In a report published jointly by DEFRA, DCLG and the Environment Agency “Improving the flood performance of new buildings” rigid PUR foam is shown to be the best performing when installed into cavity walls. The report states “Cavity insulation should preferably incorporate rigid closed cell materials as these retain integrity and have low moisture take-up. Other common types, such as mineral fibre batts, are not generally recommended as they can remain wet several months after exposure to flood water which slows down the wall drying process. Blown-in insulation can slump due to excessive moisture uptake, and some types can retain high levels of moisture for long periods of time (under natural drying conditions).” The results of the report are based on laboratory findings and classify wall components as good, medium or poor with regard to:
- water penetration – the leakage (rate and volume) through the entire wall thickness (note that this is different from “water absorption”)
- drying ability – the capability to regain its original surface moisture condition (assessed by the average drying rate and the time taken to reach the original value)
- retention of pre-flood dimensions, integrity – the lack of deformation or change in form or appearance of the wall panel.
PUR foam gained a Good rating for retention of pre-flood dimensions, integrity and a Medium rating for water penetration and drying ability with all other insulants listed having a Poor rating.
Closed cell insulation is also recommended when installing floor insulation in order to minimise the impact of flood water.