Converting Existing Structures to the Passive House Standard. Can It Be Done?

Building to the Passive House standard doesn’t have to be all about new builds. Converting existing structures can still be an effective way for your home to achieve Passive House results, if building from scratch is not an option.

Changing an existing structure to accommodate for the Passive House requirements is, essentially, retrofitting. Simply put, retrofitting in the building industry is all to do with providing a structure with a component it did not have when it was first built. You can view it as an upgrade to a building in order to be more in tune with the needs of today.

Retrofitting has increased in popularity over the years mostly due to the global drive to make buildings more sustainable and thermal efficient. Why the sudden support for these changes? Because, sustainable retrofitting means that existing structures will:

• See a reduction in CO2 emissions
• Become easier to maintain
• Eliminate health problems caused by poor ventilation and damp
• Be more adaptable to changes in the environment

The concept of retrofitting sounds all well and good, but how does this work once we get to the stringent rules of the Passive House standard? Even some new builds can’t seem to get this right. Luckily, different terms apply to buildings retrofitted to the Passive House mindset.

This is what this article will be all about. We will show how you can convert your home to the Passive House standard. Of course, this means that case studies will be presented to demonstrate that this can be done. We will also explain the guidelines that apply when you undertake a home conversion to the Passive House standard.

Converting to the Passive House Standard – Challenges and Solutions

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When tackling a Passive House retrofit, the same guidelines need to be followed to the letter:

• Appropriate insulation to be used so thermal comfort can be achieved
• Thermal bridges need to be minimised as much as possible
• Airtightness needs to be significantly improved
• High quality windows are a must
• Installation of ventilation with heat recovery in mind
• Heat generation must be achieved as efficiently as possible
• Renewable energy sources need to be employed diligently

However, even if all the above guidelines are followed, the number of existing buildings that have managed to achieve the Passive House standard, after conversion, is noticeably small. This can be explained by the problems generated because a building hasn’t been constructed with a Passive House mindset from the beginning. We are referring here to the unavoidable thermal bridges of basement walls, a building design not supportive of the compactness and passive solar gains aspect, and the absence of proper space for optimal insulation thickness.  

Fortunately, the Passive House Institute is well and truly aware of these issues and has developed the EnerPHit framework. This details how a certified conversion to the Passive House standard needs to be done. If followed correctly, the newly retrofitted building will be able to apply to be certified to the EnerPHit standard.

Converting a Victorian House to the Passive House Standard

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The stars of the first case study are a couple of Victorian semi-detached houses in Manchester. These retrofitted houses are the first ones in the UK ever to be awarded the EnerPHit Plus certification. The conversion process took place in 2018 and, as you would expect, has involved a fair share of due diligence.

Even if you are armed with the best intentions at heart, you could end up causing more damage to the building if you are not adopting a whole house approach and not taking time to understand how the existing building fabric is structured.

In this particular case, great care had to be given to preserve the Victorian architecture and add the necessary modifications without harming the original 19th century design. For example, when insulation was installed, the decision was to do it internally in order to preserve the Victorian facade. This had to be done carefully to avoid trapping moisture inside the building’s fabric. The solution to this problem was to turn it into a cavity wall with a new inner leaf built. A more detailed presentation of how the insulation aspect was addressed can be found here.

Airtightness and windows were the other problematic issues to resolve. Air leakage is common when it comes to period houses. Therefore, extra attention had to be given to ensure that any area of the house prone to such an issue, was adequately resolved. Windows, on the other hand, besides being durable and of a high quality, also had to include stained glass panels to be in tune with the overall Victorian theme.

Retrofitting an Apartment to the Passive House Standard

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For the second case study we are going to take a trip to Spain, and show you the impact a Passive House conversion has had on an apartment located in a social housing complex.

The new owners prioritised comfort and energy efficiency above else. Once they decided to convert the apartment to the Passive House standard, they elected to do the changes just to the apartment itself and not intervene in the communal areas.

Key characteristics for the building itself are:  

• 14 storeys high comprising of 72 apartments
• External walls are formed of two layers of bricks with a 50 cm air chamber between them
• Building structure is of reinforced concrete
• No insulation present in the thermal envelope of the building

Because of the structure of the building, a diverse set of challenges had to be overcome in order for this conversion to be a success. A detailed presentation of the technical side of the conversion can be accessed here.

Our focus with the second case study is more on the results side of the conversion. How exactly did the energy consumption and space change after the retrofitting was completed is what we would like to show you rather than focus too much on the technical side. In this case the key takeaways are:

• The total cost for the energy improvements made amounts to €13,726 which works out to €176.88/m2
• Because the owners focused on doing the necessary Passive House changes only to the apartment itself and not the communal areas, approval from the neighbourhood association was not needed
• The heating requirements for the structure decreased by about 70%
• Measurements taken throughout 2015 show that the only heating source needed for the apartment were three uninsulated heating pipes which go through to the upper floors
• Humidity was kept at a balanced level of under 50%

Living in a Passive House Conversion. Lessons Learned Over a 5 Year Period

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The final case study in our retrofitting journey is from Oakville, Canada. Our focus here will be to show how life is in a Passive House conversion and how it fares over the years.

The first aspect that impressed the home owners is the thermal comfort. Because the building is insulated properly throughout the outside of the house including the basement floor slab, it creates a balanced indoor temperature. Measurements taken have shown that there barely is a 1 or 2 degree Celsius difference from end to end of a room or top to bottom.

Silence was also a characteristic attributed to life in a Passive House retrofitted structure. Due to the high quality windows and the insulating layers, the house transformed itself into a quiet sanctuary with no noise coming from the outside world. The only thing heard in the house being the noise from the fridge.

If the appeal of a ‘fortress of solitude’ and thermal comfort in all seasons doesn’t quite cut it for you, then maybe the $500 utilities bill per season (consider this is Canada, with a 15 month cold season!) hits the sweet spot.

Passive House Conversions – Concluding Remarks

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Simply relying on new builds to achieve the global sustainability targets self-imposed through the Paris accord will not be enough. The existing building stock needs to be changed to meet the needs of today and even surpass future challenges.

With tools like the EnerPHit framework to guide you in your Passive House conversion, there is no reason not to give it a try. What also helps, is that dedicated professionals are here to guide you on your journey. Who knows, at the end of the project you might find a calling to be a certified Passive House designer or tradesperson.

If this should be the case, then all the information you need can be found here.

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