Wind Uplift Resistance and Other Fenestrations (Part 5 of the NBC)
Wind Uplift Resistance and Other Fenestrations (Part 5 of the NBC) - Transcript
Slide 1
Hello my name is Morched Zeghal, I am a technical advisor here at Codes Canada. I am pleased to give you an update on some of the changes that were made to Part 5 of the 2015 NBC.
This presentation covers two items:
- wind uplift resistance of membrane roofing assemblies, and
- other fenestrations.
Slide 2
This presentation is part of a series of 13 presentations on the 2015 editions of Codes Canada.
Before I begin with the technical content of this presentation, I will speak briefly about the code development system.
It is important to note that the model Codes, which are developed by the Canadian Commission on Building and Fire Codes, must be adopted by provincial/territorial authorities to become law.
This may mean that Code requirements enacted by legislation within your province or territory might differ from what is presented here. Please check with your local authority.
Slide 3
It is also important to point out that the National Codes are not a federal regulation.
This means it is not NRC or Codes Canada that decides what goes into the Codes but you!
Codes Canada facilitates an open, transparent, consensus-based process to come up with improvements.
Over 400 committee members volunteer their time to decide on changes to the next Codes.
All committees are balanced between regulators, industry and public interest so that no single category can outvote the other two.
This process is shown on the slide:
- It typically starts with someone requesting a Code change.
- It continues with technical committees developing proposed changes.
- It also involves a public review and the final approval by the Canadian Commission on Building and Fire Codes.
It's a simple process and it depends on your input.
Please go to the Codes Canada website and find out how you can:
- submit code change requests,
- participate in committees, or
- comment on proposed changes during our public reviews.
Slide 4
And before we start, here are some clarifications on the presentations themselves:
The presentations cover only the changes from 2010/2011 to 2015 Codes and not how to use or interpret the Codes in general.
The presentations contain only the significant changes - the details are in the handbook. Each presentation contains a reference to the relevant pages in the handbook.
The presentations stay strictly within the scope of the National Codes and do not cover provincial or territorial variations.
Slide 5
Here is an outline of this technical presentation. For wind uplift resistance, we will cover:
- the rationale behind testing for wind uplift resistance and why it must be dynamic,
- which systems must be tested, and
- whether there are enough testing labs in Canada.
For other fenestrations, we will cover:
- the rationale behind the changes, and
- the scope and details of the changes.
Handbook pages 35-37
Slide 6
Let's begin with dynamic wind uplift resistance.
Problem: There was no explicit method to validate the wind resistance of membrane roofing assemblies.
In other words, Code users had no means to show they complied with the performance requirements in the Code.
Insurance Companies report roof cover failure as a major cause for insurance claims after high wind events.
After recent hurricanes (Katrina, Ivan and Charley), Factory Mutual (FM) changed its prescriptive requirements for roofing assemblies by: (click)
- increasing the number of fasteners per square foot (images show fastener pullout and localized deformation) (image on left is from lab testing and right is from the field), and
- delisting a significant portion of approved roof assemblies.
What did we do? The 2015 National Building Code (NBC) refers to a CSA standard for dynamic testing of fully bonded and mechanically attached roofing systems.
An appendix Note clarifies this limitation.
Slide 7
Why do we need to do dynamic testing? What's wrong with static testing?
Static testing doesn't reflect how wind operates in real life because wind is dynamic in nature.
Look at the red point on the roof of the building on the screen.
The point is subject to both an external negative pressure and an internal positive pressure.
The net pressure to which this point is subjected is the algebraic sum of these pressures.
The graph on the right shows the pressure amplitude to which the red point is subjected over time.
It's clear the net pressure amplitude fluctuates between positive and negative.
This proves that the point is subject to dynamic loading.
Slide 8
Do we have to apply dynamic testing to all membrane roofing systems? The answer is no!
An appendix Note was added to clarify that you need to test only membrane roofing systems that use fasteners or adhesives to resist wind uplift, for example, systems shown on the screen are mechanically attached and fully bonded.
Roofing systems that use ballasts, such as gravel or pavers, to secure the membrane against wind uplift do not need to be tested.
Wind uplift resistance testing according to the CSA standard is limited to configurations with specific fastener or adhesive patterns.
You don't have to test all configurations.
An appendix Note clarifies how to extrapolate the test data for non-tested configurations.
Do we have to test systems with proven performance?
The short answer is no. The new code exempts systems with proven performance which provides flexibility for authorities having jurisdiction to decide.
Slide 9
This is the last slide dealing with dynamic wind uplift resistance.
The picture shows the prototype dynamic testing table that was built at NRC.
There are two similar testing tables in Canada:
- Exp (Drummondville), and
- Intertek (Vancouver).
A third table is being planned.
Canada needs only 3 to 4 testing labs.
Slide 10
Summary
The 2015 NBC requires dynamic uplift testing for certain types of membrane roof assemblies and refers to a CSA Standard for test protocols and other details.
This should reduce the failure of such roof assemblies in extreme wind events in Canada.
Slide 11
Let's now move to the second subject of this presentation: other fenestrations.
“Other fenestrations” is the term used in the 2015 NBC to refer to the four types of fenestration. These are:
- curtain walls,
- window walls,
- store fronts, and
- glazed architectural structures.
Window walls and curtain walls have become more and more common in recent years.
Slide 12
Problem: There was nothing in the Code to describe other fenestrations, their characteristics and performance needed to prevent failures related to:
- condensation,
- air leakage,
- water penetration, and
- structural loading, etc.
The design professionals were responsible for specifying performance requirements for these fenestration systems.
Sometimes incorrect and/or non-applicable standards are referenced.
To make things worse, there were no clear or harmonized definitions of “other fenestration products,'' their features and how they perform.
Result: There has been an increasing rate of large-scale failures, mainly in British Columbia and Ontario.
Slide 13
In 2009, Pro-Demnity, the only professional liability insurer of architects in Ontario, issued a “Window Wall Endorsement” to their policies, which required the following:
- all designs must abide by new “standard” for window wall design and installation to qualify for coverage, and
- mock-up, 3rd party review, etc. must be provided.
Ontario's Home Warranty provider (Tarion) also requires that window walls comply with the Pro-Demnity requirements.
However, the new standard addressed only one failure aspect and applied only to Ontario.
Slide 14
What did we do?
The following changes have been introduced the 2015 NBC:
- an explanatory Note that defines “other fenestrations,” their characteristics and components, and
- a new Subsection in Part 5 was added to cover:
- structural and environmental loads,
- heat transfer,
- air leakage, and
- water penetration.
For structural and environmental loads and heat transfer, refer to the relevant sections in Part 5.
Let's look at air leakage and water penetration requirements (click).
Slide 15
The picture shows field testing for air leakage by creating a pressure differential, like a blower door test.
New air leakage requirements set maximum air leakage rate for:
- the fixed portions including any opaque portions, and
- the operable portions.
They also clarify which standard (ASTM) to use.
An appendix Note explains which test methods to use for lab and field testing because these test methods have been mixed up in practice.
Slide 16
Let's now look at the new water penetration requirements: The two pictures show field testing for water penetration.
The Code identifies which lab and field testing standards (ASTM) to use.
However, there was no performance level set because there was not enough information to establish [l1]a national level at the time.
Slide 17
Key messages:
For other fenestrations, the 2015 NBC harmonizes the approach for design, construction and verification. It also clarifies the terms and establishes performance levels when the information is warranted.
Result: This will prevent failures such as those we saw in the last decade, and minimize the claims related to fenestration failures.
Slide 18
I have covered a lot of information in today's presentation. The handbook is a useful resource if you want to review the topics from this presentation in more detail.
It covers the majority of technical changes that were implemented in the 2015 National Building Code, National Fire Code, National Plumbing Code and National Energy Code for Buildings.
The handbook can be purchased on NRC's virtual store as a downloadable PDF or as a hard copy.
Slide 19
Contact Information
| Alternative title | Wind Uplift Resistance and Other Fenestrations (Part 5 of the National Building Code of Canada: 2015) |
|---|---|
| Download | |
| DOI | Resolve DOI: https://doi.org/10.4224/40002097 |
| Author | Search for: 1 |
| Speaker | Search for: Zeghal, Morched1 |
| Affiliation |
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| Format | Video, Learning Object |
| Subject | Codes & guides; construction; building; NRCCode |
| Publication date | 2015 |
| Publisher | National Research Council of Canada |
| Related publication | |
| Language | English |
| Export citation | Export as RIS |
| Report a correction | Report a correction (opens in a new tab) |
| Record identifier | d6709d27-d705-46a1-bf85-56c07b7fbc43 |
| Record created | 2021-05-04 |
| Record modified | 2022-06-21 |
- Date modified: