A roof house, known in Dutch as a “dakhuis,” is a substantial structure built on top of or within a sloped roof that is significantly larger than a standard dormer and typically provides a full additional room or living area under its own roof.
Difference between a roof house and a dormer
While a dormer is a relatively small projection from a sloped roof — usually housing a single window — a roof house extends across a much larger portion of the roof surface. A roof house often spans the full width of the building or a significant section of it, creating enough headroom and floor space for a complete room. It has its own roof form, which can be flat, pitched, or shed-style, and it usually contains multiple windows or even a small balcony.
In practical terms, if the structure is wider than about 50 percent of the roof surface, it is generally classified as a roof house rather than a dormer. This distinction matters because building regulations and permit requirements differ for the two.
Construction considerations
Building a roof house is a significant structural intervention. The existing roof must be partially removed, and the load-bearing walls or beams below must be assessed to ensure they can support the additional weight. A structural engineer typically calculates whether reinforcement is needed.
Key considerations include waterproofing at the junction between the roof house and the original roof, adequate insulation to meet energy performance standards, and compliance with local zoning rules regarding maximum building height and visual impact on the streetscape.
Application
Roof houses are commonly added during loft conversions to maximise usable living space. They are especially popular in urban areas where expanding outward is not an option. Homeowners choosing a roof house over a dormer gain considerably more floor area and natural light, though at higher cost and with stricter permit requirements.
Related terms
- Dormer
- Loft conversion
- Roof extension
- Ridge height
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