Fire performance of external wooden roofs

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Fire performance of external wooden roofs

Lazaros Tsantaridis

SP Wood Technology SP Report 2012:34

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Fire performance of external wooden

roofs

Lazaros Tsantaridis

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4 SP Technical Research Institute of Sweden Box 857, 501 15 Borås, Sweden (headquarters)

SP Report 2012:34 ISSN 0284-5172

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Abstract

Fire testing of different types of external wooden roofs was performed according to the European standard ENV 1187 Test 2. Based on the test results, a European fire class has been determined according to EN 13501-5.

All tested products fulfilled the European fire class BROOF (t2) for external roofs, in most

cases with large margins.

The following criteria have been defined for wood products fulfilling the European fire class BROOF (t2) for external roofs:

− Wood panels made of pine or spruce with thickness ≥ 20 mm

− Wooden shingles of pine or spruce with thickness ≥ 25 mm. The thickness of the shingle may be less at the upper end below to ≥ 2 mm. The shingles may be dipped in tar.

Key words: Fire safety, building products, burning brands, flame spread, damaged area

Sammanfattning (Summary in Swedish)

Olika typer av yttertak i trä har brandprovats enligt den europeiska standarden ENV 1187 Test 2. Baserat på provningsresultaten har en europeisk brandklass bestämts enligt EN 13501-5.

Alla provade produkter uppfyllde den europeiska brandklassen BROOF (t2) för yttertak, i

flertalet fall med stor marginal.

Följande träprodukter uppfyller den europeiska brandklassen BROOF (t2) för yttertak:

− Träpaneler av furu eller gran med tjocklek ≥ 20 mm

− Träspån av furu eller gran med tjocklek ≥ 25 mm. Takspånens tjocklek kan vara mindre vid övre änden och minska ned till ≥ 2 mm. Takspånen kan vara doppade i tjära.

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Preface

The results reported have been performed within the Swedish project Fire safety design of timber structures (Brandteknisk dimensionering av träkonstruktioner) sponsored by Vinnova, Swedish Governmental Agency for Innovation Systems, in cooperation with building industry partners.

The financial support from Vinnova and the technical support from industry is kindly acknowledged.

Birgit Östman

SP Wood Technology Stockholm

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Content

Introduction

8 Experimental

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Fire testing 9

Wood products tested 10

Test results

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Result summary 11

Detailed test results 12

Pictures of test specimen after fire testing 26

Fire classification

30 Conclusions

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Introduction

External roofs may be ignited through exposure to flying burning brands, heat flux from nearby fires, fireworks and during building construction or reconstruction.

Four alternatives for testing and verifying the external fire performance of roofs have been agreed within the European system and specified in ENV 1187 [1]:

1. Method with burning brands

2. Method with burning brands and wind

3. Method with burning brands, wind and supplementary radiant heat

4. Two-stage method incorporating brands, wind and supplementary radiant heat. The four test methods originate from different European countries, and no harmonisation has been possible so far. Method 2 originates from the previous Nordic method NT Fire 006 and has been used in this report.

One or both of the following hazard conditions are considered in the different methods: – Fire spread at the surface and/or immediately below the roof covering

– Penetration of fire through the roof.

The classification of external fire performance of roofs is specified in EN 13501-5 [2]. For Method 2, two classes are specified:

• BROOF (t2) with criteria for damaged length after fire testing

• FROOF (t2) for products not fulfilling the criteria for class BROOF (t2)

The classification criteria for Method 2 are :

• Mean damaged length of the roof covering and substrate ≤ 550 mm • Max damaged length of the roof covering and substrate ≤ 800 mm

Wood products are mainly used as the substrate for the roof covering. Wood products as the outermost covering is not very common, but may fulfil the European requirements which is shown in this report. It is the first general study on this topic, only data on specific wood products, e g [3] have been found in the literature.

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Experimental

Fire testing

Fire testing of the external wooden roofs was performed according to the European standard ENV 1187 Test methods for external fire exposure to roofs – Test 2: Method with burning brands and wind. The performance includes the fire spread across the external surface of the roof, the fire spread within the roof and the fire penetration. Two wind speeds 2 and 4 m/s are evaluated.

The size of each specimen is 400 x 1000 mm and the testing time 15 minutes. In total 36 fire tests of wood products were performed.

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Wood products tested

Two types of wood products for external roof coverings have been tested: • Wood panels

• Wood shingles

In addition two wood-based panels were tested. The following numbering of specimen has been used: 1. Pine panel with thickness 20 mm.

2. Particleboard with thickness 10 mm. 3. Spruce plywood with thickness 12 mm.

4. Spruce panel with thickness 22 mm. This roof panel was tested in different configurations, see below and Table 1.

5. Shingles of pine heartwood with thickness 2-25 mm.

6. Shingles of pine heartwood with thickness 2-25 mm, treated (dipped) in pine tar (dalbränd tjära in Swedish), about 1 l/m2.

The wood panels were ordinary untreated panels with a density of approximately 500 kg/m3. The wood panels, no 4a-4e, were tested in five different configurations with number of panels above or below and different distance between the upper panels, see Table 1 and pictures, to ensure that the configuration did not influence the test results. The pine heartwood shingles were 400-500 mm long, 70-120 mm wide and 25 mm thick at one end and 2 mm at the other end. They were nailed to the wood panel substrate with an overlapping leaving about 400 mm of the thicker end visible on the roof, see pictures. The roof specimen were mounted and tested on a standard combustible substrate, particleboard 20 mm for all cases except no 5-6 above (shingles), for which wood panels with a small spacing in between were used as substrates (as often mounted in practice). All specimens were conditioned to constant mass in a controlled climate chamber at 23 ± 2 °C and 50 ± 5 % RH before the fire testing.

When tested on a combustible substrate, the resulting fire classification of the external roofs will be valid for application on both combustible and non-combustible substrates.

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Test results

Result summary

The test results are summarised in Table 1.

Table 1. Test results for external fire exposure to roofs according to ENV 1187- Test 2.

No. Product

Thick-ness (mm) Damaged length (mm) Number of tests at wind speed Roof Mean/Max at Substrate * Mean/Max at 2 m/s 4 m/s 2 m/s 4 m/s 2 m/s 4 m/s 1 Pine panel 20 180/180 -/- 0/0 0/0 2 0 2 Particleboard 10 220/220 -/- 0/0 0/0 1 0 3 Spruce plywood 12 240/240 260/260 0/0 0/0 1 1 4a Spruce panel (1 panel above/ 2 below) 22 230/240 340/380 0/0 0/0 3 3 4b -“- (2 panels above/ 1 below) 22 530/560 510/580 0/0 0/0 3 3 4c -“- (2 panels above with small distance in between/ 1 below) 22 -/- 460/620 -/- 0/0 0 3 4d -“- (2 x 2 panels above/ 1 below) 22+22 420/430 -/- 0/0 -/- 3 0 4e -“- (three panels in the same plane)

22 150/150 -/- 0/0 -/- 1 0

5 Shingles of pine

heartwood 2-25 200/390 340/410 190/300 320/370 3 3 6 -“-

treated with pine tar

2-25 240/290 230/340 100/180 110/320 3 3

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Detailed test results

Specimen: No. 1

Pine panel

Test number: 1 2

Wind speed, m/s: 2 2

Observations during the fire test

Minutes:seconds

The burning wood crib is placed on the specimen

0 0

Time when the specimen ignites 0:30 0:35

Specimen damaged length, mm 100 0:40 0:45

-“- 150 1:00 0:55 -“- 200 -“- 250 -“- 300 -“- 350 -“- 400 -“- 450 -“- 500 -“- 550

The flames decrease 1:25 1:35

The flames die out 3:10 3:30

The glow dies out 9:00 9:00

Observations after the fire test

Damaged length of the specimen, mm

from the centre of the wood crib 170 180

Damaged length of the substrate, mm

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13 Specimen: No. 2

Particle board

Test number: 1

Wind speed, m/s: 2

Minutes:seconds

0

Time when the specimen ignites 0:25

Specimen damaged length, mm 100 0:45

-“- 150 1:00 -“- 200 1:20 -“- 250 -“- 300 -“- 350 -“- 400 -“- 450 -“- 500 -“- 550

The flames decrease 2:45

The flames die out 4:30

The glow dies out 9:00

from the centre of the wood crib 220

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14 Specimen: No. 3

Plywood

Test number: 1 2

Wind speed, m/s: 2 4

Minutes:seconds

0 0

Time when the specimen ignites 0:25 0:25

Specimen damaged length, mm 100 0:35 0:30

-“- 150 0:50 0:45 -“- 200 1:10 1:00 -“- 250 1:15 -“- 300 -“- 350 -“- 400 -“- 450 -“- 500 -“- 550

The flames decrease 3:05 2:10

The flames die out 3:55 3:05

The glow dies out 9:00 9:00

from the centre of the wood crib 240 260

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15 Specimen: No. 4a-1

Spruce panel (one panel above and two panels below)

Test number: 1 2 3

Wind speed, m/s: 2 2 2

Minutes:seconds

0 0 0

Time when the specimen ignites 0:20 0:25 0:25

Specimen damaged length, mm 100 0:30 0:35 0:35

-“- 150 0:40 0:45 0:45 -“- 200 0:50 1:00 0:55 -“- 250 -“- 300 -“- 350 -“- 400 -“- 450 -“- 500 -“- 550

The flames decrease 1:45 2:05 2:10

The flames die out 4:05 4:10 4:25

The glow dies out 9:00 9:00 0:00

from the centre of the wood crib 230 230 240

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16 Specimen: No. 4a-2

Spruce panel (one panel above and two panels below)

Test number: 1 2 3

Minutes:seconds

0 0 0

Specimen damaged length, mm 100 0:25 0:25 025

-“- 150 0:30 0:30 0:30 -“- 200 0:35 0:40 0:40 -“- 250 0:40 0:45 0:45 -“- 300 0:50 0:55 0:55 -“- 350 1:05 -“- 400 -“- 450 -“- 500 -“- 550

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17 Specimen: No. 4b-1

Spruce panel (two panels above and one panel below)

Test number: 1 2 3

Minutes:seconds

0 0 0

-“- 150 0:35 0:30 0:30 -“- 200 0:40 0:35 0:35 -“- 250 0:45 0:40 0:40 -“- 300 0:50 0:45 0:50 -“- 350 0:55 0:50 0:55 -“- 400 1:00 0:55 1:00 -“- 450 1:10 1:10 1:15 -“- 500 1:30 1:25 1:30 -“- 550 1:40

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18 Specimen: No. 4b-2

Spruce panel (two panels above and one panel below)

Test number: 1 2 3

Minutes:seconds

0 0 0

-“- 150 0:30 0:30 0:30 -“- 200 0:40 0:40 0:40 -“- 250 0:50 0:50 0:50 -“- 300 1:00 1:00 1:00 -“- 350 1:05 1:10 1:05 -“- 400 1:15 1:20 1:20 -“- 450 1:20 1:30 1:30 -“- 500 1:35 -“- 550 1:45

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19 Specimen: No. 4c

Spruce panel (two panels above with small distance inbetween and one

below)

Test number: 1 2 3

Minutes:seconds

0 0 0

-“- 150 0:55 0:45 0:40 -“- 200 2:10 0:55 0:50 -“- 250 2:20 1:10 1:50 -“- 300 2:40 1:55 -“- 350 2:50 2:05 -“- 400 3:00 2:20 -“- 450 3:10 2:40 -“- 500 3:20 -“- 550 3:25 600 3:35

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20 Specimen: No. 4d

Spruce panel (2 x 2 panels above and one panel below)

Test number: 1 2 3

Minutes:seconds

0 0 0

-“- 150 0:30 0:30 0:35 -“- 200 0:35 0:40 0:40 -“- 250 0:40 0:50 0:45 -“- 300 0:50 1:00 0:55 -“- 350 1:00 1:10 1:05 -“- 400 1:20 1:25 1:20 -“- 450 -“- 500 -“- 550

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21 Specimen: No. 4e

Spruce panel (three panels in the same plane)

Test number: 1

Wind speed, m/s: 2

Minutes:seconds

0:20

Time when the specimen ignites 0:30

Specimen damaged length, mm 100 0:45

-“- 150 -“- 200 -“- 250 -“- 300 -“- 350 -“- 400 -“- 450 -“- 500 -“- 550

The flames decrease 3:05

The flames die out 4:50

The glow dies out 9:00

from the centre of the wood crib 150

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22 Specimen: No. 5-1

Shingles of pine heartwood

Test number: 1 2 3

Minutes:seconds

0 0 0

-“- 150 1:00 1:20 1:30 -“- 200 7:00 7:00 7:00 -“- 250 -“- 300 -“- 350 -“- 400 -“- 450 -“- 500 -“- 550 600 The flames decrease

The flames die out The glow dies out

The test was interrupted (end of test)

15:00 15:00 15:00

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Shingles of pine heartwood

Test number: 1 2 3

Minutes:seconds

0 0 0

-“- 150 1:10 1:10 1:05 -“- 200 8:20 10:15 8:10 -“- 250 10:30 -“- 300 13:25 -“- 350 -“- 400 14:50 -“- 450 -“- 500 -“- 550

The flames decrease The flames die out The glow dies out

The test was interrupted due to heavy smoke (not a test criterion) probably caused by the spacing in the wood panel substrate.

14:50 13:25 10:30

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Shingles of pine heartwood, treated with pine tar

Test number: 1 2 3

Minutes:seconds

0 0 0

-“- 150 0:50 0:45 0:50 -“- 200 13:20 10:30 -“- 250 15:00 15:00 -“- 300 -“- 350 -“- 400 -“- 450 -“- 500 -“- 550 600 The flames decrease

The flames die out The glow dies out

The test was interrupted (end of test) 15:00 15:00 15:00

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Shingles of pine heartwood, treated with pine tar

Test number: 1 2 3

Minutes:seconds

0 0 0

-“- 150 7:10 1:00 1:00 -“- 200 9:00 -“- 250 13:00 -“- 300 15:00 -“- 350 -“- 400 -“- 450 -“- 500 -“- 550

The flames decrease The flames die out The glow dies out

The test was interrupted (end of test) 15:00 15:00 15:00

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Pictures of test specimen after fire testing

Specimen 4a-1. External roof panel of spruce (one panel above and two panels below). Three samples after fire test at the wind speed 2 m/s.

Specimen 4a-2. External roof panel of spruce (one panel above and two panels below). Three samples after fire test at the wind speed 4 m/s.

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Specimen 4b. External roof panel of spruce (two above and one panel below). Three samples after fire test at the wind speed 2 m/s.

Specimen 4b. External roof panel of spruce (two above and one panel below). Three samples after fire test at the wind speed 4 m/s.

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28 Specimen 5-1. Shingles of pine heartwood.

Three samples after fire test at the wind speed 2 m/s.

Specimen 5-2. Shingles of pine heartwood.

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Specimen 6-1. Shingles of pine heartwood, treated with pine tar. Three samples after fire test at the wind speed 2 m/s.

Specimen 6-2. Shingles of pine heartwood, treated with pine tar. Three samples after fire test at the wind speed 4 m/s.

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Fire classification

Fire classification has been carried out in accordance with clauses 9 of EN 13501-5:2005 fire classification of construction products and building elements – Part 5: Classification using data from external exposure to roof tests.

The classification criteria for tests at both 2 m/s and 4 m/s wind speed are : • Mean damaged length of the roof covering and substrate ≤ 550 mm • Max damaged length of the roof covering and substrate ≤ 800 mm

All wooden roofs included in this study fulfill the European fire class BROOF (t2), in most

cases with large margin to the classification limit.

The substrate was not damaged at all for the wood panels. The wind speed had only minor influence on the test results.

This classification is valid for external wooden roofs mounted on both combustible and non-combustible substrates, since all tests have been performed on combustible

substrates.

Conclusions

The European fire class BROOF (t2) according to EN 13501-5 may be fulfilled by wood

products.

The following criteria have been defined for wood products fulfilling the European fire class BROOF (t2) for external roofs:

− Wood panels made of pine or spruce with thickness ≥ 20 mm

− Wooden shingles of pine or spruce with thickness ≥ 25 mm. The thickness of the shingle may be less at the upper end below to ≥ 2 mm. The shingles may be dipped in tar.

Both types of products may be mounted on combustible or non-combustible substrate. Other types of wooden roofs may also fulfill the same fire class, e g thinner wooden roofs or wooden products that have been modified to increase their durability against biological decay at exterior applications. The fire performance of these products need to be verified through testing.

Class BROOF (t2) does not cover the risk of firebrands or flames entering via venting gaps,

but the major fire risk in roofs is related to the hidden fires in ventilation cavities. These cavities must not connect compartments. Air inlets must block firebrands and flames and/or roof insulation must provide sufficient fire resistance to prevent a roof construction fire from spreading downwards into compartments or attics.

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References

1. ENV 1187 Test methods for external fire exposure to roofs – Test 2: Method with burning brands and wind. European Standard. European Committee for

Standardization, Brussels, 2002.

2. EN 13501-5 Fire classification of construction products and building elements – Part 5: Classification using data from external exposure to roof tests. European Standard. European Committee for Standardization, Brussels, 2005.

3. Moelven Danmark: Stærk ceder tagdækning, Prøvningsrapport DBI, PF12992, 2008.

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SP Report 2012:34 ISBN 978-91-87017-48-3 ISSN 0284-5172

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