Help with SAP and Building Regs

[Andy Bee]

Hi All,

We are looking for some advice regarding the SAP calculations (part L), overheating calculations (part O) and Water efficiency calculations (part G) that our building control have asked us to provide.

This is our first time building a new house and we are building a 2-bed adapted bungalow for my disabled wife in Lancashire.

We had our building regs plans drawn up in May 2022 and the plans state a 100mm full fill cavity with Drytherm and we are thinking of changing the block and beam floor for the Litecast EPS floor system, so we are not sure if the plans are good enough to submit for SAP calculations.

We have been delayed from stating due to the local authority discharging planning conditions and then requiring ground gas monitoring which took 3 months to complete.

We can’t find on the net any criteria that is needed to get a pass on the SAP calculation so we don’t know if we will need to have new drawings done and whether we will have to plan to have solar and/or ground source heat pump installed.

We don’t want to install a lot of unnecessary additions to the house just for the sake of passing the new conditions for building regs.

We would appreciate any advice or recommendations to navigate through this minefield of building regs.

Many Thanks

[ProDave]

Are you employing an architect or other designer to specify the details of the building and get the building regs approval or are you doing it all yourself?

 

By far the best approach is insulate the hell out of the building and make it air tight.  If you are needing to add things like solar PV just to get a SAP pass, then the building itself is not really good enough.

[Andy Bee]

Hi ProDave,

We have had a set of building regs drawings done (attached).

We are not sure if they will pass the SAP calculations.

Many Thanks

D0156 - 202 - Proposed Elevations & Sections - BR_cropped.pdf

[DevilDamo]

Email what you have now to a SAP assessor, they’ll calculate it and tell you which areas need improving. But for starters, a 100mm cavity would not comply and that was been before the rules changed last year.

[Conor]

100mm cavity with 90mm insualtion is from the 1990s, it's not enough. Also some poor cold bridging details that will be a concern. Strange as they've got a decent 150mm.im.the floor and 400mm mineral wool in the loft.

 

Get a full heatloss model done now before you start. You certainly don't want to scrape through the assessment, you want to fly through.

[Dave Jones]

your drawings specs kooltherm sheets which will meet building regs. Expensive though and difficult to detail. May be worth moving to 150mm cavity and using full flil dritherm batts.

 

Typical with architects they have left your roof low so sorting the insulation and keeping air flow where the trusses travel over the wall will be difficult. you will not be able to fully fill this area as it will block air flow so will have a bad cold spot. A single block higher 225mm will let you do a much better job and give higher internal ceilings, does add some cost but worth it.