Must you always use battens over an existing roof?

The use of battens differs across manufacturers and profiles. Some profiles require the use of battens for every installation; others can be used with battens, or without battens. If you choose a product that requires battens for the installation then yes, you will always need battens whether the project is new construction or a reroof over existing materials. If the profile can be used with or without battens, then the use of battens will depend on the existing product on the roof, and project conditions. For example if the product being roofed-over is an asphalt shingle, you might not need the battens to make sure the installation surface is level . However, if you are re-roofing over slate, then you would need battens and possibly counter battens over the slate.

How does a stone-coated roofing system withstand moss/algae and maple tree leaves and seeds? Does cleaning either by pressure washing or sweeping degrade the granular part of this coating and to what extent of degradation? Can moss/algae be prevented?

Typically moss/algae grows on the debris that is left on the roof. It is recommended that the roof be kept clean of debris. Recommendations differ by manufacturer. Follow the manufacturer’s recommendations for cleaning the roof so as not to void the warranty. For example, our website includes directions for cleaning; power washing and sweeping are part of the recommendations, and when followed, there is no degradation of the granules, and the warranty is not voided. Some manufacturers have an algaecide in their basecoat/primer. You would need to check with the specific manufacturer concerning the inclusion of this type of product.