ECON summary of UK HSE report

by | Jun 12, 2024

UK HSE report confirms <1% risk to timbers when spray foam is used in conjunction with guidance set out in BS5250:2021.



Why is this HSE UK report welcomed by ECON & BASF?

The HSE document is an independent report providing clarity on the risks associated with the use of spray foam insulation in pitched roofs. It assesses and identifies the extent of the moisture risk associated with the application of spray foam when installed in timber pitched roofs across several UK locations. The report deals with both open cell and closed cell spray foam insulation used in conjunction with non-breathable and breathable roof underlays and applications directly to slated and tiled roofs. The research used several types of established and industry respected numerical hygrothermal simulations to assess the moisture risk.

Recent History

Ongoing concerns have been expressed by several UK industry organisations with regards to the suitability of spray foam insulation in pitched roof applications due to the possible risk posed to roofing timbers over time. These often-legitimate concerns are a direct result of technical misinformation originating from a number of material manufacturers and their representatives. Erroneous application advice has been fed through their respective contractor network resulting in unsafe applications from a moisture accumulation perspective.

Reports published by the UK PCA (Property Care Association) and RICS (Royal Institute of Chartered Surveyors) relating to concerns with spray foam roof upgrades, have created confusion and have negatively affected the UK domestic spray polyurethane industry as a whole, including new home construction.

UK new build projects are overseen by qualified design teams whose responsibility it is to review product Agrément certification and condensation risk analysis in order to ensure materials and application suitability. This is a very different environment to that of a domestic pitched roof refurb installation where the homeowner is at the mercy of the overzealous sales companies or a misinformed contractor.

Both report are only concerned with UK domestic pitched roof refurbishments.

Report Summary

The modelling indicates that the risks are “Low” when spray foam insulation is applied in conjunction with British Standard BS 5250:2021. A space between the underlay and the insulation created by a card spacer where air can circulate and an AVCL is applied to the warm side of the insulation created <1% risk of timber decay. All the charts and results show that by following prescriptive guidance in BS5250:2021, the relative humidity remains below the timber decay threshold of 85% and result in a moisture-free design.

Summary of cases modelled

The tables below provide an overall summary of the risk for each of the cases for severe climate (Newcastle) and less severe climate (London) respectively.

The table categorises the risk according to the severity of the timber decay in the outer region (timber nearest the external climate) over a five year period.

RED >25% High Risk
AMBER 1-25% Medium Risk
GREEN <1% Low Risk


Buildings are under increased stress from moisture because of modern lifestyles and our environmental conditions. Climate change is directly impacting buildings with increased penetration of driving rain, flooding and increased humidity internally and externally, all slowing drying rates. Increased insulation levels, reduction in natural ventilation, higher amounts of internal water vapour, use of underlays and sealed underlays have all contributed to increased risks of condensation within the roof construction. The revised BS5250:2021 is based on practical experience and provides robust whole building design to minimize moisture problems throughout the construction.

The research team for this project carried out extensive hygrothermal modelling to assess the moisture risk, the risk of mould and condensation occurrence and the likelihood of decay to the structural timber roof surrounded by the spray foam insulation. They reviewed both open cell and closed cell spray foam insulation, with more emphasis placed on the open cell products based on recent quantity used in the UK market. The models and graphs shown on the previous page evaluated the risk of SFI applied directly to a range of roofing membranes, both with and without AVCL.

Prescriptive Guidance

The conclusion from the research indicates that the risks are low (<1%) if the spray foam insulation is applied in accordance with the prescriptive roof construction and guidance described in British Standard BS5250:2021. The guidance recommends the inclusion of an air layer between the insulation and the underlay and the use of a AVCL on the warm side of the insulation. The researchers have recognized and recommended the use of a card spacer inserted between the rafter to create the air layer required to comply with BS 5250:2021. ECON Building Products has consistently recommended the use of BS5250:2002 and the updated 2021. We fully support the research and information provided in the latest UK HSE document on “Spray foam Insulation applied to timber sloped roofs in dwellings” and would welcome all further assessments that recommend the use of BS5250:2021.

To review the full UK HSE report please follow the link below.

Moisture risk of spray foam insulation applied to timber sloped roofs – GOV.UK (

Download PDF : ECON summary of UK HSE report

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