Passive House Design: Cool Temperate

Renovation Collaborative

Passive House design is different in every climate zone.

Over the next four podcast episodes, I talk to Passive House designers in the four Australian climate zones where most of our population lives, to discover the key differences.

Today I start with Passive House design for cool temperate climates like Canberra and Hobart. I talk to Michael Tolhurst, the director of award winning practice Envelope Architecture in Canberra.

Michael clearly explains the Passive House design specifics for cool temperate. Plus he shares heaps of other information and insights to help you better understand Passive House design

Australian Architects can claim formal CPD hours for these podcasts.

MORE INFORMATION

Find everything you need on the Renovation Collaborative website.

www.renovationcollaborative.com.au

• PODCAST Key points summary, timestamps and resource links
• FREE RESOURCES Transcript edited into clear Q&A.
• CPD Australian architects can find more information on CPD, and
• COURSES Eleven easy to read courses demystifying the entire home design and construction process.

KEY POINTS SUMMARY

1. Passive House design for cool temperate climates has a focus on warming. Of the four Australian climate zones accommodating most of our population, cool temperate is the most extreme. In Canberra, winters regularly go down to less than -5 degrees Celsius and in summer can reach the 40s.

2. Using a compact building form makes the Passive House standard much easier to achieve in more extreme climates like cool temperate. However, if you want a more linear form because of your site or to capture views etc. The PHPP tool can be used to determine building form alternatives and compensate for heat loss in other ways.

3. Windows are generally triple glazed. The window glass area reduces as the climate becomes colder to reduce heat loss. However, it's still critical to have opening windows in all habitable rooms to get cross ventilation when needed. And shading is still very important to prevent too much heat gain.

4. The fresh air circulation system is a HRV, which stands for Heat Recovery Ventilation System. The HRV provides a constant supply of filtered fresh air and incorporates a highly efficient heat exchanger to retain heat from inside the house. Some additional mechanical heating, usually from a reverse cycle air conditioner, is generally required.

As a side note, Michael clearly explains how Passive House heating is generated from three sources:

i) Solar heat gain,

ii) Internal gains from occupants, showering, cooking and equipment, etc.

iii) Mechanical heating.

The air tightness and insulation in a Passive House very efficiently retains the heat inside the house.

5. An internal air barrier is required in a cool temperate climate zone and this is in addition to the vapour permeable external membrane used for weatherproofing. Heat energy moves from warm to cold, so in a cool temperate climate this is generally from inside the house where it's warm, through the building envelope to outside the house where it's cool.

Moisture is created inside the house by breathing, showering and cooking, etc. An air barrier such as a membrane is installed on the inside face of the wall to prevent moisture laden warm air from moving through the wall structure. This eliminates the risk of condensation and mould growth within the wall.

A HRV system continuously extracts that stale humid air from spaces such as kitchen and laundry and bathrooms. Building elements and construction details that create thermal bridges are either designed out or analysed and modified if necessary to ensure that surface temperatures never drop so low that condensation can form.

And my final point,

6. Insulation is increased. The standard wall solution is a 140mm timber stud frame to allow for the increased width of an R4 wall batt. If you're using concrete floor slab construction, it requires continuous insulation to reduce heat losses to the ground, as well as to the slab edge. Depending on the engineering requirements and the preferred flooring finish, the insulation can be either below or above the slab.

And finally, additional insulation in the roof is required, creating a completely insulated envelope.

INTERVIEW QUESTIONS

00:00 Introduction

00:55 How did you start designing Passive Houses

03:35 What are the typical construction materials used in Canberra?

05:12 Do your clients come looking for Passive House or do you have to persuade them?

08:01 What is the cool temperate climate like and what are the design objectives?

10:57 Does Passive House design have to be a box form?

13:34 What are the window requirements in a Cool Temperate climate?

18:58 What window opening types do you use for Passive House?

21:35 Do you need window shading?

22:37 What sort of additional heating systems do you need?

25:43 Do you need an HRV or an ERV system?

32:42 What are the insulation requirements?

33:54 What are the thermal bridging requirements?

37:28 What are the building wrapping requirements?

39:59 Do your potential clients have any concerns about Passive House?

43:26 Are there any problems with the Passive House system?

46:12 Key Points Summary

IN THE NEXT EPISODE

Next week I'll be on holidays and hopefully so are you.

I'm taking a three week break in the podcast over Christmas and I'll be back on Tuesday 14th January 2025 and we'll get straight into Passive House design for a mild temperate climate zone.

I talk to one of the early Passive House designers in Australia, Andy Marlow from Envirotecture. Andy shares the climate specifics plus heaps of other insights to help you better understand Passive House design.

RESOURCE LINKS

Michael Tolhurst, Envelope Architecture, Canberra www.envelopearchitecture.com.au

Envelope Architecture Instagram www.instagram.com/narrabundahaus

Australian Passivhaus Association www.passivhausassociation.com.au/

Zehnder www.fantech.com.au

GET IN TOUCH

If you've got any comments or questions or there's any topic you'd like to know more about, please send me an email at [e-mail].