14.02 Contractors

Introduction
Contractors undertake to construct a building or some part of a building to the client's specification. Contractors may be:

Lead contractors working directly for the Client to deliver the whole project (building),
Sub-contractors working for a contractor to deliver part of the final works. For instance a sub-contractor may be responsible for one aspect of a contract such as sealant application or may supply labour to complete a project.
Specialist contractors who are recognised as being sub-contractors who make a large design input to the part of the main contract that they undertake. Specialist contractors include: curtain walling contractors, building services contractors and so on.

Specialist facade contractors
These companies undertake to provide detailed design of the building envelope, purchase materials, manufacture components, erect on site and hand over the completed building envelope.

The work of design, manufacture and erection can be divided into the processes image:

System design
System (component) manufacture
Wall or window (layout) design
Wall or window fabrication
Installation

System design involves the design of aluminium, plastic or steel profiles, corresponding gasket profiles and components such as cleats and brackets. These aspects of design require knowledge of extrusion, casting, injection moulding and so forth. Design of this sort is normally tested to prove novel and innovative aspects of the new profiles and associated components.

The system of profiles may be for use by multiple fabricators on many jobs or it may be the system developed for use on a single building, a bespoke or custom curtain wall.

System and component manufacture requires large manufacturing facilities and few specialist contractors have these facilities in-house. Most manufacturing is undertaken by system and component suppliers. System components may be extruded by aluminium extrusion companies to a design produced by a specialist facade contractor.

Wall design involves the arrangement and assembly of a set of components to construct a wall to the required layout and dimensions. This will require the interpretation of the architectural design and identification of suitable components to meet the performance requirements of the wall. This aspect of design also requires co-ordination of all wall components, one with another and with the structural frame. Design of these aspects of a wall on a large building may result in the production of a thousand or so drawings depending on the overall complexity, the number of one-off panels and framing members and the complexity of any interfaces between different forms of façade construction.

Fabrication of a facade, or window, involves:

The cutting, drilling, slotting of profiles,
The manufacture of panels,
Assembly of components into;

Windows,
Unitised wall,
Manufacture of brackets,
Manufacture of flashings, closers and interface components.

Installation is obviously a site based, labour intensive, activity to fix the wall to the building as panels or assemble components on the face of the building.

Company structures
The processes described above are widely different in terms of skills, plant and culture. They may all take place within a single company or separate companies. The different forms of company are:

Fully integrated curtain wall company
Bespoke curtain wall manufacturer
System supply company
System fabricator
System fabricator and installer
Curtain wall installer
Management sub-contractor

In practice there are a whole variety of companies in the facade supply chain and probably no two are the same. The models described below are the basic models that companies follow but the reader should be aware that the descriptions below allow an overlap and grey areas of activity that companies may include within their business or may outsource.

Fully integrated companies are able to produce a fully bespoke facade from aluminium billets and raw polymer through to assembly and hand over on site, including the design of all components and of the wall image.

There are very few of these companies globally. They have to be large and have sufficient workload to keep all of their facilities usefully occupied. This is seldom possible and companies of this type still resort to outsourcing and sub-contracting if they have too much work. Some of the bigger companies can only justify owning particular parts of their plant by manufacturing for others. For instance producing gaskets for others when they have spare capacity.

Companies of this type work on the large highly bespoke curtain walls that have a high cost per square metre. The overheads of running such a company are high, there are large design and testing costs and plant and labour may not be fully utilised at all times leading to inefficiency.

All companies used to be of this type but with the advent of the system supply companies it is no longer necessary for a specialist contractor to design and manufacture aluminium profiles and gaskets unless a wholly bespoke wall is required.

Bespoke curtain wall manufacturers are similar to fully integrated companies but they restrict their activities to design and manufacture and they do not install on site image. This has arisen because of the difficulties of employing curtain wall installers who are required to follow work from town to town and country to country. These companies will sub-contract the installation part of the curtain wall contract and manage the contract on site with just one or two of their own employees.

This type of operation is most commonly seen amongst companies who are large enough to work nationally if not internationally and avoids the difficulties of moving workers long distances. It has however given rise to difficulties of site workers reading drawings and instructions in foreign languages.

Because these companies sub-contract the installation of the wall they tend to have a better culture of outsourcing than a fully integrated company. It is more likely that a wall produced by one of these companies will contain profiles or components manufactured and possibly even designed by others.

System supply companies design and produce aluminium profiles, gaskets and other components that can be used to produce a facade but they do not involve themselves in the design or fabrication of walls or installation image.

System supply relies on a network of fabricators who purchase components and standard lengths of profile from which they can manufacture. It has its origins in the steel window industry where standard hot rolled profiles were available ,although fabrication was then a large scale operation, and the timber window industry who developed standards profiles that could be manufactured anywhere, the EJMA window. The modern system companies developed with the introduction of aluminium and then pvc-u into the domestic window market.

System suppliers not only sell aluminium or pvc-u profiles and supporting components but they also provide a full support for the system. This means that they will promote the system with buyers and specifiers through advertising, model specifications and cut and paste CAD details. They also provide fabricators (their dealers) with technical support. This may include interpretation of specifications, thermal and structural calculations and design charts, manufacturing advice and training.

System fabricators design and manufacture facades and windows using profiles and components supplied by a system company image. This may be a standard system for which the fabricator uses only existing profiles or it may be a modified system where the fabricator and/or the system company have produced an additional profile such as a pressure cap to produce a wall with a different appearance.

Fabrication companies may deal with design of the curtain wall in several ways.

Self sufficient fabricators are able to design additional profiles to modify a wall, design all interfaces with the structure and adjacent cladding and produce all necessary drawings. Some system fabricators are able to offer more than one system and some offer their own system and a bought in system from a system supplier.

Fabricators who do not have a full design and technical resource will have to seek advice on matters such as thermal or acoustic performance. This advice may come from a consultant or from the system supplier.

Fabricators may of course operate a manufacture only business in which they manufacture only to workshop drawings produced by others. These would come from an independent design house or a management sub-contractor.

System fabrication and installation companies will install on site in addition to manufacturing the components ready for installation image. Most fabricators have a presence on site unless they only work under a management sub-contracting scheme. However, this may amount to no more than a supervisor on each site or even a contracts manager trying to manage several sites single handedly. Some companies employ as many installation staff, fixers, as they can sustain in full time employment and supplement these with fixers from labour only sub-contractors to meet peaks of work load. Companies working in this way will have a larger presence on site.

Curtain wall installation companies are responsible only for erection of a curtain wall image. They may be a labour only sub-contractor providing fixers to work with a fabrication company or they may take full contractual responsibility to erect the wall in accordance with drawings supplied.

Window installers work in a similar way but they may be the specialist contractor working for a main contractor. In this role they purchase assembled windows which they only install.

Management sub-contracting is becoming more common for the design, manufacture and erection of curtain walling image. Under this system of working one company takes sole responsibility for all aspects of a wall. They then arrange for all of the necessary activities described above to be undertaken by separate parties. This can occur as pure management sub-contracting where the sub-contract manager does no design, manufacture or site work but simply co-ordinates the work of others. More common forms are where the sub-contract manager has a design role or is the specialist contractor for one of a series of packages and acts as lead contractor, or lead sub-contractor.

The specialist contractor
The specialist sub-contractor is the company that holds a contract with the main contractor or the client to complete the curtain wall. This may be any of the following:

Bespoke curtain wall company, with or without installation facility,
System fabricator, with or without installation facility,
Management sub-contractor,
Window installer.

Size of specialist contractors
The size of a specialist contractor and the size of contract that it can undertake are closely linked.

The upper limit to the size of contract is governed by:

Cash flow,
Skills and resources,
Customer confidence.

Contracting requires the purchase of materials and payment of staff in advance of payment by the client. This requires a cash resource to bridge the gap.

Clearly a company cannot successfully undertake a project for which it does not have the necessary skills. These may be the skills associated with technically complex projects. The size of contract that can be undertaken is also determined by the geometrical complexity and scale of the project and in particular the project management skills required to co-ordinate these projects.

Customers are uncomfortable about placing a contract with a specialist contractor if the contract amounts to a large part of the specialist contractors turnover. Different purchasers have different views but it is unlikely that a wise purchaser will let a contract that comprises more than thirty percent of the contractor's turnover.

The lower limit to the size of contract is determined by:

Profitability
Workload
Customer confidence

If a specialist contractor is set up to undertake contracts of a particular size and complexity then it carries overheads of design and development appropriate to that type of business. If it then competes with lesser companies it will loose out to companies carrying lower overheads and needing to make a smaller margin. For this reason the smallest contract undertaken is unlikely to be less than a third of the mean contract value for that specialist contractor. Of course a company may undertake a small contract to oblige a good long term client.

A specialist contractor will have many resources that have to be kept fully utilised. Companies undertaking complex work will have larger design offices and companies may have manufacturing facilities such as presses for the production of panels. Companies may undertake small contracts that are say design intensive if they have spare design capacity but their aim is to win contracts that match their company profile and use all of their resources efficiently.

A client may not feel comfortable letting a small contract to a company that normally undertakes larger contracts for fear that their contract will not receive due attention when the company's attention is focussed on the big jobs.

Scope of specialist contractors
Facades comprise many different forms of construction. Specialist contractors also come in many different forms and the first distinction to be made is by the type of construction so there are:

Curtain walling contractors
Rainscreen contractors
Window contractors
Sheeting and roofing contractors

Further distinctions have to be made. In particular there are:

Large differences of working practice and contract between domestic and commercial window installation,
Working on low rise buildings (less than four storeys) and high rise buildings (greater than six storeys). This also applies to window installation.

Increasingly facades comprise several different forms of construction and it is appropriate for one specialist contractor to be the lead contractor and for other types of cladding to be undertaken by others.

Specialisms
Although specialist facade contractors are so named there are further specialisms within facade contracting. These include:

Structural sealant glazing
Bolted glass assemblies
Structural glass assemblies
Automated facades

If a facade contract involves any of these then it is necessary for the specialist facade contractor to be competent in that field. This may be achieved by employing a specialist contractor with the skills or one who is capable of sub-contracting that part of the work. Not all specialist contractors are capable of sub-contracting work and it may not be appropriate if the specialised work is the major part of the contract.

Selecting an appropriate specialist contractor
An appropriate specialist contractor is one who having knowledge of the required specialisms is also able to undertake a contract of that size, complexity and quality. The specialisms are discussed above.

The size, complexity and quality issues can be assessed by a simple categorisation of specialist contractors. The value of the greatest contract that they have comfortably undertaken may be taken as a measure of the size of contract they can successfully complete and the cost per square metre of the contracts they undertake can be taken as a crude measure of both complexity and quality. Plotting these on a chart, image, gives a way of comparing specialist contractors and selecting appropriate companies.

The chart of contract value and facade cost can be used to sort companies as follows:

Small commercial contracts are those that are of relatively small contract value and low cost. They are likely to be based on a standard stick system with run-of-the-mill glazing and infill panels and simple windows, image.

Large commercial contracts are little different in style from smaller commercial contracts but the scale of them is larger and they are undertaken by companies with greater cash and human resources, image.

Large palaces are buildings that have high quality facades of considerable complexity. The facades may comprise stone, bronze, automated blinds and so on. They are architectural landmarks and are more expensive than simple commercial buildings, image.

Little gems are buildings or parts of buildings that are small in total value but are complex and of high quality. They may comprise no more than a glazing screen or entrance or may be a small exhibition building image.

CWCT FACETS

14.02 Contractors