Passivhaus Affiliate

Ostro 'box in a box' receives Passivhaus certification

Ostro Passivhaus once certified

In March 2014, owner and architect Mhairi & her partner Martin, from PHT member Paper Igloo Ltd, engaged in an ambitious self-build project in the historical conservation village of Kippen, near Stirling, Scotland. The 'box in a box' timber frame home received certification in October 2017 becoming the first certified Passivhaus in Stirlingshire. It has also achieved Scottish Technical Standards Section 7: Sustainability Gold Level.

The house takes the form of a Siberian larch-clad box with a flat felt roof system incorporating a Sedum green roof and a dramatic south-facing double height space.

The orientation and balanced proportion of windows both maximise the views and minimise the risk of overheating in the summer months. The windows are all triple-glazed and the doors aluminium-insulated. The timber frame twin wall features a continuous thermal break and external layer and is totally insulated with wood fibre. The house also features renewables such as solar and PV panels.

Ostro Passivhaus kitchen


Energy Performance 

Corner of the contemporary Ostro Passivhaus



Thermal Energy Demand (≤15kWh/m².yr)


Thermal Energy Load (≤10W/m²)


Primary E Demand (≤120kWh/m².yr)


Being their first Passivhaus project and having the additional challenge of incorporating elements such a double-height into the design, the owners hadn’t set themselves an easy task, but they were driven by both personal and professional motives. Not only were they enthused by the idea of living in a contemporary passivhaus, but they also wanted to showcase the Standard to their future clients.


Ostro Passivhaus


As co-owners of an architectural practice specialising in low energy buildings it seemed the logical choice when we chose to build ourselves a new home, given the proven levels of comfort and consistent performance achieved generally by buildings that meet the Passivhaus Standard.”  

Martin McCrae and Mhairi Grant, Paper Igloo Ltd



Alu-clad window on the Ostro Passivhaus

Key Stats

Number of Occupants: 3
Treated Floor Area: 170m²
Construction: Timber Frame
Project Cost: £250, 000
Unit cost per m²: £1470 (relative to TFA)
Construction Start Date: March 2014
Certification Date: October 2017


We achieved excellent airtightness in both the tests, and the compact design of the services such as the MVHR and pipework has enabled these components to perform efficiently. We gave considerable time and effort to ensure a high attention to detail throughout. Yes, all of these aspects have been and will continue to be carried forward in our future projects.” 

Mhairi Grant, Paper Igloo Ltd



Project Owner/Client: Martin McCrae & Mhairi Grant
Architect: Mhairi Grant, Paper Igloo Ltd
MVHR design/commissioning: Paul Heat Recovery
Fire supression design/installation: Aquablaze
Structural Engineer: Clyde Design Partnership
Certifier: Cocreate Consulting (now moved to Etude)

Ostro Passivhaus is now certfied


Further information

Previous PHT story: Ostro Passivhaus currently under construction - 11 June 2014

Paper Igloo blog documenting the Ostro Passivhaus construction.

All images ©Paper Igloo Ltd

24th September 2018

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