Posted By: WillInAberdeenDon't really understand the background here?

New builds have to comply with Building Regs, which don't care about the running costs - they're based on (primary) energy consumption in kWh, not £:

i have no experience myself with SAP10 , my comment was based on the conversation with SAP assessor ( i probably got it a bit wrong) BUT the fact remains a new build home will fail its design SAP unless PV or HPs are added into the calculation which will have a massive effect on the construction industry going foward (IMO)

I had a quick look at SAP 10.2, and the SAP rating seems to be established in the same way as previous rev's (final calc, rather than all reams of calcs that arrive at the numbers to be manipulated)...

------------------cut from SAP 10.2----------
13 ENERGY COST RATING
The SAP rating is related to the total energy cost by the equations:
ECF = deflator × total cost / (TFA + 45) (7)
if ECF  3.5, SAP 10 = 108.8 – 120.5  log10(ECF) (8)
if ECF < 3.5, SAP 10 = 100 – 16.21  ECF (9)
where the total cost is calculated at worksheet (255) or (355) and TFA is the total floor area of the dwelling at
worksheet (4). The deflator is given in Table 12a
-------------------------------------------------

AIUI, building regs stipulate the Target Emissions Rating (TER), and that the Design Emissions Rating (DER) must be less than the TER. SAP is just the calc tool to pull together the numbers to allow the comparison of DER & TER.

The basic model for the physical make up of the notional TER building is set out in the building regs (ie. assumed Uvalues, quantities of solar PV, heating system type and efficiencies, etc). SAP 10 uses those settings to generate a SAP rating and an EI Rating for the TER. A designer can design the dwelling any way they want, as long as SAP10 spews out the two numbers below the TER numbers.

Even in the last few houses I designed and built up to a couple of years ago, using direct electric and not having some form of generation (thermal or PV) made it near impossible to pass.

At risk of veering off on another tangent, as just a landlord and having an interest in efficiency ,i find many of the discussions on gbf fascinating / enlightening. WIA’s comment regarding the use of an older system to assess EPC’s and how any legal relevance only applies to rented property, throws up how hard it is going to be to change things on that front , the proposed improvements to the MEES for the prs in england has been ditched at least until after the next general election, there is already a shortage of property avaialble to rent and a move to a mandated epcC for rented property would have made it worse, but equally any updating of the assessment and or moving the scale to disadvantage gas and make electricity preferable will equally cause chaos in the rented sector.
I’ve bought my properties upto a C and locked that in for 10 years by bringing the epc renewal date forward,i’d likely do them again before the assessment procedure changes ( as and when it eventually does) to gain a bit more breathing space. The cost of heating my rental properties via ashp is never going to be financially viable ( unless either, there are lots of grants available or the failure to update ( and any associated legal issues) them makes them lose so much value that it bankrupts me and they are bought cheap enough for the purchaser to be able to afford to do it).
The recent changes to the oversight required for any works coming under building regs is going to make future works ever more expensive ( my last visit from building control led them to suggest that it could increase the cost of works by 10-20% depending on how it all shakes out) and compliance certs ever more important for future mortgages and sales.
The establishment response to grenfell is going to cause huge issues and tie people in knots going forward, all because our civil servants have no idea as to how things work at grass roots level, their thinking blinkered by the view that everything is paid for from an infinite pot of government money and the desire to ignore the history of grenfell and its management in the decades leading upto the disaster.
There really is a lack of joined up long term pragmatic thinking within the corridors of power.

Posted By: WillInAberdeenIf you have PV as per their spec for the notional building, then you are only credited with the PV that the building consumes itself. Not with the power that you export, or use in your EV or dishwasher.

Why is the dishwasher specifically excluded from general consumption? It sounds like those regs will make the use of PV for DHW heating comparitively more important?

SAP is to be abandoned and replaced by something called the Home Energy Model

https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap

On a slight tangent but similar subjecr. Does the solar that is being inputted into the SAP assessment need to be mounted onto the structure of the building or can they be ground mounted within the curtilage?

Just to confirm that the 2025 standard for new homes is proposed to be

U= 0.11/0.13/0.18 roof/floor/wall,
Air test 4-5 m/h@50Pa

AND
heating and DHW by ASHP or communal network


AND MAYBE (under consultation)
Solar PV AND MHRV AND WWHR

Looks like adding extra insulation and AT (above those standards) will not be sufficient, even if to PH levels, without also having ASHP and other tech.


No mention of the elephant under the floor: embodied carbon.