Owain1602

Do you know which building heat loss calculations use convective boundary conditions on the internal and external walls? The simplified spreadsheets that I've seen most use just imposes the temperature on the surfaces of the internal and external walls. You can see in the example values above, accounting for the convective boundary on a single slice of the tank reduced the heat loss by ~10%. When I look at the results of this, the external surface of the tank for the top slice was actually at 22°C (for an ambient temperature of 18°C). I will have a look at the relative magnitude of this effect on a section of wall later this evening, to get an idea if it's significant.

Then, the second point is a bit more interesting and something I'm not sure is being factored in to a lot of house heat loss calculations (not suggesting it's a big impact, haven't looked at it in the context of houses). The external wall of the insulation will not be fixed at the ambient room temperature (18°C as you have it in your example). This should be a convective boundary condition. The formal definition is a Neumann boundary condition, as opposed to a Dirichlet (imposed temperature). Where I think this could be interesting, is that the whole house heat loss calculations I've come across, assume the surface of the internal walls are at the internal temperature and vice versa for the external walls. In reality, you have a heat balance for the wall, with a convective boundary condition on either side. The top "slice" of the tank in the original example lost 4.04W Adopting the 1D heat equation in cylindrical coordinates reduced this to 3.39W Changing the external boundary condition at the wall of the cylinder from a fixed 18°C to an ambient temperature of 18°C with a convective heat transfer coefficient of 5W/m2K reduced the loss to 2.98W (already includes impact of different formulation) Would be interesting to apply this approach to the heat loss of a whole house (obviously not including the cylindrical coordinate system, unless it's a very unusual shape!)

Hello @SteamyTea You should be using the 1D heat equation derived for a cylindrical coordinate system for the heat loss calcs. It's not a night and day impact (depends on the geometry), but I get just under 10% higher heat loss using this approach.

Thank you all, we’ll have a look around for a different architect to work with.

Agree with what? I am not following any advice posted here for building regs, the approach to protect the stairway I outlined above was put forward by our architect.

Hm…that’s not a good start, nobody has spoken or used them for their build?

Not sure why you felt compelled to post this, but I really don’t need you to tell me who I should and shouldn’t take advice from regarding building regs.

Thanks all for your valuable comments. Regarding the fire regs, we are planning to implement what @torre mentioned. The corridors downstairs will have suitable fire doors (not looked yet, but hopefully we can get some with nice, big glass panes) and the upstairs landing will need to have fixed glazing for the bit that overlooks the kitchen/dining/living room. I wanted to try and avoid the sprinkler/misting systems if possible.

Hello, I visited the Homebuilding Show at the NEC on Sunday, and came across a company called Broadaxe Timber Frame. They had on display their Larsen Truss frame system with blown cellulose (very similar to MBC from a distance), also guaranteed airtightness <0.6. They also offered services beyond the frame (Kore insulated raft) through their parent construction company (think they were called Firth Construction). Interestingly, they are based in Presteigne, Wales which is where Frame Technologies are based. Was wondering if anyone has come across them? Thanks!

Thanks for your comments. I certainly agree that the South facing glazing would likely be a big overheating issue. Was taking the approach of designing in what would be the ideal scenario to start with, before pairing it back based on some calculations. Paying for solar reflective glass is a possibility (rough price comparison I saw was: standard double glazing £50/m2 and solar reflective £130/m2), although I'd prefer if it could be designed out without much compromise on the effect. @Mike That is a good suggestion on the width of downstairs corridors, will have a look how best to implement this. On your point regarding the main bathroom; we have relatives that have a very similar dimensioned bathroom and have a good idea how we'd position everything. @ETC Is your point regarding separation of kitchen from stairs and upstairs due to fire regulations? If so, there are many examples of new houses with voids directly above the kitchen to upstairs, with no separation. I can see how we could separate the kitchen from the stairs without too much trouble. We're not big window cleaning people to be honest, typically let them get dirty to the point where we can't stand it then do the bare minimum. Yes, will become a bit smaller in-light of Mike's suggestion to try and widen the corridors. Which rooms do you feel are too small/too long? I'd really appreciate if you could elaborate here so we can benefit from your expertise.

Hello, Thanks very much for your views on the original layout. It provided the necessary criticism to demonstrate that we weren't happy with the layout and that we needed to start again. We asked our architects to come up with a number of layout concepts that would test us in different ways. I have taken our favourite layout concept and made some small tweaks. I would be very grateful if you could offer an opinion on the newly proposed layout. I'm a lot more comfortable with this, we've now been through the ifs and buts. (Forgot to include on the plans, but the gable end with the living/kitchen/dining faces directly South). Some practical questions that come to mind: Can the MVHR work where I have it, high at the back of an upstairs cupboard? Planning to put the intake/exhaust sideways through the wall rather than pierce the roof. Room supply/extract would need to turn downwards with distribution through the floor joists, no cavity in the roof for this. Is central plant room important? This needs ASHP pipes to be laid under the slab, would it be preferred to accept a plant room that's not central, but could put ASHP pipes through the wall? MVHR unit could also be positioned there if on outside wall Thanks for your consideration!

I'm not sure if this is new (it wasn't on the Catnic website six months ago), but Catnic has a system called SolarSeam. https://catnic.com/products/urban/solarseam No personal experience with it, but I'm considering it for our build.

@Glenn thanks for your input. No need to apologise, that is the whole reason why I asked for feedback on the layout. I have a feeling in the back of my head that what we have isn’t quite right. You are right about the fenestration, I specifically mentioned this in my original post. We have options to centralised plumbing further, but I don’t want to compromise on room layout for the sake of running a few plastic pipes.

@MR10 I have discussed this with ETC in the past (before I was comfortable to share the plans openly). He had some great ideas, but it was so different from the design we’d had in our head, that I couldn’t really process it.

Thanks for your messages @AartWessels and @Glenn. These are plans that have been put together by a well-respected architectural firm. Whether they’re being hamstrung by our requirements, I don’t know. But as you can see, we’re not asking for too much in such a large space. Do you think I should instruct another firm to take a second look at the design?