The Passive House Conference – personal impressions

As a lay person, attending the Passive House Conference in Christchurch was a daunting prospect. After all, the Passive House system relies heavily on data, modelling and real science (yes physics!), an approach which is hard for me to get my intuitive and non-scientific brain around. However, the weekend was fascinating and I came away feeling energized by the breadth of knowledge, experience and enthusiasm on display.

So that this blog post doesn’t turn into a snore fest, here are some brief impressions and standouts gained from the talks and from, well, just being with people who are passionate about raising the housing/construction bar.

The visit to a certified Passive House under construction in St Martins offered the physical experience of looking into what goes into making a house Passive. I guess it boils down to three elements; PH certified windows (the certified windows used in this house were produced by Thermadura in Mosgiel), a mechanical heat recovery unit and a well-insulated building envelope (prefabricated panels by Theca) designed to eliminate thermal breaks. Even though this house is still in the construction phase, talking to the owner, one could sense his excitement. Because the panels were constructed off-site, the shell of the house went up very quickly. (Post script, this house has just been certified Passive House+ – the first in the South Island.)

I only attended one day of the conference so I can’t comment on Saturday’s talks however the various speakers on the Sunday looked at the Passive House system from a variety of experiences. Andrew Michler in his talk, The Passive Insurgency, encouraged us to become Passive Jedis – to take the message of fabric first to the public. As he says, the stories behind these builds are exciting and energizing. His own story, building the first certified Passive House in Colorado (using basic materials with minimal toxicity in an area which has very harsh winters), is inspiring. However, he impressed upon us the urgency of this insurgency. Incrementalism is no longer an option if carbon emissions are to be reduced to a level that sustains life as we know it on this planet. Given that building/construction is the largest carbon producer in the world, it is important that buildings are built for longevity. It accounts for 40-50% of carbon emissions both in the construction phase and during occupation (building usage).

Enrico Bonilauri spoke of a Passive House EnerPhit (retrofitting an existing building to a slightly different standard) in Italy. Italians by and large do not see their houses as ‘cash cows’. Rather, the average Italian house changes ownership roughly every 50 years. That factor, coupled with an ability to deduct the cost of carbon emission remediation against income tax, made the masonry retrofit (built in 1962) of a “tough guy with weak ankles” (the structure was sitting on walls one brick thick) an economic proposition over the life of the building. The owners of this building will be able to claim roughly 100k euros in income tax deductions over the next ten years. This has made the baseline budget of 225k euros easier to swallow.

Enrico made the point that if you build or retrofit a house to a low standard, you are locking in energy inefficiency for decades to come.

Jessica Grove-Smith from the Passive House Institute in Germany echoed Enrico’s call for standardizing componentry and working to improve existing housing stock. To this end, the Institute have developed the EnerPHit standard for existing houses, Passive Haus Plus and Passive Haus Premium which include points for using renewables and low energy materials.

Jessica talked about having a strategy at the beginning of the building project deciding whether to do it all at once or carrying out the retrofit in phases. The Institute, while maintaining rigorous standards for the Passive House system recognises that in many areas where there is limited availability of certified componentry or small houses in shaded or cold locations, Passive House certification can be hard to achieve resulting in many “near misses”. They are currently working on how to mitigate this issue with the various Passive House branches around the world.

Barry McCarron’s talk moved away from the domestic to talk about CREST – the Centre for Renewable Energy and Sustainable Technologies in Northern Ireland. This building has met not only the Passive House standard but also the BREEAM Excellent and Net Carbon Zero certifications. As Barry says “The CREST pavilion building has the purpose of being a demonstration building for pioneering design principals and construction methods. It is an exemplar for other construction schemes”. Barry did make the point that it is important when building on this scale that a contractor who has had previous PH experience is hired and this was a challenge for the project.

What impressed me on the day I spent ingesting what I could about Passive House, is that this is not a system which is just for the domestic market. Schools, offices and public buildings could/should all be built to PH as a standard. Schools especially would benefit long term from having minimal energy costs especially over the winter period. The first thing that strikes you when you walk into a Passive House is just how good the air quality is. There are no marginal rooms, cold patches or stuffy areas. One can’t help but feel that this element alone could do wonders for student concentration in schools. That would be such an interesting study to undertake……

For those of you interested in experiencing just how good Passive Houses are, there are often open days held around the country. Check out www.phinz.org.nz for details.

Overview

• Passive House (PH) is a tried and true performance standard for building extremely low energy buildings.
• The up-front costs are easily absorbed over the life time of the building because expensive plant is significantly reduced and does not require as much maintenance / replacement.
• Many parts of Europe have a requirement for all their social housing & public buildings to be PH standard.
• The PH system is most beneficial to those in our community who are struggling to pay for heating.
• Through the PH Planning Package software building performance is guaranteed.
• PH buildings are very comfortable and quiet with good air quality and high occupant satisfaction.

Benefits for social housing providers

• Social housing providers would be showing leadership in building design.
• A PH building would provide an excellent learning opportunity for other providers to learn about PH.
• Tenants who currently cannot afford heating would be able to do so because heating bills would typically be less than one fifth or less compared with a typical Code built house.
• For those tenants who are not heating their homes, the PH system would still provide a healthy home.
• Because of the high surface temperatures achieved in PH homes it is not possible for black mould to grow.
• Health issues arising from poor housing would be reduced meaning that there are benefits to other social health providers.

Thermal comfort and health

• A PH building stays at a constant temperature throughout the year and there is little difference between summer and winter or day and night.
• The internal thermal comfort can be controlled by occupants leading to fewer complaints.
• The air quality is excellent.
• There are very small variations of internal ambient temperature, so no cold / hot spots which annoy occupants.
• PH houses are quiet without the constant noise of plant cycling through cooling or heating.
• Once a PH has been ‘experienced’, it is very hard to accept anything less.

Energy / Operational costs

• A Code standard house could consume over 100kWhr/m2/annum for heating but as a PH the building would consume less than 15KWhr/m2/annum.
• There is significantly less heating plant to maintain and replace.

Construction

• There are existing pre-fabricated wall systems that could be used that already have the windows installed together with an air-tightness layer for quick construction on site.
• This project would also educate the construction community in the challenges and benefits of PH.
• It is possible that local companies could supply some of the building elements such as windows.

what is a Passive House?

The Passive House building standard originated in Europe 25 years ago, and despite what uninformed critics might say, it’s an approach to building which is entirely able to be applied to construction projects in New Zealand. If you’re thinking about a new build or a significant renovation, it’s really worth your while investigating the Passive House approach.

The term ‘Passive House’ possibly belies what a game changer this standard is as it creates buildings that are a delight to live or work in while giving serious consideration to environmental concerns and energy consumption. These are buildings which have maximum internal comfort as explained in further detail below.

But firstly, don’t confuse Passive House with passive solar.

Cheap to run

Passive Houses are ultra-efficient buildings that need very little energy to heat or cool: the standard specifies no more than 15 kW per square metre of floor area per year.

For a 160m2 house, that’s just 2400kW a year, or about $58 a month based on typical energy prices.

They are also amazingly healthy, with outstanding air quality. You can’t be sure of that in a modern NZ house built to the current Building Code.

Flexible standard

The standard doesn’t dictate building materials; just about anything can be used, from luxury modern materials to straw bales.

There are now Passive Houses in New Zealand from Wanaka to Auckland. All of these are single family homes (starting at a modest 120 m2) but overseas, this approach is also being used extensively for apartment blocks, schools, supermarkets and office buildings.

Increasing numbers of buildings in Europe are now being retro-fitted to meet the standard as countries work hard to meet climate change commitments.

Comfortable

Any Passive House building will be well insulated, relative to the climate. An unbroken building envelope and high-quality windows keep heat in (or out, in summer). You can expect a constant temperature of 18-20 degrees everywhere, all the time — with little or no heating.

It’s also peacefully quiet inside a Passive House, and not damp: no more mopping up condensation on winter mornings.

Air quality

A small, efficient mechanical ventilation unit ensures the air is always fresh. A small heat exchanger will use the heat of the stale air being expelled to warm the outside air being brought in. It’s also filtered. This means no cold draughts, cleaner air, and no heat squandered on a cold winter’s night.

Culturally, mechanical ventilation is a new idea for us New Zealanders to wrap our heads around. But it’s a clever solution to the issue that many of our homes are empty for eight to 10 hours a day, and likely tightly closed up for security reasons.

Modern homes are also more air tight than the draughty 50s and 60s buildings we may have grown up in. This can cause moisture to build up in the walls and internally. A mechanical ventilation system will allow for the fact that windows aren’t always opened, especially in winter. The Building Code assumes that if windows can open, people ARE opening them for regular periods every day, throughout the day and night.

When did you last do that? (Last summer?)

Verified

Approximately 16 houses in New Zealand have been or are on their way to being certified. This means they have been tested with a portable blower door, which pressurises the house to 50pa to check for air leaks. This is first done when the building envelope is complete but still exposed. The second test is carried out by an independent certifier once the project is complete.

The additional cost of certification is insignificant compared with the total budget for a new build. This step verifies that the building performs to the expected standard. That way the client knows the design and calculations were correct and the builders did their job well; they got what they paid for.

Chris Rowe is a Director of CORA Associates and a certified Passive House Designer.

More reading

Watch New Zealanders talk about what it’s like to live in a Passive House – YouTube

The Passive House (or in German, Passivhaus) concept is new here and not widely understood. It’s a building standard entirely relevant to New Zealand conditions. Here’s a general introduction. In this post, I want to clear up some of the misconceptions I hear about Passive House.

We don’t need that here — it’s designed for the much colder winters in northern Europe.

This objection comes from people who just don’t understand what Passive House is. Because it’s a building standard, measured by the (very small) amount of energy needed to heat and cool the building, it is extremely flexible. Yes, the examples we see from Germany are super-insulated—because they are built for their very cold winters. In almost every part of New Zealand, the same levels of insulation are not required.

I used NIWA data to develop energy models for 17 climate zones the length of New Zealand. This gives us reliable, location-specific data. Passive House designers can use this to help clients make good, cost-effective choices about building components and design.

(This compares to the three climate zones specified in the Building Code—suggesting a beachfront home in Nelson and one up a mountain in Queenstown require the same amount of insulation. You don’t need to be a building scientist to know that’s not true.)

Airtight buildings? That’s unhealthy!

Agreed. People need fresh air and homes need to be regularly ventilated. Older style homes were ‘leaky’ enough that air moved through the sub-floor, roof space and around windows and doors. There was way too much air exchange on a windy day and not enough on a still day. It’s a random and uncontrolled process that doesn’t produce good outcomes.

Modern conventional homes are much more air tight than ones built in the 1920s or ‘60s. These are the homes to worry about! The Building Code still presumes that as long as windows are designed to open, occupants are opening them: regularly, every hour, day and night. Realistic? No.

Increasingly, homes are shuttered tight for long hours as no one is home during the day and people are security conscious and don’t want to leave windows open. A certified Passive House building envelope eliminates draughts and keeps the temperature even. It also keeps out insects and airborne pollutants and irritants and reduces noise.

A fresh air system automatically exchanges stale inside air with filtered air from outside, which also regulates humidity. (A certified Passive Houses is never damp or mouldy.) When it’s cold, the warm air being expelled first heats the fresh incoming air, preventing draughts and wasted energy.

The fresh air system is made up of a mechanical ventilation unit integrated with specific extraction in bathrooms and kitchens. They are small, quiet and very cheap to run. If there’s an extended power cut, just open a window!

It’s really expensive

If you take existing plans and say to a Passive House designer, make this a Passive House, it’ll likely cost 10-12 per cent more. But don’t make it an add-on: design a Passive House from the outset. It’s not just about fancy windows or air-tight building layers.

Orientation, footprint, position of windows and how the house relates to its environment are all things to be considered. Go to a designer and tell them your budget. You can get a Passive House for what you have to spend by sensible, reasonable compromises — reducing the floor size a little, simplifying the building shape, even reducing the window area if necessary.

eHaus, which has built more Passive Houses in NZ than any other company, say the housing pressure in Auckland is spurring enquiries from people looking to build small (80m2) dwellings on sub-divided land or backyards. Yes, you can build a modest Passive House without spending a fortune.

It’s not that different from passive solar

Wrong. Building professionals who should know better have made confusing statements about passive solar or “passive design” and Passive Houses. Passive solar is about orientating the house and positioning windows to capture the heat from the sun. Glazing lets the heat in and thermal mass like concrete floors stores it.

Thermal mass only works if you like temperature variation. If it’s hotter than is comfortable, some heat will get transferred into your brick internal wall or bare concrete slab. Later when the temperature drops, heat will be released.

I live in a passive solar house with a wall of north-facing glass and it’s not pleasant. The average temperature disguises the massive daily fluctuations. On a sunny day, it can be above 30 degrees inside or more and at night it drops down to within a couple of degrees of the outside temperature.

The beauty of a Passive House is that it will stay 20 degrees everywhere, all the time — with virtually no heating source. When the temperature is constant, any thermal mass will equalise with the ambient temperature indoors and it has little or no effect.

Keep in mind that Passive House is an open source standard — it was deliberately created that way. So anyone can call their building a passive house. Only if it’s a certified Passive House, can you be sure it is what it says it is.

Jason Quinn is a mechanical and aeronautical engineer and ex-NASA rocket scientist now working as a building scientist. He is a Passive House Designer and Certifier. He consults for CORA.

More reading
The Passive House Institute of New Zealand (PHINZ) has a useful site with many resources and a great FAQ page.
Here is a list of certified Passive House designers and consultants in New Zealand.
The Passivhaus Handbook: A practical guide to constructing and retrofitting buildings for ultra-low energy performance by Janet Cotterell and Adam Dadeby is a comprehensive resource.