Ed Davies

Maybe only useful for a few but an option not many know about: I have a “wires-only” broadband service where the copper pair coming into the house has only broadband on it, no voice telephone service. There's a recorded announcement on the line saying is in use so BT engineers don't think it's unused and reuse it for somebody else. For my “landline” connection I then use a voice-over-ip (VoIP) service. Per month it's £10 for the copper pair, £25 for the broadband service and £10 to upgrade it to VDSL/FTTC. The VoIP service I use (sipgate) is free though you, of course, have to pay for outgoing phone calls which are at reasonable rates but don't have the various cheap/free rates that BT has. You can make emergency calls on the number when you've registered your address with them. The downside is that phone calls go through the modem/router and either a telephone adapter box or a computer (which may be a smartphone) so you need power to do that. The advantage for self builders is that it's easy to move your telephone number when you move to the house and for a transitional period when you might want to be answering the phone on site during the day and where ever you're staying in the evening that's easy, too. More: https://edavies.me.uk/2018/08/telephones/

Yes, but another ISP can provide broadband (but not telephone service) via BT Wholesale. I would be very surprised if, for example, Andrews & Arnold (just a happy customer) can't provide at least a basic ADSL service. I'm not completely convinced that Sam's site is fully up to date; it says my exchange doesn't have FTTC but I know it does ('cause I've got it, didn't particularly want it but it was expedient at the time I connected and it's nice to have).

I think you mean the exchange is still “bundled”. That means that any ISP has to go through BT's modems and backhaul (from the exchange to their own routers) at the exchange end but still other ISPs can be used. If the exchange is unbundled then a few other providers (e.g., TalkTalk) can put their equipment in the exchange and you can get a line from them instead of from BT, though BT Openreach still has responsibility for the copper pair from the exchange to your house. E.g., the local exchange I'm on at the moment is not unbundled (LLU services: No) so there's just BT equipment in it but still I get my broadband via Andrews & Arnold.

What's the problem with not being on the council's database, so long as you're on the Royal Mail one?

? The “correct” (i.e, standard) capitalization is kWh. The last column in your table should be labelled “kW” (not “kW per hour”) as watts are already a rate (kWh/h = kW). More details. More substantially: I'm not sure if it's worthwhile but if you want to do more detailed modelling then, yes, the angle of the insolation to the window does make a difference. Of course the simplest reason is the effect of the apparent area of the window being reduced when the sun's off the normal to the glass (cos θ) which is already taken into account by PVGIS. I think it also takes into account the effect of reflection off the outer glass surface using Fresnel's equations. However, if you're being this careful you'll have double or triple glazing so this will have a larger effect. If you want to explore that a bit more I have a calculator which might help.

You could ask the owner if you could buy an option on the land. You give them x thousand pounds to have the right to buy it for y thousand pounds in the next z years. If you can get planning permission then you buy, if you can't then you've lost x and the cost of the planning application. If they're done nothing with the land for quite a while then presumably y could be quite small and z could be quite long. You'd probably want a clause that says they can't object to the planning application!

But the grid is moving in the direction of being fossil free (and has been for short intervals in Scotland recently) whereas if a new build got an oil or LPG boiler in 2026 it'd likely still be a fossil burner in 2036 or 2046.

Went up to the site on Monday to get some 25mm sheets of Celotex out of the container into the house and cut them up into strips to go in the I-beams forming the window reveals. Got two out of the container, couldn't hold them into wind as planned so held them flat across the wind as I walked to the house door. Just as I was stepping across the ring beam for the porch/greenhouse towards the front door a gust arrived and I lost my balance finishing up stumbling downwind just about hanging on to the sheets. Managed to guide them back into the container where they're sitting now with a slight curve in the middle. Straight home again and didn't even think of going up there yesterday or today.

I've got a substantial portion of a roll of 1.5m wide TF200 Thermo sitting in my container. It's earmarked for the gable end of my porch/greenhouse but I'm pretty sure I'll have at least 10 metres left over and that won't be done for a while anyway so maybe we can arrange something. What sort of timescales are you thinking of - I'm not opening the container until all this wind's gone by.

Obviously there's a low temperature beyond which any particular refrigerant will not work but thinking about the amount of heat in the input air to a heat pump is confusing. If there's less heat in a m³ of air the cure is just to blow more air through. That'll mean a bit more electricity to drive the fan but that's all. The limitation on the CoP of a heat pump is set by the basic laws of thermodynamics. Real heat pumps will get about half this limit but do tend to scale roughly in proportion. http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatpump.html

The dew point is the temperature that a parcel of air needs to be cooled to so that condensation starts; strictly, the temperature at which condensation starts on a flat surface of pure water. In other words, the temperature at which the RH reaches 100%. That's the dew point shown (with a linear approximation/interpolation) in the graphs @Patrick and @A_L posted. Of course you can talk about absolute humidity alone. It's just the amount of water vapour present, typically measured in g/m³. If you have a jar of moist air and warm or cool it without evaporation or condensation happening then the absolute humidity will stay the same. It's the RH which is dependent on the temperature. If you take a parcel of air and heat or cool it without condensation or evaporation then the RH will change. Agreed. That's the major limitation of this sort of condensation risk analysis, it only really takes the flow of moisture from the higher-vapour-pressure side (usually the warm, indoor side) into account. However, looking at that flow does give you some idea of the robustness of the structure to dry itself out from the other types of water ingress so long as they are not too sustained. I'm not sure where you're going with this but I think you're making it all way too complicated. The mechanism driving water vapour through the wall is the difference in partial pressures. In a typical British house (not, say, an air-conditioned one in Washington DC) most of the year the partial pressure of water vapour indoors will be higher than that outdoors despite the fact that the relative humidity indoors is usually a bit or a lot lower than outdoors. The partial pressure will therefore drop from the inside to the outside depending on the vapour resistivity of the materials following “Ohm's law” in the same way that the temperature drops depending on the thermal resistivity of the materials. We have a flow of water vapour (probably µg/m²/s) and a flow of heat (J/m²/s or W/m²) each dependent on the wall's overall vapour and thermal resistance and the relevant “forces” pushing them through: pressure and temperature difference. The gradients in partial pressure and temperature across the various layers of the walls are then proportional to those flows and the relevant resistivities of the materials.

It really helps with this sort of query to include your approximate position (which county, say) in your profile. (In the unlikely event anybody knows a metal roofing contractor who wouldn't be too fazed by Velux windows here in the north east of the island I'd be glad to hear.)

The middle one doesn't have 12% softwood. Yes it is, but it's much more directly a function of the absolute humidity, the water vapour density. I think you're right, the dew point temperature will curve within the spans of materials with the same properties. However, in the past I've convinced myself that it'll curve downwards (sag) so approximating it with a straight line is safe (conservative). If there isn't a dew point problem on either side (interface) of the material then there won't be one anywhere within the material. Therefore, for diagrammatic purposes approximating it with a straight line is understandable. But then, with a bit of computer power to hand it does seem a pity not to calculate it every 10 mm or whatever.

Tom Foster likes [¹] WUFI for this. [¹] or liked, been a while.

While we're on the subject, what's the scope of a non-material amendment? Is the idea that it should be any amendment that wouldn't have made a (material) difference to the decision on the original planning application?

I think @TerryE is technically right: there has to be a region of the wall below the dew point under some conditions because we know dew forms. However, if the wall is properly designed (for 100% outdoor RH) then that region will just be a small layer near the outside and the condensation in it will evaporate away soon enough to not be a problem so for practical purposes I think @A_L's view is more useful. If there's a dew point under reasonably average conditions (just about to be condensing outside) then there's a real problem.

It's odd that the factory default settings for levels 1, 2, and 4 don't follow the 0.3, 0.7, and 1.3 x level 3 settings guide, either. They're not bumping against the 1.8 and 10 volt limits.

So you only paid 90% of the quoted price? Indeed, very reasonable terms.

Or buy an IR thermometer. A lot cheaper than hiring an IR camera and useful for lots of other things. OK, not as useful as owning an IR camera but … money.

It seems to me that flat panels are the “natural” form factor for LEDs as they can emit both their light and heat in all directions easily. Also, they avoid big holes in the ceiling. They seem to still be a bit of a niche product, I'm not sure why.

That's a bit tedious. Can you post the analysis?

Yes, difficult if there are VOCs or whatever which affect you for other reasons.

Or maybe @lizzie is over ventilating? Clearly she's not needing those ventilation rates to get rid of water vapour so either they're needed to get rid of other gasses or she is over ventilating.

Rule of thumb: the equilibrium vapour pressure goes up by 7% for every 1 °C increase in temperature (or, equivalently, it doubles for every 10 °C increase in temperature). Suppose outside air at 5 °C and 70% RH is warmed to 20 °C by being brought in via the MVHR and warmed a bit by the internal heating. Its equilibrium vapour pressure is now 1.07**15 = 2.76 times what it was outside so the relative humidity drops from 70% to 70/2.76 = 25.4%. There will be internal source of evaporation so it won't be this low in reality but low 30s is easy to understand.

It's weird. The numbers for the permeability of OSB are all over the place, it's the sort of thing people do PhD's on, literally. https://edavies.me.uk/2014/04/osb_vapour/ https://www.greenbuildingadvisor.com/article/is-oriented-strand-board-as-impermeable-as-they-say Nobody (house designer/BCO) blinked at my using 9mm OSB on the gables of my house (cladding vertical I-beams). OTOH, they were very bothered about using it on the roof. Not really sure, why, perhaps because the roof would have needed thicker OSB (18mm, I assume). OTOH, I see plenty of houses going up with T&G OSB on the roof. I'm confused.