Tuesday, September 2, 2008

Building Envelope Types

Stick system curtain wall
These walls comprise a framework of mullions and transoms arranged to hold glazing units and opaque panels. The framing members have glazing rebates in which the infillpanels are retained. The term is used to describe walls of uniform and regular construction supported from the edge of the buildings floor slabs or edge beams.

Structural glazing
In these walls the glass is attached by bolted connections rather than a glazing rebate. The glass may be attached directly to a structural support frame, for instance a stick system. Alternatively the glass may be suspended from the structure, frequently the roof, or from other glass panels.

The design and construction of these walls requires expertise and knowledge of the structural use of glass. Knowledge of structural engineering and building movements isessential. This may come from the facade contractor but often a structural engineer is involved in the work.

Structural silicone glazing
In glazing systems where the glass is attached by silicone bonding on two or four edges the correct use of silicone is critical to the success of the project. Such contracts require specialised skills and the silicone supplier is often involved at the design stage. When structural silicone glazing is to be sub contracted by the facade contractor the subcontractor should be identified and be able to demonstrate suitable experience and technical support.

Slope glazing
Slope glazing is defined as all glazing that slopes more than 15 degrees from the vertical.Although it comprises a supporting framework of glazing bars it is different from sticksystem curtain walling.

Slope glazing contracts often comprise not only the supply and erection of the glazing framework but also the secondary steelwork required to support the roof. Slope glazing has to carry snow loading and accommodate the movement of support structures that are relatively flexible. The drainage from the framing profiles is also very different from that for a vertical wall.

Rainscreen comprises panels supported from a framework placed in front of an innerwall. The inner wall may be an existing or new blockwork or concrete wall. Alternatively the inner wall may be integral with the rainscreen panels and frame. In the latter case the design and construction are more complex and the experience of the contractor is an important consideration in making an appointment.

Commercial windows
This term is used to describe windows installed into commercial buildings. The windows may be essentially domestic grade windows but the contract terms and management skills required of the specialist contractor will be different from those for the installation of windows into a private dwelling.

Commercial doors
This term is used in the same sense as the description of commercial windows above.

Shop fronts
Shop fronts are very different from glazed curtain walls or large windows. The profiles to be used are larger than those for windows yet the performance requirements are lessonerous than those for curtain walls. Glass handling and glazing become an issue and shop fronts require particular experience of shop doors.

Domestic window installers generally work in the replacement window market and their training relates specifically to that type of work. Specialist contractors should be able to demonstrate familiarity with commercial forms of contract and site working practices as appropriate.

Industrial cladding
This very broad term has been used to describe all forms of cladding that are predominantly opaque and comprise metal or similar panels.

Pre-cast concrete walls may be constructed as either panellised walls (panels of structural bay width) or unitised walls (units of smaller size). In the directory both are included under this heading. Panellised walls require specialist knowledge and skills of handling and fixing the large panels. In both cases the specialist contractor may undertake to supply and install windows off site. It is important that the necessary mix if skills and knowledge are available.

This description of wall has been included to cover specialist contractors who can supply curtain walls containing natural stone. It would also cover specialist sub-contractors who can supply stone for inclusion in a curtain wall.

Panellised walls are prefabricated as large structural bay width panels. These are either precast concrete panels or a steel truss to which the cladding is attached in a factory. Panellised wall construction requires a specialist contractor to have extensive manufacturing, and more importantly storage facilities. Panellised truss walls may incorporate many different materials and cladding types. Consideration should be givento the previous experience of the specialist contractor, for instance do they have experience of fixing stone.

Unitised walls are prefabricated into units of width 1 to 2 metres and height 1 to 2storeys. The construction of a unitised wall is more complex than that of a stick systemwall. In particular the design and construction of joints is more complex. A specialist contractor also has to have the ability to store, handle and transport prefabricated units.