Developments within coastal locations
Developments in coastal regions, particularly in the South West, West and North Western areas of the UK, are at a much greater risk of exposure to aggressive environment than inland areas. The most vulnerable areas are within 500m of the shoreline, but there can be an effect on buildings as far inland as 5km.
What are the key risks?
Gust wind speeds, in combination with rain, can create design issues for buildings sited in shoreline locations, particularly cladding and roof coverings and their associated fixtures and fittings.
The durability of materials as well as adequate levels of workmanship and maintenance also have a bearing on the longevity of a building. For example, the effects of corrosion from wind-blown salt spray and higher UV exposure can reduce the expected durability of a finish or a component in a coastal location to less than 10 years, and in some cases to as little as five years.
Failures directly due to poor workmanship rather than to any faults in the materials themselves are common. For example:
- Poor installation of roof tiles or slates because the fixings used are inadequate for the location
- Insufficient provision of correct damp proofing in walls around openings e.g. poorly fitted cavity trays
- Incorrectly positioned flashings and damp proof courses to balconies, especially around external door opening junctions
While it’s the designer’s responsibility to ensure that exposed components must be fit for purpose, some materials and particularly finishes will require regular maintenance because of the harsh environment. Maintenance plans will need to be drawn up by the designer to avoid premature failure of coatings or components. The building owner must then take responsibility for regular maintenance of exposed components and finishes. For example:
- Debris build up (e.g. wind-blown sand) must be managed, particularly to balconies. If it isn’t, blocked outlets can cause overflowing and internal leaks as well as unsightly stains to external masonry and timber claddings
- Bi-fold and patio type doors are vulnerable. Their seals, mechanisms and drainage holes may also be affected by wind-blown sand if not regularly maintained
In severe and very severe categories of exposure, external walls should incorporate additional protective features to stop masonry getting too wet. Features such as deep overhanging eaves and verges, projecting sills and checked window reveals should be incorporated into the design.
In such cases it’s best to avoid:
- Flush sills and inadequate or non-existent overhangs at verges
- Large expanses of glazing or impermeable cladding with no effective means to shed run-off water clear of the masonry below
- Rendering and masonry junctions with no effective seal to prevent water penetrating the rear of the render
The ‘background’ or substrate supporting the render must provide a suitable bond for the render and be sound and dry. Hand-mixed renders should not be used. Only pre-blended bagged render systems will be accepted that have a third party accreditation such as a BBA or ETA certification and that are also backed by a manufacturer’s specification. In a very severe location, a detailed specification from the render manufacturer will be required to justify it is suitable for the proposed conditions and the overall thickness.
Render angle beads should be appropriate for the environment. Non-corrosive render beading e.g. PVC or marine grade stainless steel should be installed.
External cladding systems including rain screens
The materials used within the construction should be able to withstand weathering and atmospheric pollution and potential chemical attack for the intended design life. The system must have a current third-party product approval, confirming the specification is suitable for a coastal environment.
Windows and doors
The choice of windows and doors must be supported by a manufacturer’s certification to confirm they meet the design weather conditions and have proof of testing to the following weather performance standards:
- BS 6375-1 Weather tightness
- Air permeability - BS EN 12207 – Classification & BS EN 1026 - Test method
- Water resistance - BS EN 12208–Classification & BS EN 1027 - Test method
- Wind resistance - BS EN 12210–- Classification & BS EN 12211 – Test method
Window and door furniture and fittings must be resistant to the effects of the saline environment.
The balcony roof waterproof covering must be designed to fall away from any external door openings into the building. An adequate step or raised threshold must be provided to avoid the risk of wind driven rain penetrating the construction. A minimum of 75mm difference between the highest point of the balcony roof waterproof surface and the underside of the door sill may be provided as shown below. In all other situations a gap of 150mm should be provided.
Drainage outlets must be easily accessible and maintainable even if decking or balcony floor finishes are applied. Balcony steelwork must be adequately protected against potential corrosion.
Protective coatings and finishes to metals
In fact, all metals should have a suitable protective coating to minimise or prevent corrosion:
- Steel used on sites within 500m of a coastal shoreline should be galvanised to a rate of 710g/m2
- Decorative finishes must be compatible with BS EN 12944 and the manufacturer’s recommendations
- Steel lintels used in both leaves of an external wall should be austenitic stainless steel, and in addition should be protected by a separate damp proof system / cavity tray
- The use of intumescent paint to achieve fire protection should be compatible with any corrosion protective coating applied. The manufacturer’s guidance should be followed
For clay, concrete and slate roofing, a full roof fixing specification from the slate or tile manufacturer must be provided that takes into account the exposure, environment and orientation of the site.
When specifying metal cladding the designer must establish how corrosive the environment is. The designer should also assess the potential for wind uplift and movement in a cladding system during severe wind conditions, particularly over party wall positions.
Learn more about developments in coastal regions and how to comply with building regulations in Chapter 2.3 of our technical manual.