RAAC Panels in Buildings

Sep 9, 2023 | Building Pathology, Building Technology

RAAC Panels in Buildings

RAAC Panels in Buildings: Identification, Assessment, and Remediation

What Are RAAC Panels?

Reinforced Autoclaved Aerated Concrete (RAAC) panels were popularly used in the UK between the 1950s and 1990s, primarily for roof constructions. These panels combine the lightweight feature of aerated concrete with reinforcement, providing both insulation and structural capacity.

Why Is Identifying RAAC Important?

Recent media reports have heightened awareness around RAAC panels, pushing many property owners and managers to determine their presence in buildings. As a result, there is an increasing demand to identify and assess these panels, ensuring the safety and compliance of structures.

These concerns are not unfounded and there is a possibility that some RAAC panels might not perform as originally intended. Potential structural deficiencies can arise due to the inherent properties of RAAC, through workmanship or design faults, or sometimes because of inappropriate refurbishment or alteration works.

RAAC Failure

Inherent Properties of RAAC – Permeability and Corrosion of Reinforcement

Prior to manufacture the reinforcement was covered with a coating to protect it against corrosion. Autoclaved Aerated Concrete is, however, highly permeable and does not protect against environmental conditions.  Where it is used as a structural flat roof deck it could be prone to moisture ingress resulting in corrosion.

RAAC Workmanship or Design Faults – Reinforcement and Insufficient Anchorage

As with all concrete elements, Autoclaved Aerated Concrete has reasonably good compressive strength (although much lower than traditional concrete). However, shear, and tensile strengths are poor. For this reason, longitudinal reinforcement bars are added to provide flexural capability with additional transverse reinforcement bars welded at the bearing points to improve shear capacity.

The design and workmanship of longitudinal and transverse reinforcement is therefore critical to the overall safety and effectiveness of the RAAC panels.

Reinforcement Positioning for RAAC

Inappropriate Alterations – Refurbishment Works and Service Hole Drilling

Numerous cases have been discovered in which renovation activities on buildings led to the creation of drill holes in RAAC panels. Such actions can diminish the panel’s overall strength, leading to concerns about the stability of the compromised panels.

For the safety of your property and its occupants, if you believe RAAC panels may be a concern in your building, act now. Begin with identification and ensure you consult a specialist for a comprehensive assessment.

Identifying, Documenting, and Assessing RAAC

RAAC panels exhibit a light-grey or white hue, with their underside presenting a smooth texture. The inner side of these panels has a bubbly appearance, akin to the look of an Aero bar. Unlike standard concrete, these panels do not display any visible stones (aggregate). They typically measure 600mm in width and feature unique V-shaped grooves at their intersections.

Typical RAAC Panel

A competent Facilities Manager or Chartered Building Surveyors should be able to identify RAAC panels in a building during the course of a survey and document their locations.

Our dedicated surveying team at David Cosby Chartered Surveyors are available to support you in this process by carrying out an initial assessment as to the presence of RAAC panels. We will deliver the data following the recommendations of the Standing Committee on Structural Safety (SCOSS) and supply the data in a format tailored to each client’s needs, typically encompassing AutoCAD drawings, PDF, and Excel formats.

If RAAC panels are identified, it is crucial to understand the next necessary steps for assessment.

Assessing the condition of RAAC panels, understanding potential failure mechanisms, and making recommendations for remediation is a specialised task. This intricate evaluation should be exclusively undertaken by Chartered Structural Engineers with experience in investigating and evaluating reinforced concrete structures. We would be happy to provide recommendations for local Chartered Structural Engineers who will:

  1. Conduct Detailed Surveys: These surveys include measuring deflections, recording crack patterns, checking for evidence of water leaks, and much more.
  2. Assess End Bearings: They will evaluate the condition of the end bearings (the point at which loads are transferred from the panel to a supporting wall or column), which are crucial for the overall performance and safety of the panels.
  3. Undertake Condition Assessment: Using specialised methods tailored for RAAC panels, they’ll determine the overall condition and structural integrity of the panels.
  4. Recommend Remediation Techniques: Depending on the condition of the panels, a structural engineer might suggest further monitoring, strengthening, replacement, or other necessary actions.

If you suspect the presence of RAAC panels in your property, start with identification, but ensure you consult a Chartered Structural Engineer experienced in reinforced concrete structures for a comprehensive condition assessment and potential remediation recommendations.

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