Jeremy Harris

I've been digging around and have found the independent test data from just after I'd decided to not go with these: http://www.narecde.co.uk/thermodynamic-panel-data/ Look carefully at the Coefficient of Performance (COP) data points. The performance seemed worse than an immersion heater at times (COP less than unity) and even on good days the COP seems to have struggled to get much above 2, which is pretty dire, and far worse than I would have expected. Our ASHP rarely drops below a COP of 3, but then it doesn't deliver water at such a high temperature.

The area used should be the swept area of the vane, when the vane type anemometer is fitted tight to the cone, as that's the area the air is really flowing through. The whole house ventilation rate requirement in part F can be a struggle for a larger house, and, iMHO, is way OTT - I run our system at around half that rate and it's fine, far better air quality than the old house. In terms of area, then you may be able to argue that it's the actual room external wall/ceiling areas, and exclude the unventilated spaces, like the semi-sealed eaves areas in room in roof houses. It's probably not strictly OK, but my experience was that building control weren't too fussed about detail.

Some do make a fuss over labels................ We had an interim building inspector (a guy brought back from retirement, part time) who produced a fail list as long as your arm. He started by saying that he didn't believe that a house built on a polystyrene block foundation was "safe", and one of his comments was that the labels on the consumer units and switches were unclear (as a consequence they all have nicely printed laminated labels now). Sometimes you just get a jobsworth, and either have to deal with him or get someone else. I thought that any qualified electrician could do the inspection and testing needed for a job like this, and any remedial work needed, can't they?

Looks like the Spanish/Portuguese imported direct system have risen above the parapet again................ Last time a couple of companies tried importing these, they got into hot water with the MCS, and had they approval withdrawn. In essence, they are just an ASHP, with no fan on the external evaporator, and with that evaporator formed as a flat plate, rather than an air-blown finned array. The interesting thing is that a lot were sold in Ireland a few years ago, and the owners were pleased with them. I wanted to fit a double panel unit as our hot water system, with the panels mounted on the East wall. I went down to Southampton to see the importer, who had a demo system running, and it was pretty impressive looking. The really big show stopper is that there was zero technical data. Not even the manufacturer (in Portugal) could provide really basic info on COP. In theory, the efficiency should be higher at high DHW temperatures, because of the direct exchange between the refrigerant and the DHW, but the manufacturers were really cagey about letting me have any data. In the end, the two companies I spoke with both dropped the product, and refused to supply it to the UK market, just because they couldn't get data from the manufacturer. This was the last email I had about these "thermodynamic" systems, back in March 2013:

It's the total extract from the room at boost that needs to be met for Part F, table 5.1a, so as long as the sum of both extracts exceeds the minimum (13 l/s for a kitchen) then you're fine. In practice, I've found that turning the trickle ventilation rate down to well below the whole house rate in the regs (the 0.3l/s/m² rule) seems fine, as long as you can boost the system up when needed to clear steamy bathrooms, cooking smells etc.

Welcome, and I'm afraid I can only agree with what others have said. There are some additional points worth noting though. Firstly, the concept of a "hold harmless" agreement has little or no legal standing in the UK. It's primarily a US construct, and one that I have used there, but even then it has only limited influence on the outcome of any subsequent dispute. Under the law of England and Wales at best it is treated as an indication of intent, at worst it's seen as an attempt to impose an unfair contract term. In this case, timing is everything. At the point where you contracted with the project manager, be that verbal or in writing, you did not contract for the supply of goods and services, nor did you contract for the supply of a service that could be zero rated for VAT. The contract came into force after three things had happened; you were made an offer to provide the service by the PM, you accepted that offer, and there was the exchange of a consideration (in this case payment is irrelevant - the work done by the PM is a consideration, in law, so the contract came into force as soon as he did work on the project, or on the date the contract was agreed). All work done by the PM under this contract must, by law, by charged at the normal 20% VAT rate, assuming the PM is VAT registered. There is no legal way to "undo" work done like this under a pre-existing contract in order to avoid payment of the VAT. What you could choose to do, to reduce the VAT liability for the contract from now on (but not retrospectively), is to terminate the existing contract with the PM, and pay him his fee, including the VAT due, to date. You could then ask your main contractor if he could sub-contract the PM, as the site manager, under your JCT contract, via a contract amendment, and any work done by the PM from that point onwards could be zero rated for VAT. The downside has been pointed out already; you lose direct control of the PM, as he now works for the main contractor. As a useful reminder to others, as this is an issue that crops up frequently, all work on a new build that is not directly a part of the construction process is generally liable for VAT at the normal rate. This includes tool hire, plant hire, skip hire, surveyors fees, project managers fees etc, plus a few others. There are many pitfalls when it comes to what is and is not zero rated for VAT on a new build, and it is useful to try and identify as many as these as you can before you start, as there are ways of avoiding some of them. The most common way of avoiding VAT on a service that would ordinarily attract it on a new build is to include it within a part of a larger supply and install/erect/build contract. For example, having skip hire, or portaloo hire, included in a contract from a builder means it can be zero rated; hiring skips or a portaloo yourself means that it cannot, and VAT is payable at 20%.

Everyone that is VAT registered is required to charge the appropriate VAT rate, or zero rate, goods and services if that is what the law requires. It doesn't matter what arrangement your tree surgeon has for paying VAT, in this case there would be no VAT payable by him to HMRC, as the work to you would be zero rated. This is something that anyone dealing with work where reduced, or zero, rates apply will be familiar with, but from the sound of things it's not something your tree surgeon has come across before, probably because he's never done work related to a new build before. Get him to ring the HMRC helpline, and they will help him understand how he deals with it on his side when he comes to do his return. Needless to say, if he incorrectly charges you VAT you cannot claim it back later.

The most impressive ones I've seen were at a place a friend worked, that made cast concrete staircases, with a highly polished finish. They used strongly reinforced plate glass moulds, with a two-part casting process, where the finish coat was applied to the glass, allowed to partly cure, then the structural layer was cast. The glass moulds were works of art. The place still exists, Cornish Concrete Products, but at the time my friend worked for them most of their business was in the Middle East, so he was based semi-permanently in Dubai.

I had this problem, and found that it was difficult to get steady readings with the wind gusting outside. I ended up averaging several readings to try and compensate for the variations due to wind gusts. If you can do this job on a still day it's quicker and easier.

Best to start with all vents/ducts about half way open initially, if you can, and see what the readings look like. It's rare that you will want any wide open, and starting from the mid point tends to make things a bit faster to adjust. If you have a system with restrictor rings in the plenum chambers, then you have to start with them all open, and it's one of the things that makes adjusting a system like this a bit of a pain. The flip side is that any terminal noise is lower, as the restrictions are well away from the rooms. In theory, all the doors should be shut, but I found that it didn't make a noticeable difference, and it was a lot easier to just leave them all open as you're running around from room to room!

I assume that you have two big holes to outside for the woodburner, not just one? If you don't have a balanced and room sealed air feed to the woodburner then the MVHR will be running massively out of balance, especially when the woodburner is actually lit. When running, with no sealed external air feed, the woodburner will extract far more air than the MVHR in all probability. So, if you don't have an external air feed, for the woodburner I'd definitely say you need to fit one. You also definitely need to temporarily seal up the flue when balancing the MVHR. Once you've fitted the woodburner, with a balanced external air feed, and good seals around the air feed, the woodburner doors and the flue, then the MVHR balance shouldn;t be affected as long as the woodburner doors are closed and sealed.

The pressure won't make any significant difference to the stiffness of the pipe in practice, as the forces on the walls of the pipe from the pressure are very low, even if the pipe is at a couple of bar or so. The inherent stiffness of the pipe exceeds anything that a bit of modest water pressure will improve, and you can just as easily crush a bit of UFH pipe that's filled with water as a bit that isn't.

I couldn't agree more. Our old house had ceilings that were just taped and filled, no idea why as all the walls were block and plastered. The living room ceiling used to annoy the heck out of me, all the time, as the setting sun would show up every ripple along all the joints. It was the sole reason I opted to skim all the walls and ceilings in the new build.

I didn't even bother to fill our UFH before the pour, as we had no water on site at the time and it seemed too much hassle to do. All went well, and there were no problems with any of the three loops. I have a feeling that MBC don't usually fill UFH loops before pouring slabs either; others may be able to comment on whether this was true for their slab pour. As for getting air out, then I found it did take a fair time for all the air to come out of all three loops. I filled the system and ran the pump at full speed, with the auto-bleed valve open, and it took a couple of hours for all the air to find its way out, IIRC.

Exactly what our plasterers said, and what I did. The result was that all the architrave sat dead flush to the walls, with no faffing around afterwards. As I was fitting oiled solid oak architrave, the last thing I wanted to have to do was faff around trying to fill under it to get it to look as if it was sat dead flush with the wall. Having the beads underneath meant the plasterers could just skim to the flat top edge of the bead, making things consistent at every doorway.

I looked at these for our retaining wall, at the suggestion of a local farmer. For us, the only downside was getting a big enough crane on site for the 2.5m high sections we needed. For us the base foundation and anti-slip key was pretty easy, just a trench foundation along the base for the pre-cast sections, keyed with a deep slot, floated level and the L shaped sections just bolted into place on top of it. There wasn't much difference in cost between using the precast sections and building a hollow block concrete filled and reinforced wall, but the precast option would have saved around two weeks in build time, I think.

I keep meaning to do some practical experiments to see the effect of accelerated convective heat loss due to wind on the outside of a house. It won't be easy, as the surface texture plays a big part in the effect, due to the large impact texture has on the boundary layer thickness. My gut feeling is that the variation in wind-related accelerated convection heat loss from external surfaces is probably quite significant, more so in a moist climate, where the external surface are more likely to be wet, and so suffer the added impact of evaporative heat loss as well. Whether it's worth modelling this is debatable, though, as just increasing the overall decrement delay factor as a part of the design process may swamp out any variation from accelerated convective loss. It would be easy to get sucked down into another rabbit hole of wanting to add ever more detail to a heat loss model!

IIRC, our guys (two of them) fitted around 450m2 of plasterboard in 5 days, then took 4 1/2 days to skim it the following week. I think they were around £150/day each, and did a cracking job. On top of that, I paid for a labourer for a day (£80) to shift all the plasterboard into piles in each room, ready to fit. I also provided an internal scaffold tower (which I later sold on to the plasterers, as it happened). So, very roughly, fitting the plasterboard came to around £1500, skimming came to around £1350. I purchased all materials, plasterboard, beads, collated screws, plaster etc. Labour cost per m2 came to around £3 for plaster skimming, £3.30 for boarding out, so around £6.30/m2 labour for the whole job.

The plaster skim will tend to taper in thickness at the edges, and may well end up uneven, so you'll probably end up having to fill under the architrave to get it to fit without gaps.

The key is knowing the cable reference numbering system. PVC rigid core T&E is 6242Y, PVC rigid 3 core and earth is 6243Y. If you search for 6243Y 2.5mm2 you may well find a cheaper source.

https://www.superlecdirect.com/cables-and-accessories-c1/bs6004-6242-6243-twin-and-earth-pvc-cables-s4/p-6243y2.5-superlec-bs6004-6243y-25mm-3-core-and-earth-flat-pvc-cable/

I had the same problem - you cannot plaster without having either the linings in, or something to give an edge of the right depth for them to plaster to, at least not without ending up with a messy edge. I ended up in a last minute rush, fixing 15mm stop beads around every door opening, before the house was boarded out. The plasterboard was then screwed in place, over the big flanges of the stop beads and leaving the edge of the beads proud of the plasterboard by the skim thickness. In hindsight, I think I would have been better fitting 120mm wide temporary linings with screws, as that would almost certainly have given a better edge, and wouldn't have cost a lot more.

Glad it worked OK, Ian. However, I'm now getting increasingly concerned that, by the "law of averages", I must be coming perilously close to suggesting something that both doesn't work and costs someone a lot of money..............................

The problem with blind adherence to a particular performance standard, as if it may be the saviour of the planet, is that some models fundamentally work to such a fine level of performance detail as to be nonsensical in terms of how people will actually live in such houses, or how other local factors may affect real-world comfort and performance. @SteamyTeas point about the neuroscientist working to a 5% confidence level is apt, except that I would say that we probably don't actually even need that sort of confidence level for a theoretical house performance modelling standard. I would argue that a house performance model doesn't really be very accurate at all, as there are so many factors that any model like this will fail to model well, and making the model ever-more complex (which is exactly what has happened with PHPP over the years) is just an exercise in futility, in practical terms. My view is coloured by having produced a very simplistic heat loss model, and then having been surprised as to how close it comes to predicting real performance, or, dare I say it, how close it comes to matching PHPP heat loss predictions (as others here have found). Take our build as an example. I used a couple of models, plus the mandatory SAP thing. Both SAP and PHPP have an over-heating risk model, neither showed an appreciable risk of over-heating for our local climate data. I went to some pains to get accurate local data, too, looking at the plots on the Met Office historical data site and interpolating to get what I thought would be the best fidelity I could from the available data. In reality, it quickly became clear that both SAP and PHPP are very deeply flawed when it comes to dealing with a house that is partially set back into a South-facing hillside, and near the bottom of a steep valley with much lower than typical wind speeds for the area. Luckily this first became clear during the ground works, when we had temperatures up towards 40 deg C in the corner where the big retaining wall was being erected. At that point I made the decision to re-check the data and the models, and realised that the temperatures we were seeing that July were much hotter than the maximum predicted by the Met Office data. The impact this had on the house was large, it massively increased the effective solar gain and decreased the heat losses. I made some on-the-fly changes, but was restricted to only being able to change the MVHR from a passive system that had originally been planned to a system with a built-in air-to-air heat pump, to provide cooling. I also found that we needed to add additional measures after the house was completed in order to reduce the heat gain still further, by fitting heat reflective film to the outside of some of the glazing and incorporating cooling into the slab. How big was the error in the PHPP prediction? Around 30% or so. I should stress that PHPP as a model is fine, as far as it goes, but that the unforeseen microclimate we created made much of the modelling in such fine detail open to question. Why model something to, say, 5% confidence, when a simple and unforeseen external climate difference can create a 30% error? On the plus side, the microclimate effect is a definite positive in the heating season, as we get more winter solar gain than anticipated and slightly warmer local air temperatures, too. I've now had two PHPP certified people look over the house and data, and both have taken on board the sensitivity of the modelling process to very local conditions. Both admitted that they were unaware of the extent that microclimate could have on modelled performance.

No real need for screened cable, unless you're going for very fast colour changes and are concerned about switching transients causing EMI. 16-2-4A cable is OK, it's rated at 2.5A with all cores loaded, so will tolerate more than this with three of the cores carrying a lower current, just need to watch for the voltage drop, really (about 40mV per core per amp per metre).