The Role of Building Envelope in Achieving High Performance Goals

ABSTRACT

In this Article, we will focus on the relationship between building envelope and green building performance, not only in Energy saving but also in other aspects of green building. We will provide a quick guide on how to enhance the parameters of the building envelope in order to fill the gap between code requirements and green building goals.

• The article was published in "Qatar Construction Sites - January 2017 Issue".
• The subject was initially presented in ZAK's World of Facade - Doha, November 2016

TOPICS

• A Building Envelope is Not Just Envelope/ Shelter!
• Functions & Performance Parameters.
• International & Local Codes.
• Building Envelope and Performance Criteria in LEED & GSAS.
• Better Envelopes, Innovations & Advancements

 WHAT DEFINES A BUILDING ENVELOPE?

A building envelope: is the physical separator between the conditioned (indoors) and unconditioned (outdoors) environment of a building. It is sometimes used synonymous with building enclosure but the latter term also includes the broader aspects of appearance, structure, safety from fire and security. It can take many forms and compositions, but basically it may be composed of the following components:

• Floors (Below-Grade Systems)
• Walls (Walling Systems)
• Roofs (Roofing Systems)
• Fenestration (Glazing Systems)
• Shading Elements

FUNCTIONS OF BUILDING ENVELOPE

Depending on many aspects of the building architectural form, the building envelope plays an essential role in “sheltering” the building occupants. The Five basic functions of a building envelope are:

• Weather Barrier
• Air Barrier
• Thermal Barrier
• Alien Barrier!
• Structural.

It means that the building envelope provides resistance to the following:

• Air (wind/air leakage)
• Heat (hot/cold)
• Light (indoor/outdoor)
• Noise (in/out)
• Loads (dead/live/wind)
• Intrusion (safety/security/privacy)

 A BUILDING ENVELOPE IS A SYSTEM

A building envelope is not just a Shelter!

A Building Envelope is a Sub-System of the Whole- Building. It is not just a wall/roof/floor/window/ door/... but, A SYSTEM!

It can be considered as a sub-system of the building. And, by turn, it is composed of various sub-systems. By applying the “Systems Thinking” approach, we find that building envelope is not only providing a “shelter” to building occupants but also contributing to the overall building performance.

Usually, we think of building performance in terms of energy saving and we think a better building envelope is improving only the energy performance. However, when measuring the performance of a building by a green building rating system (such as LEED or GSAS), it is not a surprise that the building envelope is affecting various performance criteria. For instance, the following areas can be improved by applying a better building envelope:

• Prevention of heat loss/gain and reduce Energy demand
• Urban Function and Cultural Identity
• Architectural Innovation and Advanced Technologies
• Sustainable Source as a Green Building element

Building Envelope is vital section of Building Science

A “BETTER” BUILDING ENVELOPE?

The performance of the Building Envelope con- tributes (negatively of positively) to the overall building performance. The role a building envelope plays in buildings is very similar to the role the skin plays in a human body! There are many factors that will help an architect defines a proper building envelope:

• Location (Climate Zone)
• Season (summer/winter)
• Operating Conditions (temp./humidity/...)
• Appearance (color/texture/SRI/...)
• Thickness (Composition/Layers)
• Materials (conductivity/appearance/…)
• Thermal Break (u-value/details/...)
• Air Leakage (details/sealing/...)
• Maintenance Frequency (commissioning/ cleaning/repairs/retrofits/...)

REGULATIONS AND CODES:

On a related aspect, the building envelope is also regulated at different levels:

• International Standards
• Local Codes/Building Regulations
• Project Spec’s/Developer Requirements
• Green Building Codes

 I. INTERNATIONAL STANDARDS:

* 2015 IECC (International Energy Conservation Code, by International Code Council (ICC), Section C402 - Building Envelope).

* ASHRAE Standard 90.1 (ANSI / ASHRAE / IES Standard 90.1-2016 -- Energy Standard for Buildings Except Low-Rise Residential Buildings (5.2.1. Insulation, 5.2.2. Fenestration and Doors, 5.2.3. Air Leakage, ...).

II.  LOCAL CODES (QCS, KAHRAMAA, PWA)

• Kahramaa Regulations
• QCS 2014 (Qatar Construction Specifications)
• MMUP Urban Planning Regulations

III.  SPECIAL DEVELOPER/PROJECT REQUIREMENTS

Some developers (PWA, Lusail, Barwa, Qatari Diar, Manateq,...)may impose certain requirements on their project's envelope specifications to achieve special needs during operation, such as natural ventilation, daylighting,...etc.

Building Envelope & Green Building

Building envelope has direct impact to several aspects of Green Building criteria. It affects (negatively or positively) the ability of a building to meet certain green building requirements/criteria. Two of the common green building rating systems, namely LEED & GSAS, have been analyzed to figure out the relationship between building envelope and the overall performance of the whole building.

LEED (Leadership in Energy & Environmental Design) is a globally recognized green building rating system developed by USGBC (United States Green Building Council). LEED is adopted in Qatar for a large number of projects, mainly in Education City and Msheireb Downtown Doha project.

GSAS (Global Sustainability Assessment System) is a regionally recognized green building rating system developed by GORD (Gulf Organization for Research & Development). GSAS is widely adopted in Qatar for a larger number of projects, mainly in Lusail City and governmental projects.

Both systems are performance-based, using a point-based mechanism to award projects more points for performing better in several performance categories. The following is a summary of our findings, which reflects the importance of the building envelope in achieving higher performance under LEED & GSAS:

General Considerations:

LEED - (IP) Integrative Process

• Building Orientation
• Building Massing & Shading
• Integration of Envelope Properties
• Feasibility of Different Alternatives

Urban Considerations:

LEED - (LL) Location & Linkage

GSAS - [UC] Urban Connectivity

• Acoustic Conditions of the Building Surroundings.
• Crime Prevention.
• Privacy Control.
• Security Requirements.

Site Considerations:

LEED - (SS) Sustainable Sites

GSAS - [S] Site

• Heat Island Effect Reduction - Roof
• Light Pollution Reduction
• Wind Comfort
• Shading of Pathways
• Rainwater Management

Water Conservation:

LEED – (WE) Water Efficiency

GSAS - [W] Water

• Rain Water Collection from Roof
• Water used for Cleaning Envelope!

Energy Conservation:

LEED – (EA) Energy & Atmosphere

GSAS - [E] Energy

• Building Orientation & Massing
• Envelope Area/Volume
• Window/Wall Ratio
• U-Values (Roof/Walls/Glazing/Floor)
• Shading Coefficient (SC) of Glazing
• Solar Heat Gain Coefficient (SHGC) of Glazing
• Window Frame Fraction
• Air Tightness
• Shading Devices (Internal/External)
• Integrated PV (BIPV)
• Commissioning of Building Envelope

Material Procurement:

LEED – (MR) Materials & Resources

GSAS - [M] Materials

• Responsible Sourcing of Materials
• % Regional Material used in Envelope
• % Recycled Content
• Reused Materials
• Structure Reuse
• Design for Dis-assembly
• Construction Waste Management

Human Considerations:

LEED – Indoor Environmental Quality

GSAS - [IE] Indoor Environment

• Thermal Comfort of Building Users
• Natural Ventilation (Operable Windows)
• Indoor Air Quality
• Low-Emitting Materials (Sealants)
• Day-light & Views
• Glare Control
• Acoustic Control & Quality

Culture & Identity Considerations:

GSAS - [CE] Culture & Economic Value

• Heritage & Culture Identity
• Support of National Economy
• Integration in Urban Context

Conclusion:

From the above analysis, we found that the Impact of Building Envelope in projects pursuing LEED & GSAS green building certification can be estimated as follows:

LEED:

• Total Credits = 57
• Envelope-Related = 20
• Weighted Impact* = 46 %

 GSAS:

• Total Criteria = 55
• Envelope-Related = 21
• Weighted Impact* = 48 %

 (*) Estimations are based on GSAS-Commercial v2.0 Scheme & LEED-NC v4.0 Rating Systems

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