AndySat

Well, in the time-honoured tradition, my soakaway is going in the field next door, which we own. Looked again at the papers provided by my neighbour and his assessed soakaway required is 93m2, which apparently corresponds to a trench 155m long! I'm not sure what the engineers would typically do in this case - dig a long trench or loop it back a few times? I managed to get 10m of drain rods into the pipe leading away from the inspection chamber without any resistance, so I'm hoping that it's a long linear soakaway and not some kind of herringbone design. But it looks like I'll need to get a sonde and/or camera in there to see where it goes...

Thanks both. My neighbour found some paperwork that confirms that it is the soakaway for their septic tank. The plot was part of a field when his house was built, so this was probably the easiest option back then. I lifted the cover and found two pipes as expected, one heading in the direction of the neighbour's house and one leading onwards somewhere. Paperwork shows the soakaway is a porous pipe in a gravel bed but doesn't say how long or where it goes - I assume in a straight line away from the inspection chamber. I'll see if I can get a rod in there tomorrow and find out more. I'm not too concerned about the manhole itself, but it's going to be tricky moving the garage 5m away from the soakaway and still meet the planning requirement for parking and turning space...

Apologies in advance for a newbie question.... I'm looking to build a detached garage (part of a bigger house build project, but that's another story) at the side of the plot nearest the road. So far, so good, but there's a manhole cover towards the edge of the plot, close to where the back wall of the garage will be. It's an inspection chamber for the neighbour's foul drain soakaway. Of course, it's not on anyone's plans and he knows nothing about it. Leaving aside the question of whether it should be there or not, how close to it can the garage foundations be? It's likely about 15 years old, so probably just a big hole filled with stone rather than plastic crates and it seems from the slight depression in the ground to lead in the opposite direction to where I want to build. We had an engineer on site for the soil stability tests for the house and he didn't seem too bothered about it, but I'd like to understand whether it's a potential show-stopper, or something I can work around with e.g. deeper foundations and lots of concrete! Thanks!

I agree. Having a standard unit is probably a good thing in terms of price and reliability, but my current thinking is to go with a monobloc - simpler and uses less space in the plant room. Plus it puts any potentially noisy bits outside. The UFH will be a single zone and based around WC instead of thermostats. But I may hedge my bets and at least run the wiring for a thermostat in the bedrooms...

I might be missing something, but my reading of the Home Energy Scotland Grant and Loan terms is that the grants are for improvements to existing installations and don't apply to new builds. It's not permitted to install oil or gas boilers in new builds, so perhaps there's no need for an incentive to install heat pumps? I have to admit that the question of noise never occurred to me when I started researching ASHP. I'm aware that some older external units can be a nuisance to the neighbours (not in our case though as the location is on the opposite side of the house) but I assumed that internal noise wasn't a problem. One of the ASHP contractors offered to show me around one of their recent installs, so that might give me an idea of how noisy it is in practice.

Thanks all, this is helping me get to a clear set of requirements that I can discuss with the contractors. I did try to reduce the number of zones in LoopCAD by linking the cold end of the bathroom loop to the hot end of the adjacent bedroom loop and making the spacing tighter in the bathroom, but although it looked ok on paper, I think it's simpler to keep the loops separate and adjust the flows to get the right amount of heat into each loop. This assumes that the worst loop will put enough heat into the room with 35C flow, as @Beelbeebub says. Good idea, especially since the floor area is quite small and it's a challenge to get enough UFH pipework down! Yes, MVHR is planned - that's another topic that I'll be raising soon! The house is designed to be quite airtight (around 0.5 ach/hr) but not to Passivhaus spec. Whether we get it as good as that in practice remains to be seen... I'm still to decide on a preferred make/model of ASHP. But I think I'll separate that from the UFH design i.e. I'll get the UFH designed as far as the manifold and then do the ASHP/DHW cylinder as a separate exercise. I'm not eligible for any grants, so I don't need a full system certification, just a design that will be acceptable for a Building Warrant here in Scotland.

Thanks, I hadn't considered the noise aspect... Agreed. I'm all in favour of keeping it simple and easier to maintain. I've only asked one contractor for a UFH quote so far and their design has multiple zones (one per room) which I understand, given that e.g. a bathroom needs a higher floor temp than a bedroom, but they also have one thermostat per zone, which seems excessive. I'm hoping that the flow in each zone can be set to achieve the required temp and then the whole house can be controlled by a single thermostat, as @JohnMo says. Yes, I think that is the case, at least in the Hitachi split that I was considering.

After a long road through the planning process, I'm finally reaching the point where I need to make some heating system design decisions as input into the Building Warrant on our planned 130m2 timber-frame house. Two local contractors have estimated the heating requirements at 3kW, based on a simple 24W/m2 calculation and are proposing monobloc ASHP solutions of 5kW. I've used Jeremy Harris' spreadsheet to get a total heat loss of just over 2kW. LoopCAD, interestingly, estimates the total UFH load at 3.9kW but that may be down to user error on my part! Either way, I'm assuming an ASHP around 5-6kW will more than meet the demands of UFH and hot water. So far, so good, but I'm wondering if a split ASHP solution is better, something like the Hitachi Yutaki, especially the combi version. The price of the Hitachi combi is a lot lower than the Mitsubishi monobloc + DHW cylinder that the contractors are suggesting. As I see it, the advantage of a split unit is that the piping between the units is smaller and easier to route (and less heat loss?), also the outside unit is smaller. The downside is that the system needs to be commissioned by a refrigeration engineer, but this shouldn't be a big problem. Does it make any difference if the ASHP is monobloc, split or combi?

Hi all, Just getting started with a self-build timber frame house project in the South of Scotland. The plan is to use professionals for the major works, but I'm keen to understand as much of the technology as possible (especially heat pumps, MVHR, solar PV etc), so I can ask sensible questions and (hopefully) get to a design that works, without breaking the bank. I've already found a lot of great posts in the forum, so decided to stop lurking and create an account. Looking forward to learning from the experts and making a contribution where possible...