SAP Calculations Question

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We've had our small simple extension conditionally approved by building control, but they have said they want to see SAP calculations to show compliance with L1B as we have over 25% glazing. Extension is 8 x 3 m with two roof lanterns, two sets of bifolds and a side glazed door/wall. We live with trees around the property and want as much light as possible.

I've used the following https://www.charnwood.gov.uk/files/...e_calculator_2010/L1b_Calculator_1.3_2010.xls to get the calc numbers and I can't get the new extension to comply, however, the extension is replacing an old unheated conservatory. Should this be included in the windows and doors being replaced/removed calculation? If so this would make it compliant - the new extension will be way warmer than the current conservatory!

Reading the regs it states:
"4.2: limit the total area of windows, roof windows and doors so that it does not exceed the SUM of:
a. 25 % of the floor area:
b. the total area of any windows or doors which as a result of the extension works, no longer exist or are no longer exposed."

To me that seems to imply I could use the existing conservatory in my calculations, yes?


If not, then I think I'm looking to get a SAP engineer to also generate the calculations for me, but (as expected) they won't be compliant, what does this mean? Will the SAP engineer just say increase the rest of the house insulation etc. which will allow the extension to then be compliant?

If we choose to replace the glazed side of the extension with brick, will we have to submit a whole new Building Regs drawings and application or can we just let BCA know that that is what we will do to be compliant?

Thanks, sorry for so many questions.
 
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If the conservatory was separated from the house with external-grade doors, it's unlikely b/control would let you count the additional glazed area.
From how you describe the design, it's probably unlikely that you could add compensating insulation in the new build to comply (even adding extra insulation in a new wall is subject to the law of diminishing returns).

Probably the only course is to speak with an energy assessor. However, as you will be paying the assessor, its important that you instruct him/her that you want a pass result with the minimum of insulation added elsewere. From experience, I'd say that the building inspector is very unlikely to actually sit down and go through the figures.

A little creativity with the figures works wonders; why pay ££££s to save the planet when China couldn't care less?
 
We've had our small simple extension conditionally approved by building control, but they have said they want to see SAP calculations to show compliance with L1B as we have over 25% glazing. Extension is 8 x 3 m with two roof lanterns, two sets of bifolds and a side glazed door/wall. We live with trees around the property and want as much light as possible.

I've used the following https://www.charnwood.gov.uk/files/...e_calculator_2010/L1b_Calculator_1.3_2010.xls to get the calc numbers and I can't get the new extension to comply, however, the extension is replacing an old unheated conservatory. Should this be included in the windows and doors being replaced/removed calculation? If so this would make it compliant - the new extension will be way warmer than the current conservatory!

Reading the regs it states:
"4.2: limit the total area of windows, roof windows and doors so that it does not exceed the SUM of:
a. 25 % of the floor area:
b. the total area of any windows or doors which as a result of the extension works, no longer exist or are no longer exposed."

To me that seems to imply I could use the existing conservatory in my calculations, yes?


If not, then I think I'm looking to get a SAP engineer to also generate the calculations for me, but (as expected) they won't be compliant, what does this mean? Will the SAP engineer just say increase the rest of the house insulation etc. which will allow the extension to then be compliant?

If we choose to replace the glazed side of the extension with brick, will we have to submit a whole new Building Regs drawings and application or can we just let BCA know that that is what we will do to be compliant?

Thanks, sorry for so many questions.

if there was a door or window between conservatory and house -then if that was a single glazed or old double glazed, you can use that as an improvement

also you can include any energy efficiency improvement on the house done sort of recently and include those in the SAPS (new GCH boiler, new windows, doors, CWI etc)

and you know when you were doing the extension, you decided to replace all the old tungsten filament light bulbs in the house and halogen downlighters with LED.....


TBH Im surprised you were allowed to build without having the SAPS done first -BC often want to see the calcs first before work starts -it avoids any pain for the householder later on
 
I wonder if you had no loft insulation (maybe previous owners never added any, or, it was removed for some unknown reason), whether adding some to the loft would elevate the SAP calculation in your favour
 
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Thanks all.

So, firstly to clarify, nothing is built yet. I'm still at the planning stages. Building reg plans and approval was (I thought) the last step before getting the builders in! The SAPs calculation is a condition of the approval of the building regs plans.

Secondly, the door to the conservatory is a very old metal framed sliding door with only a single pane of safety glass. It also doesn't have a lock on it, so it's definitely not exterior grade.

Based on that and from what you've all said it sounds like I could possibly use the removal of the conservatory to get the extension to be compliant. I think I'll submit a carefully worded mail to BCA to explain this with the calcs and see if they allow it.

If not then I'll have to get a SAP report with the additional suggestions - extra insulation in the main house, led bulbs (even though I 've already done this!) We're looking to update the 25 year old double glazing of the main house as part of this building works anyway, as well as have solar panels, but obviously this won't be included in the extension plans so I assume can't be used in the calcs.
 
That calculator isn't the best tool for what you need to produce, what you need is a whole house sap. You produce one with a 25% extension and one with whatever your glazing percentage is - 30%, 35%, etc. You then tweak any values that can be easily upgraded (in the whole house) until the result is comparable. In other words, having an extension with 40% glazing must be no worse overall than an extension with 25% glazing. It doesn't usually take much because you aren't finding replacement values for the whole thing - just for the additional glazing area.

My advice is get it done. There are plenty online and it's not usually expensive. pm me if you want a recommendation.
 
I assume you have gone triple glazing for everything? I don't know how long you have left to live but I expect energy prices to rise considerably in the future so you will pay one way or another!
 
Just to follow up on this, in case it helps anyone else.

I used the Excel sheet from here: https://www.charnwood.gov.uk/files/...e_calculator_2010/L1b_Calculator_1.3_2010.xls
I included the conservatory as being part of the existing glazing that was being removed in the calculation and submitted the output to the local BC.
Within 24 hours they came back to say all conditions had been met and the plans were now fully approved!! Happy days!
 

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