In this blog, we wanted to explore some of the benefits of choosing to build a Passive House. Let’s start with the main criteria for a certified passive house, which are:
Less than 15 kWh/(m2.yr) heating demand or less than 10 w/m2 heating load
Primary Energy renewables less than 60 kWh/(m2.yr)
Airtightness of less than 0.6 Air changes and hour
Excess humidity for less than 10% of the year
The internal temperature being above 25 deg C for less than 10% of the year
The heating demand and heating load criteria mean a passive house uses 70% of the energy a standard new building uses. This is the most lauded benefit of Passive House. With the current energy crisis lower energy usage means increases in electricity tariffs have smaller effects on the bills. This is because a small percentage increase on a small amount will always be a small increase. We should note that Passive Houses are often all-electric properties. This is due to the Primary energy all-electric renewables or PER criteria, a measure of the amount of renewable energy the property requires from the grid. For this reason, Passive Houses rarely use gas. This can mean energy bills are not 70% lower due to the cost difference between gas and electricity - 10.3p/kWh and 33.2p/kWh respectively as of April 2023– although this could change in the future.
The second criterion of low air changes an hour is a manner to both reduce unwanted heat loss but also ensure buildings are not draughty. This means the indoor environment feels warmer and more comfortable. There is also a benefit that when the front door or single window is open the wind does not rush through the building – meaning you don’t have to shout at people to “stop letting the heat out” quite so often.
Many argue that airtight buildings are stuffy and damp. This isn’t the case in Passive Houses as we need to be within the humidity criteria. Humidity is how damp the air is. Passive Houses require Heat recovery ventilation. Not only does this save energy by recovering the heat otherwise lost in ventilating the building but also ensures that the moist air is reliably removed all year round. This is so effective that in many Passive Houses, it’s encouraged to have indoor plants and dry washing indoors!
The last “hard” criterion means that Passive Houses are designed not to overheat. The last few years have seen scorching heat waves and they are set to continue. Whilst standard buildings have been uncomfortably hot, Passive Houses have remained cooler* without the need and cost for air conditioning. This is done by excellent ventilation, shading of glazing, and ensuring hot water pipes don’t make things worse.
But this is not the end of the Passive House benefits. In last week's blog, we briefly mentioned “soft” criteria these are additional criteria Passive House designers need to achieve beyond the certification criteria. We won’t list all of them as they are rather technical and long. However, here is a brief summary of a few:
All surfaces are a minimum of 13 deg C. This is to prevent mould growth which can only grow on surfaces less than 12.7 deg C. It also stops condensation on the inside of your windows!
Ventilation units are no louder than 25dB(a) in living and sleeping rooms. This is the same volume as a whisper so you won’t be disturbed by the fans.
Ventilation units must have F7 filters which filter 80-90% of fine particles making the indoor air clean and almost pollen free.
Temperature asymmetry of less than 4.20C. This stops one part of a room from feeling hotter than another, or one part of your body from feeling warm and another cold. The whole property is equally warm and comfortable.
Finally, having a Passive House increases your property Value. A study by Nationwide in 2021 saw energy-efficient homes having a 1.7% increase in their value**. This is without the feel-good factor of helping the environment and doing your bit to be more environmentally friendly.
We hope that this has convinced you of the benefits of Passive House and if you would like more information or have a question please call us.
* https://passivhaustrust.org.uk/news/detail/?nId=1110 A PassivTrust article from 2022 on the performance of passive houses in the UK heatwave.