EPC Ratings

[Andehh]

Just looking for general advice!

 

We are at the foundation excavation stage of a 240sqm bungalow, after a last minute refurb --> rebuild change of plans (one of the builders had a cancellation & said he'd do a full rebuild for the price of our refurb if we fitted into his cancelled slot. He was our favoured builder by a decent chunk, so we were/are utterly delighted...but it has meant the architects & builder have had to work overtime in getting all the documentation sorted - hence adjusting insulation details after construction started)

 

As a result, we only recently received our draft SAP calculation of 81 - which I couldn't believe. This was with 125mm full fill cavities. 250mm Jetfloor + 150mm PIR below UFH and 125mm PIR in roof space, MVHR etc - not exactly bare minimum in my mind (though I acknowledge behind BuildHub norms of Passive House standards!!), but I was still very surprised to 'only' get 81.

 

Scores are: Ext Walls 0.22, Floor 0.17, Roof 0.18

 

Architects have gone away to try and get me a 10% improvement to bring it up to 88/89 (Ecology mortgage as a benchmark, though not using them). 

 

However - I looked up the 2019, 3 story, semi-detached naff Persimmon new build we are renting for the duration of the project & was horrified to see it at a 86 EPC rating. I don't quite understand how we are ''only'' at 81 in a £500k bespoke new build with (in my mind) good levels of insulation...yet a mass produced cheapie (£240k for 4 bed...) property in the same locality achieves 86.

 

Does the fact we are building a bungalow impact EPC? Are EPC & SAP the same to compared? How does 250mm jet floor + 150 PIR only get us 0.17!?

 

Hoping to be educated! 

Edited December 19, 2021 by Andehh

[ProDave]

The rental house EPC I would not trust as far as I could throw it.

 

Assuming a full SAP assesment of the new build, what air tightness have they assumed?  you want to be aiming to get the building as air tight as possible and then get an air tightness test done which will allow the real world figure to be used in the full SAP assesment to improve the rating.

 

Also windows and doors will make a difference as will proposed heating system.

 

I would be looking to improve the walls to get them down to perhaps the same as the floor and roof so perhaps 200mm cavity?

 

A bungalow will have a greater ratio of walls to volume than a house so will lose more heat than a 2 storey house of the same volume.

[nod]

The sap is only a number 

We where similar build to you 

Full fill 150 insulation 200 in the ground floor 

88

No PV No MVRH 

I was quite surprised when doing our Sap for our next build that adding MVRH actually brings your score down 

As did not having openers on some windows  type of heating Type of ASHP Lots of factors seem to effect a score 

[IanR]

Your EPC looks around about correct for the U Values. All need to improve.

 

The 250mm Jet floor is 250mm hollow-core concrete is, it not? so not helping with your U value. 150mm PIR on top is insufficient if you wish to build better than building regs.

Same for the roof 125mm PIR in the roof just isn't enough, (if you wish to build better than building regs.) 

As Dave says the walls also need improving, although on a bungalow I'd invest more into floor and roof.

[BadgerBadger]

Make sure you have specified an exact model for MVHR/ASHP/Hot Water Cylinder etc. so the assessor can use actual efficiencies instead of just the defaults.  Doing only this lifted our SAP score from mid-eighties to mid-nineties.

[ProDave]

It was going from the assumed air tightness to the actual air tightness that was largely responsible for lifting our design SAP from high 80's to mid 90's

[Mr Punter]

Airtightness, boiler controls, PV (should be good on a bungalow), accredited construction details all make a bit of difference.

 

Get Jet floor to spec the floor to the u value you would like and get the SAP guy to use their value.  If they won't / can, just use normal beam and block with a bit more PIR.  Will be cheaper.  Can you do ground bearing floor, or are conditions unsuitable?  Floor insulation is cheapest and easiest compared to wall and sloped roof.

[Andehh]

Thanks very much all, some great feedback there!

 

Am also concerned ASHP (architect & builder are grinding me down into accepting one over a gas boiler ? ) will reduce that score as well, but am led to believe ASHP will be 'for the greater good' then a Gas boiler even if the SAP score takes a nose dive.

 

Yes, this was only the first pass so will be looking to enhance floor & roof, the walls will be tricky as we are fitting in a lot of rooms into the footprint, so internal space is actually tight (4 kids to cater for). The ceilings on the other hand are very high throughout, so less worried about build up here.

 

The architect has stipulated a minimum of 5 for air tightness, but have read enough stories on here to know this is an area ill need to work with the builder on (and probably seek further advice here) on how to reduce this further.

 

Jetfloor is block & beam, but using EPS insulation instead of the concrete blocks. Builder said he would use the kind that 'wrap around' the beams, but this hasn't been written down anywhere so one i am monitoring.

 

Rest of the place is twin block wall, render outside (and some Z stone feature cladding).

 

edit: we have some PV, but some massive trees in the garden which cast some shade, so this has been down played on the EPCs. 

 

 

Edited December 19, 2021 by Andehh

[Marvin]

1 hour ago, ProDave said:

 

A bungalow will have a greater ratio of walls to volume than a house so will lose more heat than a 2 storey house of the same volume.

And the roof...  

[ProDave]

5 would be poor for air tightness, aim better than that.

 

The difference between a self builder and a mass builder, is the mass builder would look at the score and say "that's better than we need where can we save money" where as the self builders says "that is not as good as it can be how can I improve it"

[Buzz]

1 hour ago, Andehh said:

How does 250mm jet floor + 150 PIR only get us 0.17!?

It doesn't according to Kingspan , and that is straight onto concrete or B+B .

 

[Andehh]

Interesting! Thanks for that, something is wrong there then, as drawings state jetfloor with infill insulation & 150mm rigid insul to achieve! I'll need to investigate 

Edited December 19, 2021 by Andehh

[Buzz]

Your wall calculations appear to be out as well , as others have said if you can go for 150mm full fill this will bring u-values down to .17

 

[epsilonGreedy]

13 hours ago, Marvin said:

And the roof...  

 

And the floor.

 

To sum up a bungalow has a greater proportion of external surface area to floor space compared to a 2 or 3 storey cube shaped house.

Edited December 20, 2021 by epsilonGreedy

[Andehh]

Thanks all, would that reduce the SAP calculations as a result? Does sap equate for total sqm or only a sqm?

 

Could explain why the 3 story semi we are in now is massively better on paper. 

[Marvin]

45 minutes ago, Andehh said:

Could explain why the 3 story semi we are in now is massively better on paper. 

Partially, the shape makes a difference the nearer to a cube the better result (or a globe if you want to be padantic). But the calculations are based on many items including method  of heating.  We installed 200mm rigid insulation in the floor, 150 in the walls and 400 fluffy in the loft and a MVHR but had a very low rating because we had to use bottled gas for heating and hot water. Result EPC an F.

 

[Mr Punter]

40 minutes ago, Marvin said:

Partially, the shape makes a difference the nearer to a cube the better result (or a globe if you want to be padantic). But the calculations are based on many items including method  of heating.  We installed 200mm rigid insulation in the floor, 150 in the walls and 400 fluffy in the loft and a MVHR but had a very low rating because we had to use bottled gas for heating and hot water. Result EPC an F.

 

How did it pass SAP?

[Marvin]

58 minutes ago, Mr Punter said:

 

How did it pass SAP?

It has not been assessed because it was neither a conversion or new build but we had to have an EPC for the ASHP and PV. Needless to say the EPC failed the government PV scheme.

[Mr Punter]

7 minutes ago, Marvin said:

It has not been assessed because it was neither a conversion or new build but we had to have an EPC for the ASHP and PV. Needless to say the EPC failed the government PV scheme.

 

I have some flats with electrical resistance heating and hot water, solid uninsulated walls and single glazing and they achieved E.

[Mike]

11 minutes ago, Mr Punter said:

I have some flats with electrical resistance heating and hot water,

Yes, electric heating is heavily penalised at the moment. SAP is changing next year and under the new calculations it should come out better.

[Mr Punter]

Just now, Mike said:

Yes, electric heating is heavily penalised at the moment. SAP is changing next year and under the new calculations it should come out better.

 

My point was that they are uninsulated and still score better than @Marvin's place which is highly insulated.

[epsilonGreedy]

8 hours ago, Marvin said:

We installed 200mm rigid insulation in the floor, 150 in the walls and 400 fluffy in the loft and a MVHR but had a very low rating because we had to use bottled gas for heating and hot water. Result EPC an F.

 

 

I would ask for a refund or very detailed explanation of that assessment score, sounds odd to me. How does the property perform thermally speaking?

Edited December 20, 2021 by epsilonGreedy

[epsilonGreedy]

9 hours ago, Andehh said:

Could explain why the 3 story semi we are in now is massively better on paper. 

 

 

So-so wall u-value, a mis calc in the floor u-value and the thermally challenged shape of a bungalow.

[Marvin]

1 hour ago, epsilonGreedy said:

 

I would ask for a refund or very detailed explanation of that assessment score, sounds odd to me. How does the property perform thermally speaking?

The assessment score was discussed at great length. As soon as you mention LPG 47kg bottled gas you've had it. Worse than electric heaters as far as EPC concerned.

As for the thermal efficency, I think I wrote it up in my blog, but basically anything higher than about 8C and no heating required. Today no heating from 8am until 7pm and temp today about 8C.

 

[Mr Punter]

10 minutes ago, Marvin said:

Today no heating from 8am until 7pm and temp today about 8C

For clarity please confirm that was the external temperature!