When do you need a ridge-raise drawing?
A ridge raise is the solution when the attic under a sloping roof is too low for full use. By raising the existing ridge across the entire home, the attic becomes a real bedroom or study with sufficient standing height. Because both the building height and the silhouette of the home change, a ridge raise is almost always subject to a permit and the municipality requires scale-accurate construction drawings for the application of an environmental permit.
Common situations where a ridge-raise drawing is needed:
- A terraced house where the attic is barely usable due to low knee walls.
- A family that wants an extra bedroom or children's room on the top floor.
- A home where a roof addition is too far-reaching, but a dormer provides insufficient space.
- Combination with a dormer or roof window to gain extra daylight as well as height.
What does a ridge-raise construction drawing include?
A complete ridge-raise drawing contains floor plans of the adjusted upper floor, facade views with the new roof pitch, cross-sections and a site plan. The floor plan shows how the gained space is laid out: new bedrooms, a possible bathroom and the run of the staircase. The facade views show the new ridge height relative to the existing facade and the roof of the neighbours.
On the cross-section, the structural adjustment is central: the existing truss structure is partly or entirely replaced, and the drawing shows the new trusses, purlins and insulation build-up. An additional roof detail shows how the new ridge is finished and how the connection with the existing side facade is resolved.
Permit and aesthetic requirements
For a ridge raise, an environmental permit is needed in almost all cases. The application runs via the Environment Desk and the municipality assesses the design against the zoning plan and the aesthetic policy. Especially for terraced houses in a continuous building block, it is strictly assessed whether the ridge raise fits into the streetscape: in some streets ridge raises are common and accepted, in other streets the aesthetic committee assesses each application on its own merits.
The Building Decree also plays a role: the new storey must comply with requirements around fire safety, ventilation, insulation and daylight access. A professional drawing that covers these aspects prevents requests for additional information from the municipality and speeds up the processing time of the application.
What does a ridge-raise construction drawing cost?
A construction drawing for a ridge raise is available from €350. The final price depends on the complexity of the existing roof structure, the desired layout of the new storey and whether existing drawings are available. A ridge raise on a through-lounge home from the 1960s is usually faster to draw than a ridge raise on a pre-war home with an unusual roof structure.
In addition to the drawing, keep in mind a structural calculation, because the existing trusses are adjusted or replaced. The municipal permit fees are also added, based on a percentage of the construction cost.
Difference with a roof addition and a dormer
The difference between a ridge raise and a roof addition lies in the nature of the intervention. With a ridge raise, the existing upper floor is retained, only the ridge goes up. With a roof addition, a complete extra storey is placed on the home. A ridge raise is therefore less far-reaching, often cheaper and faster to realise, but yields fewer square metres than a roof addition.
A dormer, on the other hand, adds standing height and daylight locally in the roof surface, without the ridge height changing. Torn between these options? During the intake, we discuss what is feasible and desirable in your situation, given the home and the aesthetic rules in your municipality.
