The Passive House payback myth
This is a topic that has been niggling away at the back of my mind for years, and I have the seed of an analogy in mind that hopefully I can develop in this blog to clarify how I feel about this and should prove useful to clients and practicioners out there as you consider this issue yourselves.
The idea of ‘payback’ is often used to justify the additional capital investment in energy saving measures in buildings. Whether it is a solar panel installation, the cost of energy saved per annum is totalled up versus the additional capital investment and you have a figure in years for when the measure has paid for itself and is now providing ‘free’ energy. Very simple.
I have an issue however when this concept is applied to the Passive House. I always did, but I couldn’t quite put my finger on why. I doubted my own motives even, maybe I am such a convert to the efficiency argument that I no longer want to look at the numbers and just wish everyone else would get on board or something. (and yes I am a bit guilty of this after 10 years).
However, this idea crossed my mind recently. See what you think.
I don’t think that the ‘payback’ concept is applicable to additional Passive House investment cost (which ranges between 0 and 10% extra depending on the building type/creativity/site options/replication etc.). With a solar panel or fridge, the additional energy efficiency if the only return on the investment. Whereas a passive house is not just more efficient, it is more comfortable. And a building’s primary function is to provide a shelter. Its job is to mitigate against the external environment and give us a warm dry safe place to live, work and play.
A passive house is more comfortable and secure
A passive house, as well as being cheaper to run, is more comfortable to live in. This is verified by the fact that you can meet the energy requirements of PassivHaus criteria and still fail to qualify if comfort conditions criteria are not met.
Comfort aspects of passivhaus.
- You don’t have any draughts, there are no uncontrolled vents in the walls that freeze you when a gale is blowing outside.
- You have clean, fresh air all the time, regardless of how cold it is outside.
- The risk of seasonal overheating is eliminated in the modelling process.
- Passive houses are quieter than old-fashioned buildings. The high levels of fabric insulation, airtightness and triple glazing make these buildings incredibly calm places, great for areas with noise pollution.
- They are more secure because there is more glass between you and a would be thief. Also you will need to leave windows open less, so trying to ventilate your building doesn’t make you vulnerable.
Passivhaus is better for the elderly
- As you get older, you need higher ambient temperatures as you become less mobile, perhaps 22 or 23 degrees is required. This is easy with a passive house. You have energy security, once your mortgage is repaid, when you retire, you will have on average €1500 per annum less to find from your pension. This is great peace-of-mind for you and your children.
Putting a value on each of these benefits
To my mind, I would put a greater value on these benefits than the reduced monthly energy costs. If a passive house consumed the same amount of energy as old fashioned buildings, but boasted the above benefits, I would still think it was a good investment. But it doesn’t, I have done cost analysis on the payback and found that a typical semi-d will have a smaller annual cost (energy plus mortgage repayments) after two years! My next job is to publish that information in an easily legible format for you to check for yourself. Follow me to keep posted and please leave your comments if you can help refine this idea.