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Who designs
Design options
Scheme design
Detail design
Scheme design for a building should include a comprehensive review of the intended building envelope. In addition to providing the required apearance the building envelope design:
  • Has a dominant effect on the energy use and hence carbon dioxide emissions from a building
  • Determines the method and speed of construction
  • Affects the safety of construction, operation and maintenance
The building envelope also has a major influence on the cost of a building, directly as a capital cost and indirectly in operating costs. The building envelope is the weathering surface of the building and its durability will determine the future value of the building.

Construction and maintenance

The method of construction and construction timescale will be heavily influenced by the scheme design.

The lead time from entering a contract to commencing work on site will depend on the originality and complexity of the design. A totally bespoke wall will take 40 to 50 weeks to detail design, gain approvals, procure materials and manufacture. By comparison the lead time for a totally standard system wall to be arranged as a single plane of the envelope will vary from 10 to 16 weeks depending on the procurement time for the glazing.

Ease of access and requirements for safe access are all dictated at the scheme design stage where complex geometries have to be matched with suitable access arrangements. The CWCT 'Guide to safe access' gives guidance on this.

Energy issues

The area of glass and its orienation are set at an early stage of the scheme design and yet they totally dominate the service requirements for the building and its energy use. As limitations on energy use have been tightened it is possible to design buildings based on precedent that are now impossible to build. CWCT 'Guide to the thermal assessment of walls' gives guidance from scheme design through to detailed calculations.


The scheme design may suit a particular construction technique or may make the building almost impossible to construct by any means.

The building envelope has to be co-ordinated with the building structure from the earliest design stages. Decisions on frame centres and panel sizes affect cost, construction method and ease of construction. The juxtaposition of components determines allowable tolerances and ability to construct and repair.


The choice of materials to be used in the building envelope governs the service life of the envelope and therefore the refurbishment cycle of the whole building.

Some commonly used materials have service lives that may be greatly reduced by inappropriate use. Conversely the service life of a component can be much extended by suitable choice of materials. The CWCT publishes a 'Guide to durability' for use by its members.

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