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Your Questions, Answered: What blocks should I use to comply with TGD A in Ireland?

 

Jason Martin, our Specification and Product Development Manager, answers a commonly asked question in the Irish construction industry in our first “Your Questions, Answered” series.

Looking specifically at small buildings up to two stories with traditional masonry wall construction, Jason explains what block strength is required to meet current building regulations, and more specifically to ourselves, what Quinn Lite block is required.

Here’s a transcript of Jason’s explanation.

What blocks should I use to comply with TGD A in Ireland?

Part A of the building regulations 2012 covers structure. The regulations themselves are quite vague, in that they don’t give a specific block strength requirement. Instead, they say that a structure must be designed with “due regard to theory and practice of structural engineering”, and that a structure must be able to sustain an applied load and transfer it down through the structure to the ground below

  1. A) safely, and
  2. B) without any deflection or deformation of the structure.

How then do we prove compliance with the building regulations?

We have two options available:

  1. Employ the services of a Structural Engineer to design each masonry panel and determine what block strength is required. However, this can be both costly and time consuming for small buildings.
  2. Follow the guidance of Technical Guidance Document A (TGD A). The Technical Guidance Documents are a set of documents developed by the Department of Environment to prove compliance with the Building Regulations. If we follow this guidance then we are deemed to satisfy the building regulations.

Technical Guidance Document A

TGD A Sub Section 1 covers small buildings up to two stories with traditional masonry wall construction. In this section it states that the below must achieve a minimum compressive strength of 7.5 N/mm2

So, has a strength of 7.5 N/mm2 has always been the requirement?

No. Prior to June 2013 TGD A didn’t reference any specific block strength. Instead, it referenced I.S. 20 (the old Irish block standard). In that standard a number of block strengths were given, with the 5 N/mm2 block being most commonly used for buildings up to two stories. And, as we now know, after June 2013 current TGD A came into effect, and a 7.5 N/mm2 is specified.

So, we might then ask ourselves, “were buildings built prior to June 2013 built with a weaker block?” Well, the increase in compressive strength is more to do with the way the blocks are currently conditioned and tested. The old I.S. 20 only gave provision for conditioning blocks by immersion. The blocks were immersed in water between 10-25 degrees Celsius for 15 hours, then taken out and left standing for 15-20 minutes before testing. However, the current test method, EN772 Part 1, gives provision for conditioning by the below in addition to immersion:

  • Air dry
  • Oven dry
  • 6% moisture

The air-drying conditioning method is what current block strengths are stipulated by, and it typically gives a 20% higher result than testing by immersion.

In addition to conditioning, the way blocks are capped has also changed. I.S. 20 gave the provision for routine rapid control testing where typically in excess of 5 N/mm2 was achieved with capping the blocks with a fibre board. However, now a 7.5 N/mm2 strength is obtained by mortar capping the blocks prior to testing.

So, the combination of the conditioning method and the capping method has given this gain of strength from 5 N/mm2 to 7.5 N/mm2.

Quinn Lite Blocks

So, going back to part of our original question “Which Quinn Lite block is required to meet the building regulations?”

At Quinn Lite we have 3 block strengths: the B3, also known as ‘Super’, which has a 2.9 N/mm2 strength, the B5, also known as ‘Standard’, which has a 5.2 N/mm2, and the B7, also known as ‘Seven’, which has a 7.5 N/mm2 strength.,

If we choose to follow the guidance of TGD A, then it’s B7, our 7.5 N/mm2 strength block, which is required. With a thermal conductivity of 0.19 W/mK, this is the mostly thermally efficient concrete block available on the Irish market which meets the strength requirements set out in TGD A. In fact, it’s 75% more thermally efficient than the closest alternative.

If we want to improve the thermal performance further still we can employ the services of a Structural Engineer to design masonry wall panels, and it could be a case that our 2.9 N/mm2 or 5.2 N/mm2 blocks may well be adequate. With thermal conductivity of 0.12W/mK and 0.17W/mK respectively, both blocks will significantly improve thermal performance further still.