Green Building Forum - The devil is in the detail. Tue, 19 Dec 2023 05:31:57 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247525#Comment_247525 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247525#Comment_247525 Sat, 24 Sep 2016 21:33:27 +0100 numenius
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?]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247532#Comment_247532 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247532#Comment_247532 Sat, 24 Sep 2016 22:15:17 +0100 tony The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247533#Comment_247533 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247533#Comment_247533 Sat, 24 Sep 2016 22:18:48 +0100 djh 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 :bigsmile:

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 :cry:]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247534#Comment_247534 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247534#Comment_247534 Sat, 24 Sep 2016 22:25:58 +0100 djh
Recommended measures Indicative cost Typical savings over 3 years
Solar water heating £4,000 - £6,000 £147

We already use PV to heat the water, so fitting 'solar water heating' is in addition to that!]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247537#Comment_247537 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247537#Comment_247537 Sat, 24 Sep 2016 23:20:55 +0100 Jeff B The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247542#Comment_247542 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247542#Comment_247542 Sun, 25 Sep 2016 08:23:30 +0100 Greenfish Came out as a B, I was so disappointed, I understand your feelings totaly. When I asked the assessor said the only way to improve our well insulated etc. build would be to add a gas combi-boiler (despite no gas supply) or maybe some additional isolated solar thermal. We have WBS, solar thermal and PV into a thermal store, so the ST is not considered to supply DWH even though it does. And the WBS is automatically given a low efficiency despite being certified as far better (and in practice too).

Rant for a while about the silliness of it all, then sit back and feel proud of the excellent house you know you have built.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247547#Comment_247547 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247547#Comment_247547 Sun, 25 Sep 2016 14:42:28 +0100 skyewright 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?]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247548#Comment_247548 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247548#Comment_247548 Sun, 25 Sep 2016 14:48:57 +0100 skyewright Posted By: djh
we came out at 82

Well done, our EPC grandly states 78
We're expecting to be certified as a passivhaus quite soon
Sure EPC is a farce.

However a superlative EPC is possible. camillitech's 'as built' EPC can be seen on Navitron:

http://www.navitron.org.uk/forum/index.php/topic,26621.msg312934.html#msg312934

The scores are:

132 for Energy Efficiency Rating (current & potential)

130 for Environmental Impact Rating (current & potential)

And that's an 'all electric' house! He does have the advantage of his own renewable electricity generation from
wind, hydro and solar (and a 60 tube solar thermal array).

I wonder if 132/130 is some sort of a record?]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247550#Comment_247550 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247550#Comment_247550 Sun, 25 Sep 2016 15:22:07 +0100 djh 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.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247551#Comment_247551 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247551#Comment_247551 Sun, 25 Sep 2016 16:49:06 +0100 owlman As It was I couldn't be bothered, and left it as a 61,"D". If I'd been prepared to spend £15-25k on a wind generator I could have had a score of 92.
All that with no alteration to the airtightness of the house. I can't see the point of the EPC in it's present configuration.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247553#Comment_247553 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247553#Comment_247553 Sun, 25 Sep 2016 19:37:08 +0100 ringi
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.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247565#Comment_247565 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247565#Comment_247565 Mon, 26 Sep 2016 10:19:37 +0100 Sigaldry
GIGO. Garbage in = Garbage out. If your assessor doesn't put the information in correctly, you'll get a wrong result.

You can overwrite efficiencies with actual tested performance if evidence is provided.

For any electric heating system, we still make electricity in this country expensively and dirtily and whilst an individual may well 'buy in' energy from renewables, there's no guarantee that if you sold it, the next occupant will. As the grid decarbonizes, the Environmental Impact rating will get better for such homes. If electricity becomes cheaper, then the SAP rating will likely improve too.

A tested heat pump that is in the database can come out reasonably due to a good coefficient of performance, but will achieve at best about the same as, or slightly better than a good gas boiler - purely down to comparative fuel costs and emissions associated with them.

(and LPG and oil also come out fairly badly).

The only real way to get above a B is to have a really low demand (insulate/airtightness/good detailing); service that demand in a cheap way (ideally also low carbon) and to generate power.


As I understand it, RDSAP is all about what you can prove - Evidence being key. There are also a lot fewer options for data entry than in full SAP.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247566#Comment_247566 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247566#Comment_247566 Mon, 26 Sep 2016 10:26:31 +0100 dickster The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247567#Comment_247567 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247567#Comment_247567 Mon, 26 Sep 2016 10:39:45 +0100 Sigaldry
While it can't account for all the non-standard combinations, it can do a lot - and if you can't get your particular setup properly entered, you can email the SAP team at the BRE, who are usually able to advise your assessor of a means of entering it for the short term and they can use the feedback for the next version to increase the options for assessors.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247571#Comment_247571 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247571#Comment_247571 Mon, 26 Sep 2016 11:16:03 +0100 Greenfish 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.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247577#Comment_247577 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247577#Comment_247577 Mon, 26 Sep 2016 13:03:33 +0100 gyrogear Posted By: GreenfishI thought that SAP was all about a house's potential, not about the occupant behaviour.

+1.

I don't think that anybody can predict occupant behaviour (any more than driver behaviour !)
(Most human beans *I* know are entirely unpredictable...)
(if they were not, they would not be as interesting - who wants to associate with robots !)
:devil:
gg]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247580#Comment_247580 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247580#Comment_247580 Mon, 26 Sep 2016 13:26:44 +0100 DarylP 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.....:bigsmile:
These are the rules.......]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247581#Comment_247581 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247581#Comment_247581 Mon, 26 Sep 2016 13:33:38 +0100 gravelld
What does that mean in practice - higher assumed numbers for repeated thermal bridges etc, without the ability to override these assumptions?]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247583#Comment_247583 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247583#Comment_247583 Mon, 26 Sep 2016 14:12:46 +0100 skyewright 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.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247584#Comment_247584 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247584#Comment_247584 Mon, 26 Sep 2016 14:19:18 +0100 ringi
Therefore the average new build detached homes will be much worse then the average build last year. So a self builder creating a detached house that rates close to what a new build flat does, is doing a lot better the most mass market developers.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247588#Comment_247588 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247588#Comment_247588 Mon, 26 Sep 2016 14:59:03 +0100 Sigaldry
"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.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247597#Comment_247597 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247597#Comment_247597 Mon, 26 Sep 2016 16:44:07 +0100 DarylP But a comparison with PHPP is not possible, they are two different tools.]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247613#Comment_247613 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247613#Comment_247613 Mon, 26 Sep 2016 21:04:47 +0100 gravelld
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 devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247618#Comment_247618 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247618#Comment_247618 Tue, 27 Sep 2016 07:13:13 +0100 DarylP Both systems have to assume an occupancy model, whether anyone lives to that 'model' or not is up to question.:bigsmile:]]> The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247619#Comment_247619 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=247619#Comment_247619 Tue, 27 Sep 2016 08:03:22 +0100 tony The devil is in the detail. http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=248136#Comment_248136 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14562&Focus=248136#Comment_248136 Sun, 09 Oct 2016 14:29:55 +0100 numenius