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Who designs
Design options
Scheme design
Detail design
Procurement
 
When designing a building envelope it is necessary to be mindful of how it will be procured and who from?  The envelope will eventually have to be design detailed, fabricated (manufactured) and constructed.

The good designer will always have in mind a specialist contractor who has the required mix of skills and capacity at the right price.  In that way he will not design something that cannot be built, other than at exceptional expense, and will normally be able to find at least a second company to bid competitively for the work.

The larger custom curtain wall contractors are used to doing most things, at a price. Small projects of completely standard solutions using a single system may be readily procured from a number of specialist contractors (the system company’s dealer network).  Greater difficulty is experienced if a system is to be partially customised, of complex geometry or include features such as automatic blinds and windows.


Identifying appropriate specialist contractors

The success of any building envelope contract depends on the employment of a specialist contractor of appropriate size and with relevant skills and knowledge. CWCT manages a directory of specialist contractors showing the size of contract they typically undertake and the scope of their work.  The directory of specialist contractors can be accessed here.


Better procurement

Procurement practice continues to evolve and CWCT runs a course on best practice for building envelope procurement.  Speakers from industry and CWCT cover: design options, specification, design procurement, shortlisting of specialist contractors and the tendering process,  Details.


Types of specialist contractor

Specialist envelope contractors take several forms.  The different business models are based on the following activities:

System design and manufacture is the design of framing members and other components.  The system may be developed for a single construction project or may be placed in the market place by a system company for use by more than one specialist contractor and on many buildings.

Project design is the arrangement of system components to match the architect's scheme design and realise the building envelope.  This may be undertaken by the specialist contractor or may be subcontracted to a design house.  Where the project is to use a system company's products the system company may advise the project designer but will not generally be responsible for design.  Note that the input from the system company will vary from system to system and the specialist contractor may not need, or wish, to take advice.  The design team will produce workshop and site drawings.

Fabrication is the machining of framing members and panels, the forming of flashings and assembly including fitting of hardware and so on.  Fabrication includes all factory based activities involved in the manufacture of the wall.

Installation is the site operation of fixing and sealing the envelope on the building.  It includes all activities of fixing, assembly, glazing, cleaning down and commissioning the envelope.
 
Basic business models exist as described below. However, there are many variations on these four models depending on whether design is subcontracted, manufacturing is factored or components and assemblies are bought in.

a) b)
System design
and
manufacture
System design
and
manufacure
----------------------------
----------------------------
Project design
and
fabrication
Project design
and
fabrication
----------------------------
Installation
Installation

In this model a single company, the specialist contractor, undertakes all of the activities required to realise the building envelope. Once common, this method of working is now restricted to the largest companies and some smaller companies undertaking small but highly bespoke contracts.

 


Companies following this model subcontract the installation to an independent installation company. This enables them to work economically over a wider geographical area. These companies may undertake envelopes of the greatest complexity but are generally smaller companies than those following model (a) and may not undertake the largest contracts. Good installation depends on good inter-company communication and adequate on-site supervision.

 

c) d)
System design
and
manufacture
System design
and
manufacure
   
Project design
and
fabrication
Project design
and
fabrication
----------------------------
Installation
Installation

In this model the specialist contractor is independent from the system company that supplies components. This has become the most common model for realising all but the largest envelopes in the U.K. Although specialist contractors rely on a system of components many are able to modify the system design if required. Companies of this form do not generally undertake contracts in excess of £5M but this limit is due to commercial constraints other than the business model. Good design depends on the provision, and acceptance, of appropriate support and advice from the system company.

 


In this model the specialist contractor relies on separate companies for both system supply and for installation. This is a common variation on model (c) for no other reason than that specialist contractors do not have to keep installers fully employed. Again good design depends on the provision, and acceptance, of appropriate support and advice from the system company. Good installation depends on good inter-company communication and adequate on-site supervision.

 


 

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