PH adopts a whole building approach with defined measured targets and is focused on high-quality construction detailing and components. The following five basic design principles must be applied to the construction of all PH buildings to achieve the required targets.

1. High levels of thermal insulation. The external envelope must form a continuous insulation layer with a minimum U-value (thermal transmittance) of 0.15W/m2K to keep heat in.
2. Continuous airtight layer to building fabric. Keeping uncontrolled air leakage to a minimum of 0.6 ACH50 to create a comfortable environment that is easy to control.
3. High-performance Triple glazed windows. PH certified systems must be specified, with a minimum U-value of 0.8 W/m2K (0.85 W/m2K installed) and a g-value of 0.5 (50% total solar transmittance, available into room) to keep heat in and sound out.
4. Thermal bridge free construction. Careful detailed planning and construction of the building envelope is critical to avoid cold bridges and the opportunity for heat to escape.
5. Mechanical Ventilation with Heat Recovery (MVHR). PH certified MVHR systems are required to deliver consistent fresh air quality, efficiently and quietly.

A certified PHD has the skills and knowledge to competently design, plan and measure a PH to ensure the quality assurance required of the standard is delivered. They work with the Passive House Planning Package (PHPP), an accurate design modelling, energy-efficiency planning tool.

All PH buildings are planned and optimised using PHPP before being verified by a PH Certifier. There are a small number of qualified Certifiers in the UK approved to assess and issue the quality assured PH Certificate. Certifiers must be separate to the main design team and provide impartial verification.

PHDs can make several choices about where to invest attention and resource to improve building performance, before using PHPP to assess and fine tune the performance impact of these design decisions.

In addition to the 5 PH principles previously highlighted, a PHD should consider: the building orientation and glazing ratios to optimise solar gains; the building form factor to minimise surface area for heat loss; renewable energy generation where possible.

To create building envelopes that are exceptional at limiting the flow of heat and air leakage, a PHD is required to make subtle changes in design patterns, that often result in several architectural impacts.

• More compact designs to minimise surface area to volume ration (A/V), however this does not limit design to square boxes. Compact buildings tend to use less energy because of their reduced exposure to the outside and thus minimise heat loss.
• Include shading devices to protect from overheating, in the summer.
• Large glazing to south elevation (where possible) and moderate areas on elevations facing away from the sun.
• Limit structural penetrations for balconies and shading devices that form a cold bridge. Structural elements are best designed to be freestanding.
• Support natural ventilation. Yes, you can open the windows! Despite the use of MVHR, opening windows are an important part of the ventilation and overheating strategy. However, opening the windows at certain times will result in reduced building efficiency and increased running cost.

Image from: The Passivhaus Trust