Lath and Plaster in period buildings

[hammer1]

Lath and plaster in good condition can provide 20 minutes fire resistance??. Is there any research material on fire test conditions and results???

Where a period building has been converted to sleeping accommodation, would it not be responsible to upgrade the ceiling to 60 minutes fire resistance using intumescent systems so to protect fire reaching the big timber roof void and basically end of building and ensure containment if fire developed in sleeping room (sneaky fag by a drunken Union Rep). Also with the owners still wanting to retain the original features and doors, would applying intumescent coating and ensuring doors have/can self close be sufficient. Obviously this would not be a all singing and dancing fire door due to not being tested to BS476, but would increase the fire protection that is currently in place.

I am looking from more of a property safety aspect than life safety. In regards to life safety building has smoke detection in all areas, travel distances are comfortably within the guidelines (only 7 rooms on 1st floor of 2 storey building),strictly no smoking, robust PAT testing and new wiring in place, good fire management with training, fire drills etc.

What would the cost implications be for upgrading the ceiling and ensuring the doors to the rooms and corridors have sufficient fire resistance?

[Phoenix]

Lath and plaster ceilings might very well provide a satisfactory level of fire resistance but how do you measure it for an existing ceiling?  You can't really.  What you're proposing sound potentially effective.  Talk to Envirograf about costs.  No, I don't have shares.

One other observation, if the building is used as sleeping accommodation, don't fool yourself that you're mainly interested in property protection here, life safety is bound to be an issue.  Irrespective of all the other fire protection measures installed, compartmentation is crucial in sleeping risks.

Stu

[hammer1]

http://www.heritage.nsw.gov.au/docs/FASAP_ceilings.pdf

From our Aussie friends doing a fie test on lath and plaster ceiling.

[kurnal]

In the care home boom of the 1980s many old buildings were converted and it was commonplace to upgrade ceilings from above and a number of systems were produced- tilcon foamed perlite and chickenwire being one common method. Theres also quite a lot of info on this and a book on the Historic scotland website. Theres also a research report on the English Heritage website somewhere in which they have submitted a number of different doors mimicing historic designs to fire tests - I have a hard copy of this somewhere.

I deal with this problem in this way. First look at the benchmark standard- the sleeping guide. Evaluate your building against the guide and identify strengths and weaknesses of your building against the benchmark. You can make certain improvements as far as you can, rather as you describe, subject to the constraints of heritage, character, layout, size and cost. Go as far as you can within reason then evaluate again against the benchmark.

The gap will now be smaller, eg your doors will have a better fire performance than they had before.  Analyse the gap from various aspects - life safety, heritage protection, property protection, business continuity.  Identify alternative  arrangements to compensate for the remaining weaknesses as far as you can- , control of ignition sources, control of combustibles  detection, suppression, staffing, briefing, planning etc. And then document it all very carefully.

[mw]

From BRE Digest 208 1988

Existing ceilings of 15-22 mm plaster on wood lath may possibly
contribute up to 20 minutes to the fire resistance of a timber floor
under BS 476 test conditions, but this will depend on the condition
and key. Therefore a detailed inspection is required before
assuming any contribution to the overall fire resistance of the floor.
Greater thicknesses of plaster will not necessarily provide additional
protection and because of the added weight may well fail earlier
than thinner plaster.

[afterburner]

Further to Kurnal's advice from Historic Scotland, there is a slight difference between the fire 'qualities' of lath and plaster in Scotland and England.

Basically this difference comes from the way the lath is applied. In Scotland it is not attached directly to the stone wall. It is held off the wall by small strips of timber called pugging pieces. In days of yore this created a nice insulation gap to keep the cold outside. It also created a very effective chimney effect as soon as fire penetrates the plaster and lath. Therefore, in Scotland, a lath and plaster fire is frequently a vertical fire spreading unseeen behind walls. Before the advent of Thermal Imgaing Cameras tracking a L&P fire could render walls with multiple perforations!

As for fire penetration through the plaster, this is more likely through time as 'works' progress throughout the building without recognition of the fire protection needs of holes and cavities being created in the lath and plaster.

[Fishy]

BS 5268: Section 4.2: 1990 (Structural use of timber. Fire resistance of timber structures. Recommendations for calculating fire resistance of timber stud walls and joisted floor constructions) would allow you to design an upgraded floor of up to 60 mins fire-resistance, based upon an existing lath and plaster construction.