Envelope

Olusola Ayodeji Oni

Tight and loose building envelopes

A building envelope is normally referred to as either 'tight' or 'loose'. A loose envelope allows air to flow more freely through the building, whereas a tight envelope restricts air or controls how it is admitted. Australia’s climate (as varied as it is), is such that a tight envelope is generally the preferred choice.

Building Envelope

What is building envelope?

The concept of a building envelope relates to design and construction of the exterior of the house/ building.

A good building envelope involves using exterior wall materials and designs that are climate-appropriate, structurally sound and aesthetically pleasing.

Walls

A structural building element which can be load bearing or non-load bearing. It is also a structure and a surface that defines an area; carries a load; provides security, shelter, or soundproofing; or, is decorative.

Windows

A window is an opening in the wall of a building for the admission of light and air.

Roofs

A roof is a structure forming the upper covering of a building or other shelter. Its primary purpose is generally to provide protection from the elements, but it may also contribute to safety, security, privacy, insulation, etc.

Precast concrete components are reinforced with either conventional reinforcing steel, steel strands with high tensile strength, or a combination of both.

Typically including 2 inches or more of rigid insulation between two wythes of concrete, insulated sandwich wall panels provide high energy efficiency, meeting the continuous insulation requirements of ASHRAE 90.1, as well as an interior concrete wall that can be painted and used as the interior finished surface, avoiding the need for furring strips and drywall.

WALL

Insulated Precast Concrete Sandwich wall Panels with bricks facing

The choice of this material ensures that high performance buildings is achieved and would be used for the residential and office areas’ cladding of the building.

This is a versatile, efficient, resilient option that meets increasingly stringent building goals.

The goal of high performance is to design and build structures that optimize all relevant high-performance attributes on a life-cycle basis rather than a sole first-cost basis.

Its composition is a mixture of aggregates (typically sand and stone) that are bound together by a binder. Admixtures or modifying agents and additives are sometimes introduced to improve the characteristics of the fresh concrete, the mixing process, and/or the final hardened material. Precast concrete consists of concrete that is cast into specific shapes at a location other than its final in-service position. It is produced by casting high-strength concrete in a reusable mold or form, which is then cured in a controlled environment at a specially equipped plant.

Sandwich insulation, can provide the continuous insulation, air barrier, and vapor retarder in one efficient system.

Functional resilience

The choice of precast insulated panels would ensure the building's ability to withstand and be quickly restored to its full functional capacity with minimal effort and resources after natural or man-made disasters, functional resilience expands the concepts of sustainability and durability.

Precast concrete has a solid track record for ensuring the attributes of resiliency, including a long service life, durability, life safety, and wind and water resistance.

Justification of choice of Wall

Structural durability

On a first-cost basis, precast systems are typically very competitive, but the long-term benefits of precast significantly outweigh the initial cost advantages. Precast's long-term durability is due to the building enclosure's capacity to withstand impact, break-ins, corrosion, weathering, and abrasion, making it essentially maintenance-free and preserving the structure's original appearance. With these elements in mind, high-performance insulated precast concrete panels have the potential to outlive conventional façade designs by at least 50 to 60 years.

Furthermore, there are fewer building cladding joints since precast concrete panels are typically wide. Joint failure is less likely to cause leaks when there are fewer joints.

Materials Resilience

The need for today's structures to be climate and environmental resilient in addition to being resistant to the ravages of time makes insulated concrete sandwish wall panels the idea envelope for this project. For example, a building's structural integrity, as well as its ability to endure the effects of natural and man-made disasters, shall be taken into consideration throughout the design process.

Off-site Production

This would help the project to meet the highest quality-assurance standards in the industry as the panels are produced in a controlled factory environment.

The speed of production and consequent delivery of panels to the site ensures that activities within the construction site are well managed (not overloaded) to ensure timely delivery of the project.

High resistance to fire Outbreak

Concrete does not burn – it cannot be set on fire and it does not emit any toxic fumes when affected by fire. Concrete is proven to have a high degree of fire resistance and, in the majority of applications, can be described as virtually fireproof.

Advantages of Precast Insulated Wall Panels

Cost and time efficiency
Energy efficient
Health benefits: maintain acceptable moisture and temperature levels, even in basements. Impede mould and mildew growth within the walls and superior sound dampening
Thermal Mass Effect: absorbs and releases heat energy without losses

Fig: Showing the use of precast insulated panels

Ref: The James F. Battin Courthouse in Montana used a precast concrete solution to meet their high-performance requirements including anti-terrorism force protection design.

Figure: showing sandwich insulation, can provide the continuous insulation, air barrier, and vapor retarder in one efficient system.

Ref: https://www.indiamart.com/proddetail/glass-curtain-wall-11014111088.html

WALL

Curtain Wall

For this project, the glass infill is recommended as the shopping center needs visibility from the exterior making it easy for goods and services displayed within the mall visible even without entering the mall.

A curtain wall is an outer covering of a building in which the outer walls are nonstructural but are attached to the building structure and used to keep out the weather.

Because the curtain wall is nonstructural it can be made of a lightweight material (e.g., aluminum-framed walls containing infills of glass, metal panels, or thin stone), reducing construction costs.

Ref: https://www.sciencedirect.com/topics/engineering/curtain-wall

Casement windows are attached to the frame with one or more hinges, typically allowing them to open to the side. They can instead be hinged at the top or bottom, making them 'tilt and turn' windows – you can find out more about these types of windows below. They usually open inwards, which generally makes them easier for cleaning. They are held open by 'casement stays' – small metal bars that open and close in a scissor motion.

WINDOW

Casement Window - Double Glazing

A casement is a window that is attached to its frame by one or more hinges at the side. They are used singly or in pairs within a common frame, in which case they are hinged on the outside. Casement windows are often held open using a casement stay.

Justification of casement Window

Ideal ventilation. With side hinges, you can open casement windows slightly to catch a breeze and direct it inside or push them wide open for maximum ventilation.
Unobstructed views.
Easy to use
Thermal and energy-efficiency.
Improved security.

Integrating Windows in Precast Panels

Ref: https://www.linkedin.com/pulse/preglazing-integrating-windows-precast-panels-rabbat-m-eng-pmp?articleId=6489524721548353536

Off-site production strategy of panels with windows

Ref: https://pceltd.co.uk/17255-dfma-and-environmental-performance-in-construction/

Double Glazing diagram

Ref: http://www.windoor.co.za

Double glazed windows

The Uk Building regulations recommend a mininum U-value of 0.8 W/m².K.

Double glazing provides a cost-effective and technical solution sufficient enough to to meet the building regulations requirement.

Building regulations Requirements

How heat escapes from a sealed double-glazed window in winter

Ref: https://www.open.edu/openlearn/nature-environment/energy-buildings/content-section-2.2.1

Picture showing the movement of sun into the building

Picture showing details of a double glazed window

Offsite Production of Panels with windows

Projet La Catherine par Saramac - La Catherine project by Saramac

Technical Specifications - Windows

ROOF

Pitched Roof

A pitched roof has a downward slope, usually in two sections at an angle from a central ridge, although it may also have a downward slope from one edge to another. It is the ratio of the roof's vertical rise to its horizontal span that determines the roof's "pitch."

Steel Trusses

They are fabricated from rolled steel structural members such as channels, angles, T-sections and plates.

They are mostly fabricated from angles sections because they can resist effectively both tension and compression, and their jointing is easy.

Ref: https://www.constructiontuts.com/roof-truss/

Warm Roof Insulation

In this project the warm roof design is preferred.

Warm roof construction is where the insulation is positioned above the rafters, and immediately below the roof’s weatherproof membrane. The key advantage of this method is the improved thermal performance. The rafters are positioned inside the insulated envelope of the building, keeping them warm and storing the space’s heat.

Good roof insulation is essential to ensure a building not only complies with Building Regulations, but also achieves the desired thermal performance to ensure the comfort of its residents and energy efficiency of the building. The natural flow of rising heat, and the more exposed position of a building’s roof to the elements, means heat loss is prominent through uninsulated roofs, so roof insulation is an important consideration in the building design.

Justifications for the choice of Steel pitched roof – roof trusses

Efficient Surface run-off due to the pitch
Suitable for light load and large span (building span is more than 6 meters)
Most economical for spanning more than 6-meter span
Durability
Longer Life Span
The pitch blends with the environment as the adjoining buildings are pitched roofs
Weather resistance: It resists the effects of weather better than Flat roofs
Simple maintenance

Specifications

The national dwelling specification recommends a U value of 0.13 W/m² K while the limiting factor is 0.20 W/m² K.

With a building of 44 meter long, suitable trusses shall be used to provide adequate structural stability (Approved Doc. A1) which is able to transmit the dead loads, imposed and wind load to the ground.

This will ensure resistance to the spread of fire (Approved Doc. B4) while also withstanding the effect of weather and moisture. The building's roof must be water-repellent so that moisture from rain or snow does not seep inside.

Adequate sound resistance (part E1, Approved Doc. E) and Thermal resistance to prevent heat loss (Part L1, Approved Doc. L) shall be provided for.

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