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  1. Welcome to Planning Portal
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  4. Volume Calculators

Volume Calculators

Sizing up your project

Are you thinking of adding an extension or making changes to the roof space of your home? Try out our volume calculators to work out the cubic metres of the space to get your project started. Select the appropriate volume calculator for your project below.
Dormer window — flat roof

Calculations needed for a dormer window with a flat roof structure.

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Lean-to — single pitch roof

Calculations needed for adding a Lean-to on a structure with a single pitched roof.

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Pitched roof — one end hip

Larger structure require a more complicated calculation. One end hip.

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Pitched roof — two end hips

Larger structure require a more complicated calculation. Two end hips.

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Pitched roof — two end gables

Complete structure require a more complicated calculation.

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    The Planning Portal is delivered by PortalPlanQuest Limited which is a joint venture between TerraQuest Solutions Limited and the Ministry of Housing, Communities & Local Government (MHCLG). All content © 2025 Planning Portal.

    The Planning Portal is delivered by PortalPlanQuest Limited which is a joint venture between TerraQuest Solutions Limited and the Ministry of Housing, Communities & Local Government (MHCLG). All content © 2025 Planning Portal.