Hambleside Danelaw is helping you to understand the requirements for ridge line ventilation
Consideration of high-level roof ventilation is a key requirement for both cold and warm pitched roofs, this is particularly relevant with cold temperatures and ever-increasing insulation requirements (see BRE Report BR262 ‘Thermal insulation: avoiding risks’ for further information).
High-level ventilation solutions, such as dry fix ridge systems and tile vents, provide routes for air, water vapour and moisture to escape the roof space, helping to avoid condensation, damp, and decay. In this article, Hambleside Danelaw will focus on where ridge level ventilation is required, while highlighting some of the products available to meet the requirements.
But first, it is important to offer an overview of the relevant British Standards:
- BS 5250: Management of moisture in buildings specifies the main sources of moisture in buildings, how that moisture would travel through the environment, as well as the best ways to manage that moisture to minimise any harmful effects.
- BS 5534: Slating and tiling for pitched roofs and vertical cladding. Code of practice was last revised in 2018 to reflect the demands of increasing extreme weather events. It details best practice for slating and tiling and the need to avoid the reliance on mortar on roofs in favour of mechanical fixing.
- BS 8612: Dry fixed ridge, hip, and verge systems for slating and tiling. Specification was published in 2018 to address industry concerns around the variable quality and performance of newer low-cost products entering the UK market. The standard outlines the minimum performance requirements for dry fix systems used at the ridge, hips and verges.
The considerations contained in the above include: the requirement for the adequate fixing of all roofing components, the importance of ventilation to manage moisture, and the wind load resistance in the roofing design.
Warm or Cold Roof
The type of roof construction also must be considered. Typically, British pitched roofing is designed to be either a ‘cold’ or ‘warm’ type or can be a combination of both. A cold pitched roof generally has the insulation layer at ceiling joist level leaving a large cavity above, whereas a warm or hybrid roof has the insulation layer following the rafter line.
Generally speaking, ventilation is always required with cold roof construction whereas it may not always be needed for warm pitched roofs. For these roofs, the main focus should be minimising the risk of condensation by providing clear airpaths across the roof and to the outside where the moisture can be dispersed.
Here the ventilation openings are usually provided at low level and as close to the eaves as possible but above the insulation layer. For roof pitches above 35° or roof spans exceeding 10m, an equivalent of a continuous 5mm ventilation is required at the ridge. This will most often be provided by a ventilating dry fix ridge kit such as Hambleside Danelaw’s CON6+, MONO6+ (for mono ridge tiles), or CLAY6+ (for use with all common baby or clay ridge tiles).
More recently we have seen the use of Low Resistance (LR) underlays dominate the market. Whether vapour permeable or air and vapour permeable, BS 5250 requires them to be treated in the same way. The use of these underlays allows for a reduction in the amount of ventilation required. For example, a property with a well-sealed ceiling may only require ventilation openings at the ridge.
Balancing Aesthetics with Functionality
With the history and heritage of the construction trade, and especially roofing, comes a lot of tradition, and traditional applications using lead or mortar reduce the opportunity for those much-needed ventilation openings at high level. While lead and other metal applications have been used for generations and offer key positives such as recyclability and durability, they can also pose an issue when it comes to water reclamation systems, theft risk, cost and the growing skills gap.
There are more and more options on the market which retain the appearance and style of these traditional applications, while meeting the latest industry requirements. SwiftRidg®+ Roll Top Ridge and Hip System, for example, is an alternative to the lead, zinc or more rudimentary galvanised roll top ridge and hip method which can provide a minimum of 7,500mm² airflow ventilation area per linear metre if required.
The traditional look of mortar can now also be retained with a ventilating ridge system using the latest innovation from Hambleside Danelaw: VentRidg™. The VentRidg system features a mortar bonding strip along lengths of a GRP flashing for mortar retention, in addition to an integral corrugated ventilation strip on the underside. Simple to install, this system delivers high level roof ventilation combined with mechanical fixing suitable for most concrete and clay ridge tiles.
Cancelling the need for Compromise
The range of products available from Hambleside Danelaw means that contractors, specifiers, and housebuilders can all meet the requirements as well as maintain the appearance appropriate for the build.
