Jeremy Harris

Yes, the heating figure is annual. The house was designed to only need a tiny amount of heating, it's a passive house in principle, although it looks pretty traditional in most respects. Over the course of a year we generate more energy from the solar panels on the roof than the house needs, so we don't actually pay anything for energy, as the revenue from electricity exports plus the feed in tariff payments significantly exceeds our annual electricity bill. We don't have gas, oil, solid fuel or whatever, the house is wholly electric. I'm far from being alone, many others here have similar very low energy homes. The problem is that the mass house builders in the UK tend not to build well-insulated, airtight and low energy homes, so it's mainly self-builders, like those on this forum, who are leading the way.

Interesting, as our wall is 430mm thick at the base, 215mm thick at the top. Any of the block systems I looked at were going to be three or four times wider than that, as the key distance for us was from the base of the wall on our side to the face of the wall on the neighbours side. The thinner we could make that the more room we got. In the end, because the lower part of the wall is under the neighbours garden, the wall only lost us the top section thickness of 215mm, plus the thickness of the render, so maybe 230mm in total.

Funnily enough, the reason I didn't use a retaining wall with batter was to reduce the footprint! Building a vertical retaining wall gave us about an extra 1.5m of garden, plus allowed the house to be positioned a bit further back towards the wall, whilst still allowing for a decent path around the back. In turn, moving the house back allowed the drive to be extended up past the front door, giving us more parking space (proved to be really useful when I got an electric car, as it made positioning the charge point I use most of the time easy).

Sounds fine, Stepoc offered that in their package when they quoted to supply blocks for our wall (couldn't use them as the neighbour wanted a stone wall on top for the boundary, rather than the timber fence that had been there...).

Our house isn't typical, as the heating requirement is very low, but in another thread I did work out the relative cost of heating it for a year, using different fuels: Our ASHP tends to run with a fairly high COP, though, as it never runs at a flow temperature above 40°C, so much of the time the ∆T between the outside air temperature and the flow temperature was around 30°C or so.

The key point that seems to be being ignored is the elephant and mouse one. A GRP lay-up, be it a boat hull or a roof, has a very large surface area to volume ratio. Heat loss rate for a given differential temperature is proportional to this ratio. The fact that the initial curing reaction is exothermic is relatively unimportant during the cure of a typical, fairly thin, lay-up, as the heat lost because of the high surface area will be significantly greater than the heat released by the initial curing reaction. That's why it's perfectly possible for a still uncured lay-up to cool down to below dew point and so attract condensation, and the reason I had to spend a night in a smelly industrial unit in Penryn making sure that the laminate temperature didn't cool below local dew point overnight all those years ago.

Out of interest, how did you get your insurance company to agree to accept the risk without any SE sign off? This was what convinced me to pay £360 to an SE, as although I'd designed a couple of retaining wall configurations that complied with Eurocode 7 my calcs weren't acceptable to the insurer.

Bottom line is that there can never be osmosis unless the roof is immersed in water for a long period of time! Heavy rain like that today doesn't really count...

The Sunamp (if it's an electric one) is the same rating as an immersion heater, so draws about 13 A nominally. The ASHP demand will depend on the model, for an inverter controlled one it will be somewhere around 10 A typically, maybe a bit less if it's a small one. The cooker demand is the highest load, after the water heater. No matter how I do the maximum demand calculations I can't get the result to comply with BS7671 Chapter 3, section 311.1, for either an 80 A or 100 A rated supply, if you have that 11 kW water heater. Might be worth mentioning compliance with this section of the regs to the electrician, as it has been known for the total demand to be overlooked before now (I've done it myself, just by not thinking about it...). This is almost the most optimistic set of load estimates I can come up with, and assumes that you only have a 32 A cooker max load (40 A would perhaps be more common): 1 off ring final circuit rated at 32 A (house) = 10 A + 50% of (32 A - 10 A) = 21 A 1 off radial power circuit rated at 16 A (studio) = 10 A + 50% of (16 A - 6 A) = 13 A 2 off lighting circuits rated at 6 A, (one in house, one in studio) = 2 x 6 A x 66% = 7.92 A 1 off Sunamp circuit at 16 A, (3 kW heating element, no diversity) = 13 A 1 off ASHP circuit rated at 16 A (need to check this, and need power rating of ASHP, no diversity) = 10 A (could be a little less) 1 off electric water heater rated at 60 A (48 A appliance load, no diversity) = 48 A 1 off cooker circuit rated at 32 A (assumes no socket on cooker outlet) = 10 A + (30% x 22 A) = 16.6 A The sum of all the above, allowing for diversity, comes to = 129.52 A This is way over the 80 A supply limit, and also way over a 100 A supply limit too. There's a fairly strong possibility that the main fuse will get very hot if run at this sort of overload. It may not actually blow, unless the overload is sustained for a fairly long period, but the possibility is there that it will. It's also possible that I've made an error in the diversity and maximum demand calculations above. Perhaps one of the electricians here might like to check the maximum demand and diversity calcs above to see if I have ( @ProDave, @Onoff ? ).

Does he know all the other loads you have in this installation, though? Worth checking, as blowing the company fuse is a PITA if it happens (and makes a fair old bang).

Thanks, that was my understanding, that, over time, tiny pockets of monomer styrene remaining within the laminate attracted moisture through the osmotic membrane created by the gel coat and adjacent thin lay-up. Certainly pierced blisters always seemed to exude liquid that smelled very strongly of styrene.

You may well have owned boats for years, but it seems clear that you have a near-zero understanding of the mechanism by which polyester resins are catalysed by MEKP. If you had, then the reason why even small quantities of moisture can inhibit resin curing will be blindingly obvious to you. If you've spent any time in a good boat building workshop you will have seen the processes that have evolved to keep everything dry. Osmosis has nothing to do with moisture resin cure inhibition, it's a post-cure (more on that below*) phenomenon that only affects laminates that are immersed in water for long periods of time. The resin exothermic curing reaction is, as I've already mentioned, primarily a pot life concern, and rarely effects a laid-up laminate that's been manufactured by people who know what they are doing. Again, this is pretty obvious, for the reason I gave earlier, the elephant and mouse problem. Your final point about GRP encapsulated timber is a combination of poor encapsulation and simple mechanical failure resulting from the expansion of timber as it gets wet. If you wish to seem authoritative, it's best to at least do some basic research to ensure that you understand the true nature of the subject, lest what you write makes you appear foolish. * I mentioned post-cure, but there is some limited evidence ( @SteamyTea may know more, I've not used polyester for more than 20 years) that the issue may have been partly a consequence of tiny pockets of uncured, or poorly cured, resin within the layup (lots of reasons for this, given the ad hoc mixing methods used in lots of boat manufacturers years ago). Osmosis then causes water to migrate slowly through to those pockets increasing their volume and causing the characteristic blisters. If you've pierced osmotic blisters you will know that the liquid smells strongly of uncured resin.

There's nothing wrong with using chopped strand mat, especially when a layup is needed that doesn't have unidirectional or orthogonal strength requirements. It's pretty nigh impossible to make good hand layup without including layers of chopped strand mat, as woven cloth layers do not bond well to each other, unless the laminate is cured under pressure, either autoclaved or vacuum bagged. Woven cloth or rovings lay-ups aren't always better, in fact I avoid using them unless the structural requirements mandate their use. Non-woven triax is probably my favourite general purpose material, as it drapes and forms almost as easily as chopped strand, but uses less resin. Even so, that really needs a layer of chopped strand between layers, much like rovings does, when hand-laid up, to ensure that the layers bond together well. The major problem with mass-produced boats years ago was that they were being made by anyone with a tiny bit of knowledge, a shed and a chopper gun. Any idiot can use a chopper gun, and as a consequence lots of boats were laid up by people who knew next to nothing about laminating properly. Chopper guns use rolls of rovings, and can make very resin-rich laminates, especially if the operators don't put down the gun and spend time rollering the laminate out properly.

I bet it's cost driven as you've said. Burying that length is going to be costly, so they will try their damnedest to get out of having to do it if they can!

Not 100% wrong at all. I've spent years making composite structures, including several boats and various aircraft parts. From what you've posted so far I'd guess that you've never laid up a composite structure in your life. The only time I've ever seen laminate overheating during construction was when incompetent people were laying up laminates that were far too thick in one go, usually using a chopper gun (should be banned, IMHO, as they produce horrible, resin-rich, lay-ups).

I did, but the concern laminators have over the exothermic reaction is really only related to pot life. Once resin is rollered out into a laminate the heat from the curing reaction has little or no effect, curing becomes dominated by environmental factors, primarily the ambient temperature and humidity.

I can confirm this is complete rubbish, too! We had a pole and over-sailing telephone wires that had to be moved. There was no wayleave in place, so Openreach free-issued us with cable and Duct 56 (their grey underground ducting) and we laid their cable for them in the ducting when we were putting in all the other services. Openreach prefer to put cables underground if they can, for reliability, the only reason they don't do this normally is cost.

Yes, it is, but that is very section dependent (the elephant versus mouse problem), so thin, large, sections get cold, as their surface area is large compared to their volume. Not sure how much laminating you've done, at a guess I'd say very little, as moisture cure inhibition, especially of MEKP catalysed polyester, is a very well understood issue.

I can assure you that ALL laminators are acutely aware of the moisture problem - even condensation on a mould can inhibit a cure (ask @SteamyTea, he's done as much, or more, laminating than I have). I once spent the night in an industrial unit, following the layup of the hull of a 36ft yacht, just monitoring the humidity and temperatures and making sure the resin surface didn't drop below dew point. A helluva balancing act, as the heating was a large industrial diesel fired heater, that produced water vapour when running.

As a rule of thumb, you need a minimum of about 100mm of PIR insulation under a heated floor, ideally more, as UFH will always create additional heat losses through to the underlying ground (as the floor is being heated to a higher temperature than the room). Building regs (which will probably apply when converting a garage to a habitable room) only require a fairly poor level of floor insulation, as they don't take account of the additional heat losses from UFH. IIRC, the maximum allowable U value for a floor is now 0.2 W/m.K for conversions, but best to check as I've not read the regs for a year or two, and they are different for conversions, I believe.

No, nothing at all to do with osmosis, that cannot affect a roof structure as there will be no continuous osmotic pressure - a roof does not sit immersed in water like a boat. Polyester resin is simply very susceptible to moisture when curing. It's a very well-known issue, and one that every laminator in the land will be intimately familiar with.

Moisture seriously degrading the cure of polyester resin is a very well-known problem, and is why so much emphasis is placed on making sure everything is bone-dry when laying up a GRP roof. Once cured, GRP is very weather resistant, and a properly done roof will last many decades. Replacing the roof with a properly installed GRP one would be my preferred choice, as it will last a lot longer than a felt roof. However, as you've found, laying up GRP outdoors does mean you're at the mercy of the weather, and any dampness that gets into the resin before it's cured will almost certainly result in curing defects and subsequent leaks. At least with a torched on felt roof there's not too much of a problem with weather during the installation. Such a roof will usually come with a 10 year guarantee, too.

Just been through the detailed costs for our retaining wall, which is around 40m long overall and 2.5m high at the highest point, ~76m² total wall area. The construction was a large reinforced concrete foundation (2m wide at it's widest) with a double width 215mm hollow block wall keyed to the foundation by being built with steel reinforcement coming up through the block, along with steel reinforcement running through the block bonds. The hollow blocks were backfilled with concrete so there are vertical reinforced concrete piers within the wall. The basic cost for the wall foundations and structure came to just under £20k, including the SE fees. On top of that there was an additional £3k to build a stone wall on top of it as a boundary and about £2.2k for the rendered finish to the retaining wall, so overall the cost came to around £25k. In terms of cost per m² of wall, that works out as being around £330/m².

I added a timer to our Claber system, that seems to work well: https://www.ebay.co.uk/itm/Programmable-Water-Timer-Garden-Hose-Faucet-Sprinkler-Irrigation-Controller-K4J4/153504987336?hash=item23bd9c38c8:g:PGMAAOSwzNtc7NaB Saves having to remember to turn the system on and off.

Sewer pipes and foul drains have a similar classification system. If you just connect to an existing foul drain that runs from a dwelling to the main sewer you still have to go through the water company, who may well say that an additional connection to a communicating foul drain must not be made. FWIW, I had this too, as our neighbour has a foul drain that runs to the main sewer, it goes under the stream that runs in front of both our houses. I was not allowed to connect to their foul drain as it isn't a main sewer. I also wasn't allowed to run a foul drain under the stream, as the EA regs that apply now don't allow foul drains to cross under a watercourse. Instead I had to install a sewage treatment plant. Surface drainage generally cannot now connect to a sewer in many areas, as the water companies are placing restrictions on the utilisation of combined sewers. In the main they are still providing some combined sewers in urban areas, but tend not to if they can help it. We have no combined sewers anywhere around here, so all new builds have to make their own separate provision for surface drainage (rainwater from hard surfaces and roofs), in accordance with the SuDS rules.