Home Extension Fallout Shelters

Conceived to comply with current UK planning regulations regarding minor home extensions, this concept consists of a shelter-annex ideally constructed to the rear of the dwelling to be out of sight.

On the ground floor is a "utility room" that contains elements critical to the underground bunker beneath it, including a hidden access, decontamination shower area, storage space for at least one cargo e-bike and water tanks.

To reduce gamma radiation from fallout by a factor of 32, the undergound shelter would require one foot of steel-reinforced concrete above it, e.g, 8 inches in the ceiling and a further 4 inches in the aboveground shelter's ceiling - see our FAQs for details on gamma radiation reduction factors and how they can be achieved using concrete, soil or combinations of both.

The actual bunker beneath the extension would technically require planning permission but we recommend not doing so; instead, the minor extension above it effectively masks the bunker element from aerial observation.

In the illustrated example, access is via ship-style wall-mounted laddering running through a hidden trapdoor.

Access into the aboveground extension is through steel doors that deliberately open in an awkward or somewhat restrictive fashion, the aim being to avoid having doors that might theoretically be readily sledgehammered open.

(Note that many details and design explanations are omitted from both the illustration and from these notes for security reasons.)

The entire design approach has been conceived to comply with the UK's Permitted Development (PD) rights, in which home extensions can be constructed without the need for formal planning permission under most conditions.

Those rules are largely as follows:

• Single-Storey Rear Extensions: Up to 3m for terraced or semi-detached homes, and up to 4m for detached. (Note: The "Larger Home Extension" scheme allows 6m and 8m, respectively, but requires a neighbor consultation - not desirable for obvious OPSEC reasons).
• Single-Storey Side Extensions: Cannot exceed more than half the width of the original house, and must be single-storey.
• Two-Storey Extensions: Must not extend beyond the rear wall by more than 3m (i.e. back from the house) and must be at least 7m away from any rear boundary
• Total Plot Size: Extensions and other outbuildings must not cover more than 50% of the land around the pre-extension dwelling.
• External Finishes: Must be of a similar appearance to the existing house