Anyone recommend a fire engineer?

[Alan Ambrose]

Hi, can ayone recommend a fire engineer? I have two things I need help on:

 

For a small block of flats - risk consultancy re reduced risk following cladding work vs. backup genset and stairwell pressurisation system.

 

For my single storey timber frame new build - plans check and recommendations for fire stopping detail etc.

[Gus Potter]

10 hours ago, Alan Ambrose said:

For my single storey timber frame new build - plans check and recommendations for fire stopping detail etc.

Interesting question. A few observations.

 

Take a single story timber frame (TF) house more than 1.0m away from the boundary. Let's make it timber clad.

 

As an overview we aim to achieve a number of things:

 

1/ We want the interior of the external,  internal walls and ceilings not to encourage surface spread of flame or emit fumes, like old polystyrene tiles to take an extreme example This protects the occupants and provides time to make a safe exit. A good material to use here is plasterboard.

 

2/ We also want to protect the Fire Brigade in case they need to enter the house. In the first instance we want to have a look at the roof. Say that needs 30 minutes fire protection (pragmatically) but on a single story house this may not always apply. Assuming we are complying with the English regs approved document B (dwellings). Our first port of call is section 5: Load bearing elements of the structure. To summarise clauses 5.1 to 5.3 and the attaching notes; provided the roof does not contribute to the structural stability of the house we can go for potentially less than the 30 min.. but as I said, pragmatically, we need to ask.. can we get 30min out of the roof anyway at no extra cost?

 

Now we need to look at the roof and determine if it is contributing to the structural stability of the house. Importantly ask (an example), is the roof say attached to a long slender steel transfer beam (or an eaves / ridge beam) that relies on the roof to prevent it buckling? If that beam requires 30 minutes protection then so does the roof.. as it is now part of the structure.

 

Turning to the walls. The first thing to ask.. what are the walls doing structurally. Are they holding up the roof or not. On a standard TF they normally do and thus commonly need say 30 minutes protection when measured from the inside. But.. if the walls are holding up the end of a steel beam that requires a longer duration of fire protection then you need to consider how much of the wall needs extra protection.. often we get round this by default as beams have heavier and more fire resisting supports running in the walls down to something solid on the ground floor.

 

However, just say the walls are infill panels between a structural frame that supports the roof and any transfer beams. The structural load path is.. snow / wind and roof access load acting on the roof.. onto a structural frame on a raft foundation slab say. Let's avoid a steel frame (takes ages to write about) and say we have a chunky oak framed building. Here the wall panels are non structural in terms of bearing vertical load. 

 

Just to qualify.. when we are considering structural loadings on a building in terms of fire we neglect wind load and reduce the live (imposed loading.. you having a party or a biggish fish tank say).. in other words we look at the probablility of the building being fully loaded coupled with a fire breaking out.. if we did not take a risk based appoach then the fire design would often drive the design unreasonably and cost exponentially upwards.

 

Ok I picked a chunky oak frame as it's easier. Oak is a great material.. when a fire starts you get a slow char which insulates the timber under. If the oak frame is chunky it will hang in there a lot longer than your 30 minutes.

 

Infill panels:

 

Just say these are a space frame / SIPS kind of wall panel fixed between the columns of an oak frame. Heb Homes et all do space framed walls. I'm being all inclusive so let's lift the bonnet and have a look at these. @Kelvinknows a lot about this so have a look at his posts, also I've picked his brains and learnt loads from him so you won't be the first!

 

Now as a point of reference we know that a standard TF wall..  say plasterboard on a 95 x 45 timber stud (provided it is not too high) with OSB on the outer face gives you round about 30 min protection. On the inside the key thing is to make sure the plaster board fixings have enough penetration into the timber. As a rule of thumb if the plaster board is 12.5mm thick we need 2*12.5 fixing penetration into the timber behind for structure  = 25mm. That is not something I'm personally comfortable with so let's say 40mm fixing screw penetration.. about the thickness of an engineered joist flange. Now we are making sure the timber and plasterboard will hang in there as the fixing heats up.

 

On the outside of the panel, timber clad.  Here we need to look at the surface spread of flame and select our cladding accordingly. It might need some treatment. Up in Scotland we have a company called Russwood, have a look at their website as they are full of ideas.

 

Last but not least there is the fire stopping. For all when we have a cavity in a wall we must stop flames and smoke having a free run. Cavities are basically a chimney and they are not "passive things". As soon as you introduce heat convection air currents build rapidly and they promote fire and smoke spread. They must be split up and isolated into small zones. Now when we have say external timber cladding the inside face of that may be a bit irregular. One solution is to use fire socks around all openings (windows and doors), at eaves level and split the wall panels lenght wise into separate zones.

 

One company, I like to brouse their offerings on passive fire protection is Tenmat  https://www.tenmat.com

 

10 hours ago, Alan Ambrose said:

Hi, can ayone recommend a fire engineer?

Now you may not need one, much depends on the attitude of BC.

 

For me as a designer I always want to make sure that what I'm doing is safe. On a low rise single house like this, say well away from neighbours then it's ok to work your way through the basics to get a safe fire strategy. Make no mistake folks.. if this was a higher risk building then I would be much more forensic.. but the Client would need to cover my design fee.

 

Hope this helps a bit.

Edited March 29 by Gus Potter

[Benpointer]

I used Grant Barker  http:// www.grantbarker.co.uk  Happy with what he has done for us.

[Gus Potter]

14 minutes ago, Benpointer said:

I used Grant Barker  http:// www.grantbarker.co.uk  Happy with what he has done for us.

Had a quick look at Grant's offering.. seems like someone that has their head screwed on the right way. No fancy website... just someone that says.. here is what I do and I know my stuff?

 

Now as an SE that sounds like someone I can relate to and have a sensible conversation with.

[Benpointer]

22 hours ago, Gus Potter said:

Had a quick look at Grant's offering.. seems like someone that has their head screwed on the right way. No fancy website... just someone that says.. here is what I do and I know my stuff?

 

Now as an SE that sounds like someone I can relate to and have a sensible conversation with.

Yep, he's done a comprehensive review for our build, identified one issue, and given us two options to address it.   And we have a report we can wave at HSE, BC, and potential insurers.