Installing insulation and vapour barriers, particularly in existing buildings not originally designed for them, often leads people to ask whether the building will “sweat” as a result. It’s possible to understand the thought processes that might lead to that question, but is there any truth in the idea?
To put things in some context: the human body produces sweat to help regulate body temperature. The body gets hot, sweats, and the evaporation of that moisture off the skin introduces a cooling effect to help reduce the temperature.
Trapped moisture
It’s a common experience, especially for anyone who enjoys the great outdoors, to put on a plastic (or, more accurately, non-breathable) raincoat and find it becomes wet on the inside within minutes. The body sweats and the evaporated moisture condensates on the inside of the coat.
In building projects, when the specification calls for a vapour control layer – especially a plastic-based one like polythene – perhaps it is this ‘raincoat’ effect that people are thinking of and worrying about. That as the building is used, moisture will form on the vapour barrier.
Condensation isn’t sweat
Building occupants generate moisture through everyday activities: cooking, cleaning, washing, bathing, breathing and – yes – sweating. The moisture vapour is held in the air, but it’s not a result of helping to control the temperature of the building. It is entirely a by-product of people living and working in buildings.
As the temperature of air changes, the quantity of moisture vapour it’s able to hold also changes; the warmer the air the greater its capacity. When warm air comes into contact with cooler surfaces, it drops in temperature and can no longer hold the same quantity of moisture.
If it was already at or close to saturation point then the moisture it can no longer hold is deposited as condensation – such as on a cold beer glass in a warm pub or inside a cold raincoat worn by a warm person.
Cold surfaces in buildings
Anywhere that insulation is missing or badly installed and allows warm air to leak from a building is a potential cold spot – and a potential area for condensation to occur. Windows are also a prime candidate for condensation, since they typically have a worse thermal performance than the surrounding building fabric.
It’s right to be concerned about condensation, because it is unwanted in buildings. It creates a damp and unhealthy environment for a building’s occupants, and can lead to mould growth. If it occurs within the building structure, unseen, and is allowed to accumulate over time, it can also lead to structural failures – for example, if timber elements start to rot.
Buildings might not sweat, but controlling moisture is very much something to think about. It’s understandable that people get concerned about installing vapour barriers and airtight layers. Positioned correctly, however, they can be very effective and help protect the building fabric.
Next month we’ll look at how airtightness, insulation and ventilation work together in modern construction to minimise condensation risk.
The Old Byre, Isle of Wight
EAL Consult worked with Gianni Botsford Architects to provide energy consultancy for The Old Byre, an innovative project to convert two farm buildings into living and offices spaces for visiting artists.
The project
The Old Byre is set on pastureland above West Cowes. This conversion of two understated farm buildings on the Isle of Wight creates a new home while also offering residency and working spaces for visiting artists. The project retains the footprint and structure of the original barns, wrapping them in insulation and corrugated cement board on the exterior.
The two buildings that make up The Old Byre have been purposefully left disconnected, with passages and crossings between private and social spaces, through the cool morning air, rain and summer heat. At night, the translucent polycarbonate windows hint at activity on the inside. In the older barn, a house within a house has been built from spruce plywood. A back alley connects the more intimate, private interiors, tempered and modulated by full-height doors without traditional handles or locks.
Assessing the Thermal Elements of the Development
EAL Consult’s role in the project was to complete the calculations to make sure the buildings complied with Part L of the Building Regulations for existing buildings. The process included assessments of the insulation, heating and glazing elements specified in the plans, all to support the intention of retaining the buildings rather than demolishing them.
RIBA Award 2025
The Old Byre has been much recognised for its innovative design including RIBA South Region and National Awards in 2025.
Thermal Assessment and Consulting for an Urban Redevelopment
EAL Consult worked with Stolon Studio architects to provide energy consultancy for Penrose Mews, a ground-breaking housing scheme in West London.
The project
The project used an innovative and original design to place eight mews houses and one flat on a challenging urban site, previously occupied by industrial buildings and an electricity sub-station.The project aim was to create sustainable, sociable housing which encouraged residents to build a community.
The resulting development incorporated a community-centric shared courtyard, roof terraces promoting urban greening, renewable technologies and highly energy-efficient homes.
Assessing the Thermal Elements of the Development
EAL Consult’s role in the project was to ensure that the thermal elements of the proposed buildings were of a suitably high standard to provide the high-quality high-performance homes imagined by the architects. The process included assessments of the insulation, heating and glazing elements specified in the plans, as well as a detailed study of potential sustainable technologies, to find the solutions most suited to the compact site.
Exceeding Energy Efficiency Targets
The assessments provided by EAL Consult included As Design SAPs, Energy Modelling, U-Value Calculations, Water Calculations and an Illumination Impact Assessment. As a result of their recommendations, the homes in the development averaged an EPC rating of B, exceeding the current Building Regulations requirements and fulfilling the client’s original vision for the site.
Energy Consultancy for a Rural Housing Development
When Stolon Studio architects were commissioned to design a pioneering rural housing development on a former dairy farm in Herefordshire, they turned to EAL Consult to provide energy consultancy, and to ensure that the project complied with Building Regulations requirements.
The Project
Stolon Studio specialises in providing ‘sociable housing’, where community-building and interaction between residents is encouraged and enabled by the design of the buildings and surrounding spaces. The Parks project required the complete transformation of the site, from a series of neglected farm buildings into eight sustainable homes, with a layout and common areas to encourage social interaction, combatting rural isolation.
The client chose best carbon footprint practices by renovating and extending the existing farmhouse, barn, and outbuildings to provide sustainable homes on the site. Assessing the sustainability of the proposed development where the existing structures were in various states of disrepair and collapse, the client’s vision included salvaging as many of the original materials and historical features as possible for use in the new homes.
Rennovation vs New Build
To meet the challenges of renovation over rebuild, EAL Consult carried out SAP calculations using the initial building designs, providing advice on the thermal elements of the proposed renovations. They used energy modelling to recommend site-specific solutions for high-performance insulation, heating and glazing.
The project also incorporated the use of renewable technology for heating, enhancing the energy efficiency of the buildings. EAL Consult reviewed various options for the site and made recommendations based on the specific requirements of the renovated structures and their rural location.
Meeting the original vision
Featuring original historic constuction alongside high-performance glazing and insulation, as well as efficient underfloor heating and air-source heat pumps, The Parks development has lived up to the client’s initial plans. Thanks to EAL Consult’s calculations and recommendations, the new homes averaged an EPC rating of B, exceeding the current Building Regulations requirements in spite of the complexity of the project.
Creating a Sustainable Home via Retrofit
When EAL Consult was asked to assess a 1930s residential property for a sustainable Retrofit, they found their clients were a professional couple with dreams of off-grid, self-sufficient living who were determined to futureproof their home by investing in renewable technology and sustainable improvements.
They knew they needed expert advice which led them to EAL Consult.
The Initial Survey
EAL Consult’s survey began with a detailed inspection. The original walls were solid brick with a cavity but no insulation, while the loft conversion and extension both used more modern construction techniques. Most of the windows were double-glazed PVC, with aluminium-framed windows in the 2018 loft conversion. The central heating ran on gas, with an ‘A’ rated combination boiler. Feedback from the clients identified construction elements that caused drafts and cold bridging.
A thermal imaging survey was carried out and highlighted cold spots demonstrating areas of low insulation and drafts. The thermal and ventilation performance of the existing property was evaluated. An EPC carried out in 2021 had given the house a ‘D’ rating, so there was certainly scope for improvement by the current owners.
Next Steps
Before recommending any renewable technologies for the house, EAL Consult was careful to build up a comprehensive picture of the property through a ‘Fabric First’ approach – assessing the existing structure to make sure that issues with insulation, cold bridging and drafts were addressed before suggesting alternative systems for heating and power.
Considering options
In order to prepare the property for the installation of a renewable heating system, it would be necessary to rectify the issues with insulation and drafts. Most renewable heating technologies require high levels of fabric efficiency and air tightness, and effective mechanical ventilation in order to work efficiently. EAL Consult was able to offer several options for external insulation, draft prevention, and upgrades to the fabric of the building.
Having considered a wide range of options for renewable technologies the team provided the homeowners with a detailed report. This included five options with calculations demonstrating the effect of each combination of fabric and energy efficiency on the property’s energy performance, with predicted EPC ratings.
Evidence-based reporting and cost savings
As a result the property’s potential EPC rating jumped from ‘D’ to ‘B’. The clients had a clear and concise specification to pass on to the contractor for accurate costings that would deliver the home of their dreams without costing the earth.
If you’d like a initial FREE conversation about how a Retrofit Assessment can help you make informed decisions, get in touch