Woodlands Malvern B&B is an award-winning, certified Passivhaus. Image credit: Mark Bolton Photography
Passivhaus: ‘green’ and versatile
A building achieving the Passivhaus standard is inherently ‘green’ and can be made even more so. This is because Passivhaus, which is the only internationally recognised, performance-based energy standard for buildings, minimises energy requirements for heating and cooling by fully exploiting the performance of the various components of a building — a fabric first approach — before considering other things, such as installing a heat pump or photovoltaic panels.
This is especially important as in the average UK home, more than 60% of all energy used is for space heating. So very substantially reducing your home’s need for this by maximising its retention of ‘free’ heat (such as from the sun) or otherwise wasted heat (such as from cooking, using other appliances, and the heat given off by people themselves) will substantially reduce your need for energy, whatever its source. Designing to the Passivhaus standard and then adding other ‘green’/ecologically-friendly approaches will maximise the benefit.
And a significant aspect of designing and building to the Passivhaus standard is that it does not restrict the materials you use or how you heat domestic hot water or the building; it simply sets limits on how much energy you can use to do this, so you can choose what else you want to do.
What are ‘green’ buildings?
There are different ways of defining ‘green’ buildings. Some might say that the difference between one that’s ‘green’ and one that’s ‘sustainable’ is that the former only focuses on the impact on the environment, whilst the latter also focuses on a building’s impact on social and cultural values and commercial considerations such as supply chain and profit. For the purpose of this discussion, we will assume that a ‘green’ building is one that:
minimises its energy use for heating and cooling;
has a very high quality indoor environment;
is sustainable, in terms of —
its impact on the environment of the materials it’s made from,
how it’s built,
the source(s) of energy it uses,
its use of water;
will be resilience and adaptable to climate change; and
is likely to remain usable for a very long time, with the environmental impact of its demolition is also taken into consideration.
The Passivhaus standard provides a solid foundation for a ‘green’ building
Passivhaus is the gold standard of building energy efficiency; and thus delivers the first two of the criteria above, that is, (i) minimal requirements for the most energy-hungry activity in most buildings — space heating and cooling, and (ii) an exceptionally high quality indoor environment.
Importantly, one of the great advantages of the Passivhaus approach is that, by designing your building using the Passive House Planning Package, if you then build accordingly, you can be certain that your house will perform as intended — there will then be no unproven assumptions or guesswork as there may be with some other approaches: it will work! We are unaware of other design methods that provide the certainty of an extraordinarily high level of indoor comfort throughout with minimal energy use for heating and cooling.
A properly designed and built passive house will thus provide an excellent basis for you to use other ‘green’ approaches to any extent you wish, as long as you do not breach the Passivhaus energy use requirements.
For example, the pictures on the right show the installation of the ground collector pipe for the heat pump at our passive house. This extracts heat from the ground, which is replenished by the sun, and provides all of our domestic hot water and minimal requirements for space heating.
Heat pumps are very efficient and ideally suited to passive houses. Their efficiency of some 300-450% is because they transfer heat from one place to another rather than generate it and, as explained in our post Our passive house heating system, they also ‘magnify’ this heat.
Installing the ground collector pipe for the ground source heat pump at Woodlands Malvern B&B. This provides a renewable source of heating for both domestic hot water and the house itself. See the section entitled Installing the ground array (collector) for the ground source heat pump in another post
The three classes of the Passivhaus standard
A properly designed and built passive house minimises operational carbon emissions (see below). And, especially if the main active energy source is ‘green’ electricity there is virtually no limit to the technology that can be added to become ‘greener’, from photovoltaic panels to LED lighting to rainwater harvesting.
Currently, there are three classes of the Passivhaus standard. These are based on renewable primary energy demand and the building’s renewable primary power production:
Passivhaus Classic — which is the original standard and without a requirement for renewable energy generation;
Passivhaus Plus — where sufficient renewable energy, such as from photovoltaic panels, is produced to approximately meet the energy building’s needs; and
Passivhaus Premium — where much more energy is produced than needed so that the excess can be exported.
The Passivhaus classes. Image credit: Passive House Trust
These classes are all based on the original maximum heat demand for the Passivhaus standard, that is, 15kWh/m²/year. Because the total demand for electricity is usually higher than this (for example, for cooking and lighting), the classes set out three different levels of renewable energy production for Passivhaus buildings.
The link under the picture, right, will take you to a full episode of Channel 4’s Grand Designs programme following the building of the UK’s first Passivhaus Premium house. (You can also read about it in the Grand Designs magazine.)
This TV programme shows just how much can be achieved in terms of renewable energy generation based on the Passivhaus standard.
Spoiler alert: despite lots of issues (and design changes during the project) the project achieved Passivhaus Premium certification.
You can design passive houses in various styles, and build with most types of materials
You can achieve the Passivhaus standard with a wide range of building types. For example, in addition to ‘ordinary’ homes, social housing, commercial / office buildings, hospitals, health centres, and primary schools and secondary schools have all been built to the Passivhaus standard.
Passivhaus is also achievable using many different materials. For example, the opposite, is a picture of the construction of a certified Passivhaus using straw bales for insulation.
Other buildings achieving the Passivhaus standard have been built using traditional cavity walls, insulated concrete formwork and timber frame; and in various styles (see pictures below). They can also be oak-frame, of which, to our knowledge, there are currently just two in the UK with Passivhaus certification — one being our own, designed from scratch by Oakwrights (picture, top). Clearly, ‘green’ passive houses can suit different personal design preferences and vernacular architecture.
Building a straw bale Passivhaus. See: House Planning Help
Passive houses can be built in various styles and from various materials. Clockwise from top left: cavity wall (Denby Dale, Green Building Store); insulated concrete formwork (Passive House Plus, Logix); traditional stone; and timber frame (Camden Passivhaus)
Oak-frame passive house
Woodlands Malvern B&B (pictured at the top) is a certified Passivhaus with an oak frame and a cellulose-filled wall and roof encapsulation (insulation) system sitting on an expanded polystyrene insulation system under the foundations.
We were especially pleased to achieve the Built It award for Best Eco Home 2021, with the judges saying:
‘By showing that beauty and sustainability go hand-in-hand, this Passivhaus-rated project ticks all the boxes for an eco-house whilst harnessing the unique character of oak'.
We believe that this shows that it is possible to achieve the highest level of energy efficiency in a home that can also have — in terms of being oak-frame — an attractive, traditional appearance. Also, Woodlands scores well in terms of impact on the environment because of its high level of embodied carbon.
Embodied carbon
Embodied carbon refers to the greenhouse gases (CO₂ and others) emitted during all aspects of the materials manufacture, erection and demolition of a building, that is, throughout its complete lifecycle.
This differs from operational carbon, which refers to the greenhouse gases emitted from the heating and cooling of a building, including domestic hot water heating and all other aspects such as lighting and cooking.
The Passivhaus standard probably contributes more to reducing operational carbon than any other approach but, obviously, the amount of embodied carbon in such a building depends upon the materials from which it is made.
The embodied carbon of Woodlands Malvern B&B was calculated by John Butler of Sustainable Building Consultancy and published in an article in Passive House Plus magazine (see extract, opposite).
In summary, in comparison to an equivalent masonry cavity wall building, Woodlands has roughly half the embodied carbon. This is mainly due to its oak frame construction and cellulose (recycled paper) insulation which both sequester carbon.
Woodlands also achieved the equivalent of a LETI (London Energy Transformation Initiative) 'A' rating for whole-life carbon. This is some 72% less carbon emission than current standard practice (see diagram, below right).
Note that the ‘A’ rating is a target for 2030 and that Woodlands was built in 2018/19.
Summary of findings of John Butler’s calculations of the embodied carbon of Woodlands Malvern B&B published in Passive House Plus. )LCA = life cycle assessment. CO₂e = carbon dioxide equivalent, meaning different greenhouse gases with CO₂ having the equivalent warming impact)
This is an encouraging assessment of our house’s ‘green’ credentials in terms of the impact of its materials on the environment.
It is also noteworthy that this calculation is based on an assumed 60-year life cycle. Obviously, the longer that a building stands the better is its embodied carbon impact on the environment because it stores the carbon for longer.
An oak-frame building can be expected to last at least 200 years rather than 60. Indeed, we have friends who also live in an Elizabethan oak frame house, but whilst ours is an Elizabeth II one theirs is Elizabeth I, that is, it’s some 500 years old (and some parts seem to be recycled oak beams so are probably older still). We therefore suggest that oak frame houses — which we consider to be especially attractive — are especially ‘green’.
London Energy Transformation Initiative (LETI): range of embodied carbon performance based on benchmarked projects, and the need to improve the average. Source: LETI Embodied Carbon Alignment
The video, left, from the United Nation’s Intergovernmental Panel on Climate Change (IPCC), looks at the embodied carbon of conventional building materials compared with those which actually store carbon (such as wood). Both types emit CO₂ during their life cycles, but those that store carbon do so from a much lower base and so release less carbon overall.
Some other ways to make a building greener
Water management, both saving water and reducing the risk of flooding are important ‘green’/ecological considerations.
Reducing water use
Especially with a new-build project, but maybe even a retrofit, you can reduce water use by fitting devices such as pressure-reducing valves, lower-flow tap and shower outlets and dual-flush toilet cisterns. There are also various ways to reduce water usage further, from fixing leaks to keeping a jug of water in the fridge rather than running the tap until it’s cold. And, perhaps surprisingly, using a dishwasher uses less energy and much less water than washing dishes by hand, especially on an eco setting.
Rainwater harvesting
Rainwater harvesting is a way of reducing the consumption of high-quality drinking water by storing it for uses such as toilet flushing, car washing and garden watering. Investing in a large tank system to collect rainwater was not feasible for us on cost grounds when we built our house but maybe something other would wish to invest in. See more at this link.
Sustainable drainage systems
Sustainable drainage systems help to reduce the effect of large areas of hard surfaces which otherwise can lead to localised flooding due to run-off in heavy rain. Different approaches to this are discussed in the video on the right.
Flash flooding in 1998 across the bridle path in front of the original bungalow on our building plot. Such flooding has not recurred despite extensive flooding in other parts of surrounding Herefordshire and Worcestershire in recent years because of very heavy rainfall; improving land drainage on our plot and a neighbouring field and having a sustainable drainage system around the house have, we like to think, have contributed to this
We were motivated to improve the surface water drainage of our plot and the nearby surrounding area when shown a photograph (left) of flash flooding at the entrance of our building plot.
In addition to installing rigid perforated drainage pipes in gravel (that is, a French drain) in our own field and in a neighbour’s one, we put smaller perforated drainage pipes around the house and its surrounding retaining wall and filled this area and the patio with crushed stones topped with flag stones with porous joints. The parking area in front of the house was also constructed of crushed stone and topped with porous resin-bound gravel — see the pictures below left.
Construction of part of the sustainable drainage system, here under the parking area, to be covered with resin-bound gravel, and (right) the paved area surrounding the house.
This created a porous area for water to drain to and to slow its flow towards a vertical ‘fin drain’ (see picture, bottom left). This collected it and took it to the field pipework and thence to a brook at the base of the valley.
You can see in the video below how porous the resin-bound gravel is.
The effect of all this is to enable water to drain slowly and, despite considerable flooding in parts of Herefordshire and Worcestershire, we have had no more flooding in our immediate area.
The edges of the patio and the paved area surrounding the house have gravel covering drainage pipes beneath, (see picture, left). The grout between the paving slabs is porous. Even in even heavy rain, there is no pooling of water — the surface just looks wet — and the water is taken into the crushed stone beneath and thence — slowly — to the fin drain
You can find more detail of our drainage systems in the section entitled surface water drainage and in the two sections entitled Flagstones for the patio and the area around the house and Resin-bound gravel for the parking area in another post.
Electricity
As electricity generation becomes increasingly fossil-fuel free shifting all your ‘active’ energy sources to electricity makes ecological sense. A passive house can be greener with the addition of photovoltaic panels, and/or purchasing electricity from a ‘green’ supplier, and using more efficient devices such as LED bulbs, a heat pump, an induction hob. And remember, the MVHR system in a passive house means that you can dry most or all of your washing indoors both quickly and without condensation issues. (We dry our washing in the plant room and only tumble dry towels to keep them soft.)
Green roofs
Depending on your house design, and that of surrounding properties, you might consider having a ‘green’ roof. There will be structural considerations for this but there would seem to be no reason why such a thing should not be compatible with a passive house.
‘Green’ passive house retrofit
Demolishing a building in order to erect a new ‘green’ one incurs a carbon cost, the benefits of which will depend on your personal circumstances and your views of such an approach.
Retrofitting may make more sense from an ecological point of view, but do consider maximising the energy efficiency of your building’s fabric before adding things such as a heat pump or photovoltaic roof panels. This is discussed in more detail in the video on the left.
And in another post we have described how to make your house more passive by retrofitting to the Passivhaus EnerPHit standard.
Resilience to climate change
For the foreseeable future, a properly designed and built Passivhaus building should be resilient to climate change, especially in terms of protecting its occupants from overheating. This is because of its very high levels of insulation and airtightness, which, coupled with a shading strategy (such as external blinds), will help to keep excess heat out. For example, in our post Passivhaus: top quality indoor environment we describe how we kept cool during the July 2022 heatwave (and kept warm in the December 2022 cold snap).
We chose to have a ‘cooler battery’ installed in addition to our shading strategy to avoid overheating. In hot summer weather, this uses the relatively cold liquid that circulates in the ground loop of our ground source heat pump to cool incoming air through our mechanical ventilation heat recovery (MVHR) system. You can read about this in the Cooler battery section of our post on our MVHR system. This reduces the temperature of the incoming air by some 5-7℃, with the added advantage that the extracted heat is stored in the ground and can be used for heating our domestic hot water. (So it’s a lot more efficient than a traditional air conditioner, which uses the refrigeration cycle and pumps hot air out of the house into the hot air outside, using a lot of electricity.) Based on our experience (for example, see the various indoor/outdoor temperature charts in our post on Passive house living and The pros and cons of a passive house) we expect our passive house to be resilient to increasing temperatures for our remaining lifetimes.
Restoring the local environment
Depending on your site and your tastes, you may wish to make the area surrounding your house more ‘green’. We are fortunate to have a reasonable area of land where there is some opportunity for this. You can find out more in our post Rewilding at Woodlands B&B.
March 2020, looking east: hedge with longstanding dead material removed and, where possible, laid. There were numerous large gaps, especially at the base, caused by many years of flail cutting
The same hedge, looking west, June 2023, following further laying, showing the beginning of filling-out of the gaps at its base and its restoration os an effective barrier
Additional standards for sustainability
Current UK building regulations must be met for all new buildings. Whilst these include energy efficiency standards, they are very much lower than the voluntary Passivhaus standard, especially in terms of airtightness. There are also optional UK technical standards (which replaced the Code for Sustainable Homes) concerning water and access and space standards. These are additional to the Passivhaus requirements for energy efficiency.
In addition, there is BREEAM (Building Research Establishment Environmental Assessment Method), which covers a wider range of sustainability considerations. For example, it measures a building's environmental impact across ten categories, including energy, water, waste, pollution, transport, and ecology. However, this is complementary to, and does not replace (ir even replicate) the Passivhaus standard, the two being entirely mutually compatible.
There is also the LEED standard (Leadership in Energy and Environmental Design, originating in the USA), which is similar to BREEAM but with a different method for certification.
And it is interesting to note that the Scottish government proposes to introduce its own version of the Passivhaus standard to which all new build housing will have to comply from December 2024. At the time of writing, this is yet to be finalised.
Find out more
Find out more about the ‘green’ potential of Passivhaus in addition to its unequalled energy conservation with a stay at Woodlands Malvern B&B. We’ll be pleased to talk with you about any project you might have and about our experience of building and living in a passive house. You can also enjoy the fantastic scenery of the Malvern Hills National Landscape whilst here.