A Little bit about me...

I'm a Structural Engineer, specialising in conservation, at Hurst Peirce + Malcolm in London. I don't wear tweeds, am not particularly "cultured" and I'm not that old, but I do care passionately about the conservation of old buildings. I am a Chartered Structural Engineer, a member of The SPAB (formerly on the founding committee of the reborn Berks, Bucks & Oxon Regional Group), a Friend of SAVE Britain's Heritage and have recently completed a PD Diploma in conservation at West Dean College, with a view to achieving CARE accreditation. I hope to give you regular updates on my trials and tribulations as well as some insight into projects I am involved with and things I believe in.

Be patient with me - I'm no writer and I'm normally up to my eyeballs at work........

All views expressed here are my own.

Hurst Peirce + Malcolm, Celtic House, 33 John's Mews, Holborn, London WC1N 2QL

07854 624692 - richardsalmon9@gmail.com

Saturday, 28 January 2012

Building Regs. & Listed Buildings

Apologies for the silence over the last six months or so, just been too busy to put anything together. I wanted to write this piece a while back, when it was a little more topical, but never mind.

We were recently involved in a project that had some similarities with Sarah Beeny's Rise Hall restoration, in terms of dealing with "the Authorities". In particular, Building Control.

I have been rather scathing about the "Beeny's Restoration Nightmare" TV programmes themselves, due to the unnecessary 'dramas' and lack of useful detail on the restoration process itself, however by-and-large I think what Sarah (& Graham) have achieved with the building is very good indeed. I would also point out that, as far as I have been able to decipher, there were never any issues with the Conservation Department (who were on-board with the project at a very early stage - and remember, simple 'repairs' do not require formal listed building consent, although I would recommend at least discussing any proposed work with your local Conservation Officer). The problems have revolved around the planning COU (change of use) issue and the subsequent Building Control "requirements" that kick in with some COU's. The 'retrospective' method of dealing with these issues really didn't help either.

Read all about what needs Building Regs approval here... http://www.legislation.gov.uk/uksi/2010/2214/part/2/made

We got called in quite late on this project in south-west London. Our client was already well advanced with converting the building into a day school/nursery, but the architect had noticed a significant dip in the lobby floor near the front entrance - so we got called in to have a look. Only after we had solved the problem and works were nearly complete did we then get hit with a load of 'conditions' from Building Control to resolve retrospectively (always a pain when you're not involved from the start). I shall now try and put prior & subsequent events into a nutshell:

Dating from c.1810, this Regency villa (Grade II) is only one of two remaining from a row of as many as 12 along this stretch of road. You can see its rather ugly new neighbour on the right, as well as the modern extensions to the left.

As far as Building Control are concerned, a COU into an educational facility is one of the most onerous kinds (as one might imagine), invoking the need to comply with most parts of the Building Regs. Doubly so if 'structural alterations' are also planned. It is part of the conservation engineer's role to try and limit the need and/or impact of these conditions when a listed building is involved, by developing reasoned arguments backed up by calculations where applicable, to avoid unnecessary and inappropriate works.

We were disappointed when Building Control would not treat this project differently from a normal 'school' in the conventional sense. Our day school was for a maximum of 75 3-11yo's spread over four floors. Not quite the same as Waterloo Road or Grange Hill is it? Anyway, the conditions that I had to deal with mainly related to Part A (Structure) & Part B (Fire). I left everything else to the Architect.

Initially, I had to figure out how this building worked and satisfy MYSELF that it was robust enough to do the job. Apart from some remodelling of partitions in the attic storey, the building was pretty much as original. The roof, an oddly proportioned 'M' shape, was never capable of fully supporting itself, so the remodelling of partitions had inadvertently changed the loadpath going down the building. This together with the cutting of a large archway into an original braced stud partition at ground floor, meant that a sizeable chunk of load was being supported on the lobby floor joists - thus explaining the excessive deflection. I decided, on balance, that some steel beams would be required to get the load back onto the brick walls of the basement. Headroom was tight, so the joists were cut to allow the steels to sit within the floor depth. Luckily for us, the basement ceiling was not original (and cracked to buggery in any case).

No structural alterations, as such, were made anywhere to facilitate the conversion of the building.

At this point, The Letter from Building Control arrived.....

Getting around the floor loading issues was relatively straightforward. Although the building had been built as a residence, it had been used as offices since at least the 1950's and I also did some calculations based on room usage data provided by the client to prove that live loads would not exceed 2.0kN/m2, as opposed to the 3.0kN/m2 required by BS6399 (and not to mention the real strength of joists that age, compared to their modern counterparts). Similar arguments re corridors and stairs (fire escapes) were luckily accepted without further question.

The one item I didn't get my own way on (completely) was disproportionate collapse. Despite my protestations, they decided that my new steelwork was an 'alteration' rather than a 'repair' - but I did manage to knock them down from a full tying scheme to just tying across the joists that had been cut (a bit of a waste of time as these joists were all spliced across the walls and not continuous in any case), and I did have to prove that the new steel beams were 'blastproof' but after some quick calcs using the reduced safety factors for 'accidental loads', we ended up just needing some bog-standard restraint straps. The client was a bit miffed as he had already replaced the ceiling by this stage, but was made a bit happier once he found out what we'd got away with.

The staircase was the last issue that needed resolving from a structural aspect. The original winding timber cantilever stair was still intact along with its balustrade. We had already decided that the low handrail and steep internal winding were not going to be particularly safe for younger children, so we bit the bullet and designed a new balustrade with infill panels to sit inside the existing and the posts were clamp-bolted to the stair risers so as to make the system fully reversible. The only downside was that this made the stair too narrow for the current Regs., but again, presentations of usage data (and a dose of common sense) persuaded the fire officer that congestion on the stair would be minimal and we had made the right decision overall.

I'm not going to mention Part L (thermal) here, other than to say that exemptions are still available for listed buildings and other solid wall buildings, though you may have to go though a few hoops to justify.

OK, sorry, quite a large nutshell there. Best I could do! I've tried to explain everything, but if you do have any questions, please feel free to 'comment' below. I'll leave you with a few annotated photos below:
The existing floor joists under the front lobby. Not really clear from this photo, but worst-case deflection measured at 100mm on a 3.5m (12ft) span.

Distortions a bit clearer here. This steel post had been previously installed where a floor trimmer beam had snapped. Slightly away from the area we were concerned about, but we took the opportunity to replace the beam and remove the obstructive post.

We tried everything possible to avoid using steelwork, but the load concentration was just too great. We got the CO onside and designed the steel so it could be lifted up to sit in between cut joists with minimal disruption. (and before you ask - no, the ceiling was not original)

The surviving original cantilever timber staircase. Had sagged a bit, but was still perfectly sound (having passed my 'bounce' test with flying colours.) Sorry no photo of the second balustrade, not been back to site to see it finished.

Not an optical illusion: The end of this original garden wall really does lean that much, primarily caused by a large tree on the other side. It remains uncracked (due to the flexibility that lime mortar gives) and is effectively propped by the later house wall. We left well alone. (The new arch in the foreground? - Just don't ask!)

However hard you try, things still slip through the net. Me: "I hope that's a lime render" - Chap: "Well, its got some lime in it" #FacePalm

No comments:

Post a Comment