The Importance of Envelopes wholesale nfl jerseys from china
It’s not the first thing people think about when buying or renting a suite in a building. However, the building’s envelope – the system of materials and components that separate the interior and exterior environments – is one of the most important elements in ensuring comfort, both in terms of interior comfort and in investment risk as the building ages and is matured by weather over time.
The target set for building longevity in SEFC is a minimum 50-year lifespan. Building design was also expected to target LEED Gold certification, requiring a high degree of performance and energy efficiency. An appropriate envelope design is critical to achieving these goals.
Building envelope knowledge has progressed since a wave of “leaky condos” made headlines in Vancouver throughout the 1980s and 1990s, as new materials and architectural styles were adopted in the city without adequate knowledge of their performance in the local climate. As a result of this experience, Vancouver is now one of the most stringent jurisdictions in North America in terms of rainscreen and envelope design, mandating the involvement of professional building envelope engineers.
Key Envelope Principles
The main function of the building envelope is to manage the flow of air, moisture and heat between different environments, typically exterior and interior. This helps prevent material deterioration, corrosion, mold growth and heat loss.
Moisture Control
Especially in a rainforest location, one of the envelope’s critical roles is to manage the penetration of rain into the building wall system. There are four key elements to effective moisture control:
- deflection: rain should be deflected so it avoids hitting the wall system, and is effectively shed from the system when it does;
- drainage: walls should incorporate a cavity behind the cladding, with drainage to the exterior in case any water does penetrate the cladding;
- drying: the wall system must anticipate the possibility of moisture being absorbed into the wall, and provide safe storage until this moisture can dry to the exterior. The design must provide a drying time that is less than the safe storage time (the wall must regularly dry out); and
- durability: the materials must be able to endure the safe storage requirements, and must perform their function without excessive maintenance, repair or renewal.
Air Leakage Control
Building envelopes must control the leakage of air between interior and exterior spaces to ensure occupant comfort (loss of heat, prevention of drafts), as well as to resist condensation inside the wall. The envelope must perform consistently through air pressure differentials that can be caused by wind, mechanical pressurization or stack effect (the movement of air in or out of a building due to temperature differences between the interior and exterior). An effective air barrier must consider:
- continuity
- structural support (both directions)
- impermeability to air flow
- durability
- constructability/quality assurance.
Thermal Performance
Reducing heat loss directly relates to maintaining energy efficiency. An effective envelope therefore plays an important role in achieving the building’s energy performance targets. Buildings at SEFC were expected to achieve thermal performance of R-16 (net) within walls and an R-value of 2.4 (net) for the complete window system. The ratio of wall to window was a consideration in developing good thermal performance, as large windows are valued by tenants but reduce energy efficiency. In addition, placement of the insulation within the wall assembly has a significant impact on its thermal performance, as described on the following pages.
(with information provided by Dave Fookes, Morrison Hershfield)
Exterior Insulated Wall Assemblies
With so many contractors and sub-trades involved, and with the City’s goal of making this a real demonstration project, many people became more familiar with building envelope technologies. Education was definitely part of the project – everyone learned from each other. Dave Fookes
Energy efficiency in the Olympic Village is greatly enhanced by a decision to use an approach to insulating and cladding that is not yet widely adopted in mainstream building. All new buildings in the Village have implemented “exterior insulated wall assemblies” – meaning the insulation is wrapped around the outside of the buildings’ moisture barriers.
“There’s a continuous moisture/vapour membrane around the whole building, and then you have the insulation all on one plane outside that,” says Dave Fookes of Morrison Hershfield. Fookes is the envelope engineer for the entire Olympic Village site.
Typical wall assemblies intersperse insulation between a building’s steel studs, then wraps the moisture barrier outside this stud-and-insulation layer. This uses the 3.5 inch space occupied by the studs, maximizing the floor space ratio and endearing the system to developers who seek to market the most space possible. However, interior insulation between the studs is not as effective resulting in a building that is less energy efficient – and can have negative impacts on durability.
“Most buildings have three-and-a-half inches of insulation between the studs [the studs themselves are a thermal bridge],” says Fookes. “At the Olympic Village, there is four or five inches of continuous insulation [not interrupted by studs], which will provide better performance.” Fookes explains that metal studs that touch the exterior membrane also conduct cold into the warm interior space, creating a risk of condensation inside the wall. “The exterior insulated approach allows you to keep all the interior components of your wall warm and dry – and your living space at a more constant temperature. You reduce the risk of condensation and corrosion of your wall stud fasteners – a potential failure point.”
Fookes says exterior insulated wall assembly construction may cost a bit more, primarily due to installation logistics (and contractors unused to the system). Reduced operating costs and reduced risk of wall failure (as happened with many leaky condos) can be expected to more than compensate for any upfront costs over time.
Materials
“What was the challenge? It was a huge project with strict budget and schedule constraints, but the world was told that these buildings would be ‘state of the art’ – so we all accepted the challenge to get them to that level.”
– Doug Dalzell
A variety of insulation and cladding materials were used throughout the Olympic Village site. These include:
Download Materials Matrix
DurabilityThe longevity of building systems and materials is an important element of sustainable building design. Buildings that require substantial maintenance or repair over their lifetime consume more resources than those that endure the elements and manage human activity with little upkeep.One method of considering the sustainability of building design is to assess the embodied energy in the materials used, factored over the expected lifespan of the building. Embodied energy includes the energy required to extract and transport raw materials, manufacture building materials, transport them to the site and install them – plus the additional “energy expense” of maintenance (i.e. powerwashing, painting), repair (replacing worn materials) and discard (or recycling) of end-of-life materials.Other key aspects in assessing the sustainability of building materials include:
- travel method and distance – not just the distance travelled from extraction to installation, but the means (i.e. rail consumes fewer resources than truck);
- reuse – reusing existing materials decreases resource depletions;
- recycled vs. virgin – materials with a high percentage of recycled content help reduce the use of virgin resources;
- adaptability, flexibility, ease of disassembly – materials that are adaptable for future uses, and easy to dismantle for reuse.
LEED Canada (Leadership in Energy and Environmental Design) offers one credit based on the durability of building materials chosen.(with information provided by Dave Fookes, Morrison Hershfield)TestingCustom wall systems designed for implementation at Olympic Village underwent rigorous testing to ensure they would perform as expected. “For Parcel 4 [the Erickson building], we built a couple of sections of wall, a couple stories high, at the testing facility out in Coquitlam,” says Doug Dalzell, General Manager of Keith Panel Systems. “They’d move the middle floor to test for seismic stability and shoot water at it from an airplane engine to see if it would leak. It’s pretty formal.”