Home Contractor's Corner(Quite Interesting) Insulation Facts BBA Building Bulletin 4, what is it and what’s changed?
Flat Roofing

BBA Building Bulletin 4, what is it and what’s changed?

by Matt Downs

BBA Building Bulletin 4, what is it and what’s changed?

Most of the roofing industry will have heard of the British Board of Agrément (BBA), and with good reason; roofing manufacturers are the largest customer group for BBA Certificates.

But how many readers have heard of BBA Information Bulletin No. 4, first issued in January 2011? Probably a safe bet to say not many, but thanks to the Liquid Roofing and Waterproofing Association (LRWA) working with the BBA on the January 2021 update more people are now aware of it than ever.

The original IB No. 4 provided clarification and guidance on three matters related to inverted roof specifications – correct drainage design, Zero pitch roofs and U-value correction factors. What this easy to read, two page document did was take the key elements of the requirements of ETAG 031 Guidelines for European Technical Approval of Inverted Roof Insulation Kits Part 1: General and distil them into an easy-to-understand document.

So, what has changed in the decade since this IB No 4 was originally published?

No significant changes in this section. The requirements for falls and drainage to prevent ponding remains, as does the requirement for drainage points (rainwater outlets) to be at the lowest point of the roof. Reference to draining at Water Flow Reducing Layer (WFRL) and waterproofing level remains. Reference has been added to installing the WFRL in accordance with the manufacturer’s guidelines from the bottom of the slope upwards.

Zero pitch roofs
Zero pitch has been changed to the more widely used ‘Zero falls’, and reference to 0 to 0.7 degrees has been changed to 0 to 1 in 80. The requirement for zero falls roofs to always be protected/ballasted has also been added, clarifying that zero falls exposed waterproofing applications are not acceptable. Designing to 1 in 80 to achieve a minimum finished fall of 0 is also included. Using deflection analysis to identify low points for outlet positioning is added, as is the need to use localised screed or rainwater outlets to alleviate negative falls.

U-value corrections
Reference to BS EN ISO 6946:2007 has been updated to the 2017 edition, and there is further clarification of the requirements of this standard; most of which has no practical impact on the installation of inverted roofs, but does impact the thermal calculations that support design and specification. Vacuum Insulated Panel (VIP) insulation has been added to the list of generic insulation board types the testing and calculation factors are applicable to.

To download a copy of BBA Information Bulletin No 4 2020, go to the downloads section of the Quantum Insulation website: https://www.quantuminsulation.com/downloads/

Contact Quantum Insulation:

T: 01895 456018 / E: sales@quantuminsulation.com / W: quantuminsulation.com

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