In the context of residential properties undergoing full wall replastering, a common query arises: should a surveyor include the calculation and potential reboarding as part of their recommendations? This question becomes particularly relevant when dealing with external walls and the implications of Building Regulations, particularly Part L1B.

Compliance with Building Regulations

Under Section 11 of the Landlord and Tenant Act 1985, repair works required to remedy disrepair do not inherently trigger the requirement to comply with Part L1B of the Building Regulations. Part L1B focuses on conservation of fuel and power in existing dwellings, including insulation upgrades. However, this obligation is not automatically imposed when addressing disrepair unless the scope of work substantially alters the thermal performance of the building.

Upgrade Considerations

If all plaster on the inner face of an external wall is removed and renewed, upgrading to insulated plasterboard is often appropriate. The rationale for this upgrade is to improve thermal efficiency and comply with modern expectations for energy performance.

However, Part L1B introduces a 50% threshold rule for external walls: if more than 50% of the surface area of an external wall is renovated, insulation must be upgraded to meet current standards.

Counterarguments can be made to mitigate the necessity of such an upgrade:

• Offsetting Other Thermal Elements: The overall thermal performance of the property might already be satisfactory due to other measures, such as:
  • Floor insulation
  • Roof insulation
  • Windows with low U-values
  • Efficient heating systems
• Cost-Benefit Analysis: The cost implications of insulated plasterboard may not always justify its installation, particularly in cases where other elements compensate for the lack of wall insulation.

Calculation Requirements

Calculations to justify or refute the necessity of insulated plasterboard can be complex and time-consuming. Preparing such calculations is not typically within the remit of a surveyor during a standard inspection or report preparation. Instead, it is reasonable for a surveyor to:

• Make a professional judgment based on the principle of “balance of probabilities.”
• Recommend thermal upgrades where appropriate, leaving detailed calculations to be undertaken by the property owner or landlord if they wish to contest or refine the recommendation.

For example, in cases where plaster is removed from an external wall, and the 50% threshold is exceeded, the surveyor can reasonably conclude that thermal boarding is necessary under Part L1B. The burden of proof for alternative solutions or exemptions should be put upon the landlord.

Cost Implications

The cost of upgrading to insulated plasterboard can be a deciding factor for landlords and property owners. A typical 50mm insulated plasterboard costs approximately £30 per m² more than standard plasterboard.

Conclusion

Under Section 11 of the Landlord and Tenant Act 1985, landlords are obligated to address disrepair, but compliance with Part L1B of the Building Regulations becomes mandatory if more than 50% of the surface area of an external wall is renovated. Surveyors should assess whether this threshold is met and recommend thermal upgrades, such as insulated plasterboard, where appropriate. However, detailed calculations should be undertaken by the landlord or their appointed specialists. This approach ensures alignment with both Section 11 obligations and Building Regulations while providing a clear framework for landlords to evaluate practical and cost-effective solutions.