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Timber Frame and fire: the risks – true or false?

Date: 11/11/2010

No one who follows the news can fail to have noticed the headlines in both the construction press and indeed national media on the subject of timber frame design and fire safety.  In this first of a series of articles, Rupert Scott MIFireE, Membership Manager for TRADA, reviews the statistics and asks are the risks true or false?

1  Introduction

The media coverage of fire in timber frame buildings, whether completed and occupied or still under construction, has been emotive and relentless. The stories raise many issues, some legitimate, others barely founded on fact.  It is important that the timber industry understands the facts clearly, to determine the real problems and their solutions.  A review of the statistics is a solid first step, in particular those produced by Communities and Local Government, the department responsible for building regulations and planning, entitled Fire Statistics Monitor, April 2009 to March 2010 Issue no. 03/10, (England only)*.

2  Fatalities and non-fatal casualties for all types of finished construction

The overall trend for England (see sections 1, 2 and 3 of the report) has been extremely encouraging with fatalities and non-fatal casualties steadily falling for three consecutive decades, up to 2010.  Fatalities have fallen every year for the last five years and are now 55% lower than in 1984/5.

Non-fatal casualties, too, are falling. In 2009/10 this was 8% lower than 2008/09 and is the lowest figures since records in this format began in 1994.

This has all happened at a time when timber frame construction had grown tremendously in England,  from around 5% of new builds to some 17.5% today.  Of course, new build makes up a small percentage of the total housing stock.  The positive downward trend in casualities and non-fatal injuries is not in any significant way down to the switch in new build - it no doubt is due to changes in social demographics and behaviours, better education etc.  As long as buildings comply with building regulations, which many forms of timber frame have adequately proven, their construction type will have little impact on the level of injuries or casualties in habited premises.  So private homeowners and social housing tenants and landlords need have no concerns whatsoever on this front.

3  Fatalities and non-fatal injuries: finished timber frame versus other forms of construction

In support of the conclusion that completed timber frame dwellings are no more likely to cause fatal or non-fatal injuries the figures quoted in section 5.1 of the report are tabled below.

 

	Dwellings				Non-dwellings
	Timber Frame		‘No special construction'		Timber Frame		‘No special construction'
	Qty	Rate / fire	Qty	Rate / fire	Qty	Rate / fire	Qty	Rate / fire
Fatalities	3	0.008	265	0.008	0	-	6	-
Non-fatal casualties	67	0.19	6100	0.18	16	0.04	488	0.05

 

The rates of fatal and non-fatal casualties per fire are very similar for timber frame and other forms of construction (categorised as ‘no special construction' in the report).  However, based on the figures provided, the likelihood of a fire causing fatal or non-fatal injury is considerably less for timber frame than other forms of construction, as the table below shows.

 

	Calculation	Percentage
Timber frame dwellings as a percentage of English dwelling stock	500,000 /  17m*	Approx 3%
Timber frame dwelling English casualities as a percentage of all forms of construction casualties.	3/268	1.1%
Timber frame dwelling English non-fatal casualties as a percentage of all forms of construction English casualties	67/6,167	1.1%
Timber frame English fires as a percentage of all English fires (dwellings and non-dwellings)	802/61,000	1.3%

 

*These are rough estimates but sufficiently accurate to arrive at a figure of approximately 3%.

One would expect the casualty and non-casualty rates to be approximately 3% given the proportion of dwellings made using timber frame.  In fact it is closer to 1% according to the report statistics.

The report comments that it is likely that some timber frame dwellings are wrongly assumed to be other forms of construction because they use brick outer rainscreen cladding.  We acknowledge this would narrow the margin by which timber frame scores better than other forms of construction - but the margin is very great from the figures taken from the report.

4  Area of heat and flame damage: finished timber frame versus other forms of construction

Chart 6 (dwellings) and chart 8 (non-dwellings) in the CLG report show the distribution of fires by area of heat and flame damage differentiating between timber frame and other forms of construction.

The commentary in the report states that:

• For non-dwellings there is no statistical difference between timber frame and other forms of construction.
• For dwellings a difference does exist in that timber frame is skewed somewhat towards larger areas of damage.

However, in terms of dwellings two important points must be made:

• The footnote explains that the difference is borderline in terms of demonstrating a significant difference using the chi-squared test (a specific test used in the CLG report for assessing the statistical significance of the results).
• According to the report timber frame buildings account for 1.7% of all fires, which is far less than the percentage of the dwelling stock. This effectively compensates for the borderline difference in area of damage experienced.
• Very few people are dying in timber frame dwellings (3 per year verses 265 in other forms of construction) and therefore the significant issue is insurance costs. Reinstatement of timber frame can be cheaper and easier as report by Chiltern Fire entitled "Reinstatement of fire damaged timber frame buildings" demonstrated.

5  Buildings under construction - total quantity of fires

Before dealing with the matter of the area of fire damage, which undoubtedly is an issue, it is worth appraising the quantity of fires experienced during construction for timber frame compared to other forms of construction.  One could be forgiven for thinking that there are far more fires on timber frame construction sites - the opposite in fact is true.

We know that timber frame accounted for approximately 17% of new build dwellings in the year considered and therefore from the table summarising the CLG statistics below, we can see that timber frame experiences significantly fewer fires pro rata than other forms of construction.  We do not have equivalent figures for non-domestic.

 

	Quantity of fires in buildings under construction
	Timber frame	Other forms of construction	Total	Timber frame as a % of total
Dwellings under construction	32	227	259	12.3%
Non-domestic under constructions	16	163	179	8.9%
All buildings	50	400	450	11.1%

 

The report comments that the ratio of timber frame fires in construction (1:8) is far greater than those for completed buildings (1:59).  This is actually irrelevant since the proportion of new build timber frame is far greater than the completed building stock.  What matters is that in both cases (during construction and completed buildings) timber frame is significantly less prone to experiencing fires than other forms of construction.

6  Buildings under construction - area of fire damage

A number of large timber frame construction projects have experienced fire damage to large areas of the building. The timber frame industry is quite clear that this is the issue that needs to be addressed.  A number of solutions exist to solve this problem on large, medium-rise projects, which include:

• Alternative phasing of construction tasks, so that large areas of structural timbers are not left exposed
• Supplying closed panel construction
• Alternative material technologies, which provide enhanced fire protection
• Tight security during the critical phase.

Given that there have been no fatal casualties and only a small number of non-fatal casualties the dominant issue is the insurance costs involved.

The dominant issue here is not human life or safety -  the statistics show that there have been no fatalities and only a few casualties as a result of these fires - but the insurance costs involved. The timber frame industry must therefore convince insurers that they are addressing the risks. One positive aspect is that although a number of projects have experienced large areas of damage, the cost of replacing only the structural timber and OSB racking boards is relatively very cheap at about one-quarter of the cost of full finished construction.

Even taking higher premiums into account, the time and cost benefits of timber frame to the developer are still considerable. Good news does not generally make for interesting headlines, so while the media might continue to stir up an emotional lobby against timber frame, the timber industry needs to keep a cool head.