill the crack with concrete. It needs to be noted that one form of waterproofing is required and two are preferable. If one of those is external drainage that works by gravity and is roddable, the other need only be the concrete. It needs to be noted that an internal drainage system, that removes water but does not stop it getting through the structure, is no longer a waterproofing option. It does not count toward your two. I would usually suggest that a bitumen based waterproof paint all over everything inside is the best second defence. Phil

if you wanted bankrolling i'd hope the builder increases their margin accordingly. Fortunately they are in a good position to pick their customers.

Hi there I have been trawling through this forum for a while and decided now is the time to actually post and introduce myself! we are a young family looking to build in our back garden and sell the main house. The idea is to live more sustainably and significantly reduce our mortgage. our neighbours have done exactly the same as we are looking to do about 15 years ago and managed to build a bungalow of about 140sqm. They have a ridge height of 5.7m, so I’m guessing we wouldn’t be able to go above that, but we are going to preplanning shortly to give us an idea of what we could build. I just had a few questions for all you experienced people that would be useful to know. - with a ridge height of 5.7, would it be possible to get any rooms upstairs or even a mezzanine to give us a little more floor space. I understand it depends on the pitch, but as a general rule wound this be possible (even though not a very cost effective way of getting useable space). We live in the SE in Home Counties. - we would like to build a home that is cheap to run, so following passivhaus principles. We have booked to see some architects that have done this type of new build before, but we just wondered if our budget was realistic. We have about 400-450k for everything (including architects fees), but both work full time and have 2 small kids so couldn’t really do much ourselves. We’d like to use prefab to reduce time (as we’d need bridging loan), timber clad, and energy efficient. I know it’s vague, but that’s all I have!! - what’s the best single piece of advice you have (for those that have done this or part way through)? Thanks so much all and I hope to share more specifics with you as our journey progresses (hopefully). K

The SE drawings for the slab include two sections where the EPS 300 is replaced by perinsol blocks, and the perinsul blocks are in turn supported by concrete pads. I guess some extra support is needed here. It looks like this: In the end we went for Partel CF200 instead of perinsul. The problem with the CF200 is it is eye-wateringly expensive. I reckon a single thermalite 100 block on top of a single quinlite block would have similar performance for a fractoion of the cost but the SE approves the CF200 and its easy to get hold of.

I wouldn’t bother taping But if your looking for something that will stick and stay stuck Jaffa tape Five quid for 25 meters

Try and get the neighbours onside. May not be possible, but will be a huge help. If someone kicks up a stink and puts pressure on the planners and/or gets a local councillor to call it in to committee it makes things much more difficult. Have a look at national and local planning framework - neighbourhood plans etc and try to comply with them. Focus on sustainability and being environmentally friendly.

Finish this off, very happy with the neoprene tube product. Floor waxed and job done. The picture if of a very uniform gap but it coped with less and more. It's about how much you stretch it for thinner gaps.

Apologies!! Should have read the thread better, I thought it was an extension being discussed. In which case ignore my previous post... £3k is a very reasonable assumption, and VAT no issue with new build on vast majority of stuff.

No The decision is yours Don’t let BC decide what you are doing Hes there to make sure you achieve the minimum

It's a Heat Only boiler . Best to leave it fire every 30 mins, as it's not exactly out of the expected use pattern for a boiler in a less-than-excellent ( thermally ) house. You can get wireless room thermostats, and getting it away from the cold at the front door would be beneficial.

If you recess the doors like the lower diagram the door will only open 90’ before the door hits the frame and this could pull the hinge screws out!!,! IMO the outside of the door must be parallel with outside of the frame as per the top diagram.

Of course there are. They are usually happier people too. And there are bad, greedy, cheating people in all walks of life. With the wisdom of age, I was never excited meeting a potential new client, and I didn't overpromise....even that we wanted the work. Some remarked on this as a positive. Also I would explain that we are not a bank, that they would be paying us about say £50k/ fortnight and that we need that promply for our bills, and we always pay promptly ourselves. Our best price will be based on these terms, and anything else causes us to charge more. Better to use your funds or bank... That can sort clients out. As soon as a QS or PM was involved we had increased risk (they like to show how tough they are) and admin.

Update. Have been putting the mulch round the roses and perennials. No sign of anything trying to grow within the pile. As instructed by Beechwood Garden and Gardeners World I am putting down 100mm. Ish. Better some plants thick and others with none, than spread, they say. Had a 100mm tree branch fallen from next door. About 5m long to the tips. Long handled chain saw, then loppers then grinder. Took an hour and the machine pulled the whole clusters through , led by 20mm branches which are easy to get to engage. Nil to brown bin. 1 hours worth of timber as logs and sticks, 2 trugs of mulch.

Leave as-is. No need to do anything more tbh. Exp foam would be my only suggestion as it is a cold mains so maybe you'd get condensation forming on it. Remove the clip, fill with foam ( behind the pipe ) and hold in place whilst the foam cures. You won't need the clip afterwards, the foam will grip it perfectly well, if not better!

I've just spent most of the weekend drilling 54 14mm holes through 5mm and 12mm thick mild steel. What I learned No-name HSS bits from Amazon do not work. At all. Screwfix erbauer coated HSS bits are pretty good but I broke a few as they tended to jam and get stuck. The gold standard for me were the cobalt HSS bits from "UK Drills". A single 7mm bit drilled about 20 holes though total of 22mm of steel in each drill (5mm walled SHS sitting on a 12mm thick UC flange). Just a 3mm pilot hole to get them started. Oil only needed when mid way through the 12mm webs. All done with a Makita cordless drill. High speed, low pressure.

I put my immersion on to an external thermostat, as I could never get the cylinder hot enough, even replaced the immersion and integrated thermostat, but it made little or no difference. Max temp I could get to was about 60, even the immersion thermostat set at 75.

Been doing my own Nick. It's a nice little workout when the sun is shining (not so much today though) Filled half an 8 yard skip so far with the wheelbarrow and spade

I do the same

You would be tar-free, sir, as the above is what is called "recognition and agreeable compromise". Apples for oranges in your above instance

I've already been digging the garden out this weekend to get to the main roots. I've not quite gone down 600 deep but these are about 450-500 below. Also uncovered what looks like a little pond (which I'm going to have to deal with as it holds water still)

Exactly the nightmare I would run away from. Also completely incorrect. As a contractor, I often get refused better terms when I buy up front ( as I do not want or need credit accounts ) as they see me as one-off business then. I have to basically tell them I'll go elsewhere, and THEN they'll magically give me the same ( better ) terms as account holders. If they'd sell to you directly and cheaper for a one-off vs selling cheaper to the builder, then the builder would tell the merchants not to expect to see any more of their money as they've essentially then undermined the builder. Merchants want life-long relationships vs servicing one-off 'hit & run' custom. For these exact reasons. My favourite is where the client couldn't get what was requested, so they "bought 'this' instead" which is useless, and un suitable. Usually because the client had very limited time to search / find / procure and that lets everything downstream fall to shit. At more cost. The client won't save money doing this, I assure you. Consider VAT, down time, bad taste from the arguments that will follow, losing traction and good people to it, and the fact that the contractors / builders will STILL want a 10% mark-up on the items you took out of their anticipated profit margins. Ask for this at the outset, and most builders will walk, as they know exactly how the rest of the job will go.....babysitting a micromanaging client who's savings schemes end up costing more in time, more in money, and frustrating everyone wanting to get on. Time is irrecoverable for everyone, and once it's gone it's not coming back!

https://www.scribd.com/document/447244443/THERM-01-Beginning-Users Heres one but its in ye olde units. http://passivehouse.nz/wp-content/uploads/2018/07/ThermInstructions.pdf This is the one I used.

Just like heat pumps.

I prefer non complicated, each elevation it’s own (I.e. timber on left elevation and brick on the right.

Not too far away from you in West Sussex (albeit on the border with East Sussex). We used Peter Ranier at DMH Stallard, although regrettably not until the appeal stage. I think we would’ve had permission much sooner if we had. His team demolished the planners arguments against our application. There’s no other word for it. I think it was about a 40 page dossier with no stone left unturned. Cost was about £3-£5k, 5 years ago I think. Not sure what the cost would be if used from the outset. No harm in asking, although I’m not sure what area these guys cover. He and his team have represented Brighton & Hove Albion a few times I think (with some extremely contentious applications). Anyone whose services are employed by Tony Bloom is very unlikely to be poor at what they do!

Standard JCT contract work on interim valuations which are then invoiced to the client, ie payment in arrears. Of course these can be amended, but it is not the norm for builders to need upfront payment.... Because their entire industry works on credit for the above reason. Walk into any builders merchants and ask for their credit terms, all will discuss, run credit checks and assess financial situation. Good builders generally will have no issues, bad builders won't generally get the credit... Hence a good way of vetting builders (to help OP) in advance. Advising a new starter to self building that paying up front is normal or encouraged is frankly dangerous, there are no shortage of horror stories on this forum where people have lost money due to builders/Companies taking money and then losing interest in the job. Most problem builds end up with the question 'I hope you haven't paid him' for this very reason....

You do not need this with a "balanced DHW and CWS" system. Stand down Red Alert

Great devices - but I do worry how often they phone home! I am working my way through the Rpi Pico W toolchain, back to the 80s without a windows IDE, to wean myself off the D32 Pro I have built my ptype kit around. Alongside the Rpi MQTT node red etc. The particulate monitoring will be a great addition - but I am not sure I want to know with my cooking skills😁

Not just that unfortunately. Our joiner was college trained, experienced, a superb worker and very highly skilled. Yet he did not understand the air-tightness thing at all. Sole plate to footings...'forgot' the mastic. Vapour barrier lapped but not sealed. when we raised the subject it generated a shake of the head, and basically he ignored it. (There is a lot of that even among the best workers....if they haven't heard of it then it must be wrong...and ignored.) So we did the seals out of hours. It follows that all the jobs he worked on in stick building, mostly as a sub-contractor I think, have been done without air-tightness being enforced. And that is a well-intentioned craftsman.

It also depends on you - or your representative - checking it at the right stages, to identify and remedy the leaks. Don't underestimate the ability of the builders to install it incorrectly. Get the BBA certificates are check that they're being followed. The builder will just go to their regular suppliers and pay what they're invoiced, plus a mark-up to cover their time, effort & profit. If you have the time to shop around, particularly for high value items, you may make savings even if you do have to pay the VAT. Or arrange with your builder that you will identify certain suppliers and they'll buy the products at cost + an agreed markup.

most reputable builders would expect materials to be paid for at point of order. They are not there to bankroll your build.

The footprint of the bedroom block is 12 metres x 7 metres, we put 2 bedrooms and and 2 bathrooms upstairs. I will send some finished external photos later. have a quick look here

Perhaps ask him what he thinks of the insulation requirements of the Building Regs? Don't say any more but note if he see it as an expensive regulation or inadequate target. If you are going for ASHP ask him what he thinks of them. He should say something about them working well if you have UFH and a well insulated house. Ask him if he thinks airtight houses are unnecessary. Hopefully he will tell you its important. If you are on a self build mortgage that has strict stage payments you might want to sound him out on what stage payments he normally wants. It's not a great idea to agree exactly the same schedule with the builder as your mortgage lender but they must be compatible schedule's obviously. Perhaps don't tell him what they have offered you. You might want to negotiate more favourable terms with the builder so you retain a bit more to the end. It's not unknown to retain a percentage for a year after completion to cover snagging. Ideally find out where he's working at the moment and go look at that house. Is the site tidy? Neat work? Messy? I've said it before - If you ask him to take you to one he's built it will probably be his mother's house 🙂

The Enphase seems to have a threshold of about 5W in either direction before stepping in (if it can, ie when not full/empty). When I asked the tech director of the next best brand at the time he said that theirs was about 30W. One UK manufacturer's director that I spoke to said their unit was 500W minimum to intervene, though he did at least listen to my observation that my night load peaked at ~100W including the fridge, and our day load would rarely hit 500W, so their unit would not actually be much use to us! OTOH, the *peak* charge/discharge rate of my system is ~1kW, so it does not fully cover the peaky things such as the dishwasher or the oven, so I prefer to run the former when the sun is out or in the dead of night when grid demand is low. Rgds Damon PS. Saga starts here: https://www.earth.org.uk/Enphase-AC-Battery-REVIEW.html

Buying a sheet of this here or a plank of that there is a recipe for getting rinsed. Try to buy say at least £2k worth of materials at a time. Ring 5 different BMs and give them a list as long as your arm and get an itemised quote from each. Then you can pick and choose the ones that are doing the best deal or get the handiest one to price match. For some reason delivery never seems to be much or anything extra either.

heres a tip for materials. You need to find a local building firm, the type that has 3 or 4 blokes on the books. Have a drive round the area, they build single houses, decent size extensions that sort of thing. Approach them and explain you are self building and are being bent over for materials. Ask if you can use their rates at jewsons/trav etc and you will pay them cash of half the saving. Get a price from the merchant for the usual 20 items timber, boards, cement, insulation etc and see what they paying. work out what you need and give them an up front couple hundred quid and couple cases beer. You will be buying some good faith, they may even answer the phone and recommend trades to you.

When given a price at trade counters my dad always said "where's my one hundred percent discount?" and quite often was give a more reasonable price.

Just watch Liam Neeson's phone call in Taken and paraphrase as required. Helps if you have the accent. I found that for in person discussions, living in a caravan & dressing like a builder / tramp did not hurt, also having a slightly battered estate car to visit merchants etc.

Thanks for that ToughButterCup, it's staying in front of me.🤣

"Thanks for that price. I have three other quotations due in the next [...] . Can I ring you to discuss your price when the other quotes are in?" "Well, the main issue is that I want to be sure to compare like with like. I'm trying to be fair to each supplier, and not simply rejecting the quote on the basis of the final figure " "The other comparable quotes are substantially lower than yours. Do you have time to discuss them with me?" "Help me understand why your quote is so much higher than everyone elses" "Why is your quote so cheap?" "Your quote is so high that it makes me wonder wether you want the business". "Your quote seems to be substantially out of line with other quotes I have. The others are all about 15% cheaper. Can we explore why that might be" "Why did you waste your time sending me a quote that high?" "Self builders are not stupid" "Do you have a line manager I can talk to, just to check a few items in this quote ...." "Really? Honestly? Have the decency to wear a mask the next time you commit daylight robbery."

CSCS cards provide proof that individuals working on construction sites have the appropriate training and qualifications for the job they do on site. Well, cscs would say that. But it is no true. It only means you got a card. Nobody in my company was required to have one, and no client ever asked. i looked through a training book for a test, and some questions were laughable. It shocked me that our apprentice struggled with some of it though. Hired a forklift driver through an agency once, who had a card for a telehandler. He couldn't operate it and we sent him home and the digger driver (no card) had to unload our deliveries.

I have said this before but I seem to be a lone voice. I don't give quotes. I give estimates, am open with my hourly rate and materials cost. Most jobs turn out lower than my estimate. If i am forced to give a quote (usually commercial customers) i have to think of absolutely everything that can go wrong to make the job take longer and price on that. Almost always the job takes less time than what I have allowed. But it is a quote so that is what they pay. People on here tell me customers don't like paying by the hour because they then expect you to just sit and drink tea while charging your hourly rate. Some might, but surely they would never be recommended? I don't and all my work comes from recommendations, I don't advertise.

Janet and I want an energy efficient house, but what does that mean in practice? The whole concept is still largely rejected by the UK building industry. In our initial research, we either found books like the House Builders Bible which are good but superficial introductions on the concepts but without serious detail or at the other extreme academic papers on micro details. There is precious little in between, and to be honest we have found far more gems of knowledge in this site. All my experience and intuition concerns living in a traditionally built house. An energy-efficient house is just a different beast entirely, so I discarded my intuition and put my trust in the physics, maths and engineering. Likewise, we only considered the views and recommendations of those who have actually lived in this type of house. One of the first things that I did was to build up my own version of Jeremy Harris's Heat Loss Calculator.xls (which he first developed on this GBF topic). I plugged in the numbers for our own house design, but in reality there are only a few parameters derived directly from the house geometry that drive this calculation (my numbers are in brackets): The internal footprint of the slab (71m²) The internal surface area of the external walls, less windows (179m²) The internal surface area of the roof, less roof windows (93m²) The area of windows (23m²) The total volume of the internal living spaces (419 m³). Each of these is multiplied by a factor derived from the design to give a heat loss per °C: a U value in the case of the first four. The last is more complex in that I had to build up a composite heat-loss based on the rate of air exchange, its unit mass and specific heat, and importantly the recovery efficiency of the MVHR. For a typical winter external temperature of 4°c and an internal 21°c, this gives a delta of 17°c for fabric heat losses. The slab delta is somewhat different in that the ground temperature under slab is far more constant – say 10°c at the centre of the slab and maybe 6°c at the edges in the winter raising to 15°c in the summer. Plugging in our current design values (from our frame supplier, MBC) gives the following heat loses for a typical January day: Slab: 97 W (9%) – 71 m² x 0.105 W/m²/K x 13° Walls: 364 W (32%) – 179 m² x 0.120 W/m²/K x 17° Roof: 171 W (15%) – 93 m² x 0.105 W/m²/K x 17° Windows: 313 W (28%) – 23 m² x 0.800 W/m²/K x 17° Air change: 180 W (16%) – 419 m³ x 0.025 W/m³/K x 17° That's 1.1 kW in total, or as I sometimes say to friends, the whole house could be heated by a single 1-bar fire. Clearly this heat loss varies according to season, so if I plug in an overall temperature profile for my location, I then get the following daily heat losses in kWhr : The house is reasonably balanced as a system: no single component dominates the heat losses. However, this wouldn't be the case if we dropped the heat recovery element of the MVHR, for example, as this would increase the air change heat losses by roughly 5x, becoming the majority of total heat loss. This is why the inclusion of MVHR is such an important component of energy-efficient design. If we look at the risks and sensitivities in this sort of calculation, then they broadly fall into two categories: failures in airtightness and thermal bridging at boundaries. (Googling these highlighted terms will give background explanations of what these are). All internal surfaces in a properly implemented energy-efficient house are within a few degrees of the internal temperature, which also means that there are no internal condensation surfaces. A serious consequence of thermal bridging is that surface temperatures can drop significantly at the bridges below the internal dew-point, causing surface condensation. Failures can occur with sloppy design or poor attention to detail during construction, so I believe that it is a lot more important to find a frame manufacturer / assembler who gives us confidence that these issues will be effectively addressed (as failures here could cost kilowatts of heat loss or mouldy surfaces) rather than whether the walls have a nominal U value of 0.12 or 0.14 (which varies the total heat loss by roughly 60W at most). However, this heat calculation isn't the whole story: We typically have three occupants in the house and being alive we radiate heat – roughly 300-400W between the three of us. The 23m² of windows can let in up to 1 kW/m² incident energy in direct sunlight. Our average daily electricity usage in our current house is 16 kWhr / day. We will cut this a bit in the new house, but this is a combination of lighting, DHW and running electrical equipment – fridge, washing machine and my live-in son's Gaming PC + Xbox. Apart from some of the DHW used (which literally goes down the plug hole), all of this energy eventually ends up as waste heat within the living environment, and therefore adds to the general heat budget – that's roughly 1kW plus the solar gain. This 24 kWhr/day or more means that we will often have a heat excess within the house. On the other hand clearly these temperatures are profile averages and there will be periods where the temperatures will be lower, and below zero for extended periods. However, even a doubling of the temperature deltas only give a running heat loss of approximately 2 kW. My overall conclusions are: Our overall heat budget will be in near equilibrium for large parts of the year. At most the sustain heat input requirement will be of the order of 2kW peak. We need to manage heat excess efficiently and automatically up to say 2kW. I want to expand on this last "automatically" point: in our current farmhouse with its 2ft thick walls, the house environment is sufficiently stable for a large part of the summer and autumn that we turn off all heating and leave windows ajar all day, relying on natural ventilation. We feel that warmer weather should result in periods where we can do the same in our new energy-efficient house. However, we don't want to be forced into the situation where we have to dash around the house a few times a day opening and closing curtains, blinds and windows just to keep the house at a stable temperature: in general, the house should look after itself. This imbalance (or a lot more on sunny days with the solar gain through windows) is a material issue and to put this in perspective consider: The mass of the liveable airspace in the house is some 500Kg with a heat capacity of just over 0.5 mJ/K or 0.14 kWh/K. The specific heat of the slab is less than that of air (0.75 kJ/kg K), but the mass of over 7m³ of slab concrete is significantly more (16.4 tonne) giving a heat capacity of 3.42 kWh/K and the plaster board, etc. within the walls adds perhaps another 10% to this capacity. There are various equations for the heat transfer between the slab and the air above it but a good ballpark is 10 W/m²/K – that is roughly 0.7 kW/K for the entire slab. The slab and the other fabric which sit within the thermal envelope of the house has over 20 times the heat capacity of the air inside the house. So if we were to heat the input air from the MVHR to 10°C above room temperature, this will transfer about 0.7 kWh heat into airspace of the house in one hour at 0.5 ACH – the same as running the slab at 1°C above room temperature. In extremes we can easily lift the slab temperature say 5°c to increase the heating slab effect five-fold, but at another 2x the air heating route will start to be problematic with noticeable effects on air quality and background noise if we increase the ACH to do so.. Our initial intention was to use an integrated MVHR + ASHP(Genvax), but there was always a concern that this would be inadequate to cope with extreme cold spells, so we planned to use a supplementary closed wood burner. However the problem with any stove is the minimum output (typically 2-3 kW) which is simply far too much for the living room to cope with. So we abandoned that idea: there's no point in installing a stove that you will never use in practice. This analysis plus Jeremy's reasoned argument also convinced us that an active UFH slab was the way to go, for the following reasons: It's a relatively low cost option. It addresses a saleability risk: "I want to fit a gas boiler" With a suitable ASHP it enables active cooling as well as active heating. In circulation mode it is extremely effective at distributing the heat throughout the entire slab from any hot spots caused by direct sunshine through the windows. With this reasoning the advantages of a combined ASHP+MVHR just seemed to dissolve, and we've now decided to abandon the Genvax in favour of a standard passive MVHR system. We have still to chose the ASHP, but we are looking at a low power (say ~5 kW) monoblock inverter-based design alone the lines of Jeremy's active slab approach, but more on this in later posts as I finalise details. We also need to think about the vertical temperature gradients in the house (our hallway / landing rises through all three floors into the loft space). Hence this is only part I of the thermal design.

This is the Part II roll up of a couple of earlier blog posts and forum topics which provide the groundwork and context. Plumbing Design – Part I Heating the Slab – an overview Modelling the "Chunk" Heating of a Passive Slab Another DHW / DCW / UFH design. in summary, so far into commissioning and early use, everything is at least achieving our expectations and the house might in fact perform better than my predictions. The key design points that I listed in part I seem to be spot on. I want to compare a figure that I gave in the modelling topic with a corresponding plot during commissioning and testing to underline this: The first graph is a theoretical model based on a few simplifications, and the second live data, warts and all, and complete with hiccups as I test and restart the control system. The bottom line is that the slab is reacting exactly as I modelled in overall behaviour, though one of the parameters is different. The UFH pump at its medium setting is under half the modelled flow rate, increasing the delta temp between out and return from 2°C modelled to 5 °C measured. However, I decided to stay with this setting because the pump is almost silent at its medium setting, and the system and its subcomponents are still operating well within specification at a delta of 5 °C. So in my view, if you are building a house with near Passive performance (wall, and roof U values < ~0.15; windows < 1 and not too much area; well sealed warm space and MVHR; decent insulated slab), then you should expect heat losses of less than 40kWhr / day in worst winter months. You therefore need to put roughly the same into the house. You only need to input the net top-up, because your occupancy, normal electrical consumption and solar gains all contribute to this input; this net is going to be 1kW or less on average. Given that a cheap and simple Willis heater can provide 3× this, using something like a gas boiler capable of 16-20 kW is just crazy, in my view; in our case even the economic case for considering an ASHP is marginal at best. Yes, in terms of running costs, the electricity unit cost per kW is more than that for gas, but you also have to factor in other running costs such as boiler maintenance. In our case, the British Gas boiler maintenance contract in our old house is less than our total expected heating cost in the new house so unit price comparisons are irrelevant to us. As I commented in the Boffin's thread, you need to limit the heating going into the slab: one way (the one Jeremy currently uses) is to throttle back the heating rate right back (e.g. using a buffer tank and an accurate thermostatic blender) ; the other way is to use a chunking approach and simply heat the slab in one (or possibly two) chunks per day. In the chunking case you instead limit the total heat injected into the slab per heating round (that is the integral of the power rather than the power itself). Doing this might seem awfully complicated, but in practice you can let the slab physics do this maths for you. You can use any moderate heating source that has a reasonably consistent but limited heat output; this could be an inline heater like a Willis heater or an ASHP with the flow temperature and rate at present set-point giving water at, say, 30°C. The slab itself slab acts as the buffer, so no additional buffer tank is needed. The algorithm is simple: Turn on the heating at a fixed time. This could be the start of E7 or in the window of peak power if you have PV installed. Turn it off when the average return temperature from slab reaches a specific set-point threshold. The actual set-point (which in my house is going be around 27°C in winter) does vary by season because what you are doing is control the total heat put into the slab, and it will need trimming for any specific house and heating scenario, but it is largely self correcting for short term temperature variations in that if the house gets a little colder due to greater heat loses in a cold snap, then the slab will require more heat to reach the set point. At the moment we are using a twice a day heating cycle. This is settling down to ~6 hrs overnight during the E7 window about £1.50 and a couple of hours top up during the day (another £1). This being said, we are still warming the house from a pre-commissioning temperature of around 13°C to a pre move-in target of 20°C as as you can see from the graph, we are currently increasing the house temperature by ~0.5°C / day on top of the sustain heat losses. This in itself takes a lot of energy as we have approximately 17 tonnes of slab, 5 tonnes of plasterboard, 11 tones of wood inside the heated zone of the house and 8½ tonnes of cellulosic filler in the insulation. Plugging these numbers and their Cp's, it takes roughly 25 KWhr to raise this fabric by 1°C, or 4 hrs of Willis Heater to raise it by ½°C. So at the moment roughly half of the heat input is maintaining heat loses and the other half is slowly raising the temperature of the house fabric . This maintenance heating element is less than the JSH spreadsheet estimated for current average outside temperatures. So another way of thinking about this is that if we do without heating for a day, then the house will drop in temperature roughly ½°C to compensate for heat losses. The daily ripple in temperature with a single heating chunk will be less than this. If we only heat the slab during the E7 time window, say from 2 - 7AM, then the house temperature will peak roughly 3-4 hours later late morning and then fall by maybe ½°C during the rest of the day. I feel that a ripple of ½°C will be barely noticeable to the occupants, and given that the heating during the E7 window is effectively half price, it is better to accept a midday peak (and possibly set the target temperature half a degree higher) than to pay double for an afternoon heating top-up to reduce the ripple.

So main house is polished and sealed took 6 days for the 2 guys, they ended up bringing in 2 machines that weighed a tonne each, through the grits then polished and sealed 100sqm back on Monday to do the garage which isnt aggregate show its a powerfloated finish with a high polished end result.