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Newsletter
7th Edition, January 2007
Protection from Precipitation
Cladding Provisions for Housing and
Small Buildings
in the National Building Code of Canada
2005
By:
Ken Rauch
Introduction
Ask anyone in the industry, except
possibly Egyptian pyramid contractors, to identify public enemy #1 for
environmental separators, and the answer will probably be MOISTURE.
Prior to the 1970s energy crisis, when we began superinsulating any
cavity that stood between us and outside, the National Building Code of
Canada (NBC) devoted more ink to protection from precipitation than
combating air leakage and interstitial condensation. Since that time,
and as understanding of the mechanisms involved increased, this has been
turning around. However, rain continues to fall, and snow continues to
melt, and measures to limit damage or unsafe conditions from
precipitation ingress continue to be an important element of the NBC.
Part 9 of the NBC, Housing and
Small Buildings, describes acceptable materials, systems and equipment
to accomplish a minimum level of performance consistent with user health
and safety and utility of these building elements for their intended
purposes. Alternative, equivalent solutions have always been permitted
by the Code, and the new, objectives-based edition is no exception. A
critical aspect of alternatives proposed to the prescriptive provisions
of Part 9 is a credible assessment of conformity to the Code’s minimum
level of performance.
Precipitation Protection in
Part 9 of the NBC
Precipitation-protection
provisions in Division B, Part 9 are grouped with other provisions
relating to specific building systems or functions. Major groups of
provisions are to be found in Sections 9.20, “Masonry and Insulating
Concrete Form Walls Not in Contact with the Ground”, 9.26. “Roofing”,
9.27. “Cladding” and its related Section, 9.28. “Stucco”. In this
article, I’ll concentrate on cladding for wall surfaces.
Cladding Provisions in the NBC
2005
Cladding provisions in the 2005
edition of the NBC are significantly expanded over previous editions.
The new edition is more specific as to acceptable design strategies and
assemblies. In the 1995 edition of the NBC, cladding performance
requirements were quite simply stated: “Exterior walls shall be
protected with cladding, including flashing, trim and other special
purpose accessory pieces required for the cladding system being used, to
restrict the entry of rain and snow into the wall assembly”. In this
area at least, the Code has, at the request of industry, become more
prescriptive.
Exterior walls are required to be
designed and constructed to:
-
minimize precipitation ingress into the assembly
and to prevent its entry into interior space, and
-
minimize the likelihood of deterioration and
reduced performance due to mechanical impact and ultraviolet
radiation.
Section 9.27.1. breaks
down the wide range of cladding materials into five groups:
-
lumber, wood shingles, shakes, fibre-cement
shingles, planks and sheets, plywood, OSB, waferboard, hardboard,
vinyl and aluminum or steel,
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Stucco,
-
masonry,
-
asphalt shingles and
-
other cladding materials.
There are extensive subsections
devoted to each group and, for all types of cladding, there is the
option of compliance with the provisions of Part 5, “Environmental
Separation”.
Acceptable Cladding System
Configurations - Two-Plane Systems
For residential buildings, a
primary and secondary plane of protection is required, as a high level
of performance is expected with, perhaps, minimal maintenance. These
planes of protection can comprise siding over a sheathing membrane,
which has been a familiar and economical system used in Canada for many
years. Also considered to satisfy the requirement for a two-plane system
are masonry veneer over wood frame and masonry cavity walls.
In geographical areas where
climatic conditions favour wetting, but do not promote drying (i.e.
lower temperatures and high moisture index), a two-plane system with the
addition of a capillary break between the first and second planes is
required for all buildings. As we read on, we find that this might not
be as onerous a requirement as it seems.
There are acceptable variations on
these systems, all of which can be classified as open rainscreen
assemblies. The capillary break could be created by furring behind the
cladding or by a layer of open drainage material. In either case, the
space between the first and second planes must be drained to the
exterior. Perhaps surprisingly, loosely-attached siding, such as metal
or vinyl, over sheathing membrane is deemed to satisfy the requirement
for a capillary break. The capillary break is not required—although it
is always recommended, if it can be shown that:
- it isn’t
vital to the performance of the system,
- the wall
or intersecting floors aren’t moisture sensitive,
- the wall
is a “mass wall” (e.g. cast-in-place concrete) or
- the
building is an accessory building.
The Purpose for a First and
Second Plane of Protection
The first plane of protection
discussed previously comprises cladding, trim, accessories and fasteners
designed to minimize passage of rain and snow due to:
- kinetic
energy (e.g. driving rain),
- surface
tension,
-
capillarity,
- gravity
and
- air
pressure differences.
The second plane of protection is
a drainage layer, complete with flashing designed to dissipate water,
that might pass the first plane, to the exterior. Both planes must be
maintained at penetrations and interfaces with other wall assemblies.
Face-Sealed Systems – An
Exception
Cladding systems comprising large
sheets or panels with well-sealed joints which effectively reduce air
infiltration and control the entry of wind-driven rain are permitted to
be installed without a second plane of protection. This provision was
originally included in the Code to accommodate mobile homes with
lock-seamed metal siding—a system that manufacturers have used for many
years. However, this provision might be useful for systems comprising
panels with battens at the joints, for example.
As well, where it can be
demonstrated that a sheathing material is at least as impervious to air
and water penetration as sheathing membrane, and where its joints are at
least as impervious to air and water penetration as the material itself,
sheathing membrane (second plane of protection) is not required.
Conformity Assessment of
Alternative Cladding Materials and Systems
Despite its prescriptive nature,
Part 9 always offers the opportunity for alternative materials or
systems. For designers, builders and manufacturers, alternatives to
explicitly-mentioned building materials and systems can offer
flexibility of design to suit particular conditions, cost savings and
the opportunity to move the technology forward. The sticking point is
often determining if proposed alternatives actually will offer
equivalent performance to the “tried and true”.
Sometimes examination, either at
the design stage or on-site can satisfy regulatory authorities as to the
“equivalency” of a proposed alternative, but more often a third-party
review is required. There are hundreds of materials standards referenced
by the NBC, and comparison of a material with the provisions of the
appropriate standard by a competent agency can pave the way to
hassle-free acceptance on the jobsite.
The NBC does not assign
responsibility for conformity assessment. This is usually the purview of
provincial and territorial governments. Immediately following the
Preface to the NBC 2005, is a discussion entitled “Relationship of the
NBC to Standards Development and Conformity Assessment”. The following
is a listing of some resources available to those responsible for
ensuring materials and systems meet the performance requirements of the
NBC along with some links to more complete information.
- Laboratory
testing is the backbone of certification, registration, evaluation and
qualification systems. The Standards Council of Canada has accredited
many organizations as capable of testing building products to
specified standards. Click on the following link for a listing of
accredited laboratories and the testing for which they are approved:
http://palcan.scc.ca/SpecsSearch/TLSearchForm.do.
-
Certification provides a high level of confidence, including, as it
does, physical examination, testing, plant examination, follow-up
plant inspections, and issuance of assurance that a product, process
or system (including, in some cases, entire buildings) conforms to
specified provisions. There are more than a dozen accredited
certification organizations including the Canadian Standards
Association (CSA) and the Underwriters’ Laboratories of Canada (ULC).
Useful information on CSA certification may be found at
http://www.csa.ca/consumers/faq/Default.asp?language=english.
- Quality
Registration Organizations, such as the International Organization for
Standardization (ISO) [see
http://www.iso.org/iso/en/iso9000-14000/index.html] assess
conformity to quality assurance standards. You have probably seen “ISO
9000 Registered” emblazoned on manufacturing facilities.
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Qualification of products
to a standard and inclusion in a “Qualified Products List”. [e.g. the
Canadian General Standards Board (CGSB),
http://www.pwgsc.gc.ca/cgsb/prgsrv/certprg/certprg-e.html].
For Your Information
Update on Adoption of the 2005
NBC by Provinces and Territories
(Thanks to John Archer of the
Canadian Codes Centre)
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BC - complete adoption
autumn, 2006
YK - end of 2006
NWT - end of 2006
NT - early 2007
AB – autumn, 2006
SK - end of 2006
MB – April, 2006 |
ON - end of 2006
QC - 2007
NB - end of 2006
PEI - no plans
NS - very soon
NF - no plans
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Provincial/Territorial Policy Advisory Committee on Codes
(PTPACC) Membership List as of September 1, 2006
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Mr. D.M.
Crawford, M.Eng., P.Eng.
Chair, PTPACC
Deputy Fire
Marshal
Office of the
Fire Marshal
Ministry of the
Solicitor General
Place Nouveau,
6th Floor, 5775 Yonge Street
North York,
Ontario
M2M 4J1 |
Mr. J. Vasey
Vice Chair,
PTPACC
Director
Building Policy
Branch
Ministry of
Forests and Range and Minister Responsible for Housing
P.O. Box 9951
Stn Prov Govt
Victoria,
British Columbia
V8W 9R3 |
Mr. D. Brezer,
MBA, P.Eng.
Director
Building and
Development Branch
Ministry of
Municipal Affairs and Housing
777 Bay Street,
2nd Floor
Toronto,
Ontario
M5G 2E5
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Mr. B.E.
Clemmensen
Ex Officio –
Chair CCBFC
Clemmensen &
Associates Limited
17 Oakland
Avenue
Toronto,
Ontario
M9M 2H9 |
Mr. R.J.
Cormier
Director of
Public Safety / Fire Marshal
Nova Scotia
Department of Environment and Labour
Office of the
Fire Marshal
P.O. Box 697
Halifax, Nova
Scotia
B3J 2T8 |
Mr. W. Fallow,
P.Eng.
Ex Officio –
Chair PTSPC
Chief Plumbing
Inspector
Technical
Inspection Services
Department of
Public Safety
495A Prospect
Street, P.O. Box 6000
Fredericton,
New Brunswick
E3B 5H1
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Mr. T. Hinds
Fire Marshal
Office of the
Fire Marshal
Dept. of
Community Government & Transportation
Government of
Nunavut
P.O. Box 490
Rankin Inlet,
Nunavut
X0C 0G0 |
Mr. D. Hodgins
Fire
Commissioner
Ministry of
Forests and Range and Minister Responsible for Housing
Office of the
Fire Commissioner
PO Box 9491 Stn
Prov Govt, 1 - 800 Johnson Street
Victoria,
British Columbia
V8W 9N7 |
Mr. C.L.
Jones
Deputy Fire
Commissioner
Office of the
Fire Commissioner
Government of
Manitoba
508 Norquay
Building, 401 York Avenue
Winnipeg,
Manitoba
R3C 0P8 |
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Mrs. D. Kelland
Assistant
Deputy Minister
Government
Services Branch
Department of
Government Services & Lands
Confederation
Bldg., P.O. Box 8700
St. John's,
Newfoundland
A1B 4J6 |
Mr. D. Kozmen
Director -
Consumer and Safety Services
Department of
Community Services
Government of
Yukon
Box 2703
Whitehorse,
Yukon
Y1A 2C6 |
Mr. R.P.
McCullough
Ex Officio –
Chair PTSFC
Director,
Building and Fire Safety
Corrections and
Public Safety
Office of the
Fire Commissioner
1855 Victoria
Avenue, Suite 310
Regina,
Saskatchewan
S4P 3V7 |
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Mr. Ted Ross
Ex Officio –
Chair PTSBC
Building Code
Coordinator
Public Safety
Division
Nova Scotia
Environment & Labour
PO Box 697
Halifax, Nova
Scotia
B3J 2T8 |
M. G. Tessier
Directeur
Direction de la
normalisation et de la qualification
Régie du
bâtiment du Québec
545 Crémazie
est, 7ième étage
Montréal,
Québec
H2M 2V2 |
Mr. C.M. Tye
Executive
Director, Safety Services Branch
Public Safety
Division
Alberta
Municipal Affairs
16th Floor,
Commerce Place, 10155 - 102 Street
Edmonton
Alberta
T5J 4L4 |
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Mr. B. Van
Tighem
Fire Marshal
Municipal &
Community Affairs
Government of
the Northwest Territories
500, 5201 -
50th Avenue
Yellowknife,
Northwest Territories
X1A 3S9 |
Mr. A. Wilkins
Director
Technical
Inspection Services
Department of
Public Safety
PO Box 6000
Fredericton,
New Brunswick
E3B 5H1 |
Mr. T. Young
Executive
Director,
Protection and
Emergency Services
Saskatchewan
Corrections and Public Safety
100 - 1855
Victoria Avenue
Regina,
Saskatchewan
S4P 3V7 |
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Mr. J.W.
Archer, MRAIC
Ex Officio –
PTPACC Secretary
Canadian Codes
Centre
Institute for
Research in Construction
National
Research Council Canada
1200 Montreal
Road, Bldg. M-23A, 2nd Floor
Ottawa, Ontario
K1A 0R6 |
Mr. D. Bergeron
Ex Officio –
NRC Advisor
Director, Codes
& Evaluation
Institute for
Research in Construction
National
Research Council Canada
1200 Montreal
Road, Bldg. M-23A, 2nd Floor
Ottawa, Ontario
K1A 0R6 |
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About the Author
Ken Rauch is a building technologist
with 23 years of service with Canada Mortgage and Housing Corporation in various
technical and building code related positions in Manitoba and at
CMHC’s National Office in Ottawa. Since 1997, he has
assisted the Canadian Codes Centre, NRC with an Intent Analysis of the
requirements National Building Code in preparation for the Objective-Based NBC.
He makes his home in Cobourg, Ontario. Ken can be
contacted by email at ken.rauch@sympatico.ca
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