Jeremy Harris

Welcome. The COP of an ASHP depends on the humidity as well as temperature, and although outside air temperature does make a difference, it's not as big a difference as many assume, as the amount of heat in the outside air is relative, with zero heat being absolute zero (so ~-273°C). This means that a reduction in the outside air temperature of, say, 10°C from +10°C to 0°C only drops the amount of heat available in the air by about 3.5%. In practice, the biggest factor that impacts on COP is the output flow temperature of the ASHP. If this is kept low, say 40°C, then the COP can be pretty high, between 3.5 and 4.0 as a rough estimate. Increase the flow temperature of the ASHP up to 50°C and the COP will drop back to something like 3.0 to 3.5. Add in cool, damp, weather, which may well induce icing in the ASHP, that lowers COP further, and then you could see the COP drop down to well below 3.0. The reality is that the average outside temperature during the heating season is well above 0°C, so if the flow temperature from the ASHP is kept fairly low the COP will be pretty good. We run our ASHP at a flow temperature of 40°C all the time, as we don't use it for hot water, only running underfloor heating, and find that the COP averages between 3.5 and 4.0 over the whole heating season. Running radiators from an ASHP usually means fitting larger ones to allow for the lower flow temperature. An oil boiler may well be running the radiators at 50 to 60°C, and that's higher than an ASHP will run at efficiently. To get the same heat output to the rooms with a lower flow temperature usually means increasing the size of the radiators. In general, ASHPs tend to work a bit better when it's windy, aren't particularly affected by insolation at all, but will tend to run at a lower COP when the RH is high.

Looks like something that belongs in my old place of work...

Both @jack's build and ours are MBC passive system builds. PHPP showed a 3% overheating risk for us, which I (wrongly) assumed to be OK. As @jack mentioned, though, our house is in the bottom of a deep sheltered valley, facing South and is deep in a cutting in the hillside, so we get higher local temperatures than the weather/climate data predicts. Our slab cooling was just a matter of switching the ASHP into cooling mode, rather than heating mode. Almost all ASHPs will reverse and cool pretty much as well as they heat. Our MVHR cooling uses a Genvex Premium 1L MVHR unit, that has a built in air-to-air heat pump, that can either cool or heat the ventilation air. In practice we never use it for heating, as heating is really a non-issue for our house, but it's handy for providing a small amount of comfort cooling. The effect of the cooling from the MVHR is modest, as the ventilation rate is so low that it never shift a lot of heat, but it's useful, all the same. If doing this again I'd not have bothered with the active MVHR, but would have fitted a cheaper split aircon system.

No problem. When you come to fit the new brass threaded collar on to the broken end of the Cobra, just clean the broken end up, cut it square at the tip and clean and lightly abrade it. The brass bit is just glued on with superglue usually, the slightly thickened version is best. The various tools for pulling cables, clearing rubbish from ducts etc, just screw on to the brass collar.

I agree with you, as I think I know where you are, and if I'm right the houses either side are significantly larger and on similar sized plots. The value of £750k to £800k sounds right for that area, maybe even a bit low, IMHO.

Looks like a Cobra, and spares are available: http://www.dartsystems.co.uk/products/cable-installation-external-9mm-cobra-duct-rod-spares-c-72_69_49/ The link is for the 9mm version, but the same place stocks spares for the 11mm and 14mm versions.

Most of our stuff comes up through the slab in ~50mm ducting, except for the power cable. That's a length of 25mm² 3 core SWA, and is in 100mm ducting just to make it easier to pull in.

Our experience has been that overhangs don't have any useful effect during the times of the year when we get a lot of solar gain, which is Spring and Autumn. The low sun angle makes it penetrate more deeply into the house. Ventilation works whenever the outside air temperature is cooler than inside, but has the opposite effect to that intended as soon as the outside air temperature warms up. We don't like the house to be warmer than about 23°C, and we've already had several days this year where the outside air temperature has exceeded that, so daytime ventilation just makes things worse on those days. Night time ventilation often works well, though, as the temperature overnight usually dips. Exterior blinds is the one thing I wish we'd been able to fit, as I know from experience of staying in a place in Portugal that had them that they work very well. Retrofitting external blinds can be difficult; for us it would now look a bit odd, but if designed in they can be very unobtrusive. I would be inclined to retain the overhangs, as they only have any effect in Summer, and it's extremely unlikely that you will need any solar gain when the sun is relatively high in the sky. You can easily do a sketch of the elevation and superimpose the angle of the sun at any time of the year to get an idea as to how effective any overhang may be.

Won't be any real difference, as the outer skin is just rain cladding really. Our house is entirely timber clad on a timber frame and it keeps out the weather just fine.

Yes, more or less. It's all detailed in the blog I put together: http://mayfly.eu PM me if you'd like to visit, we're in Fovant, about ten miles West of Salisbury, just off the A30.

Being in the same area, I'd agree, but say err on the high side, as build costs around here are higher than in some other parts of the UK. There's also an apparent shortage of good contractors now. Some of the people we used, and who only had short waiting lists back then, are now looking at not taking on new customers until maybe Christmas or the New Year. I think the multitude of fairly large developments around Salisbury that have ramped back up in the last three years or so are absorbing a lot of builders and trades.

The problem that slender block or brick walls have is that they don't have a lot of lateral strength, because mortar has very little tensile strength. This means that slender block or brick walls always need some form of bracing to stiffen them up. The wall ties do this. There are other ways to stiffen up slender walls, like adding buttresses, a technique that's often used on single skin garage walls and garden walls. When a single skin block or brick wall is tied to something like another wall (in the case of a cavity wall construction) or a timber frame, or even a steel frame, then it becomes a lot stiffer and better able to withstand side loads. If you choose to use a block or brick skin outside a timber frame then it will have to be tied to the frame at regular intervals with wall ties, in order to ensure it's able to tolerate side loads. There was a good example in the papers the year before last where wall ties weren't used on a school built (cheaply I suspect) in Scotland (https://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-38907714 ). The gable wall fell down in high winds, thankfully without killing anyone. They found 17 schools with shoddy work and inadequate ties. It's a good illustration of why wall ties are essential, though.

Three years normally, but you can lock the planning in by doing enough on site to constitute the "start of development" and then you have as long as you like. What constitutes the start of development depends a bit on the local authority, but usually it would be having had all the pre-commencement planning conditions discharged and making a start with stuff like getting services in or starting the foundations. Often it doesn't take a lot of work to tick the boxes needed to lock the planning consent in.

The outer block/brick doesn't add anything structural to the TF, the TF takes the loads and the block/brick skin is really just there to keep the rain out. The ties are needed to keep the block/brick skin together against things like wind loads, as a single skin block/brick wall isn't very good at withstanding side loads and needs to be braced. As such the ties are critical to maintaining the stiffness of the wall, but they don't take any of the loads imposed by the internal structure.

We bought a bungalow in 1998 that had a large bedroom in the loft, including a dormer window to the rear. It was clearly a real bodge job, but it was also clear that it had been used as a child's bedroom, from the wall paper, posters of ponies etc, that was up there. It was accessed via a loft ladder that dropped into the hall below, blocking the front door of the house when it was down, believe it or not. The estate agent had listed it as an non-habitable room, and we asked questions of the vendor as to when the room had been converted and whether or not it had been notified to building control. It turned out that the room had been built without either planning consent or building control approval and had indeed been used as a bedroom, shared by the vendor's two daughters. They'd used this death trap of a room (there was no easy way to escape in the event of fire) for over 20 years. Heating up there was by electric fires, and the walls were just hardboard, with zero insulation anywhere. When we sold the house the purchaser was an architect, who wanted to take the roof off and convert the house to two storeys, so the unlawful state of the loft conversion didn't bother him, which was lucky.

The ceiling joists only need to be small, as most of the load in them will be tensile, holding the rafters together to prevent spreading, I think, as @ProDave has said above . It looks like there are purlins in place, one being the one that @PeterW has marked with a red arrow, and they will be helping to tie things together too. As for possibilities for raising the ceiling, based on the info in those photos I'd say that it may well be reasonably easy to do, but that I would guess that the new ceiling joists would need to be fitted before the old ones were removed, and an SE would need to advise as to what's needed.

They are obliged to give a reason for refusing credit, so they cannot just ignore that requirement. As I wrote, in our case Santander did comply with the regulations and give their policy change as the reason, and this was confirmed when I checked (frankly I didn't trust them to tell me the truth, which is why I checked).

Given that anyone could legitimately request their credit file, and challenge anything on it that isn't either correct or lawful, I doubt that any lender would be stupid enough to reject an application on any potentially dodgy basis. When Santander withdrew our mortgage offer, I used Experian to check that what Santander had told me was true, and as it turned out it was both true and valid, in that their changed lending criteria (which were published) supported their position. Anyone could do the same, and it's not expensive to do. IIRC I subscribed to Experian, did the one check and then cancelled the subscription before the subscription payment became due (you get a free month, or did at the time I used them).

I'm pretty certain that no lender can apply any form of sexual discrimination, including penalising anyone on the basis that they may become pregnant. Employers aren't allowed to do this, and I strongly suspect that lenders aren't either, it's just one of those risks they have to accept.

Best bet is to do some research with lenders, or use a mortgage broker. Each lender will have a different policy on things like the income multiplier, which is one reason why a broker can often be the quickest way to do things. The downside with using a mortgage broker is the cost, as the market for self-build mortgage brokerage has been pretty much stitched up by Buildstore, and they are both expensive and not that great to deal with. We found the Ecology really great to deal with. Dealing with the same person on the phone each time was a big benefit and they were pretty quick at sorting things out for us. They did impose some restrictions on the build, like no PVC windows and a decent level of energy performance, but we were going to exceed their requirements anyway, so none of that had any impact. The only slight downside was that the Ecology weren't the cheapest in terms of interest rates, but my view was that it was worth paying a bit more interest for the service we received. In the grand scheme of things the interest wasn't a massive difference in cost, especially when compared to something like Buildstore's arrangement fees.

Congrats! Boy or girl?

The people that supplied and fitted our film did a fair bit of checking and they came back with about a dozen or so different film options that were OK if fitted externally. These included several films from the Solargard Sentinel range and also films from 3M. St Gobain were happy with these exterior films on both our laminated and toughened 3G units in the front gable (the upper ones are toughened, the lower ones, including the glazed door are laminated) and also on the standard 3G units in the windows. The Solargard Sentinel Plus film we have on the front glazed gable is SS 15 OSW, which reflects back 75% of the radiant heat and the film we have on the windows is 3M Prestige Exterior clear PR40, which reflects back 61%. All the windows are now a lot cooler to the touch in bright sun than they were before we had the film fitted.

That's a bit cheaper than the quotes I had back in 2012 for a similar sized passive slab. I had prices from Kore, Supergrund and Isoquick, and all came out over £10k. Looks like prices may well have reduced a bit, perhaps because there's a bit more competition in this market sector than there used to be.

The main issue seems to be fitting internal films on to double or triple glazed units, as they can seriously overheat the inside of the glazing unit, especially if the glass has a low e coating. What happens is that heat is radiated inwards, hits the internal film and is radiated outwards. Because the inner panes of glass are coated, they reflect heat back inwards again. The result is a significant heat build up. If the film is on the outside then there's no problem, as it stops the heat getting into the glazing unit in the first place.

I just got used to getting strange looks and comments from people working on our build. There's a very strong tendency to disapprove of anything new in the building industry, not for any good reason, just a seeming reluctance to accept change. We have had a few of the people who worked on our house back since it was finished, and every single one of them agreed that what we've done works OK, so perhaps that will go some way to try and get people to adapt to new methods of construction.