Fire Protection of Structure

[Nakajo]

This question relates to fire protection of structural steelwork. There are also numerous issues here relating to fire escape but I think I know how to address those...

I'm looking at a completed project which commenced work in 2017, and with very little paperwork to explain how or why certain decisions were made. It's a very substantial refurbishment of (what was originally) a 3-storey, semi-detached property, including the provision of a partial basement below a new, rear, single-storey extension and a loft conversion (a ca. 55m² office accessed from a new, permanent staircase directly off the 3rd floor landing) so now a four-storey property, plus basement.

Both the 3rd floor and loft are more than 5m from ground level.

A mist fire-suppression system is provided along the principal escape route.

Looking at the ADB2013 (with amendments), I cannot see that the 'requirement' can be interpreted as anything other than FR60 for all structural steelwork, achievable either by the provision of 2 (no.) layers of plasterboard (or possibly 1 layer of 15mm specialist pb) both sides of any partition (bathrooms exempt), or the protection of all steels with intumescant paint.

There are some notes on drawings indicating that steel work was to be protected to FR60, but no indication on drawings as to how this was to be achieved, and no evidence that it was.

Is there any scope to interpret the guidance differently? I wonder because, presumably, if the work had been done in two phases - whole house refurbishment followed by loft conversion than FR30 would have been deemed adequate. Anyway, I'm rambling now...

 

[frutbunn]

Are there two protected staircases providing means of escape from the 3rd floor?

 

[freddiemercurystwin]

Be careful here, some BCO's are getting extremely picky with regards to what they will accept and what they won't following Grenfell, for instance there is no valid test available in the UK available today for lining a loadbearing wall to protect the timber structure within for 60mins with anything other than 2 layers 15mm plasterdboard. Even though the industry has been using 2 layers of 12.5 for donkey's years. That's not to say your BCO won't accept 2 layers of 12.5 just that some BCO's will not. Intumescent paint only works if it has a clear 50mm gap surrounding it.

 

[Nakajo]

The depressing thing is, the AI already signed it off. I'm concerned that it's not really safe, but I don't want the owner to commit to spending thousands to fix it (and moving out for six months - without much prospect of reclaiming costs), if LABC/Fire Officer/Insurer are generally comfortable with this. There are separate issues relating to fire escape (which are obviously very important), but for this question, I just want to focus on fire integrity.

 

[frutbunn]

It should be one hour fire resistance, however this is only guidance.
Approved document states there should be an alternative means of escape or sprinklers provided throughout the building, you state that these are only on the principal escape route. Is there an alternative escape?
An alternative solution may have been applied such as a higher standard of detection, but this is something you would need to speak to the original PI.
Please note the fire officer is not consulted on this type of work nor is there a statutory duty to do so.

 

[Nakajo]

Maybe I'm missing something but I don't see the relevance of means of escape (including sprinklers) when talking about structural integrity, which I would have thought was more about the risk of the building collapsing on a fireman when they arrive on scene. I can speak to the PI; I doubt they'll be very helpful.

 

[frutbunn]

Maybe I'm missing something but I don't see the relevance of means of escape (including sprinklers) when talking about structural integrity, which I would have thought was more about the risk of the building collapsing on a fireman when they arrive on scene. I can speak to the PI; I doubt they'll be very helpful.

Sprinklers is certain something I would consider and a wholly separate protected staircase if I was to consider a lower fire resistance for an element of structure.

 

[Nakajo]

OK, but why? (Incidentally, sprinklers are a non-starter in this instance - other than the existing mist suppression system) (And while I'm a fan of mist suppression systems, I suspect that the one provided is pants)

 

[^woody^]

Is there any scope to interpret the guidance differently?

Yes, additional detection and suppression systems, the ADs are a guide not absolute. But I'm not sure what the question actually is.

Is this a four storey plus basement ie five storey?

As there is an office, the 2005 FSO will apply and as it's a completed project, those risk assessments can trump building regulations and so could well deem alternatives as suitable, or conversely impose greater standards.

 

[Nakajo]

'Office' as in 'domestic office/study'

 

[Nakajo]

I'm not exactly sure what the question is either. In part I suppose I'm trying to understand how such a fundamental cock-up arose, and whether it's reasonable to assess the building as if it were three-storey + basement. (Incidentally, I note that the relevant Approved Document states somewhere that 'Basements are not included in counting the number of storeys in a building'). Failing all of that, I need to consider the minimum steps necessary to rectify the issue.

 

[frutbunn]

The RRO or 2005 FSO doesn't apply its a home office.
Your correct its classed as 4 storey.

OK, but why? (Incidentally, sprinklers are a non-starter in this instance - other than the existing mist suppression system) (And while I'm a fan of mist suppression systems, I suspect that the one provided is pants)

Its something you might consider as a departure from the approved doc, perhaps coupled with a higher standard of detection obviously its difficult to assess in your case without all the details. A departure like this would normally be discussed with a couple of colleagues before making that decision, or at least at the authorities I've worked.
If you haven't got an alternative escape from the third floor then sprinklers should have been provided in any case so I would expect some other approach as a compensatory measure.