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The Permavent Easy Slate system rips up the rule book when it comes to roof pitch and slate laps. A unique patented system in the form of a strip that fits under each slate joint, prevents water from creeping sideways. Easy Slate vastly improves the performance of the slates, enabling roof pitches as low as 12 degrees. The slates are still installed in a double lapped pattern, so there is no discernible difference in appearance on the roof.
Traditional double lapped slates have been keeping buildings weathertight for 100’s of years, so the relationships between slate length and width, headlap, side lap and roof pitch are well understood. BS 5534: the British Standard Code of practice for slating and tiling, provides the rules by which we can work out the minimum headlap, side lap and roof pitch for any roof anywhere in the UK.
As rainwater runs down a slate roof, it runs into the gaps between each slate, with a slate below each gap to catch the water and drain it to the next course of slates below. Water is also drawn between the slates through capillary action and can run downward, sideways and even upwards. Gravity acts on the water, so it is not drawn as far by capillary on a steep pitch as it is on a lesser pitch, consequently steeper pitched roofs are more efficient in keeping the water out.
To minimise leakage through the slating, there must be limitations, dependent on the size of slates, on roof pitch and rafter length. But even so, during a roof’s service life, which can be 40 to 60+ years, there will be weather events in which water will penetrate the slating. If this happens with any frequency, there is a risk of long-term damage to the roof sub-structure, battens and fixings. .
Easy Slate increases the gap slightly between each slate, not only making water creep through capillary action far less likely, but also encouraging better air flow between the outside atmosphere and the batten cavity. This improves the efficiency of the vapour or air-permeable underlay in removing unwanted condensation from the roof structure, something particularly important for slates that have smooth surfaces, for example, fibre cement slates. Also, the higher airflow through the slating increases the security of the slates against wind uplift as a larger proportion of the wind load is then borne by the underlay.
In the UK all breather membranes are classified by wind zone, with the country being divided into 5 wind zones. The lowest wind speed, Zone 1, is centred around London and the south of England, through to Zone 5 covering the very far north of Scotland. When choosing an underlay, designers and installers must be mindful of the list of criteria that apply to the Zonal tables.
These are as follows:
If a project falls outside any of these parameters, the wind load may be higher than the Zonal table maximum load resistance. In these cases, a wind uplift calculation is required to determine what strength the underlay needs to be. If in doubt, please contact us for further assistance.
Permavent Max All Zones and Permavent APeX membranes are suitable for use in all UK wind zones, therefore, designers and installers can have complete confidence in their use anywhere in the UK. Max All Zones can be used without tape in any wind zone. Permavent Apex 2 TX can be used in any zone as it comes with 2 integrated tapes.
Permavent Max is a vapour-permeable underlay, produced using the latest technology to encapsulate hydrophobic film inside spunbond polypropylene layers. Because this is done in a combined 3 in 1 process, rather than simple bonding the different layers together, quality and integrity are vastly improved and Permavent can rightly claim its products to be ‘best in class’ with superior strength, breathability, flexibility and durability. At 150 grams, Permavent-MAX has been tested and certified by BRE as suitable for all UK wind zones with laps either taped or battened.
Permavent APeX is a high-performance underlay, manufactured using a unique induction bonding process that achieved superb air and vapour permeability results when tested by the BRE. Consequently, it is approved by NHBC for use in new-build cold roof applications without any additional roof space ventilation. It is also ideal for use in warm roof constructions without any additional roof space ventilation.
In addition, Permavent APeX, at 180 grams per square metre, has been tested and certified by BRE as suitable for use in all wind zones throughout the UK when installed with taped laps, with integrated tape making installation a quick and easy process.