Retrofit of ties into Existing Building Stock

Ok, me again with a few more ramblings.

Still trying to get a handle on the Building Safety Act, the Building Safety Regulator/HSE and how that impacts the industry going forward.

Also heard a few rumblings that a few buildings are earmarked for demolition recently which also lit a fire up my arse to really try and bottom this out and understand it a bit more. I don't think the demo approach will apply, they'd have to demolish and rebuild every relevant building (5 storeys and above) within England and Wales that didn't comply.

So I've mostly been trying to get our risk assessment documents pulled together over the last few weeks. Gone through the IStructE's Manual for Risk Assessments which we've based our documents on (makes sense) and then we've thrown in HSEs:

• Principles and guidelines to assist HSE in its judgement that duty-holders have reduced risk ALARP.

As an appendix, with a little influence from:

• HSE. Assessing compliance with the law in individual cases?and the use of good practice.?
• HSE. Policy and guidance on reducing risks ALARP in design.?
• HSE. Principles for the Cost Benefit Analysis (CBA) in support of ALARP decision.?
• HSE. Cost Benefit Analysis (CBA) checklist.
• HSE. Reducing Risks Protecting People (R2P2).

And back to the old classic:

• CPNI. Review of Robustness.?

Whoever wrote that last one by the way, stand up and take a bow.

So key take aways from the various HSE guidance:

• "It should be borne in mind that reducing the risks from an existing plant ALARP may still result in a level of residual risk which is higher than that which would be achieved by reducing the risks ALARP in a similar, new plant."
• "Factors which could lead to this difference include the practicability of retrofitting a measure on an existing plant, the extra cost of retrofitting measures compared to designing them in on the new plant, the risks involved in installation of the retrofitted measure (which must be weighed against the benefits it provides after installation) and the projected lifetime of the existing plant."
• "All this may mean, for example, that it is not reasonably practicable to apply retrospectively to existing plant, what may be demanded by reducing risks ALARP for a new plant (and what may have become good practice for every new plant)."

Yep. All makes sense.

• "'Good practice', as understood and used by HSE, can be distinguished from the term 'best practice' which usually means a standard of risk control above the legal minimum."

Lets call best practice horizontal and vertical ties which would make every existing building code compliant.

• "For existing plant/installations/situations, this will mean the application of current good practice to the extent necessary to satisfy the relevant law."

To satisfy the law.... that's disproportionate collapse (Building Regs, Schedule 1, Part A).

• "Where the law requires risks to have been reduced ALARP, HSE:
• Will, where the duty-holder wishes to adopt a different approach to controlling risks, seek assurance that the risks are no greater than that which would have been achieved through adoption of good practice and so are ALARP for that different approach."

cl.4.(3). Building work shall be carried out so that, after it has been completed: Any building which is extended or to which a material alteration is made; complies with the applicable requirements of Schedule 1 or, where it did not comply with any such requirement, is no more unsatisfactory in relation to that requirement than before the work was carried out.?

That last line is a big one which opens up the need for a risk assessment.

• "However, depending on the level of risk and complexity of the situation, it is also possible that meeting good practice alone may not be sufficient to comply with the law.?
• For example, in high hazard situations (those with the potential to harm large numbers of people in a single event), where the circumstances are not fully within the scope of the good practice, additional measures may be required to reduce risks ALARP.
• Furthermore, where the potential consequences are high, HSE will take a precautionary approach by giving more weight to the use of sound engineering and operational practice than to arguments about the probability of failure."

Ok, they talk about 3 things here... risk, hazard and consequence. The Hazard is a gas explosion for instance and there is a likelihood value attached to each hazard, the likelihood of a gas incident happening each year is 1 in 1,510,000 for instance. Your chances of being killed canoeing are about half of that. And a gas event falls within the As Low As Reasonably Practical (ALARP) region on the tolerability scale. Neither acceptable or unacceptable, but you should make the effort to reduce the risks where possible.

Now risk = likelihood x consequence.

And gas explosions in existing building stock are deemed low likelihood but high consequence events because much of the existing building stock isn't resistant to disproportionate collapse (horizontal and vertical ties). This leads us onto the Building Safety Act which requires Safety Case Reports and the disproportionate collapse strategy identified for each building.

This is for both relevant (5 storeys and above) as well as high-risk buildings.

• "cl.117.(2). 'Relevant Building' means a self-contained building, or a self-contained part of a building, in England that contains at least two dwellings and
• Is at least 11m high, or?
• has at least 5 storeys.?
• cl.120.(2). 'Relevant defect', in relation to a building, means a defect as regards the building that -?
• Arises as a result of anything done (or not done), or anything used (or not used), in connection with relevant works, and
• Causes a building safety risk.?
• cl.120.(5). ''Building safety risk', in relation to a building, means a risk to the safety of people in or about the building arising from -?
• The spread of fire, or
• The collapse of the building or any part of it."

Now I used to panic when I read that, as I'm sure many other people within the industry did too. But its only really mirroring what the current Building Regulations are saying in that a change of use then has to be compliant. If anything, the BSA are just making a better paper trail for that to happen.

The HSE also want people to follow best practice, or industry guidance for example. And the current recommendations from the IStructE Disproportionate Collapse and Robustness book (1st edition) is to undertake a risk assessment for vertical extension for instance. This is echoed by the HSE guidance.

• "The good practice measures set out should be adopted so far as is reasonably practicable. It might not be reasonably practicable to apply retrospectively to existing plant, for example, all the good practice expected for new plant. However, there may still be ways to reduce the risk eg by partial solutions, alternative measures etc."

Cool. So a holistic approach is acceptable.

• "An holistic approach is important in order to ensure that risk-reduction measures that are adopted to address one hazard do not disproportionately increase risks due to other hazards, or compromise the associated risk control measures."

Whoop. Good to know.

• "An effective approach for demonstrating that risks are as low as reasonably practicable is to start with the safest design option within the range of practicable solutions.?
• This should be chosen by the duty holder unless they can show that this is not reasonably practicable; in which case attention should pass to the next safest option.?
• The procedure is repeated until the lowest risk option is found which is reasonably practicable."

Now this brings us to the rambling sketch on the header of this article.

I see feasibility reports from other consultants all the time and each one of them says 'building doesn't conform to disproportionate collapse, horizontal and vertical ties needed' and leave it there kicking the problem further down the road for someone else to sort with the client none the wiser as to how to move forward with this and if a project is worth pursuing or not.

So I had a go. And I think its a load of nonsense to try and retrofit ties back into a building, ignoring the cost, there are so many technical and practical hazards that arise from this, let alone the logistical challenge of trying to juggle in-situ residents with temporary housing nearby during the works. It doesn't work.

But. I'm taking my ramblings and drawing them up in CAD with CDM risks highlighted and a sequence of works where needed because the HSE say...

• "For many ALARP decisions, the HSE does not expect duty holders to undertake a detailed Cost Benefit Analysis (CBA), and a simple comparison of costs and benefits may suffice.?
• Where major health and safety issues are being considered, a more rigorous CBA may be of value."
• "The depth of analysis should be fit for purpose, i.e. more rigour is required where the risk is higher or the consequences themselves are great e.g. multiple fatalities.

We could be dealing with multiple fatalities within the building stock, so I'm gonna suggest we go down the rigorous route.

• "A CBA on its own;
• Does not constitute an ALARP case
• Cannot be used to argue against statutory duties
• Cannot justify risks that are intolerable, or justify what is evidently poor engineering.

i.e. you can't just do the quick calculation to determine a gross level of disproportion and then say 'it costs too much so it doesn't work'. They want to see proper evidence of us considering ties into the structure, what does that look like? How are you going to do it? Have you considered all buildability aspects? How will it impact on the existing residents? This all has to be demonstrated if we are to stand any chance of justifying that we have reduced the risks ALARP.

In essence - its a lot of work for not a lot of output. We're almost giving a design solution and saying it doesn't work. But that's our duty as consultants to demonstrate that in a way that can be communicated to others easily and proves that we're taking our statutory duty seriously and not just winging it because we don't know any better.

I think before the BSA, there's a slim chance I would have been asked for all of this as a designer. Now though... I think engineers are going to have to be prepared for the question.