The following article contains excerpts, details and information from our book Understanding Passivhaus – The Simple Guide to Passivhaus Detailing and Design.
Passivhaus Cavity Wall Details
Understanding Passivhaus explores a number of different construction methods that can be used to build a Passivhaus. There is a common misconception that a Passivhaus must be a timber frame construction. This is not true, there are multiple examples of Passivhaus construction using methods ranging from masonry, steel, insulated concrete formwork, mixed timber and masonry and so on.
In this brief article we will explore some of the Passivhaus cavity wall details that can achieve Passivhaus standards. We will also look at some examples of Passivhaus buildings that have used masonry construction.
Masonry Construction for Passivhaus
In 2011 Green Building Store built the first masonry cavity wall Passivhaus in the UK. Although masonry construction is used in Passivhaus around Europe, it is often in the form of a solid masonry wall with external insulation and render or timber frame.
However, the UK has a long history of cavity wall construction and a workforce that is familiar with that method. Green Building Store set out to use a British construction methods, using materials that can be found at any local builders yard. Being able to successfully complete a Passivhaus using traditional local methods makes a Passivhaus a more feasible option for the UK market in terms of both cost and construction.
Masonry cavity construction is a flexible option, with external finishes of brick, render, stone finishes amongst others.
Considerations for Cavity Wall Passivhaus
When building a highly insulated structure using a cavity wall construction, there are a few factors that need to be considered.
The cavity will be wider than a standard cavity wall to allow for the high levels of insulation. Wall ties are thermal bridges and therefore specialist low thermal conductivity wall ties will need to be used to reduce thermal bridging.
The air barrier is formed using a wet plaster parge coat. This means that the junctions between walls, doors, windows, floors and so on, will need to be carefully managed to ensure the plaster coat maintains its airtightness. In other forms of construction an air tightness barrier is used with airtightness tapes.
You can find an excellent Technical Briefing of Golcar Passivhaus by Green Building Store over at their website:
https://www.greenbuildingstore.co.uk/technical-resource/golcar-passivhaus-cavity-wall-construction/
The Denby Dale Passivhaus by Green Building Store features in Understanding Passivhaus.
Examples of Passivhaus Cavity Wall Details
Examples of a Passivhaus cavity wall construction, foundation detail with beam and block floor.
Examples of Passivhaus cavity wall construction, window detail. 
Masonry cavity wall Passivhaus example of eaves detail
Examples of Passivhaus buildings using cavity wall construction
Parsons & Whittley Architects – Burnham Overy Staithe
This Passivhaus project features a brick and flint 300mm fully filled mineral wool cavity wall with aircrete internal block skin, a u-value of 0.096W/(m2K).
Rural Design – Portree, Isle of Skye
[photographs courtesy of https://portreepassivhaus.uk]
This Passivhaus project features an outer leaf of stone faced concrete blocks, a 375mm insulated cavity of Knauf DriTherm, and an internal leaf of 140mm concrete block.
Find Passivhaus Projects
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Have you had any experience of moisture migration across cavity with full fill insulation detailing – with pressures on NIA and Part L ramping up it is an attractive proposition to scrap the 50mm cavity. Due to problems with full fill cavity insulation, this approach has been banned in previous practices I have worked with.
A best practice is to use a surecav style system to the cavity to prevent moisture travel? Though natural stone companies specify this system to allow the stone to breath – contractors on site have never heard of the system. Building regulations too.
Shouldn’t you use a water repellent insulation type such as Polystyrene below DPC. To top the mineral wool from becoming saturated?
Are you wrapping the additional DPM up the inside face of the cavity from the B&B start because of the above? To stop saturated mineral wool insulation from dampening the blockwork indefinitely? Also no mention of the low thermal cavity wall ties spec in the text?