Robert Rock has been a structural engineer for 15 years. Here he explains his work on The Crow’s Nest project, a remarkable home perched on Dorset clifftops. The house has been shortlisted in The Structural Awards 2017.
The Crow’s Nest is in an active landslip zone, nestled at the base of a slope. The original building on the site had been irreparably damaged through repeated, severe ground movement.
A sustainable engineering solution was required for the new house, to ensure that it could accommodate the extreme conditions without the need for the improvised repairs that had characterised the previous building.
There were serious challenges: balancing an involved structural problem against the needs of a private client, on a site with limited access; and providing sufficient robustness to cater for the stability of the building in day-to-day use, as well as the infrequent extreme event of a landslip. This required a lot of initial concept work and discussions.
Massive foundations were not a viable or cost-effective solution on such potentially unstable ground. Instead we effectively placed the structure on two foundations: piled foundations capped by reinforced concrete ground beams, overlaid by a grillage of steel beams, supporting a lightweight timber structure.
The loads of the structure are carried by the pile foundations in the temporary and landslip case. In the permanent condition, the building sits on the ground beams, which act as a shallow strip foundation.
After the ground has moved a local contractor can re-level the house to suit the new ground levels using jacking points below the grillage of steel beams at ground floor.
It is common for buildings to be raised up retrospectively, but the Crow’s Nest is different in that we have accepted ground movement is inevitable and that the structure cannot be moved from its path. Instead we have integrated a bold, yet pragmatic, way of responding to nature into the design.
The client was aware of the risks the site has and that eventually the house will be uninhabitable as it succumbs to the forces of nature. They felt that, provided they could enjoy the value of its location and views before then, it will be worth the investment. The reassurance we provided to maximise the longevity of the structure was therefore of great comfort and joy to them.
The Crow’s Nest innovations show that site constraints and comparatively low budgets do not have to be limitations to complex architectural and structural solutions. Hopefully projects like the Crow’s Nest will act as a catalyst to those previously deterred by a site’s native risks.
Explore The Structural Awards