Diary Entry No.14 - The Wall Openings

After a slight delay, this week saw the installation of the windows and doors in the Crawfordsburn passive house. We have decided to use this diary entry to address how we’ve dealt with the window and door openings. In the next entry we will discuss the specific window and door units. We will include some photographs and detail drawings in this entry illustrating the design and installation of both the windows and doors. Achieving airtightness and minimal thermal bridging becomes a greater challenge when we have to address openings within the building envelope. To date we have spent a lot of time modelling and testing various detailing options for the window and door openings.

We modelled various permutations in house using our Passive House Planning Package software at design stage. This has enabled us to address issues of insulation, airtightness and thermal bridging. Translating these exact specifications and performance levels onto site is another challenge. For now we will discuss the four primary issues in more detail, discussing how we have tackled each.


The ‘futureproof’ triple glazed windows and doors that have been installed at the Crawfordsburn passive house have a whole unit U-value of 0.77Wm2K (and a glazing U-value of 0.6 Wm2K). The window and door units aren’t only triple glazed but they have low emissivity coatings and are 90% argon filled.


The timber frame came on site with each wall opening formed before the installation of the window and doors units. The window and door units were then screw fixed to this timber frame.

All junctions were taped using airtight foil type adhesive tape to ensure airtightness is maintained. This overcomes any differential movement between different materials which may be problematic for achieving airtightness.

Any gap between the window and door units and the frame was then permanently sealed with silicone to eradicate any other weak points in the openings.

Thermal bridging

The windows and doors in the Crawfordsburn passive house are also a source of solar energy to the passive house and constitute an important heat gain for the house. The aim is to gain the appropriate balance of heat loss and heat gain by having more south facing glazing and less north facing. The PHPP software will calculate the heat gain and warn against overheating in the summer months.

We can reduce the affects of thermal bridging by ensuring that the outside ‘cold’ elements are suitably insulated from the ‘warm’ side of the building.

The following diagrams illustrate the window and door opening details, starting with a section through a window opening.

Detail section window

Detail section window

The following illustrates the plan detail through a window/door opening in the Crawfordsburn passive house.

The following photographs illustrate the windows, doors and roof lights fully fitted.

Velux window installation

Velux window installation

The next diary entry will address the specifics of the window and door units. The performance of the units themselves, not just the installation, is crucial for meeting the required performance levels.