Thanks for nothing

Changes to the Building Regulations generally make sense. Global warming is real, allegedly, so improved thermal insulation is a good thing. What I’m struggling with is some of the changes to Part A of the regulations, dealing with structure, that came out last December. Don’t turn over just yet – I’m not going to get technical or go into detail, but the regulations do include a requirement that is relevant to all of us in the building business, including clients.

Remember Ronan Point, the east London tower block that suffered a gas explosion in 1968? Although the explosion occurred on the 18th floor, the weight of the building above caused collapse beneath. This is commonly referred to as “progressive collapse” but a more useful concept, perhaps, is “disproportionate collapse” – that is, the extent of the collapse compared with its cause. A 22-storey collapse is clearly disproportionate given that the cause was a gas explosion.

“Interesting,” you may be thinking, “but so what? That was nearly 40 years ago; surely you engineers have got your act together since then?”

Well, yes, a lot of thought went in to the guidance after Ronan Point and, after a bit of a false start, it was decided that buildings more than four storeys high should be designed to avoid that sort of collapse. Another way of putting it is to say the collapse of a four-storey building from one explosion is not disproportionate and therefore acceptable.

We’ve lived with that since 1970, perhaps without thinking of it so bluntly. Why four?

I don’t know precisely, but a line had to be drawn somewhere and maybe the fact that many people lived in four-storey brick buildings influenced the decision. In practice, brick buildings behave differently from a Ronan Point-style tower block in an explosion, but never mind: the 1970 regulations came in and applied to all forms of construction more than four storeys high.

The rules apply to progressive collapse in all buildings, other than single dwellings. What is considered disproportionate seems to have shifted dramatically

That has all changed now. The new regulations require the consideration of progressive collapse for all buildings, other than single dwellings, regardless of height. The view of what is considered disproportionate seems to have shifted dramatically. Building elements will now have to be tied together and, depending on building use and so on, that tying may be extensive. For new buildings fewer than five storeys, the cost of the structure will increase. Not a lot, but any increase needs to be justified.

The real rub comes with work on existing buildings. Again subject to use, we structural engineers may find ourselves tying together parts of a building that would previously have not been affected Consider, for example, a three-storey brick building with a shop at ground level and flats above. The reuse of such accommodation is to be encouraged and how better than putting an extra storey of lightweight construction on top? Just the kind of increase in density government is promoting, isn’t it? The new regulations, however, would require the whole building to be tied, meaning that significant structural work would be needed in all the units beneath. Cost and hassle would increase substantially. It was substantial enough on one scheme we were involved in for the client to consider walking away. Government thinking doesn’t seem to be very joined up on this.

What have I missed that would justify this increase in the level of safety? Yes, terrorism is sadly a real issue but not realistically relevant to most buildings. Of course safety is an important issue but a cool, realistic assessment of risk is needed. The new regulations allow for that, and hence flexibility, in the design of buildings greater than 15 storeys, but for the “ordinary” low-rise buildings now being constructed or refurbished the rules are prescriptive.

The National House Building Council has produced a useful advisory document but the real test is what the building inspectors will accept. We are hopeful that common sense and engineering judgment by both designers and regulators will allow us to reach a cost effective solution, but that can only go so far. In my example, the rules would have been bent beyond breaking point to make the scheme viable. Is it reasonable to ask an inspector to go along with that? The regulations will make some low-rise buildings “safer”, but at a cost. We should be asking for more evidence of why we need to pay that extra – and why now.