Improves ventilation
With SlateSpacer™, roofing slates do more than shed water: they become an important contributor to roof ventilation.
Improved ventilation reduces condensation and speeds drying of internal surfaces. This maximizes the service life of battens, boards, decking, rafters and other roof elements, as well as that of the slate. (Learn how water ages roof slate.)
Less than 1.2 mm (less than 1/16") thick, SlateSpacer™ enhances ventilation while preserving the water-shedding function of the roof system. Like louvers in a shutter or gable vent, each course of slate is spaced from its neighbors. Unlike louvers, slates are double-lapped, close-fitting and well supported.
On all types of roof
Condensation can occur wherever warm air meets cold surfaces. (Learn more about condensation on roof slates.) It happens in all types of roof construction, closed or open, with or without an underlay. SlateSpacer™ contributes to ventilation in each case.
Open (batten) roofs, general
Open roofs, with vapour permeable underlay
Closed roofs
A louvered vent
Another louvered vent:
When slates are held apart, air passes (blue),
allowing each course to function as a louver.
Open (batten) roofs — better than "collar-and-cuffs"
To ventilate the attic or rafter space, many roofs rely on a "collar-and-cuffs" (ridge and eaves) approach. Collar-and-cuffs ventilation is useful. But on roofs with no underlay (France), or with an underlay that allows air to pass (sometimes at the seams, and gradually through the underlay's pores), the more thorough approach adds ventilation through the "fabric" (the broad surfaces) of the roof.
Small spaces add up. Twenty courses of standard-thickness spaced slate can double the aperture that dedicated eave or ridge vents typically provide. The entire surface breathes because each slate becomes a small vent.
Open roofs: SlateSpacer™ complements vapour permeable underlays
While VP underlays reduce condensation in the spaces below them, SlateSpacer™ reduces condensation in the spaces above.
VP underlays (those that allow water vapour, but not droplets, to pass) are part of a broader system designed to reduce damaging condensation in the roof space. They are now common in much of Europe and standard in much of the UK.
In the climates that predominate in this region, VP underlays serve to remove water vapour from the bulk of the roof space. As desirable as this is, the benefit is not complete.
A consequence of reducing water vapour (and condensation) in the large space below the underlay is that vapour becomes concentrated in the small space above it — the batten cavity (the space above the rafters, between the underlay and the slates). Water vapour that accumulates in the batten cavity can condense on the cool undersides of the slates and can wet, and be absorbed by, the timber battens. Persistent moisture shortens the service life of battens and slates.
SlateSpacer™ reduces persistent wetness by holding slates apart, creating a slim, well-supported air gap between the slates' broad surfaces. Spacing roofing slates frees water trapped by capillary action and ventilates the batten cavity. The more natural ventilation that exists between the slates, the faster the cavity and its surfaces dry, and the longer the battens and slates last. (The benefit of rapid drying is evident when the exposed (fast-drying) and covered (slow-drying) surfaces of old, high-grade roof slates are compared).
With SlateSpacer™, the flow of water vapour up through the roof system need not stop (or nearly stop) in the batten cavity. SlateSpacer™ provides a continuous path to help water vapour exit the building.
Closed roofs
Closed roofs (continuous decking instead of battens) are uncommon in much of the UK, France and other markets. They are more common in Scotland and the US. They have certain advantages — but they can trap moisture.
Un-spaced slates held against closed decking permit little air circulation around the decking and slates. The wood and under-surfaces of the slates can remain damp or wet for long periods.
By providing spaces, specifiers and installers allow air to circulate across the broad surfaces of the slates and the decking. This frees trapped water and speeds drying.
Roofing slate can be more than a cover. The simple precaution of spacing slates well allows slate to become part of a ventilation solution.