Retrofitting and improving heritage buildings

We are just coming into spring and, after a cold and damp winter, for those who live or work in heritage buildings the move towards warmer weather can be a relief. However, this isn’t something occupants have to accept, the possibility to retrofit, either thermally or environmentally, to improve a property is not just reserved for twentieth century buildings. The opportunity to retrofit is available to many heritage properties and indeed required under building regulations when you have a change of use. Properties that are heritage assets, either because they are in Conservation Areas or are Listed will have some restrictions or limitations but that does not mean that improvements are not possible.

Retrofit is a holistic approach and one that requires a thorough understanding of the whole building and how it is used. No measure should be considered in isolation, without assessing how the intervention affects the strategy of moisture management in the property, new, different issues can occur. Levels of moisture in the air plays a significant role in all properties. Extremes can affect energy use and efficiency, occupant health and in the worst case scenarios deteriorate the building fabric.

One of the first measures we look to improve is uncontrolled heat loss. Draughts in properties cause discomfort and appropriately sealing gaps in floors, windows, and doors can significantly reduce heat loss. Likewise window refurbishment, secondary glazing or installing double glazing, where permitted, can improve heat loss. However these measure can also compromise the effective ventilation and so compensatory ventilation interventions are required.

Another approach is to improve the energy loss through building fabric. Incorporating insulation to heritage buildings is always a challenge due to their solid wall construction. Additionally, most historic buildings rely on the breathability of their construction materials to manage moisture effectively. The preferred approach is to insulate externally however with Listed buildings and those in a Conservation Area this is usually not possible, due to the aesthetic restrictions. Internal wall insulation is sometimes possible, however this needs to be undertaken with care and consideration. Excessive levels of internal wall insulation can result in interstitial condensation which can cause significant harm to the building fabric. Fortunately, there are a variety of products available that can insulate while ensuring the natural moisture regulation is maintained. Finally, insulating a building internally will also change how the property responds to heat storage and thermal mass. This is not necessarily an issue but the impact needs to be considered as part of the wider heating and overheating strategy.

To the principal rooms at Doughty Street, London we used a void that was once behind (long gone) silk wallpaper to insulated the wall using the Lime Green wood fibre and lime plaster internal wall insulation system

The final measure is to offset energy usage with renewable sources. Incorporating renewable energy technologies into a heritage building poses unique challenges but also offers significant opportunities for improved sustainability and energy efficiency. The key is to balance the preservation of a building's historical character and architectural integrity with the installation of these modern technologies. This process usually requires a bespoke approach to each building with careful planning and sometimes innovative design.

Solar panels can sometimes be mounted on less visible parts of the roof slopes. Air source heat pumps are easier to install but require external units that need to be sensitively placed to minimise visual impact. Every project is different and sometimes the unique location of the property will throw up other opportunities to generate heat or electrical energy.

Engaging with architects like ourselves experienced in retrofit of heritage buildings is crucial for navigating the complex balance between preservation and innovation. It is also important to remember that many heritage buildings are protected by law. Even seemingly small alterations may require consent from local authorities and we can advise and support where required.

Successfully retrofitting heritage buildings not only contributes to reducing carbon emissions and energy costs, but it improves user comfort and ensures the long-term sustainability and utility of these culturally historical buildings. Each heritage building is unique, requiring a tailored approach to integrating improvements in a way that respects and preserves its value.

Why develop a heritage building?

Heritage buildings contribute significantly to the character of the urban areas in our cities and Bristol is no exception. In terms of heritage I include twentieth century structures which are part of the history and fabric of our cities. Although these buildings can bring challenges, they bring opportunities including a connection to the past, which is important to both the urban environment and their communities.

Conservation Areas, of which Bristol has many, are desirable places to live and work due to their unique character and aesthetic appeal. Heritage buildings within these areas can help boost local economies by either being visitor attractions in themselves or creating spaces where people want to spend time. Thoughtfully repurposed buildings can become economic assets to a community, attracting businesses, residents, and tourists, and sparking broader regeneration in an area.

The conservation and adaptive reuse of buildings, including heritage buildings, is an inherently sustainable practice, reducing the need for new materials and construction. They often also preserve the craft and high quality materials that are inherent with their architectural period.  Most heritage buildings can be repurposed for modern uses while retaining their historical essence, serving the community's current needs through creative and innovative adaptations. Social benefits can include enhanced community pride and cohesion by providing shared spaces for communal activities and fostering a collective sense of history and identity.

To achieve success in repurposing building it is important to have a team that can develop sensitive and innovative strategies. Our Conservation Architects work with engineers, project managers and other designers experienced in working with historic buildings to understand what is possible within the limitations of a building. We are used to working closely with local authorities, heritage organisations and building control bodies to help navigate regulatory challenges and find acceptable solutions for adaptation. Where appropriate we work to engage the local communities in the process to ensure the building meets local needs and has broad support, enhancing its long-term viability to repurpose any building, particularly those of a heritage nature, it is important to develop a deep understanding of it. Interventions should be carefully considered to ensure the heritage asset is preserved and enhanced. This does not preclude the modernisation, retrofitting or extension of these spaces. Although each one of these elements needs consideration about to what extent these can be incorporated.

Repurposing heritage buildings is complex but when done successfully can preserve our cultural heritage, meet our contemporary needs and contribute to the vitality and sustainability of our communities.

This photo is of 3 of our projects at 80,78 & 76 Park Street, Bristol, all Grade II listed. Originally built as homes, converted to shops by the Victorians the upper floors have remained underused in more recent times. The areas above the shops are now converted to high quality flats with active retail to the ground floor.

The Importance of Thermal Bridge Analysis for Architects

All buildings lose heat (fact), even the most efficient Passivhaus, BREEAM Outstanding, EPC A+ building will still lose a some. One way the heat is lost is through the fabric (walls and roof etc) and some areas lose more heat than others. A thermal bridge refers to these localised areas in the building envelope where heat transfer occurs at a significantly higher rate than the surrounding areas. You typically see thermal bridging issues at junctions between building materials, on corners, floor junctions, eaves, window frames and balcony junctions. If you have ever noticed condensation on a door handle or mould around a window that is usually due to a high thermal bridge. These bridges can lead to thermal inefficiencies, increased energy consumption, and discomfort for occupants.
This discomfort to occupants can be due to cold spots near windows or walls, and can lead to drafts and uneven heating, making it challenging to maintain a comfortable indoor environment. They can also contribute to condensation and moisture-related problems within a building. When warm, moist air comes into contact with a colder surface, due to a thermal bridge, condensation can occur, leading to potential mould growth, deterioration of building materials, and compromised indoor air quality. Some thermal bridges can be avoided, for example in a Passivhaus project we look to reduce the number of external corners or increase the size of a window rather than increase the number of windows to provide natural light. But in reality, unless you plan to live in a windowless sphere, thermal bridges will occur. From the moment we begin the design of a project to its completion we think about how it will be built and how we can detail junctions to avoid high thermal bridging.
Detailed thermal bridging analysis is now required for new buildings as part of the overall energy model, previously typical values were used. This means the model is more accurate and reduces the gap between designed and actual performance. At Shu Architects, we have been using software to calculate the thermal bridges for our own projects. As a result, we can use the analysis as a part of our workflow to test details, construction options and ultimately design to provide the most efficient and comfortable space.
When we quote for construction drawings we will include this as a part of the package we provide. However, we can also quote for external projects on a detail by detail basis. If this is something you are interested in or would like to know more about what we do then please get in touch!

Housing Density and the Built Form in Bristol

We entered the Bristol Housing Festival design competition for 100% affordable family homes held by Brighter Places, for a site on Midland Road in Old Market, Bristol, last summer.  The competition stipulated the number of flats required which got us thinking about housing density and built forms in the Bristol context.

We think this is something people care about, and it is reported in the news.  A recent poll in a local paper asked: “Should new homes in Bristol be built on greenbelt land or should there be more high rise flats?”  Furthermore, in the UK we generally don’t associate high density or high rise accommodation with family living – that is confined to the low density developments of the suburbs and countryside. This binary choice reflects how the issue is often perceived but misses many good options which provide good quality housing, at medium to high densities, and at low to medium rise.

How to achieve this? Take inspiration from places where people choose to go on holiday for city breaks and are generally considered beautiful, livable places. For example, walking around Barcelona, Paris or Vienna it is generally medium rise, dense, vibrant neighborhoods with shops and services that are the norm. They are not alone, much of the world is like this. 

But, in Bristol we also have a history of building at this density and often these are desirable places to live. Take the compact terraces of Southville, Totterdown, Montpelier, Kingsdown and parts of Clifton, these are just a few examples.  The UK also has numerous historic examples of purpose-built flats, such as the mansion blocks found in many of the most prestigious parts of London, the list could go on, and these examples barely scratch the surface.

The story is not a new one and was well described in the book “Cities for a small country,” by Richard Rogers and Anne Power, released in the year 2000. Thinking has moved on since then with urban placemaking concepts codified in Bristol’s Urban living SPD guidance which references recent projects such as Wapping Wharf, The Paintworks, Junction 3 and Gainsborough Square as good examples of high density developments. None of these are high rise flats pierce the skyline.

It was great to take part in a competition focusing on medium rise housing which has an important role to play in the makeup of our cities and may benefit from more attention.

Our proposal integrated a number of concepts such as: ensuring each flat had its own front door accessed directly off of a communal ‘street’ and the flats were dual aspect. There was a central courtyard of private amenity space that opened up a diagonal route through the proposed block to connect the walking desire lines. We also wanted to ensure the development was true family accommodation, with space to park a pram near the front door, dedicated spaces for home working, and plenty cupboards for toys. To the main road we aimed to provide visual interest and pleasing proportions in the external façade based on our exploration of local architecture and the examples discussed above.

VENTILATION: DECENTRALISED CONTINUOUS SUPPLY & EXTRACT

In our final blog post of this series we are looking at the trickier problem of introducing ventilation into a retrofit project. Space for an MVHR unit can be especially difficult to find in domestic housing retrofits. Also, inserting new ductwork into voids between joists can be incredibly intrusive and is better suited to deeper, more extensive retrofit. Forming drop-down ceilings to accommodate ducts is often not an alternative because of the loss of room height and volume. An alternative approach could be to use is a decentralised system.

Q: What is decentralised continuous supply and extract?

A: Ventilation is provided via continuous supply and extract from paired wall units. The units communicate via wifi and cycle between supply and extract depending on factors such as humidity levels. Heat is recovered from extracted air via a ceramic plate that warms up and then transfers this heat to the cool intake air. Cycles are typically 70 seconds and units are designed to be effective for defined floor areas. They should be specified in pairs but there can be more than one pair depending on the size of the house. This arrangement typically suits low-energy retrofit where space for ducts is limited. The incoming air is filtered (typically with washable filters) but not to the degree that you would expect with a dedicated MVHR unit. Hybrid versions are available that combined wall mounted supply with ducted extract. Kitchens typically will have a recirculating hood. Trickle vents are not required.

Q: Who calculates the required amount of ventilation?

A: The calculation is complex should be carried out by a specialist consultant or subcontractor and you should expect them to design the system including the unit and the ducts.

Q: What is uncontrolled ventilation and why is it important?

A: Uncontrolled ventilation occurs through construction gaps in the external building envelope. It is often referred to as a building's "airtightness". It can contribute to drafts and results in the loss of internal heat gained through heating and occupying the house.

Q: Can I open the windows?

A: The windows can be opened for comfort control and cooling.

Ventilation: Passivhaus Standard MVHR

This week we are looking at looking at Mechanical Ventilation with Heat Recovery designed to the Passivhaus Standard. Also, we consider how the building envelope should be designed and constructed to comply with the standard.

Q: How is Passivhaus Certified MVHR different from Building Regs MVHR?

A: The mvhr in a building built to Passivhaus Standard needs to be to a certified standard. It will typically be more efficient than a Building Regs standard unit. The intake and extract ducts will be insulated to prevent both heat gain and heat loss. There will be additional noise attenuation on the supply and extract ducts adjacent to the unit and overall, the system will be quieter. Ducts can be plastic but will typically be round, galvanised steel for improved noise and durability.

Q: Who calculates the required amount of ventilation?

A: The calculation is complex should be carried out by a specialist consultant or subcontractor and you should expect them to design the system including the unit and the ducts. This information will then be inputted into the Passivhaus Planning Package software.

Q: How is stale air extracted from the building?

A: Stale air is extracted via a continuous fan from the wet rooms and is exhausted via the heat exchanger (in the mvhr unit) to the outside.

Q: What is uncontrolled ventilation and why is it important?

A: Uncontrolled ventilation is significantly reduced in the Passivhaus Standard. The maximum amount of permitted 'leakiness' is well below a even the best Building Regulations level. The building envelope will be designed to minimise the risk of air leakage and careful consideration should be given to how the building is constructed and whether what has been designed can actually be achieved on site. Air leakage can be controlled with construction tapes at abutments and corner junctions but it can also be achieved in conjunction with gypsum plaster and coated boards.

Q: How much electricity does it use?

A: Domestic MVHR units typically have two small fans which push the air through the system. The size of the dwelling and occupancy levels determine the size of the unit. For a small dwelling, an efficient unit will typically use around 20W in background mode, which is comparible to a low energy lightbulb (The Green Building Store).

Q: Can I open the windows?

A: The windows can be opened for comfort control and cooling.

Ventilation: Mechanical Ventilation with Heat Recovery

This week we look at some options if you don’t want to rely on trickle ventilation through the windows and instead want to think about a mechanical solution that can also recover heat that would otherwise be lost.

Q: What is mechanical ventilation with heat recovery (MVHR)?

A: Ventilation is provided via continuous mechanical mechanism which is usually a central extract system. The mvhr is a unit that has 4no ducts: an intake & exhaust attached to the external wall; and a supply and extract which supply fresh, warmed, filtered air to habitable rooms (such as bedrooms and living rooms) and extract stale air (usually) from wetrooms. The mvhr unit incorporates a heat exchanger that recovers heat from the stale air extracted from the wet rooms and uses this to heat the cold fresh air entering the unit via the intake. Kitchens typically will have a recirculating hood. Trickle vents are not required.

Q: Who calculates the required amount of ventilation?

A: The calculation is complex should be carried out by a specialist consultant or subcontractor and you should expect them to design the system including the unit and the ducts.

Q: How is moist and stale air extracted from the building?

A: Stale air is extracted via a continuous fan from the wet rooms and is exhausted via the heat exchanger (in the mvhr unit) to the outside. The ducts are typically plastic and can be circular or rectangular.

Q: What is uncontrolled ventilation and why is it important?

A: Uncontrolled ventilation occurs through construction gaps in the external building envelope. It is often referred to as a building's "airtightness". It can contribute to drafts and results in the loss of internal heat gained through heating and occupying the house. MVHR will be more efficient the more airtight a building.

Q: How much electricity does it use?

A: Domestic MVHR units typically have two small fans which push the air through the system. The size of the dwelling and occupancy levels determine the size of the unit. For a small dwelling, an efficient unit will typically use around 20W in background mode, which is comparible to a low energy lightbulb (The Green Building Store).

Q: Can I open the windows?

A: The windows can be opened for comfort control and cooling.

Ventilation: Continuous Extract

In our second post of this series on ventilation, we will look at another method that uses trickle vents as the basis for overall building ventilation.

Q: What is continuous extract ventilation?

A: Ventilation is provided via continuous mechanical mechanism either via individual room extracts, a central extract system or a combination of both. Trickle vents or bespoke wall-mounted vents deliver cold, unfiltered make-up air into the dwelling; and warm air will be lost from them. Window openings normally need to be sized accordingly to accommodate them.

Q: Who calculates the required amount of ventilation?

A: The calculation is complex as it includes things like typical wind speeds and should be carried out by a specialist consultant or subcontractor. The rate of extract is set by Building Regulations.

Q: How is moist and stale air extracted from the building?

A: Moist air is typically extracted via a continuous fan from the wet rooms, utility rooms and the kitchen; and will be exhausted via a duct to the outside. Any heat in the air will be lost to the outside. The ducts are typically plastic and can be circular or rectangular.

Q: What is uncontrolled ventilation and why is it important?

A: Uncontrolled ventilation occurs through construction gaps in the external building envelope. It is often referred to as a building's "airtightness". It can contribute to drafts and results in the loss of internal heat gained through heating and occupying the house. Continuous mechanical ventilation is suitable for any level of airtightness.

Q: Can I open the windows?

A: The windows can be opened for comfort control and cooling.

Ventilation - what are the options?

We are often asked by clients about what options there are for ventilation. What would suit a low-energy retrofit, a historic building or a passivhaus building? In this series we’ll explore some common types with infographics and a selection of frequently asked questions.

Q: What is trickle ventilation?

A: Trickle vents are usually mounted within window frames. They can be closed, but for the ventilation strategy to work they should always be left open. They deliver cold, unfiltered air into the dwelling; and warm air will be lost from them. Window openings normally need to be sized accordingly to accommodate them.

Q: Who calculates the required amount of trickle ventilation?

A: The calculation can be carried out be the Architect at the Building Regulations stage. There will be requirements for the size of windows and their placement for cross ventilation and this will normally be checked during Planning Stage design development.

Q: How is moist and stale air extracted from the building?

A: Moist air is typically extracted via an intermittent fan from the wet rooms, utility rooms and the kitchen; and will be exhausted via a duct to the outside. The ducts are typically plastic and can be circular or rectangular. The fan will normally have a 15 minute overrun.

Q: What is uncontrolled ventilation and why is it important?

A: Uncontrolled ventilation occurs through construction gaps in the external building envelope. It is often referred to as a building's "airtightness". It can contribute to drafts and results in the loss of internal heat gained through heating and occupying the house. Older houses are typically more 'leaky' than modern house so this is a common system in existing homes. However, as homes have become more airtight, to reduce unwanted heat loss, trickle vents do not provide adequate ventilation and can only be used in less airtight homes.

Q: Can I open the windows?

A: The windows can be opened for comfort control and cooling.

Retrofit Ventilation for Laundry?

The sun has made a welcome return this week. After spending the winter battling with the moisture produced from drying clothes inside, I was finally able to dry some clothes on the washing line.  

Key to retrofitting homes is the management of moisture. As architects we often worry about the unseen consequences of an imbalance in insulation, especially internal wall insulation and the appearance of interstitial condensation between the layers of the construction. There are also far more visible consequences of high moisture within the volume of the home and drying clothes inside will add to this moisture load.

The Design Guide for Healthy and Low Energy Home Laundering looks at the health problems associated with the passive drying of clothes in the home. In particular, high moisture, mould growth, off-gassing from fabric softeners and dust mites, and the effect that these have on wellbeing and health. It considers what alternatives are available to passive drying and what other implications may arise out of their use.

In the context of choosing what energy we use and how, it is also important to think about the amount of energy used to dry laundry. If you dry your clothes on the radiator, is that radiator on purely to dry the clothes? Is the temperature turned up in order to dry the clothes faster, or do you open the window to help things along (even in winter)? Perhaps you prefer a heated clothes rail or have a rail over the bath? Alternatively perhaps you use a tumble dryer due to the quantity of laundry or speed of drying?

The Design Guide found that passive indoor drying adds significantly to space heating demand during the heating season. It must be remembered that moisture laden air takes more energy to heat than drier air and that the temperature of the heating needs to be raised to offset the cooling produced by the evaporation of moisture-laden washing. Moreover, in the context of rising energy prices, drying clothes with a tumble dryer accounts for 4.3% of total domestic power consumption [Ibid, p11]. So what are the alternatives?

The 1963 edition of the Building Standards (Scotland) Regulations had requirements for internal drying rooms in dwellings in addition to outdoor spaces. It acknowledged the importance of providing a separate, heated and ventilated space for drying clothes that restricted moisture ingress to the rest of the dwelling. The requirement for drying rooms in Scotland continued until the 1986 edition of the regulations, but the provision of these spaces gradually became lost with the advent of tumble dryers, which obviously have a much smaller footprint when energy constraints are put to one side. Also, space is clearly an important factor to consider when there is often limited overall area for habitable rooms in the dwelling, especially when the perception is that other methods of drying are so much more effective.

The 2020 Scottish Building Standards specifically say the “occupants should have the opportunity to dry washing other than by a tumble dryer which uses a considerable amount of energy.” Whilst it acknowledges that a utility room or bathroom with mechanical ventilation would normally be used for drying washing, it also gives a minimum ventilation extraction figure, with humidistat control, for other spaces. An indoor drying space is described as wall or ceiling mounted or indeed as floor space to set out a clothes horse, but it should also have a volume of at least 1m3 with no dimension less that 700mm. Disappointingly, the Building Regulations in England only mentions clothes drying in the context of other wet rooms and does not have a specific space requirement for drying clothes.

The aforementioned design guide promotes a designated drying cupboard as the better method for providing a dedicated drying area but it also recognises the opportunity to link passive drying requirements to improved standards of ventilation. 

A method of mechanically reducing moisture within a house would be with balanced whole house ventilation with heat recovery (MVHR) and this supplies continuous fresh air to the habitable rooms, extracting that air from moisture-laden wet rooms, such as kitchens and bathroom. Extracted air passes through a heat exchanger and the recovered heat is used to warm the incoming fresh air. The water vapour from the cooled humid air condensates into the unit and drains away. It has the advantage that it filters all the air entering the building – usually with an F7 grade pollen filter combined with active charcoal for traffic fumes; and it can deliver fresh air and extract stale/humid air from specific areas. In contrast to passive window ventilation which is only effective with human control, it is effective without occupant intervention. Unlike continuous window trickle vents the system can respond to changes in humidity.

When we think about low-energy retrofit we have to weigh the benefit of a low-energy measure to the amount of disruption to the building and its occupants caused by its installation. If you are considering upgrading windows and insulation it is imperative that this is undertaken after or at least in conjunction with reducing uncontrolled ventilation through the building fabric whilst introducing controlled continuous ventilation. The installation of MVHR can be hugely disruptive within an existing building when joist runs and crossovers have to be considered along with access to fresh air and the location of the unit itself. Sometimes a step-by-step approach that takes into account the maintenance cycle of the component parts can be more appropriate for cost, but the sequencing of the work should eliminate abortive works. 

Dedicated drying cupboards or rooms can of course be added to a balanced whole house system, but also the addition of both a supply and extract into a habitable room (rather than just limiting it to the wetrooms) can give flexibility to the location of more general rail or clothes horse drying solutions.

Recently the Passivhaus Trust published a document entitled “The case for MVHR” where they challenged the rule of thumb that MVHR systems are only effective in more airtight buildings. The paper certainly challenged my preconceptions and it raises the question of whether this should be the first installed measure for a low-energy retrofit?