George

For what it's worth, my space heating backup is a wood burner or plug in electric heaters and the hot water backup is an immersion heater in the cylinder.

I'll share what I can but I have to agree with the others, there are way too many vairables to get a decent answer. However I am also looking at battery install (already have PV) so have been trying to work it out for my house. Construction Type Solid wall 90%, cavity wall 10% Insulation (walls/floor) 60mm woodfibre 75%, 100mm PIR 25%, minimal in floor, 300mm rockwool in roof MVHR? Yes Total sqm 172 Achieved Airtightness ? Like others, I haven't kept a running total and I don't trust the onboard energy meter (actually that unfair, the consumed one I trust, but not the generated one). Average annual kWh used by the entire ASHP system - 4872kWh. In winter I used about 18kWh/day, currently about 3kWh/day (have two small children who like to bath then shower!), in summer it'd be less than that. For a worse case, add an additional 10kWh/day due to other heat sources in the house for fairness. My conclusion was, if I could get on a car charging tariff, (without an EV) I'd make 100% daily use of a battery so the pay back time will be minimised. It's one of those 'if you don't use it, then it's a waste' scenarios. It's people who don't use much electricity when a battery is a marginal decision.

Yes - you can leave the existing weep holes so long as you close the cavity and put in trays above it. Obviously in an existing wall you can only remove a few bricks at a time, unless you are able to otherwise prop or support the wall above. Amusingly I have seen architects who built their own extension say 'ah it'll be fine' when I questioned them on this exact point.

Is there an impact on the FIT meter if I do that? I had in mind that alterations before the ofgem meter could only be like for like (ie replace an inverter). The inverter is approximately 7 years old but has had no issues. My original plan was to wait for the 10 year point, then add a DC battery with the inverter replacement But with the electricity prices rocketing the payback time for an AC battery seemed attractive enough. Is it possible for an AC battery to be barred from exporting and not needing DNO approval (if they refuse?).

Is that only for AC batteries which provide backup power (and hence need full grid isolation)? I'm looking at retrofitting an AC battery to my solar system, so don't want to mess with the solar set up. A side question, if I add an AC battery now, presumably I could add a DC battery if/when the solar inverter needs replacing.

Probably into the arena of diminishing returns, plus you want to keep the thermal mass (I know, I know) of the blockwork exposed to the internal environment.

Shouldn't need any expansion joints at all. May be mislabelled contraction/control joints, but I'd be looking to eliminate/minimise those with the concrete design. If the pipes are going into the structural slab then will probably need to co-ordinate the pipework layout and the actual construction joints if it can't be poured in one go. If a control joint is still required, you'll likely need some sort of former, as the usual method of a Stihl saw is out.

The likely recommendation would be to underpin. A ground investigation to minimise the extent of the underpinning could be money well spent.

Without knowing the scale of the job, it's hard to say for sure what is appropriate. It's not exactly hard to comply with CDM2015 requirements on small jobs. @PeterW - quite right. Big projects still influence my understanding and I was thinking Reg 5(3). (However there's not enough information here and a self-builder could be the designer primarily in charge in the pre-construction phase.) @LA3222 - 'self building' is fine. It's DIY. Employing trades is being a Principal Contractor and the regulations apply in full. It's all fun and games until someone gets hurt. It really depends on the scale of your job, Basically it'd be to check your fulfilling statutory duties and get another set of eyes to carry out a site audit. Yes if you had an architect they'd be the PD. But unless you pay them to do it, you're unlikely to see anything from them. As self-builders can be heavily involved in the pre-construction design work, it can make sense for them to be the PD. In a small scale job, the PD could just hand over the pre-construction information (ground info etc), the design itself and a list of non-obvious hazards and pretty much leave it there. Another major duty of a PC is to sort out the construction phase plan. This is a good template for a small job https://www.hse.gov.uk/pubns/cis80.pdf

Some good comments here already. I've added a brief 2p worth. As a self-builder you will take on the role as Principal Contractor when you are employing contractors. If there is no Principal Designer, you will also need to fulfil their obligations as well as Client duties. The regulations are well explained in L153 (https://www.hse.gov.uk/pubns/priced/l153.pdf) but not all are entirely relevant to a self-builder. Do you have any other designers? You should ask them for any residual, non-obvious hazards in their design. For example, the weight of steelwork so the contractor can plan ahead and get a dolly or crane. Or the depth of any excavations and what the likely soil conditions will be. That information needs to be given to the relevant contractors. You need to think about whether any hazardous designs can be changed, or how they may be controlled/managed - however the actual implementation of those controls will remain with the contractor doing the work. As a Principal Contractor, you are responsible for good order of the site, site welfare and co-ordination of contractors. There is a supervisory role but conduct of workers primarily sits with each contractor. Presumably you won't know the detail of contractors activities, so this is where asking for their risk assessments and method statements will come in. If they hand in a pile of rubbish, it is incumbent on you to challenge their procedures and whether they have the necessary skills, knowledge and experience. A client also has duties, in short they need to enable the project to be completed safely, with adequate time and resources and anyone they appoint is competent. As this is your own home you can stay as a domestic client. It is only when you step into the realm of design and managing contractors where you have to wear the other hats. It may be worth appointing a health and safety adviser for this project to be on hand to review anything you are unfamiliar with.

This is my set up and agree with not even trying to integrate ASHP and biomass. I briefly investigated it but found all the issues mentioned here - I did have a back boiler pre-ASHP but got it decommissioned (probably should have filled it with sand but want to replace it with an external air fed, room sealed fire sometime in the next year or so) So yes, I have an ASHP with two log burners as space heaters (both were already in the house and used to be our only reliable heat source, brrrr). Gas cylinder, camping hob and kettle in the shed. Since finishing the renovation I've only experienced one 4hr+ power cut and I dug out the territorial army hexi-stove to make a cup of tea. I do light one log burner fairly often as it's in my office and means I can switch off heating everywhere else if no-one else is around. Although I've never really needed them as the ASHP can heat the house in all conditions we've experienced so far. Log burners with flat tops can be used as ovens in a pinch, or to toast marshmellows.

My installer got Samsung UK to talk to the DNO. They had mistook the 16kW ASHP as the power demand instead of power output. Actual draw was peak 3.8kW - about the same as an electric hob and not much more than a kettle (max 3kW). Also other comments about the inverter and direct start were also clarified, although I believe it mainly came down to an ignorant DNO employee. The specification of the proposed ASHP should be easy enough to get online and that will give the power input / power demand.

Old houses built using lime mortar don't need movement joints. While movement joints are something of a sledgehammer to crack a nut, there isn't a very good alternative, especially for cavity walls (lots of bed joint reinforcement or altering the layout to avoid the need). The differing expansion/contraction is dealt with by wall ties inherent flexibility. The different direction of the movement and characteristics of brick and block means the spacing and type of movement joints are different. It is something that requires an element of engineering judgement and builders aren't always the best at putting them in. But, better to put in MJs than be dealing with an unpredictable cracked wall in future.

They can all be at fault, but gross negligence is a high bar to prove. I agree that the manufacturer appears to be the one who most knowingly gave the incorrect product. But even then, had it been installed correctly with all the fire breaks, it's unlikely to have been quite the disaster it turned out to be.

It's certainly been an unusually warm autumn, here October has been 2C warmer than last year.

Back to heat pumps, I do wonder why gas powered heat pumps (on the same basis of gas powered fridges) aren't more commonly discussed. While they have the obvious drawback of still producing carbon dioxide, the efficiency gained brings them below conventional gas boiler on running cost and closer to the carbon intensity of electric heat pumps.

There's a great long topic on eng-tips about vaulted roofs. You do need a ridge beam. When I design them, I always specify sarking as although the ridge beam does work fine globally, live loads (point loads and lateral loads from wind and snow) are harder to control. Sarking sorts that out.

Small claims court is your best bet.

None can give an opinion - only an engineer. I agree in principle with the earlier post, partial underpinning is unusual and not typically a good idea. But I don't know the other issues and situation so can't comment further. Look up the ASUC members (Association of Specialist Underpinning Contractors) - obviously most will be too larger for a domestic job but that'd be my first choice. If no luck there then most groundsworker contractors can underpin, but you'll want some sort of insurances details and reference work.

Can't see iot being an issue in a domestic setting. The legitimate alternative is 'trickle vents and extractor fans', none of which can/would be calibrated.

Jumping in on this thread, who would normally specify a radon barrier? Is it the architect or building control?

Samsung 16kW Gen6 has a power demand of 3.8kW nominal. I expect others will be similar. Do expect the DNO to see '16kW' and freak out, though. My installed had to get Samsung distributor to contact the DNO and explain how the ashp worked, they were fine it then on single phase.

I agree but that is quite an 'if' . Most people can only afford to make choices based on cost.

All things being equal, if a ASHP can effectively heat a building, it should be cheaper to run than oil. Oil is currently 60p+/litre (5.8p/KWh) and it only really dropped from that level due to the pandemic. It still only makes sense if doing a full refurb and no access to mains gas, for me ashp is the next best option if the capital cost can have a grant covering the extra over. Although capital cost may start to fall.

You can't use gallow brackets if the neighbour has removed their chimney. I'd be uncomfortable using them if it's a part removal, too (as in, one floor remains and chimney is removed above and below, as in this case).