New Universal lightweight underlays from Marley
Universal Vapour Permeable and Non Breathable underlays from Marley are a high quality selection of high performance and lightweight membranes, designed to integrate either as part of a complete Marley roof system, or used in conjunction with other manufacturers’ tiles and slates.
Each underlay is manufactured using the latest materials and processes, and each incorporates a number of useful features which assist in ensuring installation that is not only correct, but also compliant to the latest British Standards.
The recent update to BS 5534 introduced some important changes concerning lightweight underlays
A new test method establishes the resistance to wind uplift of the underlay and a new classification system. Both are aimed at preventing misuse surrounding issues relating to the amount of drape needed to permit the passage of moisture beneath the tiling battens and possible risk of ‘ballooning’ under wind load.
Stricter recommendations for the securing of underlay laps, and a new labelling system have been introduced, to assist with the specification and installation of underlays. These are based on their declared wind uplift resistance in five UK geographical wind zones for the three typical batten gauges of single–lap tiles, double-lap tiles and double-lap slates.
Underlay laps remain variable, dependent on the roof pitch and whether the underlay is fully supported or not. In all instances, laps must be secured by a naturally occurring batten or a proprietary sealant tape. They should also be laid with a nominal 10mm drape to allow a drainage path for moisture and prevent excessive deflection under wind load.
Whilst the use of an additional fly batten is possible, it is not recommended as it provides a significant trip hazard
Fully compliant underlays from Marley
Marley Universal underlays offer quality and peace of mind as standard, and are fully complaint to the British Standard with a number of benefits including:
- UK wind zones 1-5 compliant
- Integrated tape system, meaning all laps can be sealed without the need for
- Additional underlay laps to coincide with the nearest batten course
- Using a dangerous fly batten
- Guidance lines to assist with straight installation and achieving the correct lap to BS 5534
- BBA certification