Dreadnaught

If have a void, but not ventilated. The void is for heave only. And is created using large crushable ground-heave protection panels (I used the Jablite version) made of polystyrene. They sit below the insulation, atop the compacted MOT sub-base.

The screwpiles was one of easiest part of my project so far. My foundation was designed by a specialist company in Ireland that others have also used on this site. There were three parties involved with the screw piles themselves: the screw pile provider, who was in the neighbouring county, his screw pile engineer, who specified the size & required torque needed for each of the individual piles based on my ground survey report, and the screw pile installer recommended by the supplier. The installation was done over two days by the installer using an excavator with a special head (he is the most skilled person I have ever seen using an excavator … he even used the excavator to load his tools in his side-door van at the end of the job!) and he noted the screw pile torque figures for each pile on a sheet of paper as he proceeded. I then received a copy of that report and, in turn, submitted it to building control so that they were satisfied. After the installation of the screw piles, another team then arrived to shutter and cast the raft, which sites atop the top-plates of the screw piles. That raft was indeed insulated with thick PIR insulation. The design of the raft was such that it had extra thickening to form an integrated ring beam and cross members so it was not one consistent thickness across its entire span. All carefully designed with UFH and plumbing embedded within. All in all, the following engineers were involved with the screw piles: 1) ground surveyor (I inherited this survey when I bought the plot) 2) foundations designers, in Ireland 3) specialist screw-pile designer in Suffolk All in all, the process ran smoothly and, I thought, the screw piles were quite inexpensive at about 3.5% of my overall build budget.

Yes, true. I spent ages planning out all the penetrations, etc., with help from experts. And then those that poured my raft submerged two of them under the concrete, requiring a bit of remedial SDS work to find them again. Having said that, they did a good job with my raft overall. I put all my hot and cold pipework in the raft. One pipe, for cold water, has come out in a slightly wrong location, a bit far from the wall. I am told it is possible to chip away at the concrete and wiggle the pipe in to its correct position and then make good with some self-levelling compound or sand-and-cement. Haven't done it yet though.

Yes, the anaconda-like insulated double pipe is very difficult to bend. To take it from horizontal to vertical as it emerges from the ground, it needs to dive down deep before bending up so as to emerge vertical given its poor bend radius. Quite difficult to achieve. My pipe has 2x32mm MDPE pipes within it, so bigger than the typical one. My run under the raft is about 12m long so I wanted the larger diameter of pipe to ensure the pipe's flow resistance remained low.

I think it depends on where you are choosing to site your heat pump. In my case, as I am choosing to ground-mount my heat pump so the insulated double pipe emerges about 1500mm away from the external wall of my dwelling adjacent the chosen ground-mounting location. However, if I had chosen to mount it on the external wall, I would have arranged for the insulated pipe to emerge in a location suitable for that. I am just this week doing the planning for constructing the heat-pump's base, which is a surprisingly complicated exercise, requiring precise locations for that insulated pipe, but also a small soak away drain underneath the heat pump, plus two concrete piers for the anti-vibration feet to be mounted, and the runs for the duct for the electrical supply and control cable. The insulated pipe and the two ducts are all in place under the raft but I may dig them up again where they emerge from the raft and finely adjust their routes a bit so that they emerge exactly where I need them under the heat pump base.

!?!?!

Same here.

I have an L-shaped bungalow and have 26x screwpiles because of tree roots. And then a concrete raft foundation atop. I can provide the benefit of my experience if desired.

It was the manufacturer Ubbink/Brink.

I chose them because the manufacturer was relatively local to me (Leicester, while I am in Cambridge) so I could visit the showroom and factory in person. And because of the Passivhaus certification of the particular units I purchased suggested good thermal performance. As sometimes occurs in self-building, the delivery of the units had a hiccup, but it was resolved satisfactorily by the manufacturer, and I am happy with rooflights, which are now all installed.

Thanks all. I wonder why the instructions for the shower mixers all say something like this then… (This one selected at random from Google – for "Heritage Bathrooms".)

Off topic. I have been reading online that shower mixers need a minimum hot-water-feed temperature of 55º to 60º to function correctly. Does keeping your tank at 48º cause your shower mixers to go haywire 😄?

Thanks @JohnMo. I am reading that now. DIN EN 16147 seems to be a set of standard testing parameters but unfortunately it seems one has to pay £££ to read the details online. The target temperature does not seem to be specified in the manual you pasted but I suspect it's quite high, it could be 70º given how long it takes. Of course, charging to lower temperatures would take dramatically less time. (I am not worried about Legionella at all). Edited to add a correction: the temperature is indeed specified in the manual: 49.9º. My life is unimaginably simpler than yours sounds 😄. Out of interest, what temperature do you keep your tank at?

My DHW cylinder is a matching Vaillant UniTower (190 litres). I calculate to heat that tank from stone cold (8º) to 55º would take 1h 39min at 5kW, which is well within the power output of both the "3.5 kW" and "5.0 kW" models (see above). Obviously you'd rarely need to heat the whole tank from cold. More realistically, two showers (say 80 litres in total) would take 42 minutes at 5kW to heat to 45º, which is the likely tank temperature I would choose (unless I had visitors staying). (This assume 100% heat transfer from the heat pump to the hot water tank. No losses. So the figures are under estimates).

The heat-pump model I am buying is the Vaillant Arotherm Plus. At 2º air temperature and output water at 35º the 5kW heat pump can modulate from 3.00 to 7.40 kW. Note that higher top figure is a lot higher than the nominal "5kW". Conversely, the 3.5 kW model can modulate from 2.10 to 6.90 kW. The house I am building is close to passive levels of performance and I predict that the space heating demand at 0º ambient temperature is around 2kW or so.

It struck me when I saw this tariff that the second afternoon cheap window could be a good time to heat the DHW cylinder when the heat pump needs to work at its hardest. Overnight on the other hand would be good for space heating. (I have no PV, nor a battery). I am presently negotiating with the wholesaler supplying my ASHP to swap the 5kW model that I originally ordered for the smaller 3.5 kW model exactly for this reason. This is a good point.

Is Homely compatible with my heat pump? Currently, Homely is compatible with the following heat pump brands: Samsung (model number beginning with AE, manufactured post 2015) Midea We are always looking to expand the list of compatible heat pumps so please do check back if yours is not currently showing. https://help.homelyenergy.com/knowledge/is-homely-compatible-with-my-heat-pump

I gave it a go with my SMETS2 Smart Meter. Got the same response as you. "There has been a problem trying to check your meter. Please try again."

In my experience its about 50:50. And to my surprise it is not only the smaller contractors/suppliers who will not provide a breakdown. Some of the big ones do too. I tend to especially avoid them. For the small ones, I suspect its a fear on the part of the contractor is that a breakdown will lead to cheese paring. Quite understandable. For the big ones, I suspect its a wheeze to try and conceal high margins. Personally, I prefer a clear breakdown and tend to avoid contractors who will not. But I have made exceptions for small pieces of work and where I felt the level of trust was high.

Nice solution. Slightly off topic, I am wondering how such a bracket could be mounted to a metal-framed internal wall (MF).

Pretty close, yes. My walls are indeed I-beams with Smartyply nailed on. The joints and nail-heads were over-pained with airtightness paint. Windows were foamed and double-sealed with decent tapes by me. Rooflight were upstands painted with airtightness paint. The joint between wall and roof was foamed for insulation and painted with airtightness paint. The joint between wall and concrete raft foundation was painted with airtightness paint. All penetrations were sealed with decent grommets and tapes by me and mostly also overpainted with airtightness paint too. The OSB flat roof was left un-sealed, with some slightly-worrying gaps between boards were clearly visible but there is a Bauder three-membrane warm roof above. Before the air test, I was ready to spray paint the entire OSB roof deck with airtightness paint (form inside) but fortunately it was not needed and Bauder's claim that their roof build-up was airtight has proven true. Above all, the building has a simple L-shaped form. And airtightness was managed by me personally, so I kept an eye on all the details.

Thanks @Nickfromwales. I have been looking online trying to work out what you mean by a box attenuator. Is is this sort of thing? Or do you mean the round ones, like this?

I chose felt and bitumen after talking through the various options with Bauder. My impression was felt and bitumen was a good solution if you have lots of fiddly bits on the roof. And I had 9x rooflight up-stands to detail in my flat roof. In my case, I was reassured by the independent (and unannounced, even to me) inspections of the installer's work by the manufacturer. Whatever system you go for, make sure you get a 20+ year transferrable guarantee from the manufacturer, not just the here-today-gone-tomorrow installer.

Another point of view. Don't do it. Put them on the same face. The reason is wind pressure. You want it to be roughly equal on both ducts.

Hi, I am in Cambridge. For my windows, I bought from IdealCombi. They have their office in Milton Keynes. The windows are made in Denmark and imported. For my entrance door, I am buying from Spitfire Doors. They are up-North but I have a personal contact with one of the top guys and he lives less than a mile from me in Cambridge.