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TerryE last won the day on March 24 2017

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About TerryE

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    Northamptonshire, UK

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  1. We much +1 to @Bitpipe's comments. MVHR gives you lots of fresh air in the colder months without having to throw heat out of open windows or trickle vents. Brilliant -- but that doesn't stop us opening windows when it is warm enough. IMO, the only good argument for not doing this is if one or more of the occupants is allergic to pollens etc. You really need to think of the house as a system and understand where your relative thermal gains and losses are. IMO, the PH and SAP spreadsheets are just too complex to do these sorts of trade-offs. The sort of simple spreadsheet that Jeremy Harris or I developed is plenty detailed enough. The whole build process is one of trust(-ish) but validate and verify at every step. You need to understand potential thermal bridges and make sure to avoid them when practical. You need to be sympathetic to the fact that UK building trades in general have little or no understanding of the importance of the detailing needed to get good thermal performance, but this doesn't excuse sloppy workmanship. You either (i) need to pay the premium for a subcontractor that does have this understanding; (ii) validate and specify at every step, or (iii) accept that you will be disappointed with the as-built performance of your house.
  2. As @Iceverge says, I have a reasonably large stone clad "cottage style" build to passive standards. As I said recently to @shuff27 when showing him the build, I can't think of any things that I'd tweak if we were doing this over let alone fundamentally change. Have a look at my blog.
  3. Or a Jacuzzi, or more specifically not for DHW or conventional CH. It also has a flow inverter so it can cool as well as heat. Given that I only need <30°C for my slab, and I can't make the payback case for a premium ASHP, I must admit that I am seriously considering one of the rebadged Chinese imports for my UFH application.
  4. That's quite a subjective view really. The hall way can act as the focal point unifying the house. We've got a fairly tight footprint and space usage was quite an important design factor, but we still have an open hall way going up all three storeys in our house. My wife and I think that this is one of its most effective design features. It pleases us and surely that's what matters.
  5. @shuff27 has ridge height limits and this has resulted in the imposition of dormer-style windows. However I don't think this would preclude small Velux-style windows in the bathrooms. The LPA also has a think about large picture-style windows on the principle elevation, and overlooking neighbours, so increasing window areas might prove problematic.
  6. Re the issue of cycling boilers, let's say you need 2 kW and you have a 12 kW boiler, this the boiler will be on:off on a roughly 1:5 cycle. Boilers need to be on for a decent block at a go, say 20 mins, this means that you will need to be off for 1h40 between each on and you will need a buffer tank capable of storing ~ 5kWh heat.
  7. The issue here is gaps in the mortar. Let's say behind one board you have a gap near the bottom and another at the top, so you get cold air coming in at the bottom, being nicely heated to say 20°C by that nice board radiator and cycling back out at the top crack. The net result is that the void behind the board is cycling heat into the void between the brick and blockwork courses. I've seen horror story FIR walk-arounds where external walls are 10° colder than they should be because of this. You can't tell it is happening until the house is built and fully heated and by that stage the cost of remediation is prohibitive. I've also seen cases where it is clear from the FIR camera that whole areas of cavity insulation have been omitted. If this happens, by this stage what realistic remediation or recompense do you have from your builder? As @joe90 says, one option is to parge the wall with a cement slurry to seal the blockwork properly. Another is to go over it with a "fine tooth comb" before it is plaster boarded out, but this level of inspection is skilled and tedious.
  8. Consider a double wall between the office and the master bedroom with the void split say 70:30 as built-in wardrobe for the MBR and shelving for the office. Such built-in features are part of the fix of the house and are VAT zero-rated. They also work much better than free standing equivalents, IMO.
  9. +1 on the main issue with dot & dab being air-tightness. Builders tend to botch this by using the plasterboard as the main air-tightness membrane, and if you've got any cracking in or voids in the blockwork mortar lines (which you nearly always do) then you get convection cycling behind the plasterboard which just pumps heat out of the house. There are some good FIR camera walk-arounds of which show this. Far better to directly plaster or alternatively seal the block work and then batten out to carry the board. We keep our house at ~ 23 °C and I accept that we may be paying a 15-20% premium for this but that's 15% of a small bill anyway. The problem of 0.18 vs 0.12 is a more subtle one of tipping points. We loose minimal heat through our walls so we don't have or need any installed form of CH on the upper floors: no radiators, boilers or CH plumbing and this saved a lot of installation complexity and cost. You should use a Jeremy-style heating spreadsheet and have a play with the parameters and sensitivities and see what the correct mix / trade-offs is for you. Having a truly energy efficient house (if done properly) doesn't add materially the overall costs because of the consequential savings that you can make. Architects will design crappy performance houses, builders will build sloppily because that is what they are used to, and building to an energy efficient standard is just an inconvenience for them: this is the culture of the UK construction industry. But you will need to live with the consequences every day after you move in.
  10. Turning this on it's head, why has your architect spec'ed such a crappy profile? Another layer of Dritherm would drop the U-value to nearer 0.11 W/m2K for minimal extra build cost albeit with a 470mm wall profile. It seems that architect's are just so f***ing conservative to be unbelievable. See @tonyshouse blog. Even so, you can't make any as-built thermal performance predictions until you have an air-tightness and MVHR design.
  11. We've got some bad creaking spots in our 1st floor. Nothing to do with the anchoring of the flooring to the EcoJoists, and everything to do with the cross-joist brace only being nailed across the joists and not properly screwed in. Missed this until after we moved in and by then post second fit, so screwing the cross-brace to the EcoJoists would have been a total PITA. Workaround: avoid stepping on the small ~ 1m2 area which creeks . 20-20 hindsight, and I wish that I'd fixed that cross joist properly 🤣.
  12. You need to do the thermal calcs. On a new build, you can get the wall / roof / slab U-values 0.15 or better quite easily IMO, and for minimal cost. The downside is wall depth needed, but if you plan this in, then there isn't a material cost -- except that it make makes it a little more inconvenient for your building crew -- hence you need to focus on quality assurance and avoid construction flaws (like sloppy or omitted insulation installation) which cause thermal bridges and will compromise the build. Next up if you have a thermal shell of this spec, are the air-related losses which will dominate your heat budgets, so you also need a level of air-tightness and MVHR. My personal experience of building a house of this class is that the internal heat flows are 10× greater than interior to exterior losses. The bottom line if you achieve this is that you will need to top up heat -- e.g. through a in-slab UFH installation -- but that you don't need any other CH installation or rads as room to room temperatures will only vary by a degree or so. (In the coldest 3 months, we also boost the heat for the top 2 floors by using a small oil-filled electric heater on a timer switch in my office on the 1st floor for a few hours overnight.) Overall, the whole house maintains a 22½-23°C temperature 24×7. We use a Willis for my slab heating, and I can't make the cost-benefit case to install an ASHP as I won't recover the installation costs over a 10-year payback. However, that is because we have a high-spec passive-class house. IMO, an initial install of an ASHP is a safe option for most reasonably energy-efficient new builds.
  13. I agree that fitting two is good idea, but if you have a properly insulated slab then it will quickly get far too hot if pump 6kW into it.
  14. Air tightness and MVHR? Thermal bridges? You have the sums using a basic heat balance spreadsheet as per Jeremy's linked above. What is the average outside temp for your winter quarter? Ditto daily heat loss? Plug in the numbers and per kWh electricity costs. Can you live with this run rate?
  15. Something like this: 12000 BTU AC. IMO, using something like a Willis is part of a package: Wall, roof, floor U-values 0.15 or better. No major thermal bridges. Triple glazed windows and doors. Airtightness 1.0 ACHP or better MVHR with ~90% heat recovery. If you use a Willis solution, there are two separate Qs Will it provide enough heat to do the job? Will you be able to afford the monthly bills?