SAP or PHPP?

SAP, or the Standard Assessment Procedure, is the Government methodology used in the Building Warrant / Building Control process to demonstrate compliance with the Technical Standards in Scotland, or Building Regulations in England, NI & Wales.

There are several key differences between the two methodologies in terms of the data entered and the consequential accuracy of the results: if you want to learn more about the differences, Passivhaus Certifiers Etude have created a tool to compare the two methodologies.

The Performance Gap

It is essential to realise that a building is much more than the sum of it's parts: at the core of the design of any passivhaus is the Passive House Planning Package. The PHPP software is a complex set of inter-related calculations laid out in a spreadsheet format, into which key information about the construction of the building and it's geographical location are entered. This then enables calculations to be performed which indicate how the building will perform in reality from an energy balance perspective. 

The PHPP has been developed over the last 30 years using data from monitored built examples in order to inform and improve the accuracy of the results. This ensures a level of accuracy in the energy balance that the PHI state is +/- 0.5kWh! Significantly this eliminates what is known as the ‘performance gap’ when the actual real-life energy usage is more than the predicted. Our own experience supports this: we have verified in our own projects that the actual energy usage is within 1-2% of the predicted, which is very accurate indeed.

It can also be a very useful design tool and should be used from an early stage in the design process to help establish certain key decisions, from the orientation and position of the building on the site to requirements for shading from the sun, all of which significantly effect the final performance and energy consumption of the building.