Pavilion | Swimming Pool Extension in Green Belt | Sunken Design

Can You Build a Swimming Pool in the Green Belt?

The clients at Old House had a clear ambition: a swimming pool that the whole family could use, designed with accessibility in mind and available to enjoy throughout the year, not just in the height of summer. It was a reasonable and achievable aspiration - complicated by one significant constraint. The property sits in the Green Belt, where planning policy is deliberately restrictive and where any new structure must justify its presence carefully, both in terms of size and its impact on the openness of the landscape.
A conventional pool enclosure, sitting prominently in the grounds, visible from the house and from the surrounding landscape, would have been difficult to justify through planning and would have altered the character of the setting in ways that neither the clients nor the local planning authority would have welcomed. The challenge was to find a design approach that delivered everything the clients wanted whilst answering the planning question convincingly.

A Sunken Structure, a Green Roof and a Private Poolside Retreat

The solution was to think downwards rather than upwards. By sinking the pool structure into the ground, Simon Mack Architecture was able to reduce its visible mass to the point where it sits as a quiet, considered addition to the landscape rather than an imposition upon it. The roofline of the pool enclosure sits low, so that the relationship between the new structure and the old is one of deference and calm rather than competition.
The flat roof of the sunken enclosure is planted as a green roof, visible from the upper floors of the main house as a sweep of living planting that integrates the new structure into the garden landscape above it. The green roof does several things at once: it insulates the structure below, significantly reducing energy demand for heating the pool; it manages rainwater run-off naturally; and it creates valuable habitat for bees and pollinating insects, a meaningful contribution to the biodiversity of the wider garden setting. From the house, you look down not onto a roof but onto a garden.
At pool level, the sunken position creates something that a ground-level enclosure never could: a genuinely private, sheltered outdoor space around the pool itself, screened from the wider landscape and from the house above. Generous natural light enters through carefully positioned glazing, ensuring the interior is bright and uplifting throughout the day, whilst the enclosure remains comfortably warm in all seasons. The pool has been designed with accessibility at its heart, with easy entry and an environment that works for all members of the family regardless of mobility.

A Year-Round Pool for the Whole Family

Old House now has a swimming pool that is used throughout the year, not just a seasonal amenity, but a genuine and regular part of family life. The sunken enclosure is warm, light-filled and accessible; the pool itself is a pleasure to swim in whatever the weather outside.
From the grounds, the structure is discreet and considered, its green roof blending into the garden rather than interrupting it. From the upper floors of the house, the planted roof is a feature in its own right, changing with the seasons, alive with insects through the warmer months and quietly beautiful even in winter.
This project demonstrates that Green Belt constraints, handled with intelligence and care, need not mean compromise. The right design response to a difficult planning context does not water down the ambition. The sunken pool at Old House is better for the challenge it was asked to meet.

Visuals have been used rather than photographs, to maintain privacy for our client.