TerryE

The nub of this is how you agree with the architect is the value that they will charge a % of. As you say, Jack, some might be willing to use the initial estimated cost, but this can prove to be very optimistic and doesn't protect that architect from any "Grand Designs" on the part of the customer. As Colin says the other extreme is to use the finished build costs which doesn't give the right incentives to the architect to manage costs on behalf of or the customer. Or your can take the "unbiased independent expert" approach, use a QS to value the build and base the architect's fees on this. Whether to use a QS or not in itself has pros and cons. The major con is that they charge a fee usually base on a % of the costs. A pro is that this give the self-builder an honest estimate of the likely costs and a baseline for price negotiations with subcontractors. We decided not to use a QS and we didn't see the value as being greater to use than the fee. The only major cost variation that we suffered was as a result of the planners imposed constraint of using local quarried stone. Our local quarry is a pretty small one and doesn't "cut on the bed", to the stone needed a lot of labour to cut, dres and finish it and this probably added £20K to our stone skin costs. Ouch, but how would a QS estimate have helped here?

@JIH, IIRC, it's up to 300W per person for body heat. You also need to remember that (virtually) all of your electrical consumption that you haven't already accounted for in DHW etc, ends up as heat in the house. TVs, PCs, lighting, etc. Thanks largely to my son's gaming PC and electronics this totals about 7kWh/day in our case. On top of this you've also got solar gain which can end up as a non-trival amount. OK, worst case for Dec/Jan can be pretty much zero, but for calculating average hearing costs, then you should use averages. For us factoring these in brought the number of hearing days right down, and also average hearing budgets. I used the PVGIS site. This is primarily for calculating PV estimates, but you can put in your windows and one of the columns gives you incident radiation. Unless you've got special reflective coatings, well over half will end up heating the house.

You should get your other half actively involved in the forum. It does make it a lot easier to reach consensus when both of you are looking at the same posts

Sounds like you need to hook up with @Bitpipe. And also research all of his posts on this. Drop him a PM; he might be willing to have a 1-1 Skype / telephone chat, though I clearly can't make any promises on his behalf

Hi, I did the same as @ProDave, and used an AT rather than an architect. So long as you want a sensible house rather than a Grand Design, then IMO I would recommend this. An AT will convert your design ideas into AutoCAD and prepare (or help you prepare) the planning application and even some of the BReg submissions. An architect will usually insist on an independent QS to price the build and then both will charge a ℅ of the value for their services. This can be 15-20℅ of the QS valuation. An architect will also often want to retain the IPR on his or her design, so if you have a fall out then using the design that you've paid for might be problematic. You might also need a project manager to oversee the build and your contractors. Many of us used an AT and did the PM ourselves, which saves a shit load of money. However, there is no free lunch, if you go this route you will also take a lot of risk, stress and work on your shoulders, so you should only so this eyes wide open. Doing a self build is not an easy option, but if you it and accept the costs of the route for you then it can be amazingly rewarding getting exactly the house that you wanted.

Likewise I estimate that for the 2-3 heating months (that is when we need to supplement the heating) if we use the slab alone as the main heat source, it will lose roughly 1°C every 3-5 hours, so if I boost the slab's temperature to 23°C by end of E7 then this will keep the house within a comfortable window for the remaining day. Even if we need to top up or put a fan heater on in the living room for a few hours in the evening, then this is hardly going to cost a lot. So to answer @Nickfromwales Q, yes the slab can be used as thermal store. But again this is only an interim for a year or two until we've got the hard data to design and install our "optimum" solution.

IMO, using the SunAmp as a thermal store for UFH is overkill. You've already got maybe 7m³ of concrete to do that. In a passive house with typical losses you can pump the heat into the slab when economic to do so and let the temperature vary maybe 1°C, for example with E7 or E7 powered ASHP. KISS. @Stones Jason, I am going for E7, partially because I think that within 5 years we will have consumer spot pricing tarrif options. It's really only a software issue now, and doing so is really going to help the generators optimise supply / demand management. In terms of overall design, we seem to be pretty much paralleling @Alphonsox Neil apart from the sea air of course. The only main difference is that I am not going to fit my ASHP for completion, but use just electricity for the first year or so, so we can characterise and size our system needs and fit the ASHP as a year 2 upgrade.

@SteamyTea, re in roof PV. We made the same comment to the planners. Water off a duck's back. @Vijay, We've got putting holes through the twinwall off pat. The trick is to have a long pilot drill. Cut a 22mm hole on one side, use the pilot and pull back a few inches; the filler keeps it roughly in place. Cut a 22mm sole on the other side push the pilot through then use it as a guide to push through a 20 or 22mm plastic pipe. Silicon and tape both sides. Or use larger pipe if needed. Thread cables and when done, foam and silicon seal as needed. I find using a guide pipe straight forward, but there's nothing in principle taping the wire to the end of the pilot drill and using it to draw the bare cable through.

This is one where you need to keep a very close eye on how well the contractor is placing and fixing the insulation. Any looseness or gaps can allow front to back convection within the cavity and this can halve the effectiveness of the insulation. The devil is very much in the detail here, and not something that many UK builders are known for, at least in things that they don't view as material -- like thermal performance.

Nice to know that my lovely better half is worrying about such things whilst I am in Alonissos. A miracle might happen and our plasterers start work before I get back on Thursday. We've got an MBC warm roof, which is sarked, counter battened and battened so wouldn't it make more sense to run any PV cabling under the tiles and into the services room through the gable rather than compromise the roof integrity? But as far as extra circuits go, IIRC a single 2.5mm is rated at something like 20 amps but this is 5 kW and ample for a standard 3 kVA array. But given that we need an extra circuit on the non RCD side we might as well get our electrician to lay an extra 4mm cable to the CU. XX to the O/P.

We've got the same, but nowhere near commissioning it as we are stuck at first fix, waiting for our !****##@@ plasterers to turn up and do their job. Once we've got to this stage, I'll also post back. Note one thing for prospective buyers: this unit comes in left and right hand versions. You need to order the correct one. They will ship the RH one by default.

That depends very much on your usage patterns. We are a retired couple with a live in son. So three people who shower regularly and have a bath occasionally, and we do our dishes and washing overnight on cold-blooded. So based on our current patterns and use, a dual unit will suit us fine. 25 years ago when we were a couple with 3 kids it probably wouldn't. The thing about ASHP priming is that the water is on demand. You to feed hot water into the SunAmps, soo you need the ASHP running or the buffer tank preheated. It might be worth it for a bath, but think of the complexity that this will introduce. Will you ever get the payback?

Yup, that's my current plan. One doesn't cover our worst usecase. Plus in 4 years time when the planning conditions have lapsed, I'll put a load of PV on our roof. I did look a at ASHP boost but again, it just doesn't make sense. In a few weeks I'll put my design up for critique.

The Fully Charged series is one that I rate and watch regularly. It's explaining a concept new to most viewers. I am planning to use E7-heated SunAmps. No PV cos of LPA wouldn't allow us to put them on our roof. A double system heated by E7 so makes economic sense for our load profile; it gives us the max flow rates without the hassle of an UHC or its extra 3 kWhr / day heat losses.

@Sensusnow they are what I'd fair statements, the average RH in the UK is high, though where I live is below average. 20°C is far above the average delta. However, if I take your thesis that any dry surface in contact with air with an RH of 70% say has a material risk of mould growth then we'd like have mould-ridden walls and houses. I am still at a loss as to why passive houses with correctly operated MVHR represent a greater risk than stock housing: most surface are within a degree or so of room ambient; air circulation is better and sources of moisture such as kitchens and wetrooms directly exhausted and RH extremes reduced because of my previous arguments. Every member here who lives in such a house says they are healthier and mould effectively eliminated. So what is the risk? Is you next thesis that children shouldn't be vaccinated? If I find any material issue with mould in my new house then I'll post some pictures back here and an apolopy

@Sensus, From your responses I get the impression that you don't understand the difference between AH and RH and the physics which underpins this. The AH of air won't change when it's temperature is increased. Air which is at an RH of 60% at 0°C will have the same AH if heated 20° but it's RH will roughly half. Adding roughly 20° to 500m³ at 0.6 ACH gives it the capacity to absorb 2-3ltr of water per hour. This is more than an order of magnitude more than 3 occupants will add. So why are my points outrageous / unfounded? Sorry, but your sums don't add up. In my reading, you are making unfounded claims about the supposed health risks of properly designed passive house using MVHR based on anonymous anecdote and "experience". Give some facts, evidence, data and they might carry some weight - for me at least.

IMO, foam is a crap weather seal. However , it might be an effective scaffold to use to achieve a good weather seal. Silicon and other competitive sealants have established a good track record for what you want, but start to become impractical for gaps of more than a few mm. Foam cut back to form a scaffold surface is an effective compliment.

@Sensus, until JSH returns (hopefully) I've been missing informed debate so welcome ?. And taking the thread in that vein, let me gently push back on few points. First, I don't assume that all of the moisture comes in with air exchange. This is clearly not the case, so why would I come to this conclusion? However with a house of 500m³ occupancy volume at 0.6 ACH and three human (no horses, etc.) occupants, it is by far the largest component. That's assuming of course a modern passive spec house with decent VCL etc. Can you explain the wild (and entirely inaccurate) assumption, because you've lost me on that one? I don't dispute your anecdotal experience, but I do dispute how relevant it is to a properly designed and operated passive house with MVHR. I agree that mould growth is a harbinger that shouldn't be ignored. We constantly see the symptoms of this on the windows of our current farmhouse, but it is over 300 years old with wooden windows and partly 20-30 year-old double glazing units, not a modern spec'ed house with triple glazed units with a U-value < 0.7. If @JSHarris @jack @Declan52 or any of the other members with essentially the same build spec report issues, then I might start to question my understanding of the physics here. But in the meantime I will keep to my views.

I have just been reading this thread in catching up. Some interesting perspectives, and controversial opinions. Some general comments / responses. The audience in this forum is a highly biased one: people interested in self-build development. Moreover, those who want to take an interest in the informed opinion of peers. From my personal research the main risks with MVHR relate to poor maintenance and ignorance of the occupiers. I don't think this is relevant to most visitors to this forum. IMO, the risks in modern well sealed houses are in those without correctly operated MVHR (and closed trickle vents, etc.). @Sensus comments about the risks of condensation due to poor airflow and dead zones in MVHR-fitted houses, seem anecdotal rather than evidence based. They have no underpinning in the physics of gas diffusion. It just doesn't work that way. Heat exchange drops the RH of input air at 0°C and RH 60% to something like 20% at 20°C. The walls in a house like mine are typically within 1°C of room temp. Even the surfaces nearer cold bridges around the windows will only get down to say 15°C under the most extreme conditions. Gas defusion and micro circulation means that the AH in the room will rarely vary a few %. The only material condensation occurs in the MVHR unit itself, and this is designed to discharge it safely. Yes, we will be adding to the moisture levels by inhabitation, but only to comfortable and safe levels. On a different point in some regions decent self-build plots are extremely difficult to come by. We were lucky enough to a have a garden large enough to split, and survived the LPA cat and mouse game to get planning permission. The other alternative here is to buy a rundown property, demolish and rebuild. The local LPA is really only interested in supporting large developments in designated development villages.

Gosh, you call that a cow shed! Are you going to hide it behind straw bails for 7 years? But seriously it looks good, and I hope that you enjoy the final result.

I've got an RPi server that been running for about a year. Zero problems. I have it eNet connected to my router with SSH and HTTPS ports open (not the defaults) and private self certified certificates. I don't bother with openDNS. Peter comments that the Linux distro is an overhead, but running it rather than some other OS might cost s few extra watts or a kW or so extra per year. But Linux means that so many open-source packages can be downloaded for free and with minimum hassle. But IMO, using one for an IoT (Internet of Things) device is not it's sweet spot. Better an Arduino, PIC or an ESP chip for this type of role. I personally prefer the ESP8266 series, though I do have a couple of their next generation ESP32 chips, but I am a bit biased because I am one of the team that develops the Lua firmware build for the ESP devices. As far as integrating my IoT devices directly with any cloud service, then my paranoia kicks in: any direct portal to the web can create a back path to hack into your systems. So I am not going to have any direct paths from my IoT devices to the wider Internet. None. My IoT devices each typically do a single job and they talk simple encrypted protocols to a locked down server (which is an RPi). I access this RPi when needed via my public internet-facing shared service using an HTTPS tunnelled service. All geeky crap, but I am a geek so you'll have to excuse me.

We miss him as well

@worldwidewebs Andrew, you've got an MBC frame so you must do your basic heat calcs. I doubt that you will be losing more than a couple of kW on your heating days -- unless you have large areas of glass. 9 loops = ~ 800-900m of pipe or ~150m². If you reckon on 7W/Km², then you will generate ~1 kW/K across the slab, so if your slab is much hotter than a few degrees more than room temperature then you will soon get too hot. Therefore: I would really question the sense of having 5 zones from a control PoV. You will need to do a mix down in your UFH. Read Jeremy Harris's blog posts on his adventures in designing his UFH slab system: pure gold-dust.

@IanR maybe you can do a write up on your Touchwood experiences and @PeterStarck add your comments as a separate topic? To be honest, it's the first time that I've come across them.

This apples and oranges issue is really difficult to get your head around. We've discussed the issues of the slab interface, and in one site visit that we did, the builder was using a TTFC frame on his our conventional foundation. The TTFC guys used a sole plate, but the foundation was so out of true that the packing under the plate was over 10mm in places, and two internal load-bearing walls were ~50mm out. The main problem here was that there was a steel pillar landing on their junction so the base plate was only a quarter on the load-bearing wall. Our slab was done in a single pour with the UFH built in and the whole thing power floated flat to a couple of mm, so no UFH mats, having to lay it or worrying about internal screeding / alignment / thermal bridging issues. So my personal view is that whoever does the slab and whatever technique is used, it makes a huge amount of sense to embed any UFH, address and thermal design / bridging issues and power float the entire slab to better than a few mm vertically and <10mm in plan before any framing or conventional skin is erected. Another issue is air tightness. Air exchange accounts for some 13% of our total heat losses, but that is with a good seal and MVHR. Without effective HR, then our air exchange heat losses would be approaching 60%. So IMO effective air-tightness is absolutely essential in achieving energy budgets and to achieve this the design has to address some key vulnerabilities which can compromise this. A good example is how the air tightness around the floor decks and joists is achieved. Doing this post frame-erection is a nightmare, so my view is that you will have a lot of challenges if your frame supplier doesn't air tightness in the frame design criteria and be willing to offer an airtightness commitment. A third issue is weather proofing. We closely integrated our frame erection and installation of our Internorm windows, so that on Day 0 we started with a bare slab and by the end of Day 9 we could lock the door on a totally weatherproof build, and start to let the whole thing dry out and come to a moisture equilibrium. Even so the floor boarding was exposed to a couple of days rain during the build, and I can detect slight flaring along some board edges from this, I guess. This is mostly less than a mm, but it is still noticeable on some joins if you eyeball them at floor level from close up. In my view, getting the frame quickly covered and weather-tight is essential if building in the UK. If your frame provider does just that, then you need to address how you are going to get the roof (sarked and) felt and battened and the window openings sealed.