I never did a SAP for my house though I did do a thermal model.

If the house is really low energy then there is a provision which says something like you don't need SAP calculation.

Building inspector couldn't believe that I was using so much insulation, 3g, airtightness etc so let me off. I have got a completion certificate.

I didn't need an 'as designed' SAP before I started the build because the BCO accepted my PH calculations. I have now had an 'as built' SAP done which is still subject to the air pressure test, when I have that carried out.

Posted By: pmusgrove: “Do the Scottish rules really say that you have to have a SAP rating of such and such or do they say that a SAP rating will prove that the house is efficient enough.”

They say that the DER must be no more than the TER:

http://www.scotland.gov.uk/resource/buildingstandards/2013Domestic/chunks/ch07s02.html#d5e15670

Ideally, they'd just say “no fossils being burned, DER = 0, TER > 0, therefore DER < TER, QED.” In effect they (the assessors assessor, I think it was) accepts this - the puzzle is how to write it in the right way.

Interesting that PH can be accepted. Bit late to change horses and try that, though. Might have done from the beginning if I'd have known (and checked it would be).

an alternative - can you "design it" with electric space heaters - if the insulation is so high that the heat load will be close to zero then it still may pass the calculations. (although the smaller the property, perversely the harder that is to do)

Appreciate that using one in an off-grid situation isn't likely to happen, but if the point of the exercise is to satisfy the bureaucrats it may well suffice.

You can always borrow a fan heater for a few days if you need an "as built" inspection..

-Steve

Posted By: tonyI would write to them ans ask the question "if I can get close to passive house or code 6, MINERGIE heat losses will you allow me to be considered as a special case and not need calculations, my U -values will be .....

Yep, would like to just talk it over with the local BCO. House designer is not too optimistic about getting that conversation though he's (the BCO) seemed willing to discuss things with other people.

Synggapa: yes - that was the house designer's original intention: write it up as electrical heating driven by the PV without getting into if the PV is sufficient. It wouldn't be, of course, in long-term steady-state winter conditions but the house should work with the large thermal store. The problem is that the full-time assessor is worrying about this.

Essentially the problems are:

1) SAP doesn't take account of the thermal store.

2) It doesn't have any mechanism to allow solar thermal to contribute to space heating.

3) Fundamentally, it doesn't allow for an experimental and incremental approach - you have to prove up front using their rather constrained calculation methods that the house will “work”. Fair enough for an estate house which is going to be handed over to people who'll just live there but a bit tedious for an owner/occupier who's taking a bit more interest.

But isn't the EPC just a bureaucratic worthless piece of paper, so why not just do the minimum required to get the piece of paper and then throw it in the bin. If you ever move you will need a new certificate anyway, as they are only valid for ten years.

Recent experience has not been good and as far as I can see there is nothing to be gained by worrying about the actual figure, as its very much rubbish in rubbish out, particularly when my assessor would only input things he could verify, and as he could not verify himself the thickness and type of the insulation he used a default value.

Hi Ed,

DHW will be a bigger issue from the sounds of it than the building heat loss. I wouldn't worry about it, just get the building modeller to put in electric space heaters and immersion in the model if there are any issues with cold days. I can understand why you want to avoid all this but I can also see the council having a standard system whereby they can ensure buildings and their relative heating/DHW systems are fit for purpose and can keep their inhabitants safe and warm at a reasonable cost.

Triassic, SAP models for building regs purposes in Scotland are accurate in material build ups, windows sizes/orientations etc. Once the blower door test is done that will be added too. This isn't a general guesswork game like those for rental properties.

A forum member in who does SAP ratings, etc, in England and Wales has emailed me to point out that part L contains an exemption “if your dwelling does not use energy to condition the space”. The Scottish equivalent seems to be limitation d to Standard 6.1:

http://www.scotland.gov.uk/resource/buildingstandards/2013Domestic/chunks/ch07s02.html

which says:

Standard 6.1

Every building must be designed and constructed in such a way that:

a. the energy performance is estimated in accordance with a methodology of calculation approved under regulation 7(a) of the Energy Performance of Buildings (Scotland) Regulations 2008 and

b. the energy performance of the building is capable of reducing carbon dioxide emissions.

I don't see how a new building can reduce carbon dioxide emissions except, I suppose, if it replaces another building which causes more emissions. Whatever, it then goes on with:

Limitation:

This standard does not apply to:

[…]

d. buildings, which will not be heated or cooled, other than by heating provided solely for the purpose of frost protection or

Clearly taking things absolutely literally this means a building which is kept at an exactly constant temperature throughout its life (if its temperature changes then it is being heated or cooled). I don't think they mean this.

I also doubt they mean to exclude buildings which are sometimes warmed by sunlight coming through the windows. So what about buildings which are heated by sunlight falling on PV and solar thermal panels mounted on their roofs? Or by heat leaking out of a thermal store which was itself heated by light falling on the PV and solar thermal on the roof? Where does the line get drawn here?

Just emailed my house designer saying do we really need a SAP rating and, if we do, why can't we just set the DER to zero and that we really ought to talk this over with BC.

That is the difference between a 'SAP' Assessment+EPC , and an rdSAP Assessment+EPC.
rdSAP is used for existing dwellings, and the 'rd' means 'reduced data'. It uses lots of defaults, whereas SAP has a higher level of data input.

Neither allow for non-grid tied dwellings tho'!

Ed,

SAP does allow for the Thermal Mass Parameter (TMP) to be input accurately, and will reflect this.
Whether this gives you the result you are after is another question....

It would appear that the issue comes from Regulations and SAP having standardised requirements and your and Govt's/DECC's expectations of how a house should be able to perform.

i.e. your house will still be there once you've sold it / shuffled off this mortal coil. You can't therefore assume that a replacement occupant will be happy to live at 15.5°C ( just above the point of potential condensation issues).

The heat losses are fairly easy to calculate if you know all your areas, lengths, constructions and their junctions performances, air tightness you can achieve and proposed ventilation parameters.

The standardised metabolic gains etc will be based on the house's floor area, because you will not necessarily always be the occupant.

Likewise hot water requirement will be based on typical number of occupants taken from the floor area.

Solar hot water can be entered and may well fulfill much of your requirements, but the hot water cylinder is going to need supplementary immersion at some point in the year if the solar isn't fulfilling your needs

Solar gains and really good insulation levels will take you a long way, but a back-up heating system (which could be classed in SAP as your main heating, would likely be necessary for at least a few months of the year, especially as the solar gains won't be very high during the period when you will be needing the most heat (equally the benefits from solar hot water and PV will also be at their lowest in the period when you most need it).

There's nothing to stop you assuming a dual electric immersion cylinder, with solar hot water input, nor to stop you putting an electric room heater as your main heating, or a closed log burning room heater if you prefer, as long as you can prove TER/DER compliance and better than limiting values.

SAP honestly is fairly robust compared to any other tool these days (especially SAP2012, although with Scotland, compliance is still using SAP2009, which is still pretty reasonable). There's a few issues (especially regarding lighting still tied to floor area), but overall it's not so bad.

The design stage SAP is required because too many houses were just being built and then had awful performance when assessed at the end. Understandably, modelling what you propose to do and then changing things at that stage is the best way to go, not least because it spares you from expensive c**k-up's!

A knowledgeable assessor and a open minded Building Standards officer should be able to sort it.

None of the regulations require an SAP assessment. The regulations require you to build a reasonably efficient property.

-The secretary of state will accept a property meeting the TER as assessed by SAP as being reasonably efficient.

-A Passive House is also reasonably efficient and some more enlightened local authorities will accept this.

-Technically you are also free to provide your own evidence that the property is reasonably efficient, but good luck in your endeavours without a brand name behind you.


In the absence of a formal heating system, SAP assumes electric fan heaters and instantaneous electric hot water. Provided DER<TER with supplementary heating provided by fan heaters/instantaneous electric hot water, you've nothing to worry about. This is a piece of cake for a grid-connected house as supply is 'unlimited' and carbon intensity is 'known' with ease.


For an off-grid house the same assumptions apply. (supplementary heating => instantaneous electric unless another means of providing heating is available) The SAP assessor wants to know that your PV will be adequate for this backup instantaneous electric heating. It very likely won't be: if it were your solar DHW and passive solar gain would have heated the hot water and house already.


Throw a little Honda genny into the mix. You've now got unlimited electricity at a 'known' carbon intensity. It's probably something you want on-hand anyway, for when the big freeze of 1963 returns or your inverter blows up or... ...and isn't outrageously expensive. Provided that your fabric is good enough the emissions from it won't be an issue.

You could also throw a woodburning stove or propane stove at the problem. You need never use the things or spend huge capital sums on them, but they tick the regulatory box more easily than resorting to paperwork. A small woodburner or propane stove might even prove useful when the big freeze of 1963 returns.


Plenty of other off electricity grid houses: (or houses on private-wire CHP systems)

http://www.thermaskirt.com/downloads/casestudies/Off-Grid-Farmhouse-on-Renewables.pdf

Posted By: markocosicNone of the regulations require an SAP assessment.

Standard 6.1, which I quoted above, seems to in most cases (this is not England). AFAIK SAP is the only method approved for regulation 7a of the EPC.

Throw a little Honda genny into the mix. You've now got unlimited electricity at a 'known' carbon intensity.

Good point. Yes, I have thought that I might well finish up with one if only for providing site power during construction but hadn't really thought that its emissions would be low enough. Could be, I suppose.

Is there a requirement for space heating in building regulations?

In effect, yes:

http://www.scotland.gov.uk/resource/buildingstandards/2013Domestic/chunks/ch04s14.html

3.13.1Every dwelling should have some form of fixed heating system, or alternative that is capable of maintaining a temperature of 21°C in at least 1 apartment and 18°C elsewhere, when the outside temperature is minus 1°C.

The following section covers systems like my proposal so, in principle, things should be fine - the question that looks like being resolved after a flurry of email to BRE and the like is how to convince the SAP software to allow it.

Hairydude, yes, Highland Council have, so far, been pretty good to me. My pre-application enquiry and actual planning application were dealt with about as quickly as the various consultations and so on allowed and in a helpful and positive way. The roads department were also very sensible and helpful with sorting out my road opening permit for access to the site.

As you say, there's lots of room in the standards for alternative approaches. The last section of:

http://www.scotland.gov.uk/resource/buildingstandards/2013Domestic/chunks/ch04s14.html

is quite explicit about that for heating.

What it's less clear about is how a SAP rating should be done when such alternatives are used. As I mentioned above, I'm no longer convinced the house actually needs a SAP rating at all but for the moment I'm leaving the SAP assessor and her food chain to mull it over while BC look at the rest of the building warrant application. If they can't come up with a SAP assessment that fills the bureaucratic gap then, yes, the next step would be a talk with the senior guy in Wick.