Can I fix into a Siporex RAAC deck?
- Read time: 3 minutes
- Date: 30 Jan 2023
- Flat Roofing
Reinforced Autoclaved Aerated Concrete (RAAC) is a lightweight form of aerated concrete that is made from fine rather than coarse aggregate. It is much weaker than traditional concrete and has a low bonding capacity to any embedded reinforcement.
It was largely used to manufacture lightweight masonry blocks and structural units such as roof planks, wall and floor units between the 1960s to 1980s. It has an estimated ‘lifespan’ of around 30 years, which means that most RAAC building elements are now past their serviceable life.
The SPRA states that the following issues have been identified with RAAC deck:
Rusting of embedded reinforcement leading to cracking and spalling of the AAC cover
Cracking, of varying degrees of severity, is thought to be associated with moisture and temperature related movements in the planks
Excessive deflections due to creep
Floor and roof planks tend to act independently, rather than as a single structural entity
View the full guidance: SPRA-Technical-Guidance_Concrete-Decks-and-Roof-Slabs
Can I fix into a RAAC deck?
If you discover that a flat roof has been constructed using RAAC planks, then you should stop work immediately. The SPRA states that:
If planks are visible from the underside, then it is important to inspect these for warning signs which include visible cracks (particularly in the vicinity of the end supports), evidence of water ingress, rust staining or spalling. Consideration should be given to conducting a small intrusive drill sample to assist the inspection.
If it is suspected that RAAC planks are present, then an appropriately experienced Chartered Structural Engineer or Chartered Building Surveyor should be appointed when conducting identification and inspection work.
If the surveyor determines that the RAAC is structurally sound, you should then speak to your chosen fastener manufacturer to request onsite testing to determine the correct number, frequency and type of fastener for any refurbishment works that are required.
