Wall Insulation
Traditional masonry buildings that have been well maintained using appropriate compatible materials will provide a degree of resistance against floodwater and will readily recover after a flood event. This is because, ordinarily, moisture rises only a small distance, often no higher than the first masonry joint.
In a traditional building, walls in good condition with appropriate lime mortar will slow the passing of floodwater through the substrate. They will also accelerate drying due to the superior durability and intimacy of bond between traditional mortar mixes and masonry units. For substantial capillary rise to occur a very strong and persistent source of water is needed, such as a broken water main or sewer, or floodwater. Usually, this must be coupled with the presence of a material that slows or prevents evaporation at or around the base of the wall, such as cement render, waterproof coatings or non-permeable insulation.
Earthen structures are not covered on this webpage because these buildings often have good thermal performance and, as such, there is limited opportunity for thermal upgrade of fabric.
When repairing or altering a masonry wall, it is important to select the most appropriate mortar/plaster/render for the building's substrate. It has been shown that the moisture permeability of the substrate and its mortar/plaster/render should be of similar properties to accelerate drying times and managing moisture ingress.
The efficacy of insulating walls either internally or externally is still being researched. In either case both will be impacted by floodwater in the same way. However, external wall insulation has the added risk of impact from debris.
Where a whole building approach has identified that it is appropriate to reduce heat loss by improving the thermal performance of the walls, it is important to choose the most appropriate insulation material to do so. However, it is also important to ensure that it does not adversely impact the building's natural ability to manage moisture and buffer external environmental temperatures.
As explained on the insulation materials page, where an impermeable insulation is used (except for loose fill insulation) it is more likely to recover after a flood event and still perform a thermal function. Whereas both vapour permeable insulation and loose fill impermeable insulation are more likely to need wholesale replacement following a flood event.
Therefore, it is currently not recommended that insulation materials are installed in traditional buildings at risk of flooding, unless the materials can be removed before a flood occurs. Where removal is not undertaken, then it is likely to cause longer periods of drying to the property, be more disruptive to the occupants and result in increased carbon emissions being lost as the life expectancy of the material is reduced.
In relation to increasing flood resilience and recovery, some guidance recommends using lime plaster on an entire wall surface, whereas others suggest using it only to a height of 600mm or above the estimated flood level. There are several reasons for not incorporating two different materials on the same surface. The main reason is because it will result in different hygrothermal properties and differential movement in response to the internal environment. This can result in the junction cracking, different surface condensation risk, and variable thermal performance. Even with two different lime plasters, there is the potential for them to have different properties that do not complement one another. Thus in traditional buildings it is best to use lime plaster for the whole wall surface.
In summary, until such time as an insulation material is designed and manufactured to work both with the moisture permeability of traditional buildings, and can recover after a flood with minimal intervention, then energy efficiency measures should focus on those associated with improving the thermal performance of roofs, windows, doors, and via mechanical and electrical systems.