HPH009 : Retrofitting a Victorian House to Passivhaus Standard #2 – with Alex Rice from Green Tomato Energy
Alex Rice, Senior Engineer at Green Tomato Energy, explains that there are few technical challenges that remain when retrofitting a period home into a low energy building and it is a case of how you apply those solutions to the given building.
Interview with Alex Rice
Alex talks about the process of how his clients (often a husband and wife team) get started. He stresses the importance of trying to understand their needs and ideas, as well as discussing what is possible. This enables a clear brief to be written with objectives about which everyone is clear.
Create and Stick to an Energy Target
In many of projects undertaken by Green Tomato Energy they set targets to reach the Passivhaus (15kWh per m2 per year) or EnerPHit (25kWh per m2 per year) standards. Where listed buildings are concerned the target might be slightly higher due to the constraints. However, it is really important to nail down an energy target, because without knowing what you are trying to achieve in terms of energy it is nearly impossible to make the technical trade-offs that are required. This target guides the decisions that are subsequently made, thus changing your target practically changes the entire design.
Understand the Building Itself
Each building is unique and so understanding how it was originally intended to work is imperative. Alex highlights how Victorian dwellings function in a very different way from modern buildings in terms of how moisture moves around the building and the way they’re ventilated. Even the way people lived in them was different. In order to take that building as it was designed and make it work in a way that is almost completely different, you’ve got to have a really good understanding of the materials and the methods of construction that were used.
Moisture is Death to a Building!
Ben confesses he doesn't really understand about moisture but he knows you don't want to trap it. Alex explains that nothing kills a building more quickly than it being wet. He illustrates the point by saying a derelict building will stand for ages until the roof falls in and then it will disintegrate very quickly. Moisture causes wood to rot and bricks to undergo freeze-thaw damage. The primary aim of a building is to keep the building materials dry. Controlling sources of moisture from within and outside the building is crucial to the long term survival of any building.
Where is The Moisture Coming From?!
People are a source of moisture inside the building! They do things like wash and cook. They dry their clothes on radiators and water potted plants, etcetera. Then the other source is water outside the building including rain falling on the walls, water soaking up through the foundations, leaking out of gutters and coming in through faulty roofs.
When Setting an Energy Target, Why Don't We Always Go For The Best?
The best target depends on the building and what you’re trying to achieve. For zero energy consumption, your house would be infinitely big which is clearly not possible. Trade-offs have got to be made between how thick your insulation is and what energy sources are available to provide heat. For example, if you have a Passivhaus that has very poor orientation so that you can’t get some south facing windows, then your insulation is going to need to be thicker in order to make up for that. There’s a trade-off between how much energy the building consumes, how expensive it is to build it, how much space it takes up and how costly it is to service the building, so the concept of Passivhaus is that you make the building envelope perform well enough that you can dispense with some of the techie bits of the building – parts of the heating system.
The Passivhaus and EnerPHit standard are carefully selected
The whole point of 15kWh per m2 per year is that it's a point of minimum cost for that level of performance. The same principle applies to the EnerPHit standard, because in a retrofit project, getting the insulation in and getting the thermal bridges insulated is more expensive so it becomes cost effective to spend a little bit more on the energy and a little bit less on the building. Those two points 15kWh per m2 per year and 25kWh per m2 per year were picked carefully as the best level of energy performance but built into those two numbers are assumptions about how much it costs and how difficult it is to achieve those standards, which is why when you go to things like listed buildings that number moves up, because it becomes cost effective and practically achievable to consume a bit more energy a year but make it much easier to build.
Internal Wall Insulation vs Reduction of Floor Area
It is Alex's experience that you can put a surprising amount of insulation on the inside of a room and that once it’s all detailed in, you hardly notice it. When you're putting it on it looks huge, but once it's detailed in with the plasterwork, it really does disappear. The only exception is where space is already limited and therefore things like beds and wardrobes no longer fit into spaces that they previously did. There are higher cost ways of achieving the same level of insulation performance in less thickness using aerogel, vacuum insulated panels, etcetera. Generally speaking phenolic foam and those types of insulation materials are perfectly adequate and are the most cost effective choice for retrofit projects.
Add Space as Part of The Project
If you are retrofitting to Passivhaus or EnerPHit, then this is a major undertaking and thus this is the perfect time to extend your property. At this Lena Gardens Victorian terrace, a basement was dug out to provide space for the services and an extension at the rear enlarged the kitchen. So in this case there was more floor area at the end of the project.
The Geometry of Old Buildings Make Insulating More Challenging
One of the biggest challenges in a retrofit is working around the existing structure of the building. In a new build the walls can be made with the insulation in it already and it’s quite easy to design a thermally bridge free well insulated envelope. In an existing building there are often areas which are geometrically difficult to insulate.
Removing The Timber Bricks!
A lot of old buildings contain some timber in the walls. It was typical in Victorian construction that if something was brick-sized and brick-shaped then it would be stuck in the wall! This can only be assessed once the plaster is removed. It's important to make sure the pieces of the building you are covering up are in a fit state to remain covered up behind insulation for the next few decades.
Avoid an Adversarial Culture in Your Team
Alex emphasises that communication amongst the team is key to the success of the project. The guys on site need to report issues as they arise and not feel that they will get an earful of criticism in return. As Alex can perform many of the tasks himself, he sees this as crucial in building up credibility with the tradespeople.
Tradespeople Want to Work on a Passivhaus Project
One of the indicators that a tradesperson is going to be good on this type of project is that they have previous experience. Tradespeople are becoming aware of this and they want to do a Passivhaus project because they realise it will be good for them to be known to deliver this level of quality. Passivhaus is becoming a hallmark of quality. Alex describes how after seeing a blower door test for air tightness for the first time, tradespeople often leave the site excited about the new knowledge they have learned.
Alex Inspired By Ken Schaal From CommonWealth Solar in Virginia
After studying for a degree in new and renewable technology at Durham University, Alex worked at CommonWealth Solar in the United States for Ken Schaal. Ken was part of the passive solar homes movement of the 1970s and had built a geodesic dome (using materials such as foam and concrete) for next to no money that also used practically no energy. Having lived in Victorian properties all his life, Alex describes this as an eye-opener as he always expected low energy buildings to be complex and expensive. Ken taught him that if you make a building well-insulated and airtight, you need the minimum of stuff to make it work.
British Housing Stock is Very Different to America
In the United States, buildings are often knocked down every 25-50 years to make way for the new designs. In the UK, the average life of a building is often a hundred years or more. Thus retrofitting is a major challenge for the future.
Download a transcript of the interview with Alex Rice.
UK Passivhaus Conference
Having become more and more interested in a Passivhaus approach over the last few months, Ben Adam-Smith attended the UK Passivhaus Conference in Nottingham. There were some very interesting talks and Ben reveals that he has been taking notes on who he needs to speak to for future episodes!
Is Cladding with Brick Pointless?
Ben is confused about the options for his own project as he prefers more traditional aesthetics, yet he can completely understand why many Passivhaus buildings are finished with wood (which is far more sustainable) as the external surface. He wonders whether he just has to get used to it, as using an unnecessary layer of bricks on the exterior of a house is a waste of time and resources (even though he still likes the effect).
Voicemail Message from Shauna Wyldeck-Estrada
Shauna contacts House Planning Help to share information about her renovation of a Victorian house in Catford South. She talks about how she used sheep's wool insulation in the loft and cellar, and how it has had an amazing effect on reducing her bills. A wood stove provides heat when required, making her central heating system redundant.
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