Jeremy Harris

Never heard of that, but it's great to hear, all the same!

Me too. Our ASHP cost around £2k installed (by me, in about half a day, call it a day to allow for reading the manual, and I'd never seen one before), but the MCS installation price I was quoted was about double this, for the same size ASHP. Quite how any company can justify charging that much money for such a small amount of work is beyond me. I couldn't claim the RHI, as I didn't have an MCS install, but the RHI would have only given me a bit over £80 a year for 7 years, and I concluded that saving a couple of thousand on the install more than made up for gaining around £600 of RHI payments...

+1 to the above. Our ASHP performs very well indeed, and the performance doesn't noticeably change in very cold weather at all.

Not enough to worry about, I think. We've discussed it before as a way to make a reliable PCM charging system, as it's the way the Sunamp PV works. There are some things to watch out for, and the most critical is managing the charging water temperature and flow rate, especially if fed from a variable power source, like excess PV generation. It's only really a control problem, but does need a bit of thought when it comes to both the sensors needed and the control mechanism. With the Sunamp PV, they chose to not control the heating element, but to allow that to accept whatever power was available from the excess PV diverter. They then needed to ensure that the charge loop was maintained at around 65 to 75°C (IIRC) which meant sensing the temperature of the charge water flow, the flow rate of the charge water (using an ultrasonic flow sensor) and a variable speed circulating pump (looked to me to be a standard Grundfos one, not sure of the model). The trick is then to control the flow rate so as to maintain a near-constant temperature in the charge loop, despite wide variations in power to the heating element. Not too hard to do, but coping with the varying response time of the system would need some fine tuning, I suspect. The easiest way to get a working system might be to try and acquire the charging circuit and controls from a Sunamp PV...

Welcome Matt. Around here PP seems to take around 12 to 16 weeks minimum, and I get the feeling this sort of timescale is now pretty common, with the cutbacks in staffing that have been impacting on local authority services. I'd definitely agree that designing the house before getting the plot would be a waste of time and money, as what's needed initially is to establish the principle that a house could be built there. Once that's established it's just a matter of getting a design that will be accepted. You'll need to do a fair bit of work between now and the auction date to try and remove risk, although some risk is bound to remain. Perhaps the most important thing is to dig out all the history of the plot you can, and research why it's being sold (the real reason, rather than any stated reason). You should be able to check the planning history, perhaps initially by searching the local authority website, and if that doesn't raise any alarm bells you could make a request to see any planning files that the LA may hold. Often there will be detail on planning files that never gets uploaded to the LA website, so a root around in those files can tell you a fair bit (assuming there are any such files). Likewise do all the research you can on the vendor. A plot being sold at auction can itself ring alarm bells, simply because plots are in short supply and a plot with planning consent is worth many, many times more than one without. However, churches sometimes sell good plots at auction, as do some other organisations, as it seems they sometimes aren't interested in increasing the value by getting PP (I've no idea why).

Sounds like a reasonable plan to me, especially if you can fit the PV without too much expense. You can get simple flat roof PV mounts that pretty much anyone could install, as all they need is a bit of ballast: http://www.windandsun.co.uk/products/PV-Mounting-Structures/Flat-Roof-Mounts/ConSole The only thing to watch is the roof loading, so it would be useful to make the flat roof a bit stronger, perhaps, to take the additional load.

I think I've won the MVHR battle, now, as there was a comment a few weeks ago about how fresh the house seemed. I just casually mentioned that this was because the windows were closed and the MVHR was doing its thing, and I've noticed since that the outside doors are being kept closed and the latches pulled up to get them to seal, without me having to go around closing them up. The final observation was this weekend, when a spider was found in the utility room. I mentioned that they could only get in when a door was opened (they hide under the rain deflector at the base of the back door). I suspect that the fear of spiders will be the clincher when it comes to keeping the door closed...

Welcome. As above, the best bet is probably to work on the basis of the total internal floor area (the areas of all the floors added together) and then multiply this by the cost per m². The cost per m² can vary a great deal, depending on the spec of the build and the build route chosen. At the low end we've got members here that have done practically all the work themselves and come in at maybe £800/m² (or less, but that's really pushing it) and at the top end we've members who've come in at well over £2,000/m². For someone self-building with subcontractors, to a basic spec, then £1,600/m², less in some regions, more in other regions.

TBH, I only know about it because it was drummed into my head when I initially did aeromedical training, and then again every two years for a bit over 20 years. The demonstration of the effect of Dalton's Law of Partial Pressures was by sticking me in a hypobaric chamber every two years and then being told to remove my oxygen mask at 25,000ft. Tends to ram home the message about hypoxia being very insidious...

Interestingly (perhaps...) there's pretty much the same percentage of oxygen in the air at the top of Mt. Everest as there is at sea level, more or less 21%. What changes with altitude is the oxygen partial pressure, which has a significant impact on the efficiency of human respiration. The problem is that the affinity of haemoglobin for oxygen is dependent on the partial pressure of oxygen in the air we breathe. If the partial pressure decreases less oxygen is diffused into our blood. At sea level, with an air pressure of around 1013mbar the partial pressure of oxygen is about 213mbar, but at, say, 5,000m, the total air pressure will have dropped to around 533mbar and the partial pressure of the same ~21% oxygen level will have dropped down to about 112mbar. As respiration efficiency varies pretty linearly with the change in partial pressure, at 5,000m our ability to diffuse oxygen out of the air reduces to about 52.6% of that at sea level. The other curious thing (which goes against all the crap you see in films about people suffering from hypoxia) is that there are few outward symptoms. Your respiration rate doesn't change, as that's controlled by the level of dissolved CO2 in the blood, so people don't "gasp for air" at all. What happens to most people is that they just stop functioning properly, may appear intoxicated, visual acuity will be adversely affected and loss of consciousness and death may ensue after a period of time, depending on the persons fitness level, age and the altitude. I know that I can stay conscious for about 5 or 6 minutes at 25,000ft, but I'm seriously impaired after about 2 minutes, and most probably wouldn't be able to recognise that I was spiralling towards unconsciousness and death after the first couple of minutes.

No, not yet, but I've been sent a photo of the inside of it, so can see that they've changed the contactor for a larger relay.

I'm also a fan of enamelled steel baths, and fitted one in our second bathroom. It would look to be pretty easy to bond one of those electric underfloor heating mats, or perhaps one of the silicon sealed mirror heating mats, to the underside of the bath, as a way of keeping it warm.

I'm not sure that the ground prep was the same for both of us, though, as I chose to do all of the slab sub-base work before MBC arrived on site. I seem to recall that they normally include this work, including laying ducts and drain runs etc that go under and up through the slab, in their price, as I remember negotiating the first quoted price down initially, because we were doing some of the work. Looking at the ground works chaps cost breakdown, he has listed costs for the house base prep, laying and compacting the passive slab sub-base and supplying and laying the various ducts, drains and pipes under the slab and laying the garage base (MBC just built the garage on the base I'd provided). Chucking that into the mix increases the price a bit, to around £460/m², but I've no idea how things like differing structural design elements influence the cost. We don't have any large openings, for example, so their are no steels or large lintels anywhere.

As @PeterStarck mentions above, I'm not sure that prices can be compared that easily from site to site. In our case we had to do a lot of preparatory ground works on the site anyway, to level it and put in the retaining wall, treatment plant and drainage runs, borehole etc in, so we had already laid the stone sub-base for the house, the slab for the garage and put all the ducts and pipes in where they were supposed to be, with a surveyed and clearly marked out location for the foundation slab, so I'd guess this reduced the amount of work that went into laying it by a fair bit. I've no idea what impact that had on the cost from MBC though.

I remember workshops at work being coated with an epoxy finish that self-levelled and turned fairly rough concrete into a smooth, hard wearing, finish. Probably not that cheap, but might be an option, perhaps.

No, just missed your earlier post, that's all. Our package was a fair bit more than just the frame and foundations, as it included all the insulation (slab, walls, roof), UFH in the floor (which was floated smooth enough to directly lay flooring on), guaranteed airtightness of <0.6 ACH @ 50Pa (so internal vapour/airtight layer plus all airtightness taping of joints, around doors and windows etc) and the roof sarking boards, counter battens, membrane and slate battens. The total cost of this package was £408/m². Of that cost, the passive slab foundation system was probably about £90 to £100/m², based on other prices I had for passive slabs with UFH installed. P.S: I'm not peddling anything, either, as I have no commercial interest/connection with anyone. Our costs are what they are, and seem to be no greater than the costs of other similar builds to me.

Worth noting that this contactor failure looks to be an isolated event, as I've not heard of any other contactor failures. However, the contactor used in our controller has been changed to a very different relay in the newer controllers. Whether this is due to any concern about long term reliability or not I don't know. My instinct is that the change may have been made to reduce noise, as the contactor originally fitted did make a very loud clunk as it operated.

The thing everyone here is missing is that a passive slab is a fair proportion of the build cost for a well-insulated, airtight, build, and that slab will often include the UFH (ours did) in the price. Comparing an all-inclusive insulated, and guaranteed airtightness, weather proof, house shell (it's far from being just the frame) and passive slab package, to any other build method, needs to be done on a like-for-like basis. For example, you can't reasonably compare the cost per m² for a single storey build on a passive slab, with a two or more storey build, of the same sort of total floor area, as the ground floor cost (which includes the passive slab, UFH etc) will always be a lot higher than the upper floor cost, so a single storey build will always look around 15% to 20% more costly, per m² total floor area, than a multi-storey build. The cost of having 300mm of insulation under the slab is always going to push the price up; it did for our build. We could have opted for conventional foundations and frame for maybe 20% to 30% less initial cost, but we'd have then had to add loads of insulation, install UFH, and screed the floor afterwards, so spending as much as we would have for a passive slab, and not getting an airtightness guarantee, either. We had no additional costs for the ground floor at all, as the UFH was in the slab, the surface was dead flat and I was able to lay flooring laid directly on it (and I'm aware that @lizzie's slab had problems that needed rectification, caused by the poor workmanship of a subcontractor).

@lizzie, I think what you're saying is that the insulated frame was even less than 25% of your build cost, so that makes it relatively cheaper, as it didn't dominate your build cost. You could have used any build method available and it wouldn't have changed your final bill by much (given that the insulated structure is only a modest part of the total cost).

I accept that, but you've already mentioned here that your build costs were over £2k/m², IIRC, so it looks like the well-insulated structure was still around 25% of your build cost, maybe a fair bit less, unless my arithmetic is haywire, so as a proportion of total spend, the insulated structure is far from being the dominant cost element.

The key is being wholly in control of the design and build process. I don't agree that it's "not cheap" at all. Our build is a similar thermal spec to yours, from the same supplier, and came in at ~£1,380/m2. If I'd been "hands off" and used sub-contractors for everything it would probably have come in at around £1,600/m2, which is still well inside the sort of normal self-build range. We could have pushed the cost up to around £2,000/m2 or more by going for a higher spec, but we already have a reasonably good finish, with solid oak joinery everywhere, loads of travertine flooring, a kitchen that cost around 10% of the total build cost, etc. The core, well-insulated and airtight structure, was only around 30% of the finished build cost anyway, most of the cost was in all the other stuff, that played little or no part in making the house thermally efficient.

Before you cut a hole, is there any chance you can take the downlight out and have a look inside to see if the leak is where you think it is? Water has a habit of running along pipes and dripping down some distance away, so you could end up cutting a hole, only to find that the leak is some distance away. I've got a USB endoscope thing that works reasonably well if you want to borrow it for a look see.

Good job it wasn't in the ladies, I've known one or two that wouldn't have been able to get their backside into a gap that narrow (I should add that "known" wasn't in the biblical sense, and was a consequence of going drinking with a bunch of submariners who were having an ugly contest).

This is exactly how it seems to work in practice for us. I'd not want to have a floor that didn't include a fair bit of heat capacity in our house.

Looks like a @Nickfromwales job to me! The diverter valve in the shower/bath tap at our last house constantly gave problems. That was a lever operated valve on the shower valve assembly that just selected shower or bath fill, and the failure point was an O seal. Taking that apart was easy, as the handle came off by just removing a screw under the cap on top, then the cover sleeve pulled away, revealing a brass nut that secured the valve shaft in place. The O seal that kept failing was the one that sealed around the shaft, with the failure always being due to scale build up. It's not clear from that photo as to how you get the thing apart, though. Your guess of just trying to unscrew it seems as good as any, and one that I'd (gently) try if it was mine.