SBEM & SAP out of step with reality

[d000hg]

We're in the process of SBEM calculations and the fact we're using electric underfloor heating is hurting us because according to SBEM, electric is the worst way to provide heating.
Yet as our consultant tells us, UK now produces about 50% of electricity from renewables and this is only increasing... If you have gas heating it's fixed but electrical heating gets better as infrastructure becomes greener.

He advises SBEM is behind the times but should be updated at some point... has anyone else come up against this, did their consultants offer any useful advise?

 

[tony1851]

Are you required to produce calcs because of excessive glazing?
Rather than hurt your brain trying to come up with stupid thickenesses of PIR and shedloads of ££££s, use one of those assessors on the internet who 'guarantee' a pass.

You don't want to pay £150-200 or whatever for a piece of paper which says FAIL.
Over the years, I've used assessors who know which side their bread is buttered on and always - without exception - come up with a Pass
no matter how much glazing. Using approved private inspectors rather than LABC also helps.

These things are never checked by Building Control - they just file that piece of paper away and everyone's happy.
Don't spend your hard-earned in a futile attempt to save the planet while the Chinese are busy trashing it.

 

[d000hg]

Are you saying they'll lie? Or that they'll produce a spec that BC won't check too carefully?

We were recommended an SBEM guy who seems reasonable and trying to help, but as I understand it they all use the same iSBEM software do how can they guarantee it?
As well as testing everything against the regs minima it also takes into account your heating and hot water energy sources, and electric is rated the worst so everything needs to be more highly specced to compensate, because historically electricity came from coal and SBEM is really all about emissions.

In fact even insulating walls roof and floor, it STILL fails unless he includes a 5kw PV setup!

He mentioned that the SBEM parameters are due for review which should make electric more favourably viewed so I wondered if anyone else is in this position and how they handled it.

He did say BC might not check whether PV is installed but I can't see them not noticing insulation isn't installed when they inspect.

 

[tony1851]

Are you saying they'll lie? Or that they'll produce a spec that BC won't check too carefully?

Perish the thought

Is it a SBEM you need, or just a SAP?
With an SAP, the assessor inputs data about the existing house as well as the extension; insulation values about the existing house are taken from a list of default values depending on the age of the house. They also input areas of walls/roof/floors etc. They can be 'flexible' on these inputs if need be to get the result you need.
Be honest - do you really want to stick ££££'s worth of panels on the roof to produce enough to power the tumble drier on a warm sunny day
when you could use the washing line for free?
I know what I'd do....

 

[d000hg]

It's the SBEM we need as it's not a residential property, and it's a new detached structure, but I get the impression it works along the same lines as SAP. Ultimately all it cares about is the emissions due to the building, not the energy efficiency or energy use though of course those are the major factors.

Our building we've given him details of is just the wooden shell - a 11x7m garden shed effectively - so clearly not very efficient.
We're trying to get him to tell us the minimum we have to do for a pass so he's set it up and is trying different combinations of insulation thickness, etc etc. Start off with the obvious things like insulating floor and roof and go from there.

We're not particularly keen on PV, or at least not given the cost, but using renewables is a good way to 'game' the system because they only care about emissions. If you theoretically are generating all your own electricity there are none and it can be as inefficient as you want.

It's a shame insulation is so expensive. Couple of grand for 150mm PIR on the roof alone. Otherwise you could just go crazy with it.

 

[Leofric]

because they only care about emissions. If you theoretically are generating all your own electricity there are none and it can be as inefficient as you want.

really ​

Ultimately all it cares about is the emissions due to the building, not the energy efficiency or energy use

see comment above
Basically as Tony has said , energy rating consultants will advise what needs to be done to obtain a pass in a sensible way. The consultant would normally expect to be given more details of the building than just the shell to work from. You have to work to the rules as they stand now.

 

[d000hg]

Yes really. At least that's what multiple professionals have told me the principle is (subject to getting BC on other areas).

The guy put in typical insulation as a baseline but by default the software assumes the worst if you don't give exact specifications. As a new build we can give him arbitrary insulation to test but he's happy to work from a blank slate and run various permutations. So we're sourcing which products... Though they seem virtually identical in the .02-.022 range. IIRC the default in the software is .04 which presumably is based on glassfibre so choosing PIR will help.

He suggested we might delay/defer BR since SBEM is rumoured to be due to change, if our BC guy is amenable. I think he said he was going to ask whoever administers that (stroma?) to get an idea when it might be. If it's in a couple of months we could stall, if it's 6+ months then we'll have to work with current regs however daft they are.

 

[Leofric]

Yes really. At least that's what multiple professionals have told me the principle is

- energy rating consultants are concerned

with energy efficiency .​

it can be as inefficient as you want.

don't know what 'professionals' are telling you that

 

[d000hg]

- energy rating consultants are concerned

with energy efficiency .​

don't know what 'professionals' are telling you that

They're concerned with energy efficiency and energy usage as far as it affects emissions and EPC. Hence the exact same setup can pass with has heating but fail with electric, but pass with electric if you install PV.

Conversely residential EPC is actually based on energy COST not kWH or emissions. All these things are based on some metric or other which means you can sometimes play the letter rather than the intent of the rules.

 

[Leofric]

They're concerned with energy efficiency and energy usage

Exactly, therefore -

it can be as inefficient as you want.

- isn't correct.

Conversely residential EPC is actually based on energy COST not kWH or emissions. All these things are based on some metric or other which means you can sometimes play the letter rather than the intent of the rules.

what was the original question

 

[Leofric]

Quote ' SBEM is the Simplified Building Energy Model. This is a government approved methodology which is used to calculate the energy required to heat, cool, ventilate and light a non-residential building over a 12 month period when used under ‘normal” circumstances.
The amount of carbon dioxide the building emits is also calculated, before then assigning the building a numerical rating.'

 

[d000hg]

I don't think my building will emit any carbon dioxide, other than from people inside breathing! Well, or it's on fire.