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Technical Note (National Research Council of Canada. Division of Building Research), 1961-06-01
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Galbreath, M.
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DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
TEClHIN ][CAIL
NOTlE
No.
335
NOT FOR PUBLICATION
PREPARED BY M. Galbreath CHECKED BY RSF
FOR INTERNAL USE
APPROVED By NBH
DATE June 1961
PREPARED FOR Fire Rating Board, Associate Committee on the
National Building Code
SUBJECT ESTIMATING THE FIRE ENDURANCE OF EXTERIOR STUD WALLS
The National Building Code of Canada (1960) requires fire endurance ratings of 374 hour and I hour in exterior .walls of combustible construction for certain occupancies.
Information will be reqUired for the interpretation and
administration of these regulations. Unfortunately there is very little informs tioD available on the fire endurance of exterior stud walls. A study of published test reports suggests however that by careful selection of interior and exterior surface materials it should be possible to specify exterior stud walls having the required fire endurance.
In an exterior wall it can be anticipated that only the inside of the wall will be exposed directly to the fire. !!he outer surface is not expected to be in close contact with combustible materials and it is further protected by the
space separations imposed by the National Building Code (1) which are designed to reduce the possibility of ignition by radiation, should neighbouring buildings be on fire. It seems reasonable to assume therefore that if the interior surfaoe corresponds to a tested construction, some substi-tution might be possible in the materials used on the
outside. !!his approach has been taken in a New York State Code (2) which allows the results of fire tests on partitions to be used for certain specified external wall construction provided the interior lining is the same as in a tested assembly.
o
;
2
-The ｂｵｾ･｡ｵ of Standards, Washington, have made a
series of tests on wood-frame loadbearing partitions with
a variety of surface finiShes (3). A selection of those which provided a fire endurance exceeding 45 minutes is shown in Appendix A. Some of the partitions contained insulation
either loose or in the form of batts. In each case the walls had the same finish on both sides.
A number of exploratory tests on plywood-covered wall panels have also been carried out by the United States
Forest Products Laboratory (4). The test panels were
exposed to the standard furnace temperatures (ASTM El19) •. Some panels were tested full size S ft by 16ft, the remainder were 2 ft square. The insulation used was found to have a
considerable influence on the fire endurance. Loose fill insulation tended to settle in the wall or to fallout when a hole developed. Batt insulation, however, was found to be capable of increasing the fire endurance by 20 to 55-minutes depending on the weight of material used. Satis-factory fire endurance was also dependent on careful fitting and caUlking of joints between plywood panels.
An S- by l6-ft panel tested in this series attained a fire endurance of 52 minutes. llle facing material was
1/4
in. phenolic bonded plywood with mineral wool batt insulation weighing 2 lb/sq ft. Tests on smaller panels indicate that plywood-faced stud partitions might beexpected to have the fire endurance as shown in Appendix B. The figures are taken directly from the report.
The exterior finishes likely to be generally used in Canada are as follows:
I. 5/S-in. lumber Sheathing, bUilding paper and a siding material.
2. 7/l6-in. fibreboard sheathing, building paper and a siding rna terial.
30 l/2-ino gypsum board Sheathing, bUilding paper and a siding material.
4.
5/l6-in. exterior grade plywood, bUilding paper and a siding material.3
-The following lists of wall constructions that would probably have a fire endurance of 1 hour and 3/4 hour have been assembled using the information contained in the above reports. The internal wall finishes and the batt insulation have been tested in standard fire tests. The element of guesswork enters with the selection of the exterior surface. The combinations of sheathing and cladding which have been selected are those that appear to provide a reason-ably close fitting seal. The assemblies such as wood shakes on I-in. by 4-in. nailing strips have been rejected because it appears possible that the opening of the joints might permit flame to
pass through. This is an area in which a further program of testing might be valuable.
ESTIMATE OF FIRE ENDURANCE OF EXTERIOR STUD WALLS 1. Exterior stud walls having I-hour fire endurance
(a) Internal Finish
(i) two 3/S-in. gypsum wallboard
(ii) 1/2-in. gypsum and sand (1:2 1:3) on wood lath (iii) 1/2-in gypsum and sand (1:2 1:2) on 7/S-in.
flameproofed fibreboard
*
(iv) 3/4-in. gypsum and sand (1:2 1:2) on expanded metal lath
(v) 7/S-inc portland cement and lime (1:2 1:3:2) on expanded metal lath
(vi) 3/S-in0 phenolic bonded fir plywood *{:.
(b) Batt Insulation
(i) fibreglass weighing not less than 0.6 Ib/sq ft of wall surface
or (ii) mineral wool weighing not less than 1.2 Ib/sq ft of wall surface
*
batt insulation not essential for 1 hour fire endurance with this construction**
with mineral wool batt insulation weighing not less than 1.5 Ib/sq ft,J
..
4 -(c) External Finish
(i) 5/S-in. t
&
g lumber, building paper plus approved siding(ii) 7/S-in. flameproofed fibreboard, building paper plus approved siding
(iii) 1/2-in. gypsum board, building paper plus approved siding
(iv) 5/l6-ino exterior grade plywood building paper plus approved siding
(v) 3/S-ino exterior grade plywood without sheathing.
20 Exterior stud walls having 3/4-hour fire endurance (a) Internal Finish
(i) 3/S-in. gypsum wallboard
(ii) l/2-ino gypsum and sand (1:2 1:2) on 3/S-in. gypsum lath
*
(iii)
3/4-in.
gypsum and sand (1:2 1:2) onpaper-backed wire lath
*
(iv) 3/S-ino phenolic bonded fir plywood Ｊｾｾ
(v) anyone of l(a)(i) to (vi) above. (b) Batt Insulation
(i) fibreglass weighing not less than 006 lb/sq ft
02' (j i.) ｾＧＱ Lneral wool weighing not less than 1.2 Ib/sq ft
(c) External Finish
(i) anyone of l(c)(i) to (v) above 0
·If· batt insulation not essential for
3/4
hour fire endurancewith this construction
**
with mineral wool batt insulation weighing not less than 0.S6 lb/sq ft." ,,/' 5 -REFERENCES
.
10 National Building Code 1960 Subsection 3.2.2.
Regulations to resist fire spread between buildings. 20 Code Manual for State Building Construction Code
State of New York
State Building Commission New York
30 Building Materials and Structures Report BMS 71
Fire Tests of Wood and Metal Framed Partitions by So Ho Ingberg and Nolan P. Mitchell. Natural Bureau of Standards, Washington.
40
Fire Resistance Tests of Plywood Covered Wall Panels Go Co McNaUghton and C. A. HarrisonUnited States Department of Agriculture Forest Service Forest Products Laboratory
APPENDIX A
Fire Tests of Loadbearing Wood Stud Partitions, (3)
.e
Wall Finish on Both Faces
1/2-in. gypsum wallboard. Mineral wood batts 0.6-1.5 Ib/sq ft
two 3/S-in. gypsum wallboard. Fibreglass blanket 0.6 lb/sq ft
1/4-in. phenolic resin ｢ｯｾ､･､ fir plywood with mineral wool fill 2 lb/sq ft
1/2-in. gypsum plaster (1:2, 1:3) on wood lath. Mineral wool batts 0.6-1.5 lb/sq ft
1/2-in. gypsum plaster (1:2 1:2) on 7/S-in. flameproofed fibreboard
1/2-in. lime and Keenes cement (3:l:S, 3:1:12) on wood lath. Mineral wool batts 0.6-1.5 lb/sq ft
1/2-in. gypsum plaster (1:2, 1:2) on 3/S-in. gypsum lath (no space between laths)
3/4-in. gypsum plaster (1:2, 1:2) on paper-backed wire lath.
3/4-in. gypsum plaster (1:2, 1:2) on expanded metal lath. Mineral wool batts 0.6-1.5 lb/sq ft
7/S-in. portland cement/lime (2:1:S, 2:1:10) on expanded metal lath.
Time to Failure, minutes 51 1/2 60 52 1/2 73 74 54 54 54 S9 62
- - -
-APPENDIX B
Fire endurance of non-loadbearing partitions with plywood of the thickness noted below on both faces and the space between studs filled with batt insulation (information taken from nFire Resistance Tests of Plywood Covered Wall Panels" (4)).
I-hour fire endurance
Plywood, phenolic resin bonded. Batt Insulation
Thickness, ina Weight, Ib/sq ft
3/8 1.5
1/2 1.0
3/4-hour fire endurance
Plywood, phenolic resin bonded. Batt Insulation
Thickness, ina Weight, Ib/sq ft
1/4 2.00
3/8 0.86
