Britain is a damp kingdom not withstanding periodic droughts. That has implications for building outdoors in wood. I constructed this deck about 18 years ago and it is reaching the end of its useful life. Some of the boards and joists are rotting to the extent they're no longer trustworthy.

 I used pressured treated (i.e. tanalised) timber which is claimed to have a lifespan of decades but realistically expect 15-20 years. Take a fence post for example. The length waving in the air might last for decades, so might the bit encased in concrete in the ground. But where the post meets the ground there is an inevitable accumulation of moisture and matter which hastens rotting causing it to snap at that point.

 I lived in California back in the day where decks are very common but that is a dry climate. I remember the first deck I built when I was back in the UK; the end result was pleasingly Californian. I happened to be working in the next garden several years later and looked over the fence- the deck had turned green! Algae, lichens, liverworts and moss thrive in damp places and particularly in shady spots.

 A while back I was chatting with the distinguished botanist Roy Vickery. He mentioned in passing that he spent seven years of his career studying lichen at the Natural History Museum. Indeed after his retirement he continued working on the lichen collection one day a week. Botanically speaking this deck has a lot going for it but as a place to hang out on its days are numbered.