Explaining Passivhaus to your Client.

It’s all about Comfort really.

That’s where it all starts – comfort for the end-user. Passivhaus seems quite mythical when it’s not understood properly. It is a simple principle that looks to assist the end-user in living life comfortably.

As designers, understanding this concept of providing comfort influences our design choices, in accordance with our clients’ requirements.

Why Passivhaus?

Living in a Passivhaus means that we can live in our homes and buildings comfortably without; draughts causing a chill, overheating causing headaches, cold spots in the building fabric meaning we cant put the sofa under that window, and breathe in fresh clean air even in polluted environments. Not to mention the incredible economic savings on spiraling energy bills.

In addition to the above, Passivhaus addresses the performance gap the construction industry is notoriously associated with, outperforming government regulations and providing a quality assurance that is recognised globally.

What is Passivhaus?

As defined by the Passivhaus Trust,

A Passivhaus is a building, in which thermal comfort can be provided solely by heating or cooling of the fresh airflow (without using recirculation), which is required for good indoor air quality.

How is it Achieved?

To make the above happen, Passivhaus employs the following pillars. The first four pillars are comfort driven, while the last two relate to the energy necessities. We will look broadly at the comfort pillars and performance requirements in this post and the energy pillars in another post.

Insulation: Higher levels of insulation in a continuous layer means reducing heat loss through the fabric of the building. This must include eliminating thermal bridges often found at roof/wall, wall/floor junctions.

Building Regulation Requirement: U-Value=0.20-0.30W/m2K

Passivhaus Requirement: U-Value=0.10-0.15W/m2K

Windows: Windows form part of the building fabric, and now that we’ve gone through the effort of making our walls warm, it is important that poor performing windows do not compromise this warm fabric. Triple-glazed windows are often used to maintain the integrity of the fabric by reducing heat loss, but their frames are usually highly insulated to assist. This means we can through the radiator out and can put our couch under that window without experiencing draughts.

Building Regulation Requirement: U-Value=2.0W/m2K

Passivhaus Requirement: U-Value=0.8W/m2K

Airtightness: Increasing airtightness levels means that the path that air finds, through the gaps in the fabric of the building, to escape is minimised. In many of the buildings we live, we pay hard-earned money to heat our buildings, only to see the £’s leak through our walls, roofs and floors.

Building Regulation Requirement: 10m3/m2/hr

Passivhaus Requirement: 0.6ach @ 50Pa

(this standard is at least 10 times tighter than Building regulations)

Ventilation: Once we have created airtight construction to reduce the leakiness of our building, we need to ensure that the building is being supplied with fresh air while removing the stale air we have used. This is usually done with a mechanical ventilation system with heat recovery (MVHR).

Passivhaus Requirement: 30m3/hr.person

As highlighted, the Passivhaus also include energy requirements (heating and primary energy), which will be explored in another post.

Your client will be hard-pressed not to see the benefits of the above. And the biggest client challenge so far, cost, is worth discussing with capital costs of passivhaus ranging between 3-8% above standard construction costs, but, also competing with standard construction costs in some cases (for example, Architype who designed and delivered the Wolverhampton Passivhaus schools at no extra cost), this issue can be a dying conversation in the future. It is always worth prioritizing value over cost.

As designers, while we cannot control heat gains such as solar gains and internal gains through occupation, however, we are able to influence the heat losses through fabric (walls, roofs, floors, windows) and air movement (ventilation and infiltration).

Passivhaus is worth exploring deeper and we aim to that in the next blog!

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