162 / 228
6. PERFORMANCE OF LVL IN FIRE
The requirements of reaction to fire classes for different ap-
plications are defined in national building regulations. In gen-
eral, LVL panels and structures may be left exposed in a build-
ing under the same conditions as other solid wood products.
In the classification, the first letter A-E denotes combusti-
bility, with D being typical for wood products.The second sym-
bol, s1-s3, denotes smoke production and the third symbol,
d0-d3, denotes the risk of flaming droplets. The class for LVL
is similar to most untreated wood products. Some manufactur-
ers specify for some applications a smoke production class of
s1 based on separate testing, which is slightly better than the
typical class s2. The flaming droplets class d0 assigned to wood-
based products means that no flaming droplets or particles are
produced. Although the European systemhas been in use since
the beginning of 2000, national classification systems are still
in parallel use in some countries.
The reaction to fire classification can be improved by fire
retardant treatments or with inorganic surface laminates up to
a class B-s1,d0, which is the highest class for combustible ma-
terials. The fire retardants are mainly salt-based chemicals that
are usually hygroscopic, meaning that they absorb humidity
from the surrounding air. It is therefore essential that the du-
rability of the treatment is verified for the intended use class for
the whole service life of the product.
LVL manufacturers provide fire retardant treatment as an
additional service for their products, details of which can be
found from their product information material.
6.3 FIRE PROTECTION ABILITY,
K-CLASSES OF COVERINGS
The encapsulation requirements of fire protection ability class-
es K10 - K60 of coverings are used in building regulations to
Table 6.1.
Classes of fire protection ability performance of LVL – laminated veneer lumber according to EN14374. The table has been published
as a draft annex of (EC Ref. Ares(2017)2463446 - 15/05/2017) pending formal issuing as a European Commission Delegated Regulation
38
.
protect underlying products against damage. The classes may
be achieved by LVL panels, when the minimum thicknesses are
according to the Table 6.1. However, in some applications only
non-combustible materials are approved for the encapsulation.
Note: the same layer in a structure can give fire protection in ac-
cordance with the K-classes and at the same time be taken into
account for fire resistance time of the structure.
6.4 FIRE RESISTANCE OF LVL
STRUCTURES
The fire resistance of LVL structures can be calculated ac-
cording to the structural fire design specification of Eurocode
5 (EN1995-1-2) and its National annexes. The model of the
structural system adopted for design shall reflect the perfor-
mance of the structure in the fire situation.
6.4.1 Fire resistance design process
The fire resistance design process has the following steps:
1. Determination of the charring depth
The charring depth is the distance between the outer sur-
face of the original member and the position of the char line.
It is calculated using the time of fire exposure and the relevant
charring rate which depends on the material of the structure
and possible additional protection layers on the structure. The
original size reduced by the charring depth on exposed sides is
defined as the residual cross section.
2. Determination of the effective cross section
Due to the increased temperature, the mechanical prop-
erties of wood reduce which is taken into consideration by
LVL 06, Table 6.1
Product
1)
Product detail
2)
Minimummean
density [kg/m3]
Minimum thickness
of a board [mm]
Field of
application K Class
Laminated
veneer lumber
products
covered by the
harmonised
standard
EN 14374
With and without tongue
and groove and a minimum
layer thickness of 3 mm
4)
450
15
Wall and ceiling
covering
K
2
10
3)
With and without tongue
and groove and a minimum
layer thickness of 3 mm
5)
450
26
Wall and ceiling
covering
K
2
30
With and without tongue
and groove and a minimum
layer thickness of 3 mm
6)
450
52
Wall and ceiling
covering
K
2
60
1)
Mounted directly on the substrate (particle board 680 kg/m3 according to EN 14135) without an airgap
2)
Joints with square edges or tongue and groove profile and with the same thickness as the wood product and without gaps.
3)
K
1
10 for substrates ≥ 300 kg/m3
4)
Screw length minimum 30 mm and spacing maximum 200 mm
5)
Screw length minimum 50 mm and spacing maximum 200 mm
6)
Screw length minimum 75 mm and spacing maximum 200 mm
160
LVL Handbook Europe