Building Regulations and Energy Efficiency of Buildings of Traditional Construction

When installing energy efficiency measures or low or zero carbon technologies, it is essential that the structural integrity of the building is retained both during and after the alterations. In some cases, structural reinforcement (for example, of roof carpentry to bear the load of solar panels) may be required.

Below are some examples of structural issues that should be considered. The list is not exhaustive, and every case should be assessed on its own merits.

If adding photovoltaic panels (PVs):

• Consider additional downforces. Consider how the load travels down to the foundations through the roof carpentry and walls and the fixings between them. There may also be additional loading, such as the weight of the panels and any associated equipment (batteries, for example)
• Consider additional uplift/wind forces and how the panels will be fixed to the roof structure
• Consider the potential of thermal-induced loading due to temperature variations of the panels, which may lead to their deformation or to stress concentration at junctions between different materials
• Look at whether the structure will need to be cut out to accommodate new wiring
• Establish what the fire risks are and consider whether additional fireproofing will be required
• Ensure the structure will remain waterproof both during and after installation.

If adding thermal insulation:

• Ventilation may be compromised
• Condensation may accelerate timber deterioration/metal corrosion for both elements and fixings
• Consider whether the insulation will hide any structural defects (or areas that are susceptible to structural defects, such as joist ends), which cannot then be easily inspected and repaired

When devising energy efficiency interventions, it is crucial that fire safety is not compromised and that fire safety requirements are met.

It is particularly important that any proposed energy efficiency measures comply with the relevant requirements of the Building Regulations 2010: Requirement B2: Internal fire spread (linings) and Requirement B3: Internal fire spread (structure). Approved Document B specifies details of the minimum classifications required for fire resistance.

You will also need to consider emergency escape routes. If a window is part of the emergency escape route, ensure that energy efficiency interventions do not prevent it from being used for evacuation.

Regarding working in historic buildings, Approved Document C states:

The need to conserve the special characteristics of such historic buildings needs to be recognised. In such work, the aim should be to improve resistance to contaminants and moisture where it is practically possible, always provided that the work does not prejudice the character of the historic buildings, or increase the risk of long-term deterioration to the building fabric or fittings.

To protect the building fabric, occupants and users from harm, it is essential that proposed energy efficiency measures consider the likelihood of moisture-related risks. For example, if the energy efficiency measures include solid wall insulation, moisture accumulation and condensation risks will need to be assessed and minimised. Recent research by the Department for Energy Security and Net Zero (DESNZ) Demonstration of Energy Efficiency Potential (DEEP) notes that increasing the thickness of internal wall insulation increases the risk of interstitial condensation (condensation occurring within or between the layers of the building envelope).

Care must be taken when considering a traditional building's resilience to climate change, with buildings being exposed to higher moisture levels both externally and internally. The exposure values to wind-driven rain noted in Approved Document C (Diagram 12: UK exposures to driving rain) are extracted from 'BS 8104:1992 Assessing exposure of walls to wind-driven rain'. However, these 1992 values are lower than current estimations due to climate change.

More recently, DESNZ and the Met Office carried out research on projected wind-driven rain in the UK. They found that the annual average amount of wind-driven rain is not expected to change considerably under 2°C and 4°C warming scenarios. However, there will be more notable changes in the seasonality, direction and intensity of wind-driven rain. There is a projected increase of around 33% in winter precipitation, and more frequent intense rainfall events are predicted. The UK is also expected to experience shorter but more concentrated wind-driven rain spells, especially in winter months. Notable increases are anticipated in projected annual wind-driven rain from the west, southwest and south.

Approved Document F states that infiltration (or air leakage) is uncontrolled ventilation that forms part of the overall ventilation provision of a building. Some energy efficiency measures, such as airtightness or draught proofing interventions, may reduce infiltration. To meet the requirements of Building Regulations when implementing such measures, you will need to demonstrate that there is adequate fresh air provision for occupants and users and that moisture and indoor air pollutants are managed.

A fundamental objective of Approved Document L is to ensure that energy efficiency interventions do not lead to fabric deterioration, and it recognises that it is not always technically or functionally feasible to meet the target U-values prescribed when considering historic and/or traditional buildings. It also notes that it may not be cost effective for some energy efficiency interventions to be undertaken (that is, to achieve a simple payback of 15 years or less). In these circumstances, the U-values after implementation of energy efficiency measures should be as close as practically possible to the target values.

The energy efficiency of historic and traditional dwellings should be improved only if doing so will not cause long-term deterioration of the building's fabric or fittings. In particular, this applies to historic and traditional buildings with a vapour permeable construction that both absorbs moisture and readily allows moisture to evaporate. Examples include those built with wattle and daub, cob or stone and constructions using lime render or mortar.

Additionally, Approved Document L refers to Historic England's 'Energy Efficiency and Historic Buildings: Application of Part L of the Building Regulations to Historic and Traditionally Constructed Buildings' and recognises that for listed buildings, buildings in conservation areas, scheduled monuments and historic and traditional buildings, a higher U-value than that required for new buildings may be acceptable.

Generally, a thermal element once upgraded should not have a U-value greater than 0.7W/(m²·K). A lesser standard for the thermal element may be acceptable where work complies with Part C of the Building Regulations on protection from the harmful effects of interstitial and surface condensation.

The exemptions noted above are particularly relevant in light of the recent Demonstration of Energy Efficiency Potential (DEEP) research project funded by the Department for Energy Security and Net Zero (DESNZ). The research concluded that the installation of internal wall insulation leads to an increased risk of interstitial condensation, particularly with U-values lower than 0.8W/(m²·K).

It was found that installing IWI [internal wall insulation] increases the risk of interstitial condensation, although the increase in risk is lower up to a U-value of 0.8W/(m²·K), and mitigations are available.

Approved Document O: Overheating only applies to new residential buildings and includes 2 methods to demonstrate compliance (simplified method or dynamic thermal modelling). It focuses on overheating mitigation through building design (limiting unwanted solar gains in summer and providing adequate means to remove indoor heat) as well as by considering environmental factors (such as noise at night and pollution).

However, it does not consider building use and how this may increase or reduce overheating risks. Also, it does not discuss energy efficiency interventions for historic and/or traditional buildings, which need to be assessed against heritage significance, any potential loss of historic fabric, and any potential damage to the building or its occupants.