So today I got the results of the SAP calcs for our new build and was dismayed to see that despite over a total of 240mm insulation on the walls and roof, doubling up the underfloor insulation, airtight detail, careful avoiding of cold bridging way beyond normal builds etc etc, we came out at 82.... looked up what that actually means and I found 81 listed by the government as the average build last year, so in effect, all the shoddy volume builds you see with the airtightness of a sieve get the same rating! This made no sense to me at all and made me wonder about saving thousands in insulation costs. BUT, when I enquired I was told it was dragged down because we are going to use an ASHP (orientation and being in a National Park makes solar PV all but pointless/impossible as you'd think I'd said I wanted to paint a swastika on the roof when I originally asked the National Park about it - and they absolutely forbid us fitting it later once the house is occupied (when we can afford to better) in a bizarre planning condition!) and bought in electricity is more polluting of course. So it looks like we will get a better rating and save a few grand if I fit an LPG gas boiler and burn fossil fuel! (we buy our electricity form a 100% renewables company - so this will actually make our carbon footprint worse... but improve our rating and save me a lot of money!) On one level we don't care about the rating as the house is being built for us to see our days out in, not sell, but on the other hand it is frustrating to take so much care about limiting the energy used, to have it classed as no better than the slapdash stuff I see being built with no care. Having watched some guys putting "insulation" into a cavity wall on a volume build the other week leaving massive gaps makes it even more galling to know that house and tens of thousands like it will be given the same (or possibly better) rating even though it will use **masses** more fuel to heat than ours.

I encountered similar several years back when EPCs first appeared. Our then home was actually featured in the press and on the Energy Saving Trusts own web site as a good example... but when we came to sell it the EPC gave us a D! That came down to the fact we had a log fired heating system and the software in use was so rigid that it basically recognised mains gas on a housing estate type house and nothing else (for example such systems have pipestats, not a tank stat - but the software then only recognised a tank stat - so lots of points lost because it "saw" an completely unregulated heating system, and so on) - so I've never been a huge fan of this particular industry as the systems seem even now to be too rigid. Though thankfully found a helpful assessor who explained it all to me this time.

But it does make me think is this stuff really worth the paper it's written on?

Posted By: numeniusbeing in a National Park makes solar PV all but pointless/impossible as you'd think I'd said I wanted to paint a swastika on the roof when I originally asked the National Park about it - and they absolutely forbid us fitting it later once the house is occupied (when we can afford to better) in a bizarre planning condition!)

I remember a few years ago there were a number of cases where appeals were successful because councils were misinterpreting the rules. I think they were mostly conservation areas rather than national parks, but it may be worth considering an appeal.

we came out at 82

Well done, our EPC grandly states 78

We're expecting to be certified as a passivhaus quite soon.

But it does make me think is this stuff really worth the paper it's written on?

I know it's not

Despite insulating our place really well, we got a D rating on our EPC because our wood pellet boiler is automatically given some ridiculously low efficiency rating when we know that it is actually 92% or so! We would actually get a better rating if we reverted to burning heating oil!

Posted By: djhI think they were mostly conservation areas rather than national parks, but it may be worth considering an appeal.

We used to live in the Peak District National Park. Their planning guidance book (you certainly couldn't call it a booklet) was very comprehensive. Effectively they had invented something like a composite[ vernacular style and there was little if any leeway from that theme, even IIRC down to the finished colour of window frames. That was heading for 25 years ago and long before PV arrays were a consideration. Maybe things have changed, but I suspect not?

Posted By: skyewrightHowever a superlative EPC is possible.

Of course but that's part of the joke.

No criticism of Paul's house implied, BTW. All power to his elbow.

I can understand SAP giving a very bad rating for WBS as most people put too much wood in them, then overheat and have to open the windows. A heating system that costs a lot to use, when used by a normal person should get a poor rating.

A average British person should not need any training when they move into a property, in real life, at best the key is often handed over by a 21 year old that is very skilled in “sales” but having no understanding of anything more complex then the on/off switch (that we call a thermostat) that controls the heating system.

Well insulated, but LPG boiler to run underfloor heating (to be used when we can't do logs anymore) was our downfall. Never used it, just the small logburner to heat the whole house. Think we scraped a C.

Posted By: ringiI can understand SAP giving a very bad rating for WBS as most people put too much wood in them, then overheat and have to open the windows. A heating system that costs a lot to use, when used by a normal person should get a poor rating.

Well if we are going to rate things because they COULD be used badly then not only WBS should be penalised. I still know people that open the window rather than turn down the gas fued heating. I thought that SAP was all about a house's potential, not about the occupant behaviour.

I also don't know anyone that has to cut, lug and stack firewood that then burns it extravagently. My WBS running cost is £45 a year or so for the chimney sweep. The fire wood I gather for free rather than have it burnt on the hillside. It is a shame that SAP can't take those factors into account.

The silly thing with SAP is that you can insulate to passive house levels and beyond, i.e. build a house that does not need heating, but still be less than an "A". Or get an "A" with a house that consumes far more gas, oil or electricty off the grid. So "A" really doesn't tell you how a house performs even with normal lazy idiots living in it.

SAP = Standard Assessment Procedure
It is a yardstick for which all new dwellings are assessed. It is not aimed towards PH or passive house, but as a CO2 reduction tool for mainstream housing.

Specifically, WBS that can burn coal/smokeless are penalised, because the occupants 'might' burn mineral fuel one day, rather than cut/dry/store their logs.....
These are the rules.......

Posted By: djh

Posted By: skyewrightHowever a superlative EPC is possible.

Of course but that's part of the joke.

Indeed. One of the reasons that Paul's house has such an fantastic result will probably be that the software never expected to see anything like that!

No criticism of Paul's house implied, BTW. All power to his elbow.

Likewise.

To gravelld's comment:

"What does that mean in practice - higher assumed numbers for repeated thermal bridges etc, without the ability to override these assumptions?"

You can over-ride assumptions.

Repeating thermal bridges are taken account of in U-value calculations which are separate to the SAP, but used within it - and these can be varied to match whatever is actually being built; there are conventions for if you don't know, but these can be adjusted.

Non-repeating thermal bridges, i.e. Psi values for junctions are included in SAP and the defaults or Approved Detail values can also be accounted for.

There are an awful lot of potential thermal bridges now included in full SAP; I would say that you can take account of thermal bridging in SAP quite reasonably. The issue is more that PHPP and passivhaus encourages one to look at details with a better performance.

If anything, I would say that the SAP default allowance if you don't know what a thermal bridge is is on the low side.

Of course a key difference between Passivhaus and SAP is the method by which the thermal bridges are accounted for. Passivhaus I understand, uses external measurements for areas, so junction losses are accounted for by that. Whereas SAP works on internal measurements and then junction losses on top of the planar. Likewise when thermally modeling a junctions's losses Psi(external) is calculated differently to Psi(internal), so the same junction has different associated losses depending on how it is calculated - both are correct, but you need to be certain that you are entering the right thing in the right place.

I've thermally modeled junctions for both PHPP and SAP and you can have the same junction be negative for PHPP purposes, but positive for SAP purposes.

Not to be awkward but how are they different tools? I'm trying to educate myself, not question what you said.

Both measure heat loss.

Heat loss occurs via conduction, convection and radiation.

So it must be the algorithm or the assumptions that are different?

Does PHPP model 'normal' houses accurately?

The thermal models for my house were both very accurate and in concordance, heat loss in October 100W, Mike did one using TAS and Paul used the free one from Canada Hot 2000 now Hot 3000.