Tweaks on the way for SAP10.3

Just six months to wait until the new Part L (the Future Homes Standard) goes live in England.

Developers have two routes to compliance (SAP or HEM). There’s still uncertainty about the launch date for the Home Energy Model, but at least we can rely on SAP10.3, right?

Five changes to the new methodology are under review with a fix expected before the end of the year. In some cases, these changes could affect existing SAP10.3 results.

Existing SAP10.3 results could be impacted by these changes, which won't be implemented into the approved software until the end of 2026.

Here's what to look out for:

🏠 WINDOWS: The option to use BFRC certificates in SAP is being removed. This is to align with a paragraph in the new Part L that requires every window to have its own U-Value and g-value calculations.

BFRC calcs are based on a standard sized opening, which isn’t sufficient under the new requirements. Glazing suppliers will need to supply individual calculations.

That said, SAP Conventions still allow the assessor to enter average values. The ‘average’ will have to come from these bespoke calculations.

♨️ HEAT PUMPS: One of SAPs quirky calculations reduces the heat pump efficiency by up to 60% depending on the hot water cylinder set up. The actual and notional should apply the same reduction for a fair comparison, but this isn’t happening for all heat pumps, which is creating incorrect targets.

☀️ PV: Currently, SAP can only handle three PV arrays per dwelling. With FHS requiring higher levels of PV, many low-rise apartments will need solar panels on all four roof orientations.

SAP is being changed to allow as many different PV arrays as necessary.

🏙️ HEAT NETWORKS: If a dwelling is connected to a shared heating system, and that system isn’t listed on BRE’s database, SAP applies default system losses at 50%.

This is a ridiculously poor assumption for a newly installed, single building heating system. An ambient loop, for example, would only have losses around 5%.

The 50% default is staying for heat networks, but a lower default (to be confirmed) will be applied for single building systems, improving SAP results.

🖇️ CHI-VALUES: It’s a rare occurrence, but where you have steel rods puncturing the wall insulation, the SAP model should include point thermal bridge loss. These are also

known as chi- or χ-values.

Currently, if you apply a point thermal bridge, the notional copies the actual, so there’s no impact on SAP compliance. This is changing to remove chi-values from the notional. If any point bridges are applied, they will make the SAP performance worse.

Any SAP10.3 models that use BFRC data, or use particular heat pumps, or single building heating systems, or have more than three PV arrays, or have point thermal bridges, could see results change following this update.

Some of these changes will make results worse, others will make results better. The impact will vary site to site, with most SAPs not seeing any change at all.

I'll share more when the full details about the changes are released.