Sustainability & Built Environment Defective Concrete Blocks Requests

Background and Request from Government

On the 30th of November 2021, the Government agreed to several enhancements to the Defective Concrete Blocks Scheme. The National Standards Authority of Ireland (NSAI) was requested to consider a number of technical matters relevant to its remit as a standards and certification body. One of the requests included a review by NSAI’s Sustainability & Built Environment Department of existing certification for pumped cavity fill insulation products and to assess the potential impacts of cavity wall insulation on DCB homes.

Review Undertaken by NSAI

NSAI’s Sustainability & Built Environment Department undertook a structured technical review of NSAI Agrément certification relating to pumped cavity wall insulation, in response to the request from Government and in line with NSAI’s role as a certification body. Committee Document N237, dated 28 June 2024, documents this review. It sets out the scope, methodology and outcomes of the assessment of NSAI Agrément certified pumped cavity wall insulation systems, including the associated installer competency arrangements. The document outlines the assessment criteria and technical requirements applied by NSAI Agrément for Irish dwellings, with particular reference to compliance with the Irish Building Regulations. It also describes the controls and limitations inherent in the certification and installer scheme framework.

Arising from this review, NSAI Agrément identified the assessment of moisture behaviour within cavity walls containing aggregate concrete blocks as the only outstanding technical matter requiring further investigation. Committee Document N369 supplements N237 by addressing this issue in detail. In the absence of sufficient field based data at the outset, advanced hygrothermal modelling was initially employed to examine the potential impact of cavity wall insulation on moisture levels. As scientific and field data subsequently became available through the Defective Concrete Blocks Scheme, this empirical evidence was used to directly evaluate moisture content in cavity wall constructions. The investigation therefore reflects a progression from predictive modelling to analysis informed by measured data, supported by independent third party technical assessment.

Committee Document N369 supplements N237 by investigating the impact of cavity wall insulation on moisture levels in cavity walls constructed with aggregate concrete blocks.

Published Reports and Public Interest

The review and associated investigations are now complete and are documented in the reports published on this page. These documents set out the scope, methodology, and outcomes of the work undertaken, together with supplementary technical investigation.

In the interest of transparency and public information, NSAI is making these reports publicly available. The documents should be read in full and in context, and the findings relate solely to the defined scope of the review and the evidence available at the time of assessment.

Outcomes of the Review and Associated Investigations

• The N369 study utilised the best available data to quantify the moisture content of the external leaves of masonry in properties participating in the DCB scheme, enhancing the technical understanding of material moisture contents in the context of cavity wall construction in Ireland. The insights arising from this work have been presented to relevant technical committees undertaking reviews of relevant standards and have also informed related research projects being progressed by Construct Innovate.
• While the retrofitting of cavity wall insulation is associated with a marginal rise in average moisture content of masonry units, the data indicates that external wall leaves experience fluctuating moisture levels due to multiple factors on a seasonal basis, irrespective of whether retrofitting has taken place. These inherent variations in baseline moisture content are greater than the changes attributed to cavity wall insulation.
• Although cavity wall insulation has not been shown to cause degradation or increase the rate of wall degradation, a precautionary, risk based assessment is being applied to all retrofitting certification schemes, in liaison with the Sustainable Energy Authority of Ireland, to avoid the retrofitting of buildings containing defective concrete blocks that may be subject to future remediation.
• While hygrothermal modelling could not be applied conclusively within this study due to data limitations, NSAI remains committed to advancing the appropriate use of modelling in Ireland and has initiated internal projects to support the safe, robust, and evidence based implementation of hygrothermal modelling in future applications.
• Although not examined as part of this investigation, it is noted for completeness that independent research undertaken in the context of the Defective Concrete Blocks Scheme since the original Government request indicates that degradation in affected dwellings is understood to be associated with the presence of deleterious minerals within the masonry blocks, including their mineral form, concentration, and associated reactivity.
• NSAI Agrément remains committed to sharing its knowledge and insights with relevant stakeholders, thereby supporting current and future studies focused on enhancing our understanding of these materials.