Fears over safety can mean that access to the open air is often denied to people with dementia.

Wrongly so, says Mary Marshall, emeritus Professor at the University of Stirling and founding director of the Dementia Services Development Centre (DSDC) there.

"Instead of protecting people, making the outdoors out-of-bounds does a great deal of damage. Too many care providers are still not aware of that," she says.

For architect and landscape specialist Annie Pollock, it was hearing about the experience of a man with dementia, confined to a locked ward on the second floor of a large Scottish mental hospital, that affected her most deeply. "He had been a policeman, an active person who loved gardening, and now he wasn't allowed out. He kept asking his family why he was in jail," she says. "For him, this was a living death. And so it must be for many others."

Ms Pollock is an expert in dementia-friendly garden design. It is her mission to change the mindset that people with dementia must be confined indoors for their own safety, and she has teamed up with dementia design guru Prof Marshall to edit a book that demonstrates how it can be done.

Designing Outdoor Spaces for People with Dementia, co-published by the DSDC and Australia's HammondCare organisation, shows the evidence of the considerable physical and mental benefits being outside can bring. There is a powerful chapter arguing that access to the open air is a human right.

The new book presents illustrated case studies from Japan, Australia, Norway and Scotland that show how backyards, balconies and roof terraces can be adapted to suit the needs of people with age-related cognitive decline. "Dementia is a worldwide phenomenon, and there is much that we can learn from each other," says Prof Marshall. "We should keep an open mind to the potential for enhancing the quality of individuals' lives."

Dementia tends to throw thoughts back towards childhood and gardens can provide a therapeutic link to the past with smells, tastes, sights and sounds used to trigger comforting memories. But the book stresses that it is important to approach dementia-friendly gardening with cultural sensitivity: what might be familiar to people who grew up in the outback of Australia would be alien to most Scots.

"It is important to explore what outside space means to the people for whom a garden is intended," says Prof Marshall. "If you've grown up on a farm, keeping chickens might be your thing, or cultivating a vegetable patch. There's no one-size-fits-all."

As well as presenting examples of garden layouts and planting plans, the book explores the physiological considerations that have to be taken into account when designing for dementia: special thought has to be given to sun angles and shadows, shaded areas and sightlines, and even landscaping materials.

"I learned most about the technical stuff – things like site choice, noise reduction and wind protection," says Prof Marshall. "There are important subtleties when it comes to designing for dementia that we can all be much more aware of."

For Ms Pollock, the biggest surprise was the body of evidence for health benefit. "Spending time outdoors can improve sleep patterns, appetite and continence, reduces falls, distress and aggressive behaviour, and boosts overall wellbeing," she says. "It is good for people with dementia, and those who care for them. And as well as being the right thing to do, it saves money in the long run because the need for drugs and even hospital admissions is reduced."

As societies age, rates of dementia are projected to rocket around the world and both Ms Pollock and Prof Marshall believe dementia-friendly design will become increasingly necessary in the wider public realm. Their book explores how neighbourhoods and community common spaces can be adapted to better meet the needs of a growing number of people who might otherwise have to be confined indoors, and it is aimed at town planners and architects as well as care providers.

"Access to the open air should be central to dementia care, and not an optional extra," says Prof Marshall. "I have it specified in my own advance statement that should I lose capacity, I must be allowed out. Many more people ought to do the same."

Designing Outdoor Spaces for People with Dementia, £35, is available from www.dementiashop.co.uk. On September 15, there will be special tours of the DSDC's dementia-friendly building and garden as part of Stirling Doors Open day. Call 01786 467740 for information.