Usually, slipperiness is caused by algae or dirt on top of the deck or terrace. A full cleaning treatment should restore the natural grip of the wood or stone. If slipperiness is a persistent problem, consider installing grip mats in high traffic areas of the deck.
Carlisle
Bordering Scotland, Carlisle has a population of more than 100,000 and keeps lots of its history and origins following the colonisation from King William II in 1092. With a wide variety of home types backdating 100s of years, maintenance levels vary throughout the city and what's plausible will vary from property to property.