Overlooking Ventilation Requirements in Loft Insulation Could Lead to ‘Unintended Consequences’

Loft insulation is one of the most common retrofit measures to be installed. However, through our PAS 2035 Compliance work, we have recently seen numerous properties that do not meet PAS 2035 and PAS 2030 compliance in terms of design and installation.

PAS 2030 accredited installers have installed loft insulation for years under numerous government schemes, however with the introduction of PAS 2035, there are more demanding criteria to meet when it comes to ventilation, namely compliance with BS5250, and it seems designers and installers either aren’t aware of these requirements or are simply ignoring them.

cold roof insultation

The retrofit assessment is of vital importance and should provide the designer with a good overview of the existing roof space and should capture the following information:

  • Whether the roofing membrane is “High Resistance (HR)” or “Low Resistance (LR)” as defined in BS5250
  • The location and condition of the loft hatch (including any draughtproofing)
  • Any defects/leaks within the roof void
  • Any services which are contained within the roof void (water tanks/mechanical ventilation)
  • Thickness of Insulation and coverage
  • Whether the roofs on the property are joined (accessible) or independent
  • An inspection should be made at the eaves to identify whether there is any eaves ventilation to the roof space and, if so, that it is not blocked by insulation

Phil Partridge, Retrofit Designer at VOR, says, “Ensuring adequate airflow within the roof space is crucial for preventing issues such as condensation, damp, and mould. It’s essential to consider the existing use of the roof space, access requirements for ventilation installation, and the type of roofing felt used, as this can significantly impact the amount of ventilation required to comply with BS5250.”

The key things to consider are;

  • Ventilation requirements post insulation – ensuring adequate airflow within roof space, BS5250 sets out the requirements for this. 
  • Roof access to install ventilation such as tile vents. 
  • Loft hatch – thermal bridge/condensation risk at loft hatch junction if not insulated adequately.
  • Existing roof space use – often limited post insulation (raised loft floor legs/decking required
  • Condensation in roof space – can lead to damp / mould problems and/or structural defects due to rot of roof structure. 
  • Existing services through ceiling/recessed downlights. 
  • The biggest issue is old-type roofing felt (bituminous) and the amount of ventilation required as defined by BS5250. Modern roofing membranes are much easier to deal with as they significantly reduce ventilation requirements.

Condensation is a risk following loft insulation due to the following reasons:

  • Older/traditional buildings relied on natural ventilation/infiltration through building fabric elements, increasingly sealed up.
  • Homes are typically warmer today. 
  • Roof spaces (post insulation) are now colder, resulting in a more significant temp difference between air entering loft space, increasing the risk of condensation
  • Inadequate ventilation of roof space.

The key guidance for this measure is:

  • PAS 2035
  • BS 5250: 2021 Management of moisture in buildings – Code of practice
  • CITB – Loft Insulation Guide TRM 152/1
  • CITB – General requirements and guidance for the installation of cold roof loft insulation

In summary, loft insulation is vital to improving home energy efficiency. However, Proper attention must be paid to the ventilation requirements to avoid potential issues with moisture build-up, damp and mould. 

Retrofit designers and installers need to be aware of the industry standards and ensure the specific ventilation needs of each property are properly designed to BS5250 to ensure that the retrofit measures comply with PAS 2035.

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