Oct 18, 2018 Last Updated 10:41 AM, Oct 15, 2018

Declining damp: Divining the best methods to avoid condensation and mould

Published in Talking Point
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There are few things which strike fear into social housing tenants’ hearts more than the potential of damp and mould lurking within the walls, floors and ceilings of their home. It is a distressing prospect, which, if it materialises, can have a major impact on residents’ health, whilst also incurring a large cost to those managing the property, writes Tom De Saulles, Sustainability Senior Manager at Modern Masonry.

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Let’s be clear from the start that damp and mould can affect all forms of construction as it is caused by issues largely unrelated to the type building construction. It is aided by multiple factors, which include (but are not limited to): levels of insulation, heating, ventilation and moisture produced by occupant activities (cooking, washing, drying clothes etc.).

It is a problem affecting old and new properties alike and something which needs to be taken into account early in the design phase in order to ensure durable, fit-for-purpose social housing. The big questions are, what’s the current main cause of structural damp and mould, and how can we address it?

New problems

We are very familiar with damp and mould issues in historical social housing, and a good number of design lessons have been learnt from previous oversights and deficiencies in construction, particularly poor insulation.

However, new housing is not entirely immune to damp- and mould-related issues. Although they are much better insulated, surprisingly they can be susceptible to inadequate ventilation and poor air circulation. This is certainly the case in modern airtight homes with very low air leakage rates.

A progressive tightening of Part L requirements is largely behind this. In a nutshell, these regulations seek to reduce heat loss from buildings and have driven down air leakage rates in new homes. Of course, this is beneficial for heating bills, but without good ventilation design (and operation), it can impact on the internal air quality and moisture levels, leading to the formation of mould – an unintended consequence.

A bridge too far?

Thermal bridging is another potential cause of damp within social housing. This phenomenon describes the heat loss which occurs within the building envelope where an area has significantly higher heat loss than the surrounding fabric.

This is often due to the geometry or the presence of materials with poor insulating properties, creating a bridge for heat to escape. Local cold spots in a wall caused by this can encourage condensation and mould, not to mention impacting energy efficiency.

Some thermal bridging is inevitable in all forms of housing; its impact, however, can be greatly reduced by careful attention to the detailing of junctions.

An eye for detail

To simplify this task and ensure the highest levels of thermal performance, the masonry sector has produced a comprehensive set of standardised, high-performance construction details that are freely available from three key providers: the Local Authority Building Control (LABC), Constructive Details and the Concrete Block Association.

Each of these details has its own calculated heat loss rating (psi value) for use in the Standard Assessment Procedure (SAP) and is also accompanied by a simple 2D drawing showing how it is constructed, along with dimensions and a specification of key components.

Use of these details offers an easy win, as they provide a low-cost means of enhancing thermal performance, preventing damp/mould, and are also fully compliant with current Building Regulations.

The alternative option of using unverified construction details will attract a significant performance penalty in the SAP assessment, resulting in up to a 60% increase in heat loss from junctions than would otherwise occur. It also requires greater effort and cost to be spent on other aspects of the design to compensate for the loss of performance and ensure the fabric energy efficiency target set by Part L of the Building Regulations is achieved.

Practical solutions

In terms of heating the home to prevent damp and mould, continuous low-level background heat is preferable to short periods of high heat when the house is occupied. This approach is helped by masonry construction, which provides a useful level of thermal mass (the ability to store and release heat), helping to avoid significant temperature swings across the day. This allows for the maintenance of a relatively stable and consistent temperature.

Masonry and concrete also work really well with modern, energy-efficient underfloor heating systems, which are most effective when operated continuously, using relatively low-temperature hot water from a condensing boiler or heat pump. The lower the flow temperature, the greater the efficiency of the boiler or heat pump, with the thermal properties of masonry and concrete helping to achieve this.

Where occupants do operate their heating intermittently (as most will), the slow release of heat from masonry and concrete usefully prevents the internal temperature dropping as much as occurs in lightweight housing when the heating is off.

In a survey we conducted earlier this year, damp and mould were significant concerns for people looking for their next home. Further results from the survey can be found in our report, ‘A Dream Home: An Exploration of Aspirations’ (http://www.modernmasonry.co.uk/HomeownerSurvey).

Should damp occur within a wall construction in a residence for whatever reason, the moisture tolerance of masonry will ensure its continued structural integrity and stability and the avoidance of unwanted mould and rot.

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