Methods and Metrics for Moisture Risk Assessment- Solid Wall Insulation (MRA-SWI)

Lead Research Organisation: Loughborough University
Department Name: Architecture, Building and Civil Eng

Abstract

If the significant numbers of dwellings with solid masonry walls (SMWs) are to be insulated, there will have to be a paradigm shift in the way that moisture risk is assessed. Methods must be developed to clearly demonstrate that insulation solutions are effective, robust and resilient to moisture even when considering the vagaries of our future climate and the way that people choose to live in their homes. This research will result in new methods and metrics, backed by rigorous scientific evidence, that enable moisture risk assessment of SMWs to be carried out routinely, new insulation materials to be developed and more homes to be insulated.

Insulating the UKs existing housing stock will be an essential step in achieving greenhouse gas reduction targets and alleviating fuel poverty. The highest levels of heat loss occur in the c30% (8 million) homes that have SMWs. Insulating these walls offers significant potential for fuel savings but may cause moisture problems. Water accumulates within SMWs when it is raining outside or humid inside and diminishes with drier conditions. This water can pass from one face of the wall to the other as there is no cavity to act as a capillary break. Applying insulation to either the inside or outside face of the wall changes the temperature of the masonry, the rate of wetting and drying at each face and the locations where water vapour might condense and accumulate. This moisture can lead to mould growth, interstitial condensation and freeze thaw damage. These problems can cause severe damage, are expensive to repair and can affect the health of occupants.

Current guidance in the UK Building Regulations (approved document C) and related standards is not adequate for assessing moisture risk when insulating SMWs. The simplified steady-state vapour diffusion model is not appropriate because dynamic liquid moisture conduction is the dominant moisture transport mechanism when SMWs are exposed to rainfall. There is a distinct lack of guidance on how to use more advanced transient heat and moisture simulation software, what inputs should be used for the boundary conditions and how the results translate into moisture risk. Straightforward design principles, based on many years of practical experience and research, have led to contradictory advice e.g. there is no clear consensus on how permeable the insulation material should be to water vapour. Thus only a small handful of hygrothermal experts might ever attempt a quantitative risk assessment for insulating SMWs and fewer SMWs are being insulated as a result.

This research project will address these problems. Firstly, a framework will be developed for using advanced heat and moisture simulation software to carry out moisture risk assessment. This will include guidance on the boundary conditions to be used at the inside of the wall, and outside especially for wind driven rain exposure. It will also identify appropriate criteria to minimise risk from moisture accumulation within the wall, mould growth at the indoor surface and freeze/thaw at the outside surface. A number of insulation materials will be compared to understand which can best reduce the risk of moisture damage when insulating SMWs. Secondly, probabilistic modelling methods will be used to understand how robust different insulation solutions are to moisture damage given that there is considerable uncertainty in boundary conditions and material properties. Thirdly, new approaches to moisture risk assessment will be explored. A 'moisture safety factor' might describe how resilient an insulated SMW is to extreme events such as flooding. It may be possible to develop a completely new laboratory test for assessing insulation solutions. The underlying strength of this research comes from the collection high quality primary data, in the new state-of-the-art Hygrothermal Test Facility, for validating the results from the models.

Planned Impact

The project addresses a serious and growing concern: insulating older buildings can result in moisture damage that is unsightly, expensive to repair and can affect the health of occupants. This may cause financial or reputational damage to those that recommend, design, manufacture, certify, specify, purchase, guarantee or install insulation. This perceived risk has resulted in fewer older buildings being insulated. Reliable methods and metrics for moisture risk assessment would lead to more solid walls being insulated and this would result in a significant reduction to the UK's greenhouse gas emissions. It would also result in homes that are more comfortable, healthy and affordable to heat.

The new knowledge and the methods created in this research will have positive impacts on a number of key stakeholders. The government are required to reduce greenhouse gas emissions and solid wall insulation can play a significant role in this. This research will provide methods that can be developed to enable a step-change in the uptake of solid wall insulation by demonstrating which solutions are safe for which walls and in which locations. This will also protect our oldest and most valuable building stock from potential damage caused by the use of inappropriate insulation. The manufacturers of insulation systems can use this research to demonstrate which of their solutions is appropriate for a particular building in a particular location, increasing their sales. They can also use them to develop new and more effective insulation materials and systems, adding market and employment opportunities. Notified bodies will be able to use the methods developed to provide a testing and accreditation service for solid wall insulation, providing government, building control, local authorities, architects and insurers with greater confidence in products and systems. Refurbishment companies will be able to carry out their own moisture risk assessment as a matter of course, giving them confidence that they are installing a suitable product and providing suitable warranties to the building owners. Standards companies can develop new standards with international reach that create the much needed paradigm shift in how moisture risk is assessed.

The research project will also nurture the skills, knowledge and expertise required to develop the UK as a world leader in moisture risk analysis and Loughborough University as an academic centre of excellence.

Publications

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Description High quality data on the hygrothermal performance of solid masonry walls have been collected in the Hygrothermal Test Facility.
These data have been used to calibrate models for predicting the risk of moisture problems in solid masonry walls in different UK locations.
Exploitation Route The work will continue through PhD research.
Sectors Construction,Energy