BUILDING ENVELOPE
DESIGN & CONSTRUCTION
REQUIREMENTS
NEW RESIDENTIAL WARRANTY PROGRAM
Prepared by:
RDH Building Engineering Limited
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Document: 570303:03
June 14, 1999 BUILDING ENVELOPE
DESIGN AND CONSTRUCTION REQUIREMENTS
Contents
1 Overview
1.1 The Role of the Architect
1.2 The Role of the Building Envelope Professional
1.3 The Role of the Warranty Provider
1.4 Building Envelope Design Fundamentals
2 Design Requirements
2.1 Exposure and Environmental Design Criteria
2.2 Selection and Documentation of Assemblies
2.3 Details
2.4 Components and Materials
3 Construction
3.1 Mock-ups and Testing
3.2 Field Review
4 Post Construction
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Document: 570303:03
June 14, 1999 BUILDING ENVELOPE
DESIGN AND CONSTRUCTION REQUIREMENTS
Page 1 of 20
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)
· 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 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 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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Document: 570303:03
June 14, 1999 BUILDING ENVELOPE
DESIGN AND CONSTRUCTION REQUIREMENTS
Page 5 of 20
Figure 1.1
BUILDING ENVELOPE RISK MANAGEMENT PROCESS
PROCESS / CONCEPTUAL DESIGN /
Æ / DESIGN
DEVELOPMENT /
Æ / CONSTRUCTION DOCUMENTS /
Æ /
TENDER /
Æ /
CONSTRUCTION /
Æ / POST CONSTRUCTION
ARCHITECT
(based on NPP
Document 6) / Program of Requirements
Review Construction Budget
Design Approaches
Review Regulations and Code
Prepare Schematic Design / Prepare Design Development Drawings and Other Documents
Prepare or Review Construction Cost Estimate
Review Applicable Codes, etc. / Prepare Construction Documents Including Drawings and Specifications
Review Construction Cost Estimates
Review Permit Requirements / Assist in Obtaining Bids, Awarding and Preparing Contracts for Construction / Review of the Work
Payment Certifier
Interrpet the Contract Documents
Review Contractor Submittals
Issue Instructions Regarding Adjustments to the Work / Undertake Warranty Inspections
Prepare or Assist in Development of Maintenance and Renewals Plan
BUILDING ENVELOPE PROFESSIONAL / Ongoing Consultation
Review of Schematic Design / Ongoing Consultation / Review of Construction Documents / Consultation as Required / Supplementary Field Review and Testing / Preparation or Review of Maintenance and Renewals Manual
WARRANTY PROGRAM REVIEW / Approval of Architect and BEP
Review of Schematic Design / Consultation as Required / Review of Construction Documents / Confirmation of Trade Contractors, Suppliers and Materials / Monthly Review of Field Review Reports and Change Orders
On-site Review as Required / Review of Maintenance and Renewals Plan
Post Construction Examination of Envelope Performance Throughout Warranty Period
Document: 570303: 01 BUILDING ENVELOPE
June 14, 1999 DESIGN AND CONSTRUCTION REQUIREMENTS
Page 8 of 20
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
Below ground environmental loads
Interior environmental loads / Heat, air, moisture transfer calculations
Wind load calculations
5.3 Heat Transfer / Intended temperature differential
Required resistance to heat transfer / Minimize surface condensation
Minimize condensation in assembly
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
Vapour pressure gradient / Minimize moisture transfer by diffusion into assemblies to
5.6 Precipitation / Wind uplift loads Sealing, Drainage, Accumulation, and Disposal
Snow
Formation of ice / Minimize ingress into assemblies
Prevent ingress into interior space
Design cladding to shed precipitation
Minimize likely hood of snow and ice accumulation hazard
5.7 Surface Water / Accumulation of water / 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 CSAS478 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.