pdf27

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  1. My understanding is that you can put in your VAT reclaim at any point, but that any costs incurred after the reclaim point get hit with the full rate of VAT. That **should** mean that e.g. buying stuff for the bathrooms prior to the reclaim and then fitting them myself afterwards is OK. At least half of the other parents at my daughter's school seem to work in London. Annoyingly I work at a factory nearby which has been gradually moving out of London in the 90 or so years since the company started but never quite got far enough for me!
  2. Have you got anything about it you'd be willing to share by email? The main concerns I have are making sure we take the correct value-engineering decisions at the very start of the design (i.e. now) and ensuring that once we start we've got sufficient cash to finish. Any lessons-learned I can take away from the fact you're doing it second time around would be particularly helpful with the value-engineering side of things. If we could do it for £300k that would give us a reasonably comfortable contingency. 90% of my day job (mechanical/electrical/aerospace engineering) is on the very far left of this graph, so I've naturally got an interest in applying it to any house I might build!
  3. Current footprint is fairly small (136m2 including the garage on a 900m2 plot), the model I've got has a footprint of about 170m2 which doesn't feel unreasonable (19% of plot). The current shape factor is pretty poor, however, so the increased footprint doesn't really make a huge difference - it's mostly coming in otherwise awkwardly shaped bits of grass at the side. I've been wondering about fitting a bathroom to the second bedroom - it's an awkward shape so fitting one in wouldn't be a major drama. That tentatively would be the guest room, so would make the most sense (my in-laws live in South Carolina, are retiring in a few months and our children are their only grandchildren - so I would expect some extended visits in our future). The mixture of VAT and complication are what killed it last time - by the time we had sorted out the various problems we ended up with a relatively small house which was badly compromised and a handful of not very nice walls. The QS estimate was nearly £400k+VAT for a 160m2 house. At least one quote explicitly said that it would be cheaper to knock down and start again than extend. No asbestos survey done to date - for now I'm going to allow a provisional sum since it's safe if undisturbed but if we find something there is a risk that we'll have to deal with it and rectify even if we can't afford the build. It's a 1920 original extended in the 1970s so I need to assume that there is Asbestos present but I haven't spotted any of the usual suspects yet. Current assumption is a static caravan in the back garden, most likely scrapped in situ at the end because the cost of a very large crane to remove it would exceed the value of the caravan. Having services already available makes that a lot more tolerable. Certification is an open point, the quality control aspects of it are worth money in my mind but the standard itself is somewhat arbitrary. If (when) the budget gets tight that's something we would drop. It certainly isn't for money reasons. I'm pretty sure that an airtight door on a garage would be against the rules (carbon monoxide risk - would certainly have a CO alarm in there linked to the house fire alarm in any case). I'd only extend the underfloor to it (on a separate circuit) if it was really cheap to do so. The logic for having the garage there is that we want it to have a weather-protected link to the house and having it side-on completely eliminates any chance of having a semblance of a garden at the front (as next door has done). I've tried to value-engineer it where I can do so reasonably subtly - the shape is part of that, and I've done a few things like sizing the 180 degree turn on the staircase to be part of the frame so the staircase is cheap and simple. Until I start doing a cost model, I won't be able to really understand if I've got it about right however. Part of the logic for the downstairs shower was that it's a relatively cheap way to achieve an extra bathroom, with the benefit of helping future mobility-impaired people who visit. At the moment it has 3 bathrooms between 5 bedrooms, which isn't too bad. Adding an en-suite to Bed 2 does look like a logical change though. My dad has Parkinson's, which may or may not run in the family (his father and brother died of it, but he's been tested and doesn't have any known genetic risk factors). That means I may need it if we stay long-term, and putting it in now is relatively cheap and easy. I'm really not sure if there is any sensible way of adjusting the floorplan to give them some sort of private social space in 10 years time - then again I'd be quite happy hiding in my study (I'm somewhat outnumbered - we've got two girls and even the cat is female) and my wife will probably be as happy curling up in bed as anywhere else, so I think it's feasible to adapt. One of the headaches is that the garage means the ratio between upstairs and downstairs is wrong for us - we'd really like it a bit smaller upstairs relative to the downstairs volume, but I don't see an easy way around this. That's one of the things I want to go into in some proper detail - what we actually want is relatively austere, and there are quite a few things we wouldn't finish until some years later (only doing first fix on most of the bathrooms for instance with me doing second fix later) if it meant we could do the house. That way I can do the working out how bit a house we can afford and whether that's acceptable to us before we start paying professionals to tell us the same thing. Budget is probably a bit below £400k but not massively. Going much above that means it has to be a really special house however, as it would probably take us into needing to sell it at a premium if we ever move given what we bought the current house for.
  4. Having been stung last time around (emotionally at least - financially we stopped before we spent too much) when we started down the retrofit+extend route only to find out it just wasn't viable, I'm trying to be quite cautious with whether we can knock down and rebuild our current house. Can I please ask the buildhub hive-mind to take a look at the attached floorplans and comment if they make sense? The idea is if they aren't too far out I can try to build a cost model based on them with some level of confidence it will be accurate before going down the route of modelling it in detail, applying for planning permission, etc. We're both in our thirties, working full time with two young children and retired parents who might on occasion stay for extended periods of time. We're in a commuter village in Buckinghamshire, just outside the edge of the green belt. Target would be Passivhaus, probably certified (I'm an engineer and not properly validating it would really annoy me). Most of the model should be obvious. Stairs extend up to the loft (warm roof) with a Velux above them in the rear roof - my wife is a hoarder packrat and the only way to stop her leaving stuff everywhere is to make it really, really easy for her to store it somewhere I won't always be falling over it. I've also assumed dormers to the rear to bring the ridge line down without compromising the ground floor space too badly - it's currently ~1m taller than the house next door and without them starts to look a bit big. First Floor Model.pdf Ground Floor Model.pdf
  5. Under those circumstances I really don't think even a DIY system makes sense - night venting via the MVHR will probably provide all the cooling you need even without opening the windows, and the power used by the MVHR defrost heater will be minimal. If you're only trying to provide a small amount of cooling and have an ASHP anyway, it's almost impossible to beat for a well-insulated house. Small total heat flow and very high COP (from the small temperature difference) means virtually no running costs and zero installation costs. It's very easy to get carried away by a good idea which almost works. Solar Thermal does this for me - I really want it to work, but because we would have an ASHP then more PV is simply a better and cheaper solution to achieve the same thing. Both systems are very similar - they turn a small amount of electricity into a lot of heat: however, that is the wrong problem to solve because it ignores the impact of capital costs and the ability to spend the same money generating electricity.
  6. So far as I can see, the only difference in up-front cost is that you're using piling contractors rather than a groundworks guy with a digger to make the hole for the foundations/basement wall, you aren't paying for someone to dig the soil out of the centre while nothing is there (pretty cheap as access is the best it will ever be) and you aren't paying to lay a floor in the basement. It's worth costing out properly, but unless you have issues with deep excavations (e.g. close to a boundary) my suspicion is that a basement will be cheaper than piled foundations of the same depth. The extra work is all stuff that is really cheap to do now but expensive later, while piling (particularly if it has to be fully continuous) has a reputation for being expensive.
  7. They've got some data on power consumption too... Antifreeze pump is 3-45W, assume 15W. Air resistance when cooling is 70Pa at 250m3/hr (about right for a 200m2 house if I'm understanding correctly) -> 5W additional fan power @ 100% efficiency, so allowing for real life efficiency total system draw will be about 30W. Using their example for cooling, with air into the MVHR at 16°C and ambient at 28°C the cooling power you get (assuming no dehumidification) is (1010 J/kg.K) x (1.2 kg/m3) x (250/3600 m3/hr) x (28-16)= 1kW of cooling for a COP of about 40. Cooling power is 84W x temperature difference attributable to the ground loop (16°C in this case - their figures). DegreeDays.net gives 73 degree-days above 16°C in the past year at Aldergrove (closest station I could find to you) - 84 x 73 x 24 = 147,168 Watt-hours (147 kWh) of cooling. In reality this will be a bit better because it will also do some dehumidification. Same calculation for heating power gives 103 degree-days below 5°C: a 208 kWh saving. To me the numbers don't stack up as a means of energy saving - 400kWh/year is the output of a couple of PV panels, and in reality probably overstates things since night venting will probably deal with a big chunk of the cooling requirement for free and the frost protection on most MVHR systems probably kicks in significantly below 5°C. The only times I think it makes sense is if you're trying to hit a very strict energy requirement for some sort of standard when the very high COP is of value, or if you have a restriction (planning or similar) preventing you from using an ASHP for summer cooling.
  8. As soon as you do that you've either got a direct air path to the drains, or you've got standing water in the bottom of the tees. You're also starting to add complexity and hence cost. The real problem is that in a UK climate it saves very little energy - you don't need the defrost heater on an MVHR, and it provides a little bit of comfort cooling in summer. That means it's got to be seriously cheap for it to make any sense - if not you're better off spending the same money elsewhere, for example on a couple of extra PV panels. The running costs are also non-zero - either a longer inlet duct with a bigger pressure drop across it or a circulating pump for the brine loop - which needs to be set against any energy saving. For other climates - e.g. in the US - it makes much more sense: they regularly spend extended periods of time well below freezing in winter and have extended periods of high heat and humidity in summer, when it will help very significantly with the dehumidification load.
  9. Have a read of http://passivehousepa.blogspot.com/2012/12/earth-tubes-heating-and-air.html : they used a system which actually makes a lot of sense to me but nothing like it is available commercially. They use a corrugated pipe (of the type used for field drains) slit along the bottom over it's entire length. It has to be in free-draining soil, but if it is then any condensate will drain straight out cleaning the walls and presumably giving a relatively inhospitable environment for mould/bacteria when compared to a sealed tube which is at risk of spots of standing water. Best of all, it's really cheap - about £1.50/metre plus the cost of digging and back-filling the hole - and provided you ensure that you have an alternative air inlet if it all goes horribly wrong then it looks like a good gamble to me. It's totally dependent on soil conditions though - needs to be free draining and well above the water table (mine is neither!).
  10. Spec sheet says otherwise - the internal unit is always 28dB(A), outside units are between 55 and 69 dB depending on size and load. Remember that fridge compressors are essentially inaudible in modern fridges - my fridge makes a weird squeaking noise (fancy expansion valve?) but that's it. A well balanced sealed compressor should be all but inaudible.
  11. If you want to put it a long way away, consider split units. Some of the Panasonic ones can be up to 50m long on the refrigerant lines, and the energy transfer is as a phase change rather than heat directly so losses should be small. It's more expensive - not a DIY job - but shouldn't be horrific.
  12. Pictures might help? It's a box which you put in the ceiling like a smoke alarm. The cable goes in the back where you can't see it, and it gives you WiFi. You can also get waterproof ones, which if you have a big garden like me might well be worth it - my normal WiFi is rubbish at the end of the garden.
  13. Trina 325W All Black Mono (1698*1004 for GSE) from Midsummer appears to be £72/panel from Midsummer Wholesale at trade price (assuming the values quoted by easy-PV are correct - it looks like a trade-oriented tool, but they might just be out of date), £100 at retail. Even at retail it isn't too bad at 32p/Watt, it's 22p/Watt if you get them for £72. Edit: while I think about it, easy_PV has a tool to let you model up flashings, spacings, etc, on the roof with GSE mounts.
  14. Thanks, that's very helpful. It does raise more questions though! How come you used liquid screed downstairs and biscuit screed upstairs? What is the floor like to walk on, and how is sound transmission? What temperature do you run the flow from the ASHP at?
  15. I think I'm more confused than I was earlier. Does this therefore mean that all regular TRVs are unsafe as they won't protect the slab? How come? Are they just cheaping out on the ASHP water pumps? Is there an additional bypass valve within the TRV? If not then presumably it would be trying to send 100% of the flow through the ASHP and be blocked by the zone valve. Edit: at least some of them do which is starting to make more sense. Sadly, that's kind of my day job - among other things, ensuring double fault cases are treated differently to single fault and we don't try to prevent them unless it's safety critical (as in, everybody dies). I'm still short of a house to put it in at the moment .