Jeremy Harris

Not quite. I've mentioned before that block and brickwork won't be very airtight, unless parged or wet plastered, but cast in-situ concrete should be pretty airtight I'd have thought. It very much depends on the nature of the ties between the inner and outer skins of ICF, as they are about the only places where there is a small risk of air leakage.

FWIW, the movement of any vapour through any solid (including membranes) is solely dependent on the permeance of the solid and the relative vapour pressure either side of it. Vapour will always want to move from a higher vapour pressure region to a lower vapour pressure region, and vapour-permeable membranes try to allow this to happen, in both directions equally, by being fairly vapour permeable whilst retaining a high resistance to the movement of moisture through them.

I managed to modify the carbon filter on our old cooker hood by just removing the grilles either side of it and re-filling the core with activated carbon granules, intended for use with fish pond filters (they are cheap and easy to buy from places like eBay). Worked a treat, and if you wanted to really save money then you can wash and bake the used granules to reactivate them.

My brother set up a firewood drying shed on the farm, using the old Dutch barn we had. He covered the floor in pallets, stacked two high, then stacked a few dozen tonnes of logs in there to season. Worked a treat, as air was able to circulated through the stack pretty easily. The fact that the edges of the stack used to get wet from the rain didn't seem to matter at all, as they ended up just as dry and the logs in the middle after a couple of years or so.

The movement of water vapour has nothing at all to do with hot air expanding, or cool air contracting.

You are confusing water vapour permeability with liquid water permeability. The membranes won't let liquid water through (in either direction) but they do allow water vapour through (in both directions).

Nice to see Paul Buckingham getting some well-deserved attention at last. I've posted links to his papers on this before, but they are well-worth a read: https://www.aecb.net/still-taking-disgraceful-approach-build-quality-waving-goodbye-energy-savings/

Breathable membranes work both ways equally well, they aren't just a "one way valve", if they were then they wouldn't work well at all.

It depends on the local conditions, as water vapour migrates in to the cooler outer layers of the structure from outside when the outside air is warm and moist, and then migrates out again when the conditions reverse. This can be quite a dynamic process (hence my concerns about the validity of steady-state condensation risk analysis) as conditions can change very quickly over the course of a few hours. For example a wet night that soaks the outer surface and ground, followed by a sunny morning with little wind that then tends to create warm, high humidity conditions in any external ventilated cavity, may cause water vapour to migrate inwards towards the cooler layers on the outside of the structure (cooled by lower temperatures the previous night, perhaps). As the humidity outside drops, this water vapour should be able to move back out again before the outer layers of the structure cool again. The trick is to ensure two things; that water vapour doesn't condense inside the structure (as the phase change energy needed to get liquid water back to vapour is high), and to ensure that water vapour can always move outwards through the structure quickly enough through the day to deal with the dynamic changes in outside temperature and humidity.

Does Internorm have a big share amongst self-builders? Off the top of my head I can think of about 4 or 5 members here with Internorm windows, and most of them have had installation-related problems. Not sure what window make is the most popular here, might be worth starting a poll thread to find out, purely in the interest of balance.

Pretty much what several members of this forum have to say about Internorm installations, I should think. I think we've had more observations about leaks around Internorm windows than we have for any other make. Given that Internorm are a premium product (they were far and away the most expensive of the four companies we had quotes from) I'd expect better.

We were told much the same by the Internorm agent near us about 5 or 6 years ago now!

Depends how vapour permeable you need the board to be, which depends on what's the other side of it and also how well ventilated the space is outside it. I doubt there is a "one size fits all" answer, and it probably needs a interstitial condensation risk analysis for each specific build up to determine whether any particular outer panel is OK or not. The challenge with that seems to be the wide variation in permeance for OSB, as that could well skew the results from any condensation risk analysis.

I've connected the MVHR drains, PRV overflows and the softener drain to the same trap, down on the ground floor (all that kit is up on the first floor). Having the trap downstairs in the utility room makes it easier to get at, and because the water softener will cycle every few days it keeps the trap topped up. The condensing drier is connected to the utility room sink trap, which tends to get used enough to keep it full. On the more general subject of traps drying out, as we very rarely use the bath in the second bathroom, we do find that the trap dries out. We've just got into the habit of running the bath tap for a few seconds every few weeks.

We have a fair few bits of kit that need drains, the MVHR, water softener, condensing tumble drier and a couple of sealed systems that have low temperature pressure relief valves. All drain into the main soil pipe stack, that runs under the passive slab. There are water traps to stop any smells coming back up, just as you'd fit to a sink, basin etc. To stop the internal soil pipe stack from acting as a cold chimney up through the house, it's capped with an AAV inside the roof space. The foul drain is vented externally down at our treatment plant, to comply with the regs.

This has made me go back and check the spec for the OSB we have as sarking and as racking layer on the outside of our frame. It seems I was wrong about the specs. The sarking is 18mm OSB, T&G boards that seem to be specified for use as sarking boards, but there's nothing in the spec about what they actually are. I suspect they may well be roofdek, or similar, as looking at the photos the boards seem to be a lighter colour than the OSB/3 boards. Our racking layer wall boards are definitely 9mm OSB/3. Both the walls and roof have a ventilated space that should ensure that water vapour can escape from the boards OK. I may try and see if I can try and measure the RH at the surface of the boards, as it shouldn't be too hard to get a sensor up under the eaves and in contact with the board surface. Not sure how useful the data might be, but it'd be interesting to see the relationship between the RH of the air outside and that at the surface of the boards. Have to wait until summer, though. It's still snowing here, has been on and off since yesterday evening.

As far as heating the room goes, then it's only the surface temperature of the slab/flooring that matters, but I've no idea how far down into the slab the heat from solar gain goes. My best guess is that it will probably go a fair way into the slab, as concrete has a reasonably high thermal conductivity (around double the thermal conductivity of water, or around 45 to 50 times that of air).

That's more to do with the relatively high thermal conductivity and heat capacity, of water, I suspect. Mains water will probably be close to the ground temperature around 1m down, which tends to be between about 6 deg C and 8 deg C in much of the UK. Comparing air and water, air has a heat capacity of around 1,012 J.kg-1.K-1 whereas water is around 4,200 J.kg-1.K-1 , so for any given cooling condition, water will tend to stay around 4 times warmer after a set period of time than air. Add in the effect of thermal conductivity from warmer water below ground, up through the pipe filled with water (water is around 23 times more thermally conductive than air) and it's perhaps a bit easier to understand why pipes filled with water can take a long time to get cold enough to freeze.

No, that's true, in fact we rarely fry anything, which probably makes a significant difference.

MDPE pipe has a bore of about 20.1mm, so the CSA is about 3.46cm², which gives a volume per m of about 346cc, or 0.346 litres.

Unfortunately overhangs don't really address the issue here in the UK. They work OK in mid-summer, when the sun is high in the sky, but we've found that we don't have an over-heating issue then, the problem is Spring and Autumn, or even mid-winter (we had a hot day a week or so ago). The key thing is that when the sun is low, on a clear day, it penetrates deeply into the house and so tends to warm up a larger area of floor, wall etc. This then tends to heat up the whole house. It's made worse in mid-winter as those surfaces will already be fairly warm from the heating, so it doesn't take much for a bit of solar gain to increase the room temperature a lot. As an example, right now our floor is sitting at around 23 deg C, the room temperature is a bit over 22 deg C and the floor is putting about 7 or 8 W/m² of heat into the house (around 500 W or so of heating is being delivered to maintain a bit over 22 deg C right now, but it's not very cold outside, around 2.5 deg C). If the sun warms the floor up by 1 deg C, to 24 deg C, then the heat output from just the floor alone would increase to about 17 W/m², more than doubling the heat output into the house which will cause the temperature to increase a fair bit

I'll do it now - should be active in a couple of minutes time. You can just create one once I've changed the settings for you.

FWIW, we have no problem at all with the MVHR or ducting getting dirty. I cleaned/changed our MVHR filters last week, and as usual the fresh air intake filter was very dirty, but the house extract filter just had a very light coating of dust, so I just cleaned it with a vacuum cleaner and put it back. I fitted an OSB panel and additional wiring behind the ceiling plasterboard above our hob, so it's pretty easy to retrofit a cooker hood, but we've found that we don't need a cooker hood in practice, as the kitchen MVHR extract terminal seems to do a very good job of drawing cooking smells etc away from the rest of the house. One thing I did that probably helps this is fit an additional fresh air supply terminal in the ceiling outside and above the kitchen door. This ensure than fresh air is supplied as a sort of "air curtain" outside the kitchen, which seems to stop any cooking smells from escaping.

When we were looking, Internorm were not offering the external blind option, only the blinds fitted behind the extra external pane. I seem to remember that they could still offer a PH certified solution like this, though. I'll dig out the quote we had from them and check, as it's around 5 years ago now.

The Internorm windows with internal blinds we were originally going to buy had 4 panes of glass, yes. The outer pane of glass was separately hinged, so that the blind behind it could be accessed. I can't recall the model number now, but remember that they were unable to provide the internal blind option for any glazing that needed toughened glass, so the blind option wasn't available for our gable. They weren't cheap, but then it's just cost us £2.5k to fit internal blinds to our gable glazing, plus we spent over £1k on fitting solar reflective film to the outside face of it, so having a solution that addresses both privacy and solar gain within the glazing may not be that different in terms of overall cost.