BRE worked with a PFI consortium to produce an energy-efficient variant design for a barracks building. The overall project value was approximately £4m.
Key elements were analysed: air leakage was reduced, wall thickness and insulation of walls and roof were increased and heat recovery and passive environmental control were utilised. Both capital and lifetime costs of services and fuel were improved.
The additional capital cost of the variant design was approximately £72,000. The whole-life cost savings over 60 years were approximately £1.4m. The net present value (NPV using a 6% discount rate ) of the savings was approximately £237,000. The payback period was about five years.
Factors causing defects
How the wall interfaces with masonry, mortar, ties and plaster will determine where defects and deterioration occur. Examples include:
- Cracking and splitting: Occurs through structural/thermal/moisture movement or chemical interactions. Appears at the junction of mortar and bricks or blocks, above DPCs, at slip joints, at fixed ties, between applied coatings and the substrate, at localised bearing points of lintels and so on.
- Staining or spalling: Where water damage has facilitated algal growth or breakdown of the masonry surface. It often occurs at changes of material or penetrations
- Unacceptable sound transmission: At the junction with floors or service penetrations
- Unacceptable thermal transmission: Between joints in insulation slabs, where ties or other penetrations prevent continuous insulation layers; at cold bridges; at changes in construction details (for example, where separating wall becomes external envelope).
Factors affecting lifetime cost
The condition of the wall will be affected by its location as wind-driven rain, pollution and the building's use determine how quickly materials degrade. The rate of degradation may change if the building is refurbished. For existing construction, the following issues could affect costs:
- Restoration of historic materials or construction methods, which may be unavailable, unrecognised or prohibited under current legislation. The use of restoration specialists to renovate the walls will add to costs.
- For listed buildings, a requirement to retain as much of the existing fabric as possible and use sympathetic or identical methods to original construction will affect costs
- Identification of existing materials, which often entails detailed examination and even laboratory analysis
- Cleaning: Older materials require specialist techniques
- Use of lime mortars
- Identifying and repairing damage, particularly cracking
- Upgrading to existing thermal and acoustic regulation requirements.
Environmental life-cycle costs
BRE's Environmental Profiles scheme is designed to help architects and specifiers compare the environmental performance of different construction materials and products. It also enables manufacturers to demonstrate the environmental performance of their products.
The first companies to have construction products formally certified under the Environmental Profiles Scheme were awarded their certificates by BRE Certification recently.
Marley Building Materials and Eternit Building Materials in the UK, Tegral Building Products in Ireland, and all Etex Group companies have been awarded certificates for their product ranges, which include Thermalite aircrete blocks, clay and concrete roof tiles, fibre cement and resin slates and polymer modified slates.
The Environmental Profiles Scheme allows manufacturers to present environmental information about any type of construction product.
Environmental profiles measure performance throughout a product's life:
- Manufacture and transport (including raw materials)
- Use in a building – taken over a typical building life and including maintenance and replacement
- Demolition – the waste produced, allowing for recycling or reuse.
The profiles are based on seven key measures of sustainability:
- Primary energy use – the total energy consumed including energy production
- Climate change from CO2 and other greenhouse gases particularly associated with energy use
- Ozone depletion from gases affecting the ozone layer
- Acidification – contribution to the formation of acid rain
- Consumption of minerals, water and fossil fuels
- Emission of pollutants to air and water, including toxicity to humans, ecosystems and chemicals responsible for low-level smog
- Quantity of waste sent to disposal.
At its simplest level, the profiling method is able to consider the impacts of a single building material, such as wood. However, to make valid comparisons designers need information about a building element such as a wall. A component or building element is likely to be made up of several materials and environmental profiling takes this into account by adding together the contribution of the component parts. All products that are profiled are awarded an Ecopoint rating.
The BRE has devised a method of ranking and scoring different environmental impacts. This means that the different impacts can be combined into a single score, allowing environmental criteria to be considered alongside other issues in the product selection process. More information is available in BRE Digest Number 446.
Manufacturers with BRE-certified environmental profiles have their product data checked on an annual basis, and certificates are issued every three years. This ensures that information is valid and up to date.
ReferencesBRE and other publications can be found by searching on www.brebookshop.co.uk Books
BRE Building Elements: Walls, Windows and Doors – Performance, Diagnosis, Maintenance, repair and Avoidance of Defects
Thermal Insulation: Avoiding Risks (2001 edition) Digests
293 (improving sound insulation)
338 (insulation against external noise)
441 Parts 1 and 2 (technical issues of clay brickwork)
449 (two-part set on cleaning exterior masonry) Good Building Guides
13 (surveying brick or blockwork)
44 (insulating masonry cavity walls) Good Repair Guides
20 (repairing frost damage)
22 (improving sound insulation)
28 (repairing freestanding walls) BRE Information Paper 11/00 (recent developments in wall ties) BS/ISO 15686 – the Service Life Planning Pack – from BSI. BRE Construction Helpdesk on: 01923-664200 or www.bre.co.uk