HPH271 : Common questions about the Passivhaus standard – with Ben Adam-Smith
Ben Adam-Smith shares some of the questions that got asked about the Passivhaus standard during a question and answer session at the National Self Build & Renovation Centre.
Twice a year the National Self Build & Renovation Centre (NSBRC) hold a Passivhaus workshop in association with the Passivhaus Trust. This explains everything from the origins and principles of the standard to the benefits and how you might go about building your own Passivhaus.
The event is hosted by Passivhaus Trust members who are also exhibitors at the NSBRC.
The panel was slightly different each day but included Alan Budden from Eco Design Consultants, Jae Cotterell and Anna Carton from Passivhaus Homes, Paul Smith from Green Building Store, Jasper Meade from PYC Insulation, Robin Miller from Beco Wallform, Clarissa Youden and Michael Hunt Total Home Environment and self-builder Juraj Mikurcik.
Before the Q & A began, Chris Herring asked the panel to give their top tip for building to Passivhaus standard.
- Put Passivhaus on the brief from day one
- Take a fabric first approach, investing your money in achieving Passivhaus standard before you even think about renewables
- Get buy in from all your team
- Make sure you hire someone with Passivhaus experience
- Don't skip steps, like missing out the PHPP modelling
- Get the form factor down
- Keep it simple (and it will be easier and cheaper to achieve the Passivhaus standard)
- Design out the overheating risk
How do you heat a Passivhaus?
There was no definitive answer for this.
But first, a variation…
“I've heard you don't really need heating in a Passivhaus. Is that true?”
This is a bit easier. Yes, you do need additional heat in a Passivhaus but it will only be a small amount of heat.
If you're going with renewables, an air source heat pump can be a good solution. Ground source heat pumps are generally overkill and therefore unlikely to be used.
My own Passivhaus uses a gas boiler and although these are clearly on the way out, the gas main may still exist in some capacity in the future. So our logic was to connect now and then we can always dump that connection at a later date. And it's much easier to do this than trying to connect at a later date. It's also useful for resale purposes.
Some of the panel suggested, as the grid decarbonises, that electric is the way to go. Jasper Meade talked about building their Passivhaus office with no heating at all and testing it for a couple of years. With a couple of electric heaters downstairs the whole building quickly reaches temperature in winter.
Alan Budden followed a similar logic, saying that electric panel heaters could be good. And they're portable too.
What do you think about having a wood burning stove in a Passivhaus?
While this is possible, it's a good question to ask why you want this. Is it because all your other houses have had one?! Maybe you've been huddled around the fire in the winter. Well the experience of living in a Passivhaus is going to be quite different.
The other thing to remember is, no matter how sealed the system, when you add your fuel the stoves will give off particulates. So there are health risks attached.
But if you do still want a wood-burner (perhaps you have your own supply of wood) make sure it has its own air supply.
Is thermal mass important in a Passivhaus?
The panel agreed that having some thermal storage capacity was a good idea, but it doesn't have to be a lot. This has the effect of just smoothing out the temperature, particularly in summer.
And interestingly, some build systems might have more thermal mass than you think. While concrete is often cited, Jae Cotterell talked about the PH15 timber frame system having significant thermal mass in the form of the cellulose insulation!
What is the value of certification?
This is about quality assurance and is particularly important when your team has limited experience of achieving Passivhaus standard.
If a company has built lots of certified units before, they probably could deliver a Passivhaus with little trouble and the certification may be less important. However, if hiring someone with less experience, following the principles will not necessarily get you to Passivhaus standard.
So certification may just seem like a badge but there is a whole process behind it.
The other aspect to bear in mind is resale. Those looking to buy a Passivhaus are likely to want a certified property rather than taking homeowner's word that they've built a Passivhaus.
It's also worth remembering that you can get certification at a later date; just make sure you gather all the necessary documentation at the time of the design and build.
Can you make a Victorian house into a Passivhaus?
Yes, this is entirely possible (such as Tom Pakenham's retrofit).
However, it's not straightforward, you're making the building do something it wasn't designed to do and it won't be cheap.
Even the Passivhaus retrofit standard EnerPHit is still a challenge. It's slightly less stringent but still demanding.
We've covered various different retrofits on the podcast including Harry Paticas's phased retrofit of a town house.
We've got a plot, what are the first steps to designing a Passivhaus?
- Put it on your brief and go in search of professionals who have done it before (check that someone on the team is a certified Passivhaus designer).
- Read the guidance on the Passivhaus Trust website.
- Visit Passivhaus properties as part of the International Passivhaus Open Days. Quiz the owners about their own experience and the team they hired.
- Get familiar with the requirements of the Passivhaus standard so that you can make good decisions (and avoid complicating it and adding extra costs).
Does the Passivhaus standard take you down a timber frame route?
Passivhaus can be achieved with any build system. You could make an argument that insulated concrete formwork (ICF) makes the airtightness easy while a masonry approach involves putting together a big jigsaw… but fundamentally you can reach Passivhaus standard with any construction system.
But the choice of build system comes down to personal preference and takes into account a number of factors such as cost, ecological criteria, ease of assembly, and so on.
When it comes to planning, how easy is it to adjust the orientation of a house?
As with anything connected to UK planning, it can boil down to the local authority. Some are better than others!
However, most authorities can see the benefit of having more Passivhaus buildings and understand the need to optimise the orientation.
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