TerryE

We have just mounted a 42" TV on a swivel arm much the same way, but ours uses a vertically orientated mount and comes highly reviewed. As it happened one of the vertical battens (stud in our case) was in a suitable position so we could screw directly into that. It might be worth using a stud finder to locate your studs because if one is suitably positioned, then putting any mounting bolts through this, so the stud acts as the stand-off will save a lot of work.

Ian, health and safety would have a fit looking at your scaffolding, IMO. I thought that you're supposed to have a kick board around the perimeter of the scaffolding to prevent material accidentally falling off the boarding, and you're also supposed to have a safety rail and netting. As this incident shows it can get very windy up there, and the last thing is that you want to happen as the final chapter in your build is getting blown off the scaffolding while finishing off the roof. ?

@Ed Davies you seem to be implying some form of hysteresis in this. Can you cite a basis for this? I can see possible mechanisms for supercriticality, etc, but I wouldn't think that they are critical in the real world. As to EVP vs Dew Point: clearly they aren't the same as one is a pressure and one a temperature, and the only occasion that they are locked is at the triple point, but for a given material such as H2O, they are directly related. But the EVP for a given temperature is the pressure at which the rate of evaporation from a liquid/gas interface is the same as the condensation rate: there is no net evaporation. Coming back to @Triassic's OP and Q, my assertion is that the dew point is largely irrelevant as far as the interior of a well designed insulated wall: so long that there are no construction flaws which lead to internal circulation or mass air flow through the wall profile. For a given temperature profile, the dew point can only be well defined if the AH of the water vapour content can be well defined. For an open celled medium such as wool or cellulosic filler with an interior air tightness membrane, I can't think of any mechanism why the AH should have a systematic gradient as the gas laws would tend to self-level this subject to diffusion rates, and you'd need some form of forcing or pumping mechanism to sustain a gradient. At worst the cavity will be at dew point and since there almost always is a positive thermal gradient through the wall profile, the entire profile should be above the dew point IMO. The only possible interface where this could occur in practice is where there is discontinuity -- e.g. of AH between the room environment and the wall interior at the airtight membrane. And this could lead to surface condensation on such surfaces. But this isn't an interior issue.

Firing on 3½ cylinders is a lot better than on 2½

@Ed Davies Ed, I've spent this last week pondering this one on and off. First, you say "the temperature at which condensation starts on a flat surface of pure water", and I talk about the "equilibrium vapour pressure": there is a shared understanding here, but we are simply using different terminology to describe the same mechanism. Returning to @Triassic's original Q: "what is dew point and why does it matter", we can agree on a definition of the due point, but in my mind the issue is really "when does it matter?" and in my mind what this comes down to is when there is sufficient mass-flow of moist air to create a systemic condensing out of water vapour into its liquid phase on or within the fabric of the build. Direct leakage of water is always going to be a problem and dew point is irrelevant to this. My thesis is that dew point is only relevant when you have mass flow of air, as this is an essential precursor to the delivery of moisture for transfer to the liquid phase at the dew point. So this mass flow scenario and dew point is relevant in the case of MVHR design which is why units include condensate collection and waste removal. It might also become an issue for leaky houses where there are material exhaust flow paths from the interior though the insulation fabric, but for airtight walls the only possible transport is gas diffusion. In the case of closed cell insulation mediums such as PUR/PIR, the very closed cell isolation of insulating gasses is core to their insulation performance: they typically embody a hydrocarbon pentane as the filler gas that has roughly double the R-value of air which is why these materials can claim roughly have the U-value of the same depth of an open cell material such as wool which relies on still air as its main insulating material. However there could be clear flow and circulation paths around slab insulators if poorly fitted and not sealed, but whilst packed materials such as wool and blown cellulosic filler rely on air as the insulator, they are also intrinsically void filling and prevent mass flow: the only transport mechanism is diffusion. In our case we have a Larson strut TF with metal wall ties to an outer stone leaf. In cases of driving rain I could image scenarios where the gap-side surface of the stone skin becomes wet by driving rain through the odd pointing gap, so the air-gap could set to saturated water vapour pressures relative to the temperature of the stone skin, but there are only pathological circumstances when the inner panelling will be at a lower temperature than the stone skin to cause a condensing transport of water across the air-gap. Any surface water on the tenting surface of the frame will cause liquid phase transport of water into the frame structure, but can you think of any circumstances dew point mechanisms (vapour -> liquid transition) will cause material transport of water into the frame? I can't.

Accepting 99% right instead can often do wonders for your stress levels and have no material difference to anyone other than you. I've been really quite poorly this past year and it is taking ages for me to recover my health. OK, a series of viral assaults caught from my new grandson has been a factor here, but I am sure that the overall impact of the long-term stress of doing the build has been just as much of a factor.

Poor old Ian. You really need to work on your karma, build up a bit of resilience and also maybe read up on the problems that people moving into a typical new-build development often face.

I think that a leaf blower and a jet wash are two essential pieces of kit that you might only use once or twice a year, but when you do need them there's not much by way of a substitute. IMO, patios and paving get really grungy, if you don't wash them down occasionally, and using a decent jet wash at least saves the back-break. Our last jet wash lasted about 15 years -- until we lent it to our nephew who I think left the pump running with the water off -- but when we got it back it was on its last legs, hence the need for a replacement.

We have a 3 floor house and over one year in and, as Jan says, our system works fantastically. We only have UFH on the ground floor slab. Nothing on the upper floors. Last year, our 1st floor was the coldest -- at around 21°C rather than the 22½°C on the ground-floor. Though this winter I've had a 1kW heater in my 1st floor study with door open to the hall (in the coldest -- around 30 -- days) on a timer kick on for 7 hrs over night to use E7 rate. This has easily been enough to lift the overall temperature in the upper floors almost a degree. Compared to an ASHP at a CoP of 3, this has cost us maybe 30×7×0.66×8.5p or just over £11 p.a. This might seem a lot, but work out the payback decade compared to say putting in skirting heating on the first and second floors. Key learning: you really don't need upper-floor heating in a true passive-class house.

OK, I missed the previous table to the graph. The higher R-value is consistent with this. Strike this one Yes it is, but it's much more directly a function of the absolute humidity, the water vapour density. No. The dew point is occurs at the point where the RH is 100%, though the RH is a function of the AH and the temperature. You can talk in terms of RH, or AH and T, but not AH alone. Re your first statement: EH??? Sorry Ed, you've lost me on this one. (The reason for the robust response is that you are someone that I know that I can have a useful debate around this.) Can you cite any physics or engineering references that support your conviction? I've been trying to get my head around this on and insulated TFs will broadly suffer three types of water ingress: Direct leakage of water in liquid phase as a result of failures in weather sealing. The moisture gradients will typically follow some 2-D dispersion from the actual water path, but this is entirely avoidable with proper detailing in the design and construction. Transit of moist air through the TF as result of failures in the airtightness barrier, e.g. an air pathway from a hole in the inner airtighness layer out through the TF. Such systemic air flow can end up dumping lots of air into the frame if undetected -- which is why houses of this class should be properly air-tightness tested and any paths identified and remedied. This time moisture gradients will typically follow primary a 1-D deposition alone the air path depending on the moving dew point with some 3-D dispersion from this path. Transit of moist air through the TF as a result of internal convection cycles. This can be a real issue with TFs using loosely fitted slab (e.g. PUR) insulation, but this rarely an issue with blown insulation or well packed wool. Even if there is some internal convection, then you still need an external source of moisture to transport this along the convective path. Internal absorption transport. I think that we are really discussing this last mechanism, and I am trying to get my head around it. With something like an animal fibre (wool) based model with no material transit (from the fist three points), this should be treat as a largely static air, IMO, in that there are vapour paths to allow diffusion, but the extremely high internal surface area (the crenelated keratin wool hair surfaces) to volume will prevent any bulk flow. Can you think of or cite why Raoult's law, etc. would not apply here? The overall gas mix and pressure across the air-infill will be constant. I can't think off the top of my head why the AH of any water vapour in the interior would be anything other than uniform, so the RH will vary across the profile in lock with the equilibrium vapour pressure at the corresponding temperature. What causal mechanism could there be to create any gradient here, and even if we found a boundary value differential, what is the causal mechanism for the straight-line fit -- other than the "accountant's rule": pick any two fixed points and the answer is a straight line between them. We would need some physical mechanism for pumping, transporting, a gas (water vapour) in a convection free medium. One boundary is an air-tight membrane and therefore unconstrained in terms of moisture, the other is a tenting fabric between air in an airgap and some frame covering such as panel vent. What have I missed here? I am pausing due to brain-freeze

@A_L your figure might to a computer generated graph, but it makes no sense to me. Heat flow through a wall cross-section is approximated by a 1-D Fourier equation. In the thermal gradient is proportional to 1/Rvalue so if your three infill materials are all similar mineral wool slabbing, then the gradients of all three are the same, but they aren't on the graph with the middle layer being about 30-35% steeper. Why? Ditto the dew point temperature. This makes absolutely no sense to me. The dew point is largely a function of RH, so no way would this again have a piecewise linear profile. @JSHarris Jeremy, can you make sense of this?

Like we've got no radiators or the like an any wall in our house so no buying and fitting rads or having them clutter up walls. The major advantage -- if you need it -- is the responsiveness of having 2-3 kW wall mounted heaters in every room, but why bother if your house temperature is always within ½°C of your target? Yes but that is the single most expensive bit of the CH system. Try costing out the supply and fit of rads everywhere. Another poster was talking about it costing him £17K for his DHW and CH.

Physics trumps instinct, and I can't say that I am sorry to say it either: the sun seems like it revolves around the earth but we (or nearly all humanity) accept that it is is v.v. The dew point has to occur somewhere within the profile when the outside is below the dew point and the inside is well about it. Given that you want to live at the latitude that you do and you want the inside of your house to be a comfortable living temperature, then you don't really have any alternative. Yes That's what happens to dry any residual moisture out if the TF internals. The gas laws still apply. What you don't want is a condensation pump.

You've got some pretty good thermal sensors on the soles of your feet; just take your socks and shoes off, and turn the heating on, and you'll see what I mean

And forget this one. Just forget it as you will never use it. Even the smallest efficient wood stove will generate at least two kilowatts. Do the math, let's say 3 kilowatts; putting this into a single room in a passive class house will get the room temperature up to about 40 degrees within a few hours. I remember one guy who had a passive house with a wood stove telling us that the only time that he used it was one Christmas when the family was round; after 2 hours they had to evacuate the living room and open all the doors to let the house cool down. My wife @JanetE originally wanted a woodstove in our house, but she soon saw the sense in my argument that we would never dream of lighting a stove in the middle of the summer, but a passive house internally has that summery feel every month of the year, so we would never use it. We have never regretted this. So UFH scores about 1 or 2 on the 1:10 complexity scale, trying to implement usable wood stove maybe 8 - 9, ditto large acres of glass like you propose. As @jack says, the main issue in a passivhaus isn't working out how to add the extra heat when you need it, it's how to dump the excess heat when you don't need it.

@A_L, think of the heat equation: the inner skin is above the dew point, the outer skin is often below the due point, so the due point will be somewhere in the wall profile. So what? Our frame has its airtightness membrane on the inside and a breathable membrane on the outside. There is no flow of (moist) air so no moisture condensing out. Any moisture within the profile will slowly evaporate off during the summer. What you don't want to occur is having the dew point or below at any surface where there is air flow, as this will create a condensing surface.

Of all of the complexities in building our house, this but was one of the most trouble-free, so I can't follow this logic, to be honest. There's about half a dozen blog examples of this done here. Why not pick a few and visit them; talk to the self-builders about what went well and works well and what doesn't. A raft with UFH is a huge storage heater and is simple to heat. Our house is smaller, about 180m², but we currently heat the house with a 3kW immersion coil in a Willis Heater through the UHF loops and this comes on at the moment for about 4 or 5 hours on overnight E7, so there is something way off with your 7kW estimate. If you build the house to spec, then your daily average should peak at maybe a quarter of this.

Jim, all you need to do is a bit of research. Wikipedia is a good starting point for most uses, but always be willing to look at the debate on the associated talk pages or point check quoted sources if the topic is controversial. Take costs for global movement of goods, googling "shipping costs per tonne km" gives Wikipedia:Freight rate as its first link, so for example "bulk coal long-distance rates in America are approximately 1 cent/ton-mile" and the reference is a US Energy Information Administration article so this is going to pretty accurate. Bulk and container shipping costs are almost an order of magnitude cheaper: a fraction of a cent per tonne km, thanks to automation and scale of international shipping, so take your jumper example, another link gave this 2018 Overseas Cargo & Freight Costs From The UK reference, which gives the cost of moving a standard 40ft container from Bangladesh (Chittagong) to the UK as $1,874. Divide that by the number of jumpers you can fit in a standard container: 10s of cents. If you don't believe me then the sources are there for you to come up with your own figure. That's why everything is global these days; the shipping costs are in the noise. We have a passive-class house. The timber is Finnish grown CLS and OSB3, the skin is locally quarried stone, so no inner concrete block leaf and no bricks. Yes we have a raft slab, but the total concrete @ 10 m³ isn't much more than would have been used in conventional trench footings. Our LPA prevented us using PV, so I can't claim any 7-year payback period, but what is more relevant is the point at which the gross carbon cost falls below that of an equivalent conventional build and that is already true at day 0.

My point was that we did the same for a few £K (sorry, plus the £2k my TF company charged to include the UFH loops in the slab). OK, I designed the system myself and Jan and I installed it which saved a lot of money, but IMO going for some of these incentive schemes can be a false economy. Leaving aside the morality arguments, and just focusing on pure economic grounds, if you really are getting a payback of £5.5K over 7 years then you should be paying no more than £4K extra upfront. I suspect the premium charged by an RHI accredited plumber, plus the cost of over-sizing the system is working out far more than that.

So you spent £17K upfront to get back £5.5K over 7 years. I don't understand this logic. I didn't bother applying for any RHI and so avoided getting ripped off by approved installers; I did the procurement and install myself and we will spend about a quarter of that in total if I include our still-to-be-bought ASHP. Our house sits at 22-23°C throughout 24×7. Must have done something wrong.

@ProDave read up on using the deep sleep timer.

Yup there's nothing to stop having a plant room on an upper floor, but just remember that you'll end up carrying some heavy kit up there and the floor has to be designed to take the required load.

You must be using some simple serial protocol to handshake data. What not just add a "request time" command, or alternatively use HHMMSS<cr> as the ack string from the host? The Arduino can use relative reckoning to sync into near enough calendar time.

Need to think this one through. Hummm. I feel a conversation with Jeremy coming on ?

Like @joe90 we don't have a plant room per se. We have a plant cupboard off in our ground floor toilet which houses our potable water and UFH manifolds, SunAmps, Willis, etc. It's central location (keeping all runs balanced) is more important / useful than size. Our MVHR manifolds are directly above in an eaves cupboard on our second floor. Again it's central location helps balance the runs. The MVHR itself is in an adjacent storage room.