Jeremy Harris

Very true. Our slab is 100mm thick, with embedded UFH pipes, and seems to work just fine. Much of the heat capacity in the house will be the plaster/plasterboard layers inside, as gypsum has a higher specific heat than concrete (it holds around 25% to 40% more heat per kg per deg C than concrete).

No underlay should be used if bonding flooring down, unless you opt to use the Sika system that uses a membrane with large holes in for the adhesive, with that adhesive being applied with a gun. The Sikabond I used is a modified silicone polymer, that cures to a fairly soft rubber-like consistency, not that different to an underlay. The stuff will take up a certain amount of unevenness in the floor.

Very true, and the reason that several discussions here have focussed on external methods for preventing solar radiation from getting to the inside pane of the glazing. However, the Internorm solution uses external blinds that are fitted behind an additional, opening, glass layer on the outside of the sealed unit (or at least the "internal blind" Internorm windows we looked at did). As such, they are outside the E coated panes, so work pretty much as well as external blinds or shutters.

I had a similar experience of a noisy floating floor, so in this house I bonded our bamboo flooring down. Makes for a really solid floor, with no noises at all. The only downside is the cost of the adhesive. I used Sikabond 95 and it was around £80 a tub.

We are inside an AONB and in a CA, plus we're opposite a GII listed building (inside the 100m radius) so had some pretty tough planning restrictions imposed.

OSB does vary, and I should have been more specific. Don't use OSB/3 or /4 for sarking, as it's not anywhere near as vapour permeable as OSB/1 or /2.

Good idea. If we had been able to fit external blinds (planners wouldn't allow it) then that would have been my first choice. I stayed in a place in Portugal a few years ago that had concealed metal external roller shutters and they were really great at cutting down solar gain. I wanted to fit them, or perhaps wooden shutters, but it was made very clear early on in the planning process that there was no way they would have been allowed.

FWIW I went through this decision-making process for our shower room. We (she) wanted a big shower area, and having made a few scale models (complete with 1:50 scale model lady in a bikini in the shower - I kid you not) we (she) settled on a minimum acceptable shower area of 2000mm x 900mm. I made the shower room 2010mm wide, and then had a long, hard think about how to construct the shower area. In the end I chickened out of fitting a wet room former, as I know my tiling is crap, and unlikely to improve (I hate tiling with a passion). I found a local supplier offering a 2000mm x 900mm low profile shower tray (not cheap...) and opted to fit that. I set the tray on a flexible tile adhesive bed (it was one of the very heavy ones, ~70kg) and then fitted 9mm marine ply to the rest of the shower room floor (glued and screwed to death) and had 12mm travertine laid over that. We're very happy with the result. The tray only projects up about 20mm above the travertine and so there is no feeling of stepping up into the shower. I did have to fit the 50mm drain under the floor though, but as this was on the first floor it was reasonably easy. The Gods were with me, too, as the openings in the Posijoists allowed a straight run to the soil pipe stack. Probably of more relevance to your case is the shower bath I fitted at our old house. That had a larger, lower, shower area, and the floor beneath was concrete. I didn't find it too much work to Kango a channel across the floor for the waste pipe, and make a hole under the bath trap. After fitting the waste pipe and testing it, I just fitted floor tiles over the top of the channel. That lasted a bit over 10 years with no sign of any problem. Finally, because I hate tiling, I used AB Building Products Multipanel, both in the bathroom of our old house and in the bathroom and shower room of our new house. I'm dead impressed with this stuff. Far quicker and easier to fit than tiles and no nasty grout to try and keep clean. The only snag with it is that the standard bottom edge seal is complete and utter crap, and should have been binned as an idea years ago. Easy to get around though, just space the lower edge of the panels up by around 4 or 5 mm with tile spacers, then just run sealant into the gap. Let that cure and either run a finishing bead of sealant, or, as I did (I hate cleaning grotty sealant too) fit a PVC trim bedded on clear sealant.

So, 2 kWh for the treatment plant pump is ~ 83 W, which seems on the high side. Probably well worth looking at fitting a timed relay or SSR to cycle the pump on and off I think. Our pump is rated at 40 W, but in reality it seems to use around 44W. I have it cycling on and off, 30 minutes on, 30 minutes off, so the mean power consumption is around 22 W, or a bit over 0.5 kWh, so around 1/4 of the energy yours is using. Our usage will be a little lower than yours, with just the two of us, but I doubt that makes a significant difference in terms of the BOD of the effluent, as much of that seems to come from "other than human waste" that goes down the drains. Our Bio Pure unit is near-identical in design to your unit as well, so probably has a very similar air demand.

Yes, OSB is sufficiently vapour permeable to be used on the outside. Our roof build up (warm roof, with rooms in the roof space) is, from the inside out: 12.5mm plasterboard 50mm service void (50 x 50 battens) VCL membrane 402mm deep I beam rafters, with pumped cellulose insulation between them. 22mm OSB sarking boards 50 x 25 counterbattens nailed along the line of the rafters to give a ventilated space Non-tenting vapour permeable roofing membrane 50 x 25 slate battens Slates or in-roof PV panel trays

We have 22mm OSB sarking boards nailed to the outside of our rafters, then 50 x 25 counterbattens nailed along the lines of the rafters, then a layer of roofing membrane, then 50 x 25 battens for the slates. Works very well, as it stiffens up the roof and makes it easier to work on. It also improves airtightness a fair bit and decreases "wind wash" through the insulation. We have no gap between the sarking and the cellulose insulation, as the OSB is sufficiently vapour permeable to not need it..

Pretty, isn't it? Our windows were all frozen on the outside this morning and some of the ice crystals were really nice looking.

For a cheap, easy and quick to install small retaining wall it's hard to beat stone-filled gabions. If the wall isn't going to be seen then the baskets can just be filled with rubble.

I've never been sure why mass seems to be connected to the thermal time constant of a house, as the factors that control that are mainly heat capacity and thermal conductivity, with ventilation rate playing a small part (assuming the house is fairly airtight). I agree that having a very long thermal time constant can pose a challenge for the heating control system, as you can get to the state where the heating system has to try and predict the amount of heat to inject into the house many hours before, so if the temperature changes in an unpredictable way the heating system can get caught out. This happened to us this week, as the temperature suddenly dropped a lot and the slab wasn't really warm enough to maintain the temperature. For the first time in ages I turned the temperature up on the MVHR and warm air at ~40 deg C from the MVHR fresh air supply terminals did warm the house up over the course of a couple of hours. I can't say either of us really liked this much, though, as the RH dipped down to about 27%, which we find a bit too dry. Most of the time I find that just charging the slab up overnight at the E7 rate seems to work fine, as to some extent the temperature then becomes self-limiting. If the house warms up from solar gain, cooking etc, then the slab just reduces or stops heating the house, as the temperature differential drops. As the house cools, then the heat output from the slab increases to warm it back up, from the change in differential temperature. This seems to work OK because our slab sits at around 22.5 to 23 deg C pretty much all the time and the house seems to sit at around 22 deg C or so. Upstairs, where we have no heating, apart from towel rails in the bathrooms, sits at around 19 deg C, which we find comfortable.

I think I'd just use the ASHP, perhaps with a duct cooler as well. Buying the Genvex MVHR was very much a hasty (and expensive) change of plan, following on from discovering that the temperature in the area we excavated out of the hillside got very hot in summer, when we were doing the ground works. As the house foundations and frame were all on order by then, I couldn't easily change the design, plus, as you say, opening the windows when it's hotter outside just heats the house up. The running cost for the cooling is always free in practice, as we always have an excess of PV generation whenever we need it.

Not that easily, I suspect, as you'd need a couple of motorised valves, plus you'd have to have both the ASHP and the boiler on the same hydraulic circuit, and I suspect you may well have to put in some form of protection to ensure that under no circumstances could the boiler accidentally feed the ASHP and vice versa. You might be able to do it using a plate heat exchanger and two separate hydraulic circuits, but TBH it sounds like a lot of expense and complexity, If you have an ASHP you may we well use it for running the UFH in heating and cooling mode. Perhaps look at using a DHW only gas boiler?

AFAIK they need PP, yes.

My experience with TH was not good. Their supposed design service was, like the price of the equipment they sell, massively over-priced and I was far from convinced from the detailed quotes they provided that the system would even work properly, let alone be effective and efficient. I'd have a look around at a range of possible suppliers I think, and see what others can offer. The bottom line is that any MVHR system just cannot do that much in terms of shifting heat, as the flow rates are so low. Solar gain can easily be ten or twenty times greater than the rate at which an MVHR can remove heat, with the net result that using MVHR to heat or cool a house really only works for a house that's close to passive house standard, where the heating and cooling requirement are a lot smaller. If you're looking to build to this sort of insulation and, more importantly, airtightness level, then using active MVHR (one with an internal heat pump) can work well, but it wouldn't be very effective for a house built to just meet current building regs. We can heat and cool our slab using a cheap ASHP. The cooling works far better than I expected and is noticeably more powerful in its effect than the MVHR in cooling mode. Dead easy to do, as the vast majority of ASHPs have a reversing valve and are quite capable of running in cooling mode, it's just a matter of wiring up a cooling thermostat to set the ASHP into cooling mode and turn on the UFH.

Worth reading this thread, perhaps: There's really no such thing as "thermal mass" at all, it's a made-up term, that describes something that cannot be measured and has no units of measurement associated with it anyway. It's easy to build a timber frame house, without any masonry, that has a long thermal time constant. We've done just that; our house is all-timber (except for the foundation slab and slates) and has a thermal time constant that is a lot longer than 24 hours, which means that temperature changes between day and night are effectively ironed out. The key thing is to ensure that the structure ends up with a long decrement delay. There is a useful article on decrement delay here: http://www.greenspec.co.uk/building-design/decrement-delay/ that describes what it is and why it's important. In general, using low heat capacity construction will tend to give a low decrement delay, whereas a high heat capacity structure with the same overall U values will give a long decrement delay. We opted to use 300mm of blown cellulose in our walls, and 400mm of it in the roof, which has given us a structure with a long decrement delay, and hence long thermal time constant.

Yes, that's the sort of system. We have a Genvex Premium 1L MVHR with a built-in air-to-air heat pump (this model - and this is the cheapest/best supplier I know of: http://www.sundthus.dk/genvex-ge-premium-1l-hoejre/ ). Total cost, including delivery to the UK, came to £4,305, after we'd reclaimed the 25% Danish VAT. The same unit from Total Home Environment was quoted at well over £8.000 delivered, with a higher delivery charge than we paid to get the unit from Denmark... MVHR cannot shift much heat though, so unless you have a house that's built to close to passive standards I doubt that an MVHR cooling system would work well for you.

Yes, use the black, grey or white stuff anywhere it may be exposed to light, the brown stuff is fine underground or anywhere where it's not going to be exposed to light. I have a run of the brown stuff as a soil stack, running up inside an insulated box in the house to the first floor, and it's fine for that. As above, the brown stuff is fine under a suspended floor where it won't be exposed to light.

You shouldn't use solvent weld soil pipe underground, I believe, as underground soil pipes are subject to a degree of slight movement that can stress a solvent weld joint and cause it to crack. I believe the rule is to always use push-fit soil pipes underground. As for the colour, then the brown/orange underground pipe isn't UV resistant, so isn't supposed to be used above ground as the outer surface will degrade. Black, grey or white soil pipe is UV resistant so can be used above ground.

Yes, it's mandatory that you provide a site toilet and clean water for hand washing. If managing the site you may also be expected to provide other H&S elements as well. I provided an eye wash station, first aid kit and a plastic box of gloves, safety glasses and a couple of helmets in our garage as soon as it went up, not that anyone used any of the provided PPE, or their own come to that...

That's a lot better than the quotes I had around 5 years or so ago when looking at fitting a sprinkler system. The best price I managed to get was a bit under £6k, for a 130m² house, so more than three times that price. About £1.5k of that was for a tank and independent pump system, because we have a borehole, but even the £4.5k base price is nearly £35/m². Was there a significant discount for fitting 7 houses at the same time, do you think?

I agree wholeheartedly with @vivienz I opted to use a very non-local (at the time) contractor for our foundation and house build; they were based in Tipperary at the time and the team, and the whole house and garage, came over on the ferry to build our house. Best decision I made in the whole build, as not only did they do a cracking job, but the guys had nothing else to do whilst they were over here except build our house. Having contractors not turn up for a few days, because they've got another job on, seems commonplace. By using a contractor that's coming from a fair way away you remove that issue.