BUILDING ENVELOPE
DESIGN & CONSTRUCTION
REQUIREMENTS
NEW RESIDENTIAL WARRANTY
PROGRAM
Prepared by:
RDH Building Engineering Limited
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BUILDING ENVELOPE
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Contents
1 OVERVIEW ............................................................................................................ 1
1.1 THE ROLE OF THE ARCHITECT ............................................................................................... 1
1.2 THE ROLE OF THE BUILDING ENVELOPE PROFESSIONAL.................................................. 1
1.3 THE ROLE OF THE WARRANTY PROVIDER ........................................................................... 2
1.4 BUILDING ENVELOPE DESIGN FUNDAMENTALS ................................................................... 2
2 DESIGN REQUIREMENTS .................................................................................... 6
2.1 EXPOSURE AND ENVIRONMENTAL DESIGN CRITERIA ........................................................ 6
2.2 SELECTION AND DOCUMENTATION OF ASSEMBLIES........................................................ 12
2.3 DETAILS .................................................................................................................................... 14
2.4 COMPONENTS AND MATERIALS............................................................................................ 16
3 CONSTRUCTION ................................................................................................. 17
3.1 MOCK-UPS AND TESTING ....................................................................................................... 18
3.2 FIELD REVIEW .......................................................................................................................... 19
4 POST CONSTRUCTION ...................................................................................... 19
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1 Overview
The risk management process for the design and construction of the building
envelope will involve the Architect, Building Envelope Professional (BEP), various
contractors (general and trade contractors), and with the new warranty program in
place, the warranty provider. Other consultants (structural and mechanical most
notably) play lessor roles in determining the performance of the envelope
assemblies but we believe that the key parties listed above can influence and
control their impact.
This document provides requirements with respect to the role of the Architect,
Building Envelope Professional (BEP) and the warranty provider in the building
envelope risk management process. Please see the flow chart (Figure 1.1) at the
end of this chapter for a summary of the involvement of each in managing the
building envelope risk throughout the design and construction process.
1.1
The Role of the Architect
The Architect’s role must follow the basic agreement for services outlined in the
National Practice Program for the Profession of Architecture in Canada – Document
6 and the Architectural Institute of British Columbia (AIBC). The Architect will have
responsibility for the design of the envelope. They must follow these requirements,
in addition to building codes and standards, other reference material and good
practice to arrive at a design.
In addition to the Architect's basic scope of services the Architect is required to
prepare a building envelope maintenance and renewals manual. The Architect may
rely upon the BEP for the completion of this and other design tasks.
1.2
The Role of the Building Envelope Professional
The BEP provides additional expertise to the Architect to assist the Architect in his
or her design and field review services with respect to building envelope assembly,
component and material performance issues. The BEP's service does not replace
any of the Architect's basic services or responsibilities. The BEP provides specialist
consulting to the Architect and builder with respect of Part 5 Building Code issues,
good practice and these requirements. The BEP provides the following services to
the project:

Ongoing consultation with the design team during the schematic or
conceptual stages regarding envelope assemblies

Review of the completed schematic design and preparation of a design report
(sample format provided in Appendix B)
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
Ongoing consultation with the design team during design development and
construction document stages of the project regarding envelope performance
and detailing issues

Review of the construction documents and preparation of a construction
document review report (sample provided in Appendix B)

Supplementary field review and field testing of the envelope construction as
is appropriate for the project and in accordance with municipal requirements
in this regard

Review of the building envelope maintenance and renewals manual.
1.3
The Role of the Warranty Provider
The warranty provider is not part of the design team. However, since the warranty
provider is providing the warranty there is a need to assure itself that appropriate
design and construction decisions are being made so that it is not exposed to
unnecessary risk. In this context it will be conducting independent reviews or
checks on the quality assurance measures being taken by the design and
construction team. It will rely on the reports prepared by the Architect and the BEP
throughout the design and construction process and may on occasion conduct its
own review of the design, construction documents and completed construction.
The warranty provider will maintain and make available a list of approved Architects,
BEPs, general and trade contractors, and approved materials. The builder must
select an approved contractor from this list. If the warranty provider has not
provided the lists, the builder must obtain written approval to the contractor of its
choice. Failure to do so may void the warranty.
The warranty provider's review does not relieve the Architect or the BEP from their
obligation to meet their statutory and other obligations as well as the minimum
design standards outlined in these requirements.
1.4
Building Envelope Design Fundamentals
Fundamental performance expectations and design principles for building envelopes
are described in numerous documents including a variety of NRC-IRC, CSA and
CMHC publications. Perhaps the most locally relevant document of this type is the
recently published Best Practice Guide - Wood Frame Envelopes in the Coastal
Climate of British Columbia (BPG) and it is therefore referenced throughout these
requirements.
These requirements addresse moisture management issues as required by the
warranty and therefore are closely linked to Part 5 of the building code. They do not
address many of the other functions and performance criteria which the envelope
must meet, such as acoustics, fire protection and structural issues. The design
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team must address these issues and integrate these design provisions with the
moisture related warranty provisions outlined in these requirements.
The approach taken in the BPG and the one which is believed to be most
appropriate for the Coastal Climate areas of BC is to focus on managing exterior
moisture sources. Other moisture sources must also be managed, but the dominant
influence in design decisions is rain penetration control.
The BPG can be used for other non coastal climate zones of the province, however
the emphasis must be shifted more to cold climate issues such as air leakage
control.
The BPG is directed at 3 and 4 storey wood frame buildings and therefore its details
are not directly applicable to high rise construction. However, building science does
not change from low rise to high rise construction and therefore most of the
principles described in the BPG are also applicable to high rise construction. Key
differences include the larger impact of stack effect in taller buildings, the fact that
exposure to wind and exterior moisture sources is expected to be high on taller
buildings, and the fact that much more exterior moisture can collect on wall surfaces
as it runs down the building from floor to floor. The evaluation of exposure is
therefore focussed more on how high rather than a decision between low, medium
and high. Other materials are used for the structural components (steel and
concrete instead of wood) and for envelope assemblies (window-wall, curtainwall,
metal panels etc.).
The basic approach therefore starts with the consideration of the building form,
location and orientation and the evaluation of exposure conditions. The guidance
provided in Chapter 5 of the BPG is appropriate for this purpose. Once an exposure
category has been determined for the building, or various parts of the building, then
the selection of assemblies can proceed. Essentially Rainscreen assemblies are
required for medium and high exposure conditions and face sealed or concealed
barrier assemblies, if permitted by code or other regulations, can be considered for
use in low or no exposure situations.
Once basic assemblies have been selected, details can be developed and decisions
with respect to component and material selection can be made in anticipation of
specification preparation.
These requirements refer to and incorporate design guidance from other sources.
While the requirements attempt to consolidate design guidance into one fairly
comprehensive yet concise package, it is not possible to prescribe requirements
which adequately cover all issues and all design situations. It is for this reason that
the warranty provider and the BEP are reviewing specific building designs to assess
risk and for the builder and the architect to ensure the specific building designs
comply with these requirements.
The following sections of these requirements outline requirements for selection of
assemblies, components and materials. In addition to the general requirements
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regarding selection and development of the building envelope assemblies there are
some prescriptive do's and don'ts which are referred to as rules.
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Figure 1.1
BUILDING ENVELOPE RISK MANAGEMENT PROCESS
DESIGN
PROCESS
CONCEPTUAL
DESIGN
ARCHITECT
(based on NPP
Document 6)
Program of
Requirements
Review
Construction
Budget

DESIGN
DEVELOPMENT
Prepare Design
Development Drawings
and Other Documents

CONSTRUCTION
DOCUMENTS
Prepare Construction
Documents Including
Drawings and
Specifications
Prepare or Review
Construction Cost
Estimate
Review Construction
Cost Estimates
Review Applicable
Codes, etc.
Review Permit
Requirements

TENDER
Assist in
Obtaining Bids,
Awarding and
Preparing
Contracts for
Construction
Design Approaches
Review Regulations
and Code
Ongoing
Consultation
WARRANTY
PROGRAM
REVIEW
Approval of
Architect and BEP
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Review of the Work

POST
CONSTRUCTION
Undertake Warranty
Inspections
Payment Certifier
Interrpet the Contract
Documents
Prepare or Assist in
Development of
Maintenance and
Renewals Plan
Review Contractor
Submittals
Issue Instructions
Regarding
Adjustments to the
Work
Prepare Schematic
Design
BUILDING
ENVELOPE
PROFESSIONAL

CONSTRUCTION
Ongoing Consultation
Review of Construction
Documents
Consultation as
Required
Supplementary Field
Review and Testing
Preparation or Review of
Maintenance and
Renewals Manual
Consultation as
Required
Review of Construction
Documents
Confirmation of
Trade
Contractors,
Suppliers and
Materials
Monthly Review of
Field Review Reports
and Change Orders
Review of Maintenance
and Renewals Plan
Review of
Schematic Design
Review of
Schematic Design
On-site Review as
Required
Post Construction
Examination of Envelope
Performance Throughout
Warranty Period
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2 Design Requirements
The design requirements set out in this section shall be considered minimum
requirements. The builder can modifiy these design requirements by an alternative
approach only upon submission to and acceptance by the warranty provider of a
request for an alternative approach. The intent of any such requests must be to outline
how the intended performance objectives are being met by other means.
2.1
Exposure and Environmental Design Criteria
This section describes environmental factors to be used in the selection of assemblies.
This includes exterior climatic design data, interior conditions and exposure.
The builder must prepare a sheet which describes how the exposure category was
rationalized for each wall and glazed assembly, as well as all exterior and interior
design criteria.
Part 5 Requirements
Part 5 of the BC Building Code does not provide specific design solutions for envelope
design. Rather it specifies design process and criteria and relies upon the designer to
make appropriate design decisions to meet the performance objectives. The 1998
Code is intended to be a move towards objective based requirements. In general, this
type of code places more onus on the designer to employ technology to match
performance requirements.
A list of abbreviated part 5 clauses, design criteria that the builder must consider, and
the design decisions for building envelope assemblies associated with them are listed in
Table 2.1 below. The use of the word minimize occurs frequently in Part 5. The
Appendix to the Code indicates that 'minimize' means reduce to a level that prevents
long term damage to materials.
It is critical that the design consider all potential moisture sources identified in Part 5 of
the Code.
Table 2.1: Summary of Part 5 Code Requirements
Section
Design Criteria
Design Tasks
5.1
Environmental
Separation
All environmental loads and effects
of loads that can be reasonably
expected, compatibility of materials,
mechanisms of deterioration
Components and assemblies to have
sufficient capacity to resist
environmental loads, materials to be
compatible, resistant to deterioration,
and designed in accordance with good
practice such as CSA S478
5.2
Loads and
Procedures
Climatic loads
Heat, air, moisture transfer calculations
Below ground environmental loads
Wind load calculations
Interior environmental loads
5.3
Heat Transfer
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Intended temperature differential
Minimize surface condensation
Required resistance to heat transfer
Minimize condensation in assembly
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Section
Design Criteria
Design Tasks
Meet interior design conditions
Minimize condensation at cold bridges
Prevent convective air flow in insulation
5.4
Air Leakage
Air leakage limit for Windows and
doors and air barrier assemblies
specified wind load and safety
factors
Wind load transfer to structure and
deflection of the air barrier system
5.5
Vapour
Diffusion
Temperature differential
Minimize moisture transfer by diffusion
into assemblies to
Precipitation
Wind uplift loads Sealing, Drainage,
Accumulation, and Disposal
5.6
Vapour pressure gradient
Snow
Formation of ice
5.7
Surface Water
Accumulation of water
Minimize ingress into assemblies
Prevent ingress into interior space
Design cladding to shed precipitation
Minimize likely hood of snow and ice
accumulation hazard
Prevent entry into building
Prevent damage to materials
5.8
Moisture in the
Ground
Soil moisture and continuous
hydrostatic pressure
Prevent moisture transfer into interior
space
Durability
The 1998 BC Building code makes specific reference to the durability of materials in the
building envelope assembly in section 5.1.4. It requires that the materials be
'compatible' with adjoining materials, and 'resistant' to any mechanisms of decay that
can reasonably be expected given the use of the material. The code further references
CSA S478 which provides guidelines on service life and materials use. These
requirements more clearly establish the obligation for durable designs, although it does
fall short in articulating specific durability performance expectations.
Mandating design for durability requires a service life for building envelope components.
Achieving appropriate specifications for building envelope components therefore
involves all of the usual Part 5 requirements for performance in service with the
additional requirement that the function be preserved for a specific term. The design
team must be able to identify design service lives of materials components and
assemblies. It is also necessary to do so in order to develop a maintenance and
renewals plan for the building envelope.
Suggested normal periods for the design service lives for residential buildings and most
major components are summarized in the table below:
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Table 2.2: Design Service Lives
Building or Component
Normal design life
Residential building
50 to 99 years
Primary and most secondary structure
Same as the building
Cladding, Window Frame
More than 25 years
Window Insulated Glass Unit
More than 10 years
Roofing
More that 15 years
Interior finishes
More that 5 years
These design lives are not specified in CSA S478 but in the absence of specific
performance criteria set out by authorities having jurisdiction they would be considered
reasonable by most owners of homes in BC. They must therefore be used as the
starting point for the establishment of service life criteria for elements of the envelope.
Specific building materials or components can be expected to last shorter or longer
periods of time depending on where they occur within the assemblies (easily replaced)
and how maintainable they are. For example, brick ties in a masonry veneer wall is a
component that has a high requirement for reliability in service, is difficult to inspect,
maintain, or repair, and therefore requires a service life which is equal to or exceeds
that of the masonry veneer cladding. The CSA A370 Masonry Connectors standard
recognizes this through a requirement for stainless steel ties.
Exposure
In order to assess and design wall and window assemblies for control of rain
penetration there is a need to know the intensity and duration of wetting. The
assessment and exposure of walls and windows to wetting is not dealt with explicitly in
the code or its appendices, and therefore warrants the following specific guidelines:
The determination of exposure is a process that involves the consideration of both
design and environmental factors. Design factors range from building orientation to
how the building and its elements deflect water. Environmental factors include duration
and intensity of rainfall, and wind velocity and orientation during these rain events.
Together these factors will determine how often, and for how long, the building walls will
be wet. The process of evaluating exposure can be simplified by considering only the
three most influential factors; climate, overhang and terrain.
Although the coastal climate zone contains various microclimate zones where rainfall
intensity and wind directions vary, it is reasonable to establish the entire coastal climate
zone as a severe wetting environment for the determination of exposure categories for
all buildings. Similarly, areas of the province not in the coastal climate zone may be
characterized generally as a relatively cold and dryer climate zone. The following two
nomographs must be used for these two climate zones to determine exposure
conditions. Locations which are not clearly in one zone or another must use the more
conservative determination of exposure.
The consideration of exposure conditions can be simplified to an examination of
overhang and terrain.
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Overhang is usually created by the roof but may also be created by other features of
the building such as awnings or floor assemblies which are extended. An overhang
ratio can be defined as:
Overhang Ratio = Overhang Width
Wall Height
Where:
Wall Height is the height above the lowest moisture sensitive element (eg.
wood framing but not concrete foundation wall height)
Overhang is the horizontal distance between the outer surface of the
cladding and the outer surface of the overhang
Terrain has a large influence on how much wind driven rain will impact on the walls of a
building. For the purposes of this guide we have defined four categories which are
described in the nomograph figures.
The nomographs can be used to deterime a general exposures category for different
combinations of overhang ratios and terrain.
While the range of exposure categories are somewhat arbitrary and require an
assessment by the designer they could be summarized as follows:
High
-
Wall is not wet under normal service conditions and is subject to
significant exposure to wind
Medium -
Wall is often wet under normal service conditions
Low
-
Wall is rarely wet under normal service conditions
None
-
Wall is not wet under normal service conditions
An example of a wall in exposure category None would be a recessed ground floor level
wall effectively protected from wetting by large overhangs.
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Figure 2.1: Coastal Climate Zone Exposure Nomograph
Figure 2.2: Interior Climate Zone Exposure Nomograph
Ratio
Overhang
Ratio
0
0.1
Exposure
Category
Terrain
D - Building located within 1 km of direct
waterfront exposure, or small or few
surrounding obstructions, or located on a hill
or cliff overlooking adjacent buildings
0.2
C - Rural areas, moderately treed, or buildings
mostly fewer than 4 stories within 5 Building
heights
0.3
B - Many large buildings within 2 building heights
0.4
0.5
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A - Adjacent buildings of equal or greater height
located within one building height in all
directions
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Overhang
Ratio
Exposure
Category
Terrain
0
D - Building located within 1 km of direct
waterfront exposure, or small or few
surrounding obstructions, or located on a hill
or cliff overlooking adjacent buildings
0.1
0.2
C - Rural areas, moderately treed, or buildings
mostly fewer than 4 stories within 5 Building
heights
0.3
B - Many large buildings within 2 building heights
0.4
A - Adjacent buildings of equal or greater height
located within one building height in all
directions
0.5
The tables which follows identify acceptable exterior assembly moisture control
strategies for walls and windows and various exposure levels. The BPG describes the
intent of the various exterior moisture control strategy for commonly used wall and
window assemblies.
Table 2.3: Wall Assembly Exterior Moisture Control Strategy
Exposure Level
Face Seal
Concealed
Barrier
Pressure Moderated
Rainscreen
Rainscreen
High
Not Acceptable
Not Acceptable
Not Acceptable
Acceptable
Medium
Not Acceptable
Not Acceptable
Acceptable
Acceptable
Low
Not Acceptable
Acceptable
Acceptable
Acceptable
None
Acceptable
Acceptable
Acceptable
Acceptable
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Table 2.4: Window Assembly Exterior Moisture Control Strategy
EXPOSURE LEVEL
WINDOW ASSEMBLIES
None
Low
Medium
High
AL-1: Aluminum – Face Seal


AL-2: Aluminum – Concealed Barrier


AL-3: Aluminum – Concealed Barrier (Improved)



AL-4: Aluminum – Rainscreen




VY-1: Vinyl – Concealed Barrier




VY-2: Vinyl – Rainscreen




Exterior Design Conditions
Exterior design conditions are referenced in Appendix B of the BC Building Code. For
the purposes of calculating condensation potential it is acceptable to use temperatures
higher than the 2.5% January design temperature. The intent is that no adverse effects
shall occur as a result of condensation, and since many building materials have some
capability to safely store moisture to be released at a later time, it is not a requirement
that no condensation occur. It is therefore permissible to use temperatures which are
2ºC to 5ºC higher than the 2.5% January design temperature. The determination of the
design temperature must be made based on the moisture storage capability and
moisture sensitivity of each assembly. Thermal bridging (concentration of studs, non
thermally broken window sub-sill flashings) can be more significant considerations than
the preciseness of the design temperature.
Interior Design Conditions
Recent interior suite measurements of actual in service conditions in multi-unit
residential buildings in BC have indicated that actual relative humidity levels may
exceed those previously felt to be acceptable for design purposes. For the purpose of
building enclosure assembly design the interior winter design conditions must therefore
be at least 22°C and 60% RH. Higher levels must be used if the building use and
occupancy or ventilation capability are expected to result in different conditions.
2.2
Selection and Documentation of Assemblies
The selection or development of assemblies based on an exposure category for wood
frame buildings must proceed on the basis described in the BPG. If not using one of
the assemblies specifically described in one the data sheets of the BPG then a work
sheet (enclosed in Appendix A) must be prepared which documents the assembly
materials and layers and describes how they manage all moisture sources. Sample
sheets for two non combustible assemblies are enclosed for reference purposes in
Appendix B.
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RULES:
General

High humidity locations such as swimming pools, and hot tubs require special
consideration with respect to ventilation and assembly design to
accommodate large moisture sources.
Wall Assemblies

All combustible and non-combustible rainscreen wall assemblies in a medium
and high exposure categories must be compartmentalized at building corners
and at each floor level

All combustible and non-combustible rainscreen wall assemblies in high
exposure categories must utilize a continuous exterior bituminous membrane
as the air barrier.

Rainscreen wall drainage cavities to be unobstructed for 70% minimum of
wall perimeter, with unobstructed drainage paths at all details and
penetrations.

Medium and high exposure walls may utilize mass wall assemblies which
have adequate storage capacity to retain water without damage to wall
assembly materials until the following drying period. Mass walls must contain
water stopped control joints caulked on the exterior, and fully grouted tie
holes.

Prefabricated EIFS panel systems must not be used unless they are exterior
to a continuous water shedding surface. EIFS assemblies are not permitted in
high exposure categories. In medium exposure categories EIFS assemblies
must be mechanically fastened and placed over a sheet waterproof
membrane

Wall claddings must only be used in vertical applications; all sloped surfaces
greater than 15º from the vertical must be treated as roofs.

Wall claddings must be sufficiently durable to withstand damage from
intended access equipment such as ladders, swingstages and boatswains
chairs.
Windows, Doors & Other Glazed Assemblies

Windows and curtain wall assemblies must be used only in vertical
applications.

Secondary sloped sub-sill drainage must be used for all glazed assemblies
and doors in medium and high exposure conditions
Roofs, Decks, Balcony & Walkway Assemblies

Waterproof membrane roof assemblies must be designed so that the
waterproof membrane and the air-barrier are the same component. Pitched
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water shedding roofs which are vented to the exterior must have different air
barrier and moisture barrier components within the assemblies.
2.3

All roof, deck, balcony & walkway assemblies must be designed with positive
slope to drain (minimum 2%) after permanent long term building movements
have occurred (shrinkage, creep).

Unprotected membranes must not be used on decks located over living
spaces (can't act as both a waterproof membrane and wearing surface)

Membranes must not be buried under concrete or asphalt unless membrane
life expectancy is greater than 20 years. Drainage mat must be used above
membrane and all landscape elements must be able to be relocated on site
for membrane replacement. All toppings (pavers, wood wearing surface etc.)
over other types of membrane must be removable by hand for servicing of
membrane.

All roof or waterproofing assemblies for pools or water features over occupied
spaces must be a double waterproofing system which eliminates hydrostatic
head on the lower membrane surface.
All penetrations through the
membranes must be located to minimize hydrostatic pressure at the
penetration.
Details
Design detailing and construction of the interfaces between the envelope assemblies is
critical in ensuring performance of the assemblies themselves. The design details must
therefore incorporate the following:

The details must show all of the typical interfaces between assemblies and
sufficiently illustrate the intent.

The details must show the intent for difficult or atypical details.

The details must be drawn at a scale that allows the design intent to be
clearly illustrated and individual components, layers & connections to be
identified.

The details must be drawn in 3-D or as isometrics if it is necessary to show
the intent of the completed assembly.

Details must indicate the intended location, materials and components
comprising the air barrier, moisture barrier and vapour barrier on the drawings
(in a similar manner to that shown in the BPG)
In addition to these general detailing principles the following rules must apply to the
development of details.
RULES:

Positive drainage path must be incorporated at the moisture barrier.
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
Sub-sill drainage path must be provided under all windows and doors and
must be sloped to the exterior.

Cross cavity flashing must be provided as a minimum at every second floor
level for medium and low exposure conditions, every floor level for high
exposure conditions.

All cap flashing must have a minimum 1:6 slope.

All other drip flashing and cross cavity flashing must have a minimum 1:4
slope.

End dams must be utilized on all cross cavity flashing

Sealant must not be relied upon as a part of the primary moisture barrier in
medium or high exposure situations in a location which is exposed to direct
exterior moisture, UV rays or cyclic temperature movements greater than
20°C.

All doors must be protected by an overhang with an overhang ratio of 0.33
relative to the threshold.

All roofs, decks, balconies and walkways must be designed and constructed
to slope both the wearing surface and the waterproof membrane away from
door thresholds and towards drainage points

Scuppers must not be used as primary drainage mechanisms except with
PVC coated metal and heat weldable PVC surface membranes.

Clamped membrane floor drains or direct runoff from drip edge must be the
primary drainage mechanisms for balconies and walkways

Drain locations must be clearly marked on concrete pavers and in planters
and be easily accessible for maintenance.

Protect traffic paths on roofs with additional wearing surface.

Metal flashing must not be used as the moisture barrier except in low
exposure situations. Metal flashing must shed the majority of the water and
protect a waterproof membrane below.

The type of waterproof membrane to be used on a roof must be selected
depending on the complexity of the roof configuration. For example, a multiply reinforced liquid applied membrane may be the best selection for a
complex roof configuration with many details and irregular shapes.

Vent hoods must be designed so that water drips away from the building.
Vent hoods must be designed so that screens can be maintained. Vent
systems must be designed so that they can be tied into the building air-barrier
system.

Cladding must be designed to accommodate daily and seasonal thermal
movements without permanent deformation or cracking.
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2.4

Sandwich slab systems must not be used without concrete perimeter curb
and membrane which extends 100mm above upper slab surface.

Window-wall assemblies must create a rainscreen cavity in spandrel areas
which directs all water in the cavity to the exterior over a waterproof moisture
barrier. The barrier must terminate on a vertical surface, to the exterior of,
and lapped over the moisture barrier for the element below
Components and Materials
The selection of materials and components for a project is a complicated process
involving consideration of exposure conditions, maintainability, compatibility with
adjacent materials, aesthetics, and costs. There is a great deal of guidance with
respect to the selection of building envelope components and materials for wood frame
construction provided in the BPG. As a guideline it is not prescriptive by nature and
thus is open to interpretation. The generic specification for a material is often not
enough to ensure that good quality products end up being used on the project. For
example, various manufacturers of self adhesive membrane have different performance
characteristics as well as different application requirements. Similarly, some window
manufacturers use their own forces for installation and others contract this work out.
Even if the proper materials are specified and used, the application may be full of
deficiencies resulting in failure of the detail. As a result, specific products and trades
will need to be reviewed by the warranty provider on a project by project basis to
ascertain that acceptable materials, suppliers and installers are being used. The form
for use in indicating proposed trade contractors and materials is enclosed in Appendix
A.
The following general rules must be followed in the development of specifications.
RULES:

The builder must develop appropriate mock-up and testing requirements for
inclusion in the project specifications

Specification of wood products must follow the Wood Product Selection
Guide in the BPG

Sheathing Membranes - Breather Type in medium exposure conditions must
only be used with an air cavity greater than 12mm located to the exterior of
the membrane. Only non-breather type to be used in high exposure
conditions.

The use of waterproof sheathing membranes on wood frame structures
creates a situation where water vapour can not readily migrate to either the
interior or exterior. The wood products must therefore be at or below 19%
moisture content at the time the wall is enclosed

The builder must follow CSA A370-94 requirements for corrosion resistance
on metal connectors in masonry
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
Minimum level of zinc coating required for corrosion protection on
inaccessible sheet steel products located outside the moisture barrier is
G200. This may require the use of thicker sheet steel than is required for
structural purposes.

Windows and doors are required to meet CSA A440.1-M98 User Selection
Guide performance criteria with respect to air leakage, water leakage and
wind load resistance. Minimum condensation resistance for windows must
be TF48 and for doors D1 as described in CSA A440-M98

Only factory glazed unit skylights, pressure cap drained skylights, and
pressure cap pressure equalized rainscreen skylights (as defined in the BPG)
are to be used in assemblies which separate indoors from outdoors

Exposed polyurethane membranes must not be used on wood surfaced deck
and balcony sheathing

Metal fasteners must have sufficient corrosion resistance for the exposure
conditions (corrosion potential), and reflect the location within the assembly
the fastener is located (ability to replace and maintain). Fasteners hidden
behind the cladding but exposed to wetting within the drainage cavity must
have at least as much corrosion resistance capacity as the life expectancy for
the cladding.
3 Construction
The specific quality assurance process for the building envelope will vary from building
to building, however, in many ways the risk management process described within this
documents forms a fundamental part of the projects overall quality assurance plan.
The guide follows the normal design process and incorporates a series of checks by
both the BEP and the warranty provider. Specific ways in which the process outlined in
this guide can be incorporated into the overall quality assurance plan with contractor
activities include the following:

The builder must submit a qualifications statement for the site superintendent
and all other office and site personnel involved in the construction of the
envelope.

The contractor must have a project specific quality control plan developed
and presented to the warranty provider in writing.

The Architect and BEP must review the contractors quality control plan.

A building envelope start-up meeting must be held on site with all of the
envelope trades, the builder, architect and BEP. The purpose of the meeting
is to review the design intent, answer questions related to the construction of
the envelope and to review the quality control plan and responsibilities.

The contractor must ensure that moisture content of wood products are at or
below 19% moisture content at the time the assembly is closed in.
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3.1

The BEP together with the contractor is to undertake on site window water
penetration field testing as described in the BPG.

The BEP together with the contractor must flood test all roofs for a minimum
of 24 hours.

The warranty provider must be provided with copies of all field review reports
conducted by the Architect, BEP, material supplier or manufacturer as well as
any site instructions and change orders relevant to the building envelope.
Mock-ups and Testing
Mock-ups have become an accepted and even desirable part of the construction
process supported by both the designers and contractors. Mock-ups are full size
construction of important or difficult assemblies and details that are intended to form
part of the construction for the building in question. They can be done separately from
the actual building (mock-up) or they can be built to be incorporated into the final
construction (field demonstration).
The purpose of the mock-up is to confirm and convey the design intent for typical and
difficult interfaces. They are usually done prior to construction or at the start of the work
for typical details, and during the construction for atypical details.
The key to successful use of mock-ups is to identify the scope, size and location of
mock-ups as much as possible at the design stage, and to include a mechanism for
requesting additional mock-ups should a difficult detailing situation arise during
construction. Furthermore the construction of mock-ups must be undertaken by the
actual trade contractors who will be performing the construction of the building, and
upon completion the mock-ups must be available as a reference standard expected for
the balance of the envelope construction.
Testing has also become an accepted part of the construction process. Aside the from
the results of component testing which can be requested prior to construction, on most
projects there will be a need to test the installed assemblies to confirm performance of
not just the assemblies but the interfaces between the assemblies. Wording must be
included in the specification documents to define the extent and nature of this testing
on a building specific basis.
Depending on the size and nature of the mock-ups, performance testing can be
undertaken on them. Alternately, testing can be undertaken in the field on selected
elements of the construction. Decisions with respect to number, location and timing of
tests needs to be made on a individual project basis.
Testing must be done by the builder or trade contractor as part of their quality control
procedures. In addition, testing can be undertaken by the developer, architect, BEP or
warranty provider as part of the quality assurance process. This testing essentially acts
as a check on the builder or contractor's quality control procedures.
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3.2
Field Review
Field review of the envelope construction is part of the quality assurance process and
must be undertaken by both the project Architect and the BEP. The architect has the
primary responsibility for field review but may rely upon the supplementary review
undertaken by the BEP. The warranty provider's reviews are not part of the project and
must not be relied upon by the architect as supplementary reviews.
The field review effort must be coordinated between the architect, BEP, builder and
trade contractors. A specific plan must be developed for this work which deals with the
following:

How are issues identified as discrepancies by the BEP to be resolved

How are issues not dealt with in the construction documents to be resolved

How is the resolution of discrepancies tracked and who takes responsibility
for completion of each item

What is the schedule for field review activities

Who is to receive copies of field review reports

How is information regarding discrepancies relayed to the trade contractors
4 Post Construction
Maintenance and Renewals Plans
A key to managing risk in the post construction period is the development of a
maintenance and renewals plan for each building. These are now becoming more
commonplace with new developments, and the preparation of this plan is part of the
warranty providers requirements of the design team.
The maintenance and renewal plans must be reasonable in terms of scope and costs,
however the provision and implementation of the plan must ensure that the building
does achieve the desired performance throughout the warranty period. If followed, it
must provide a reasonable opportunity for the building envelope to achieve it's design
life.
An outline describing the typical contents of a maintenance and renewals plan is
enclosed in Appendix A.
The warranty provider will review these documents.
Post Construction Performance Assessment
Throughout the warranty period there will be a need to review the performance of the
envelope. The purpose of these reviews is be twofold; to ensure that maintenance and
renewals work is being undertaken, and to identify small warranty issues before they
become bigger issues.
These reviews for the purpose of the building envelope warranty must be undertaken
after the first year and just prior to the expiry of the envelope warranty period. These
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reviews will be conducted by the Architect, BEP and the warranty provider and will
normally consist of a visual examination only. A report must be produced for each
assessment.
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APPENDIX A
FORMS AND REPORT FORMATS
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APPENDIX B
SAMPLE REPORTS
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BUILDING ENVELOPE
DESIGN AND CONSTRUCTION REQUIREMENTS