Has anyone had experience with the new SAP10?

i am designing and building a small 2 bed detatched bungalow (in total 58m2 int floor) it follows our usual building fabric design:

-insulated raft foundation conncted to EWI connected to EPS loft insulation (totally unbroken insulation element and lots of thermal mass)
-ATness below 0.6 m3/m2
-MVHR (90%)
- 3g window and doors
- 3kW slimjim direct to UFH
-direct cylinder with twin immersion or instant water heaters(budget dependant)

i had this run through the new SAP10 (pre design) and it failed, not due to the fabric efficiency but becuase of the fuel price calc, it seems the only way to get a new building through the new SAP10 is with bolt on PV or ASHP (good news again for installers) In this particular build the budget is very tight and both are costly the ASHP has to low return due to the the low kW/m2/yr and the single occupant has low daytime electrical usage and no EV resulting in a low return value.

IMO SAP10 sends the wrong message, should'nt we be rewarding liftime energy efficient construction methods not short term panels and pumps?

I've just submitted a very similarly sized dwelling for planning, who want to know all about the energy usages etc, so have crossed this bridge, al-be-it not having run SAP yet.

Can't justify a wet ASHP, but for the first time am proposing an air-air ASHP, plus solar panels. There are a number of people on here, who extoll the virtues of air-air, and certainly the £500/£600 unit costs make it a winner, in my book, for small dwellings (not excluding large dwellings, just more to consider).

Good luck buying a few electric rads for £500, or the slimjim and wet UFH. Instead enjoy the A-A's usual SCOP of 4+. As I think Tom was maybe alluding to above, the DHW could be direct elect, but with some solar PV and an excess solar diverter, much of the year would be covered for DHW.

Leaving out conspiracy in favour of fossil industry, what makes UK Bldg Regs so perennially stupid - even after major revision following criticism? The men at the ministry who design SAP are smart and fully understand PH etc - so why this crack brained UK-centric 'version'? There must be a rationale - what is it?

Posted By: fostertomwhat makes UK Bldg Regs so perennially stupid

The same thing that makes almost all British committee decisions stupid. Politeness plus vested interests. The smart people who design SAP are more interested in doing something interesting and continuing (i.e. designing an energy modelling system) than in doing something boring and unlikely to lead to further work (i.e. approving some pre-existing system designed by foreign johnnies, don't you know). They're willing to listen to all inputs, in the interest of fairness, and the manufacturers employ people who are fairly smart and who know how to write to give them some input to listen to.

The DHW HP water heaters I have seen involve making two (more) large holes in the exterior wall of my house. Not something I'm comfortable with. All the holes I have were designed in and made during construction.

My 2p, the rules are probably devised with the volume housebuilders in mind, the goal being maximum output with a simple design, availability of materials, little real training required, can be thrown up quick and most important a decent profit margin when its sold.

Actually I've just had a response from the Scottish politician Alex Rowley which says something abou the process:

"... the resources required to have every property verified and certified by Passivhaus Trust approved verifiers are unfortunately not available, and as such an alternative approach needs to be found. My suggestion is to make the Passivhaus standard a requirement through existing building standards and then changing the approach of building standards to verification to appropriately verify that the new standards are being met. The only difference in my proposal is that verification would happen through existing building control measures - albeit, the resources for this may need to be expanded to accommodate new verification requirements."

and there's a link to the working group: https://www.gov.scot/groups/energy-standards-review-scottish-passivhaus-equivalent-working-group/

So it seems the vested interest is the building control people (are they public or private in Scotland?). But given they aren't trained in PH at the moment, it will likely cost just as much to train them and new recruits as it would to increase the number of PH-trained qualified certifiers. JMHO.

Building Standards are public officials in Scotland (local council staff), but as at present they won't have to do the thermal modelling or airtightness testing themselves, just inspect the certificates issued by the specialists who are hired by the developer. Alex Rowley is an opposition politician, not necessarily representing the government's view on PH enforcement.

SAP is a product supplied by a private company (BRE) so its developers are not the wo/men from the ministry. It's actually supplied to several completely separate ministries in England, Scotland and (sorry idk) Wales and NI for use in different laws (building regs, building stds, EPCs, etc)

To be fair, sounds like the issue in the OP is with the recently-tightened Building regs, rather than with the SAP method itself.

Scottish government said:

'Some stakeholders have called for SAP and RdSAP to be substantially amended, or
replaced entirely, and an alternative assessment methodology used [PHPP]. This is within
the power of Scottish Ministers, as set out in The Energy Performance of Buildings
(Scotland) Regulations 2008. However, we do not propose to amend or replace the
methodology at this time. This is for three reasons:
• Firstly, a major update to the SAP and RdSAP methodologies is under
development by the UK Government. We are working with the UK
Government and other devolved administrations to ensure SAP 11 meets the
needs for use in Scotland and have received assurance from the UK
Government that SAP 11 will address many of the concerns stakeholders
have raised about the accuracy of SAP;
• Secondly, development of a new methodology (and associated ongoing
management work) would need to be undertaken in parallel to the current
methodology. This is because schemes and services that operate across the
UK using EPCs would require the existing methodology to be maintained;
• Finally, we intend to make clear both on the EPC and in its usage, that the
EPC (and its recommendations) is based on a relatively basic assessment of
the building, and uses standardised values, and so is not a substitute for in-
depth professional retrofit advice."
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17921

Posted By: fostertomWhat's the 'fuel' load split, space heating vs hot tap water? Approx?

Taken from the design SAP

Space heating- 762 kWh/yr (13KWh/m2 /yr)

Water heating- 1411 kWh/yr

Posted By: WillInAberdeenBuildings should be rated based on how many tonnes of carbon are emitted, both during their use and during their construction. IMO.

Fuel cost isn't actually a criteria for new builds in English building regs but the alternative is almost as bad, rating buildings on 'Primary energy' which (surprise!) favours gas oil and coal over electric.

Here in France EPCs are dual-rated for primary energy and CO2 emissions. Whichever scores worst becomes the overall rating. I like the simplicity.

Interesting though that the Primary Energy Factor here is 2.3 (reduced in 2021 from 2.85, which had been set in 1972), so way above the new 1.501 factor in the UK. Principally because the nuclear reactors that provide around 70% of the electricity are only rated 33% efficient. However, the change is enough to tip the balance in the French SAP-equivalent in favour of electricity. It apparently reflects the movement in the generating mix over the next decade or so as nuclear drops to 50% and renewables rise to 40% (which could bring the factor down to closer to 2.1).

Posted By: djhThe DHW HP water heaters I have seen involve making two (more) large holes in the exterior wall of my house. Not something I'm comfortable with. All the holes I have were designed in and made during construction.

Yes although I have seem someone just feeding it from internal air instead.

Posted By: WillInAberdeenBuilding Standards are public officials in Scotland (local council staff)

When building my house, I was discussing this with the BC and he was saying it was being privatised so in effect the council was buying the service.

BC just do not have the resources to monitor the quality of build. Many large builders self certify and do not us the LA BC service.

No quality control results in s^&t build quality.

Posted By: Mike1Here in France EPCs are dual-rated for primary energy and CO2 emissions. Whichever scores worst becomes the overall rating.

Confusingly, there are two different laws in England:
-Building regs for new buildings such as the OP's are now rated on Primary Energy (with metrics for carbon and fabric)
-EPCs for new and existing buildings are rated on Cost (with carbon on the back page that everyone ignores)

They're both enforced using SAP (but different versions) so we get confused between them all. And it's different in Scotland!

Posted By: Mike1Interesting though that the Primary Energy Factor here is 2.3 (reduced in 2021 from 2.85, which had been set in 1972), so way above the new 1.501 factor in the UK. Principally because the nuclear reactors that provide around 70% of the electricity are only rated 33% efficient.

It's bonkers that zero-carbon DHW heated by power from radiation in a 33% efficient power station gets a punitively high Primary energy factor of 3, whereas zero-carbon DHW heated by radiation falling on your own 20% efficient PV panel gets treated as 1.5 (but more if it's located in France), and zero-carbon DHW heated by radiation on your own solar thermal panel scores 0. They're all zero carbon, so why aren't they all rewarded better than coal heating (1.06), which scores better than gas (1.13)?!

Primary Energy made some sense for comparing fossil usage across national economies, but is pretty much irrelevant for comparing houses. Especially over the 100yr lifetime of a new house when the energy mix will change in ways the architect cannot control. The CCC think PE sends out damaging signals discouraging electrification, so have recommended it be ditched in favour of Imported Energy.

Posted By: fostertomI mean people have an idea of how much electricity goes on their tap water heating, and that it's traditionally almost insignificant compared to what goes on their space heating, and that's why they've use 'cheaper' fuel for space heating but put up with 'expensive' electricity for hot water. Now you've reversed that - space heating is just a 50% add-on to water heating, so if electricity's OK for water heating, just 50% more of same for space heating makes sense.

Posted By: WillInAberdeenThe design is impressively successful in reducing 'fabric' energy, fantastic! That means the biggest problem is now the hot water, which Tom said often gets forgotten when people talk about 'fabric', but needs more attention in new houses now that newer regs have clamped down on insulation etc.

Building regs start off on reducing hot water by specifying WWHR and solar PV. Or you can have an ASHP instead. None of these are really 'fabric' improvements, but that's the nature of hot water.

This explains the need for expensive bolt on tech (PV,ASHP) to pass the design SAP.

In this case the SAP assumes an occupancy 1.9persons and a average daily HW useage 54L/day- is this an assumed figue by the assessor or fixed by SAP? What if the DHW system was based on instantainous heating (electric showers, under sink water heaters etc) not stored HW maybe this would reduce the useage? and reduce the yearly KWh

Update.

Following another discusion with the SAP assessor (Paul Taylorson) and some realtime adjustment of the SAP10 software to removing the bath and DHWc, now using direct water heating to an electric shower and undersink water heaters we have reduced annual DHW kWh usage from 1411 to just 442, alas this still fails the SAP assesment unless renewables are added. the fails is due to the current high cost of electric skewing the running cost figues.

i wonder how much a saving PV or ASHP makes against its purchase, instalation and service cost vs good old 240v on such a low energy demanding home?

Posted By: djhBut if adding some PV means you can build and otherwise you can't then it's a no brainer

yes, But that means that every new build house in England will have to have PV, can you imagine what this will do to the industry in the next 6 month? MSC installers will be stetched to breaking point and big spec building companies bulk purchasing panels and inverters.

Posted By: WillInAberdeenThere's an argument that PV panels are more usefully deployed in solar farms than on rooftops - but that's not in tune with the public mood!

The French 2021 Climate & Resilience Law requires PV panels (or a green roof) to be installed on all new & renovated commercial buildings >500m², over all car parks >500m², and over all office buildings >1,000m². Seems like a good place to put them.