Part 3: The Details Behind Passive House (Passivhaus) Construction

19 May 2016 Brent Ackerman, Delta Project Management
Potton Elsworth Kitchen

What is the Passivhaus Standard?

There’s no specific way of constructing a Passive House (also known as Passivhaus in most of Europe), nor is there a requirement to build one using a particular construction method. Instead, the most important aspect is whether or not the performance criteria have been met.  

Potton are specialists in creating high-performance building envelopes using timber-based systems and as mentioned in Part 1: Building a Passive House (Passivhaus), we are building a Passivhaus show home to see just how far we can push the performance standard.

In Part 3 of the Passivhaus Design, we discuss Passivhaus construction details. In regards to which building materials to use, many Passivhaus homes around the world are built using timber-based systems, which is an obvious choice for the superstructure of this showhome. We chose to use the Kingspan TEK® Building System (structural insulated panels) as we have previously used this to construct hundreds of low-energy buildings and as a result, we understand its performance characteristics.

The system is ideal to use in projects which require low U values (heat transfer rating), as well as low and defined thermal bridging characteristics and excellent airtightness. It’s also certified by the Passivhaus Institute which, if nothing else, provides some comfort.

When developing the structure of a Passivhaus, the main challenges are:

1.  Ensure that it performs structurally well like any other property (i.e. it meets building regulations).
2. Ensure that the structural design is able to achieve the thermal and airtightness performance targets, as well as achieving them as simply as possible.

The Passivhaus Substructure

As with any property, work starts in the ground. Many or most Passivhaus buildings are constructed using a solid reinforced concrete raft that sits or floats on a bed of insulation. The Potton Passivhaus is no different in this regard, with a 225mm thick reinforced concrete raft which sits or ‘floats’ on a 250mm thick bed of insulation.

One of the challenges for our structural engineer was to ensure (for the simplicity of construction) that the raft was one thickness throughout. This enables the raft to provide sufficient resistance for the loads applied by the posts, frames and walls.

Most Passivhaus builds exclusively use lightweight cladding systems, which are carried by or fixed back to the building structure. One of the unique things about the Potton Passivhaus is that it uses masonry cladding in the form of Terca Megaline bricks from Wienerberger — the long, narrow format provides a contemporary appearance, but it is also a nod to traditional brickwork elevations of the vernacular.

To use the masonry cladding and not introduce any thermal bridging, this meant that we had to construct a separate foundation to carry the brickwork façade. This was a simple strip foundation, which is completely isolated from the main insulated raft.

Structural Insulated Panels (SIPs) Superstructure

Structural Insulated Panels groundfloor

Having sorted out the foundations and ground floor construction, we next turned our attention to the superstructure. As with all Potton projects, we design and build using the Kingspan TEK® Building System, which consists of 142mm or 172mm thick Structural Insulated Panels (SIPs), which are connected with a unique jointing system.

This system is typically used for the external walls and roof structure of buildings. We have combined the SIPs external walls and roof with open metal web floor joists, along with timber frame internal load-bearing and non-load-bearing walls.

Our walls are constructed using TEK 142mm panels with an external layer of Kingspan Kooltherm insulation to help achieve the required U value and there is also a 40mm service zone on the inside of the panel. The roof is constructed using TEK 172mm panels — this time with an internal layer of Kingspan Kooltherm insulation. We used the thicker panels for the roof because they are capable of spanning further without requiring additional support.

We then wrapped the entire structure externally using A Proctor Group’s Wraptite System, which is a self-adhesive, high-performance breathable membrane and air barrier combined in one.

The Kingspan TEK® Building System panels are manufactured using an almost unique continuous casting process, in which the two sheets of 15mm oriented strand board (OSB), that form the skins of the panel, are suspended apart from each other on a slow-moving production line.

The liquid mix for the rigid insulation core is introduced into the gap between the boards which fills in the space between. The whole panel then goes through a press that controls the thickness of the finished product and therefore its density, thermal and structural properties. At this point, the panels are then processed using a CNC router to create the shapes required for the design of the building.

The construction and manufacturing drawings for our Passivhaus have been developed using specialist 3D CAD software. This starts with the structural concept, checking the design will work within a Passivhaus environment, which then moves on to developing the detailed manufacturing design. These checks provide a useful opportunity to spot any last-minute issues and ensure that we end up with a structure that is as easy to build as possible.

Read Part 4: The Passivhaus Foundation

Potton Elsworth Show Home

Potton are specialists in the provision of high-performance building envelopes using timber-based systems and accordingly a timber system was an obvious choice for the superstructure of the showhome.

We chose the Kingspan TEK® Building System (more on this later), because we have used it to construct literally hundreds of low-energy buildings and understand, in some detail, its performance characteristics.

The system is ideal for use in projects which require low U values, low and defined thermal bridging characteristics and excellent airtightness. It’s also certified by the Passivhaus Institute which, if nothing else, provides some comfort.

When developing the structure of a Passivhaus, the main challenges are firstly to ensure that structurally it performs like any other property (i.e. it meets Building Regulations), and secondly to ensure that the structural design is both able to achieve the thermal and airtightness performance targets and makes achieving them as simple as possible (primarily because they’re pretty onerous in the first place).

Building a Passivhaus Show Home

A complete step by step guide, we take you through the story of building our Passivhaus show home. From the design process, constructing the superstructure, achieving airtightness right through to the finishing touches.
 

Download the guide here.

Building a Passivhaus Download
Potton Elsworth Passivhaus Show House

The Elsworth is open to the public

We have five self-build homes for you to browse, but the Elsworth is the UK's first permanent show home built to Passivhaus standard, created using our Kingspan TEK Building System. Come and experience the Elsworth show house for yourself.

Editor’s note: This blog post was updated in May 2019 for accuracy.

 

Potton

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