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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.

No, not an MBC build, but a 'supply and erect' package from a local timber frame manufacturer (who supplies nationally), using a local architect as part of the deal. I suppose it was a bit unusual in that the architects 'design' stage was paid for through the TF company (discount rate) as part of the frame contract, but the BC part I paid for directly. I've had loads of support and advice from the architect and consider it money well spent.

Thank you, you've been very thorough as ever. I will definitely ask about the insurance and rights for the drawings as well as electronic copy. The visits are not included and are charged separately, I am aware of the cost as we paid the same during PP stage. The end point is not specified - definitely something to discuss. One of my concerns is the number of unknowns all of which will be charged at a standard rate. Though reasonable, it has added quite a significant % (about 90% of the starting price) to the overall cost of the PP stage and I guess would add much more here.

Like this pic.

Washing in cold water is the norm in Australia. Australians find the idea of washing in hot water a little odd. I think it's partly because the climate is so warm, and the UV (on average) so high, that when clothes are dried outside - which is the case for a lot of the year - they're effectively sterilised.

If you can, wait until Friday as you should find better deals on Black Friday it's not even a week away.

The hardest wear on our thresholds is people traffic not water. I have to sand and re-varnish every 3 years and I use a floor varnish.

Our 90m2 Isoquick passive slab with 300mm of insulation was around £18000. This was with a 200mm thick reinforced concrete slab. It was around 50/50 materials and labour.

Parts 1 & 3 sound reasonable. I would have thought part 2 wouldn't be above £200.

Difficult to judge for me, as I have not done it. From here it looks like a not unreasonable quote, subject to bits around the edges. One benefit you have with a fixed (=ish) price is that the risk balance may be less tilted towards you. Add up the packages you have had .... PP and now Building Regs .. and see how it compares with others figures as quoted in various places here for the total. One comparison is that at a rate of say £400 a day (picking a number out of the air to allow for junior staff on some of it) that is 11-12 days of work, which is probably not unreasonable. You have a dozen different work items in there, though some are those that some here have I think done themselves (eg demolition spec?) even when using an architect. Where is the architect based - are site visits going to involve chargeable travel time each way? I think I would ask for an estimated cost per site visit as one query. If it will be reasonable and he is based in Dorking that should be OK; if he is based in Lancaster or St Peter Port then that could hurt. How clearly specified is the end point of the work package - eg what happens if there are extra complications that need extra architect time? I think I would ask for the right to use the drawings you will be paying for without limitation for this project, and an electronic copy / model copy to be included or at a nominal price. Given that there is potential overlap with MBC. I think I might ask for clarification on who's insurance covers what risks - I might frame that q along the lines of "your insurance does cover *these* items, doesn't it?" So, I think the basic thing looks OK, but that there may be an opportunity for some nurdling around the edges. I have just obtained a PP in a business setup, where we had excellent service from a Planning Consultant, but the extra "talking to the Council" bill added a chunk and took my co-owners by surprise. Ferdinand

From memory, I paid about £2k for item number 1 of the building control stuff, so on that basis, you're getting 2-9 FOC, although 5,6,7,8 sound like 'bulkers' to help justify the price. SAP/EPC modelling was included in my BC application - they've already done the spec, so I'd have thought it was only half an hours work; a quick google suggests < £100. For me, section 3 feels like it's just into the realms of project management, and its value depends on how you feel about it. Personally I wouldnt have been happy with an architect specc'ing the job past the BC stage, and inviting/comparing tenders isn't rocket science. Gut feel is that even though they've made their role sound more detailed and complicated than it actually is, and spread some of the cost over the epc, the overall cost is actually quite reasonable.

£10K for strip foundations. Obviously does not include the suspended timber floor, or the insulation that went into the timber floor and does not include UFH or any drainage work. My cost is artificially low because I had my own digger at the time so I did all the digging and earth shifting. I think what I am saying is your price does not look too bad.

Contract ...?? What's a contract ..?? They are useful documents for the lawyers to argue over in court when it's all gone wrong, and they will spend your money for you advising why spending money on a contract was a good investment ..... and that's about it ..! Is this a standard JCT terms contract ..?? Small works ..? Less than £25k..? If so, the only schedule you need is the payments and milestones and the agreement about who buys what. Anything else and you're into micro detail that is irrelevant for something of that size. Trust doesn't start with a contract ....