SAP - carbon emissions

[Omi]

Hello,

 

We're preparing the SAP assessment for submission to building control and have been told that we are failing the carbon emissions target by a small margin. The assessor apparently cannot pinpoint the exact reason but has suggested adding on a 1kW PV system to compensate.

 

I'm finding it hard to believe that nothing can be changed in the house design itself to meet the target. While I wait for the draft calculations to take a look myself, what are the typical factors that affect carbon emission and the strategies to deal with them?

 

Thanks!

[A_L]

Hello,

 

1) Are you using default values for thermal bridges?

 

2) What ventilation rate have you assumed?

[nod]

Ours was quite Anal when it came to the final Sap He also included PV But we chose not to install it He wouldn’t budge on this So we used one of the online Sap companies Cheaper and no hassle 

[Omi]

@A_L - it's the timber frame company that's dealing with the SAP assessor so we don't have direct contact. I've asked for the draft calculations so that I can see what has been assumed but haven't got it yet.

 

@nod - it's part of the building warrant package that we get from the timber frame supplier so we're not engaging/paying directly.

[SteamyTea]

There is probably a way around it, an extra 50mm insulation for the floor.

But why would you not put in PV at the build stage?

[Omi]

@SteamyTea - our budget is already overstretched so trying to avoid adding on further cost as much as possible. The ground floor area is roughly 110 m2. Would additional floor insulation end up costing more than a 1kW PV system?

[saveasteading]

The SAP assessment programme is rather unrealistic. It also used to have some errors, such as extra insulation sometimes making it worse, and there were some boxes to tick that no-one quite understood. Perhaps improved now.

Your assessor can only do so much within the parameters, and so needs a change from you.

 

If you are looking for such a small improvement then I agree that you could agree to add PV. Then fit it when budget allows, or you have chosen the ideal supplier with due care over the next year or so. It is getting cheaper and better so no harm in taking your time.

[SteamyTea]

1 minute ago, Omi said:

The ground floor area is roughly 110 m2. Would additional floor insulation end up costing more than a 1kW PV system?

Hard to say.

Depends on the floor construction.

You may find that using a roof integrated PV system costs about the same as a traditional roof. Just keep an eye out for bargains, it is very easy to overpay.

 

Insulation and airtightness (and cold bridging) is more than just passing SAP.

You have to look into the way they interact with each other. Why a condensation risk analysis is done.

 

Regarding the budget, you may have to swap some 'nice to have' to 'perfectly adequate', kitchen and bathrooms being the main ones. These, like cars, can be easily changed at a later date, and like cars, they are functional items, not artwork.

[Omi]

21 minutes ago, SteamyTea said:

Regarding the budget, you may have to swap some 'nice to have' to 'perfectly adequate', kitchen and bathrooms being the main ones. These, like cars, can be easily changed at a later date, and like cars, they are functional items, not artwork.

 

Sadly we're already there - getting services in cost us around £23k more than we had anticipated ...

[nod]

2 hours ago, Omi said:

@SteamyTea - our budget is already overstretched so trying to avoid adding on further cost as much as possible. The ground floor area is roughly 110 m2. Would additional floor insulation end up costing more than a 1kW PV system?

More floor insulation would cost less than PV

and at least you will get some benefit from upgrading your floor insulation 

[SteamyTea]

1 hour ago, Omi said:

getting services in cost us around £23k more than we had anticipated

Ouch.

 

I would have gone 'off grid'.

At todays prices (around 60p/litre), that would have bought about 400 MWh of diesel.

I use about 4 MWh/year.

[Omi]

Problem averted - apparently the efficiency of the ASHP was not factored in. With that included, it's now passing with "flying colours"... apparently...

 

Many thanks for the suggestions nevertheless.