Ridge raising: complete explanation

What is a ridge raising?

A ridge raising is an extension of the roof height by elevating the ridge of the roof. The existing roof is partially dismantled, a new structure is placed, and the new ridge is positioned higher. The result: more headroom in the attic, often across the full width of the house.

Single-sided ridge raising

With a single-sided ridge raising, only one roof pitch is elevated, usually at the rear of the house. The other roof pitch remains intact. Advantage: a modest intervention, often easier to align with the aesthetics committee (welstand) and neighbors. Disadvantage: less additional space than a double-sided variant.

Double-sided ridge raising

With a double-sided ridge raising, both roof pitches are elevated symmetrically. Result: a completely higher attic with optimal space gain. Structurally and visually a larger intervention, and therefore stricter in terms of planning permission and aesthetics.

Difference from a dormer and roof extension

• Dormer: local protrusion, roof shape remains intact.
• Ridge raising: roof shape is altered by elevating the ridge.
• Shifted ridge: ridge is moved horizontally to a higher point.
• Roof extension: entire extra floor on top of the existing roof.

In terms of impact, a ridge raising sits somewhere between a dormer and a roof extension.

Construction

A ridge raising requires an assessment of the existing roof structure. Questions a structural engineer will ask:

• Can the existing wall plate bear the new load?
• Do load-bearing rafters need to be replaced or reinforced?
• What does the increased wind load of the new roof mean?

Often, the new rafters or purlins are mounted on the existing wall plates, with additional reinforcement where necessary.

Planning permission

A ridge raising almost always requires planning permission. The zoning plan often limits the maximum roof height, and the aesthetics committee checks whether the new roofline fits into the streetscape. In areas with standardized housing schemes, there are sometimes municipal guidelines for uniform ridge raisings.

Space gain and attic use

A ridge raising provides a significant amount of space because the attic gets headroom across its full width. This allows for layouts that won't work with just a dormer: for example, two side-by-side bedrooms, or a spacious home office with a bathroom.

Materials and insulation

The new roof pitches must meet current requirements for insulation and airtightness. For the roof covering, you can choose between roof tiles (in the same style as the rest of the street), zinc, or EPDM for flat-finished ridges.

Common mistakes

• Ignoring the aesthetics committee, resulting in rejection.
• Insufficient insulation in the new roof pitches.
• Forgetting ventilation in the new attic space.
• Poor connection to the original wall plates.
• No consultation with neighbors in the case of terraced houses.

Construction phasing and logistics

A ridge raising happens in steps that must follow each other closely — the roof is temporarily open, so the weather is a factor.

Common sequence:

• Stripping roof tiles, tile battens, and counter battens, often in a single day.
• Dismantling the existing ridge and the upper part of the rafters.
• Placing the new purlins or wall plates at an elevated position.
• Installing new rafters and top edge detailing.
• Closing with roof boards, vapor-permeable foil, counter battens, tile battens, and roof tiles.
• Lead flashing and finishing at the gutter, facade, and any dormers.

An experienced team completes the "roof open → roof closed" phase within one to three working days. Schedule this week during a dry period and always have an emergency tarpaulin ready.

Insulation and airtightness details

A ridge raising is the perfect moment to completely optimize the building physics of the attic. The existing roof usually has an Rc-waarde (thermal resistance) of 1,3–2,5 m²K/W; the new requirement is Rc 6,3 m²K/W. You can only achieve this with a well-thought-out package.

Points of attention in the detailing:

• Continuous insulation line without interruptions at the wall plate, ridge, and valley.
• Vapor barrier foil on the inside, with airtight taped seams.
• Vapor-permeable foil on the outside under the tile battens.
• Counter battens for a ventilated cavity under the roof tiles, so rain blowing past the roof tiles can dry.

Do not forget to remove or continue the old insulation between the joists of the upper floor — it is now inside the insulated envelope and no longer plays a role there.

Window frames, skylights, and light

With a ridge raising, there is almost always room to replace or enlarge existing skylights, or to add skylights where there were none. Combinations that work well in practice:

• two skylights in a zone where no dormer will be placed;
• one wide dormer combined with two skylights on the opposite side;
• a long band of skylights in the new ridge zone for a studio effect.

Keep the position of the partition walls in mind when making this choice. A skylight that partially disappears behind a wall is annoying and irreversible. Therefore, always plan skylights after the final layout, not before.

Frequently asked questions

Brief answers to frequently asked questions on this topic.

What is a ridge raising?

A procedure in which the ridge of a pitched roof is elevated to create more headroom in the attic.

What is the difference between single-sided and double-sided?

Single-sided elevates one roof pitch, double-sided elevates both. Double-sided provides more space gain but represents a larger structural intervention.

Is a ridge raising exempt from planning permission?

Almost never. Both the zoning plan and aesthetics committee are decisive.

How long does a ridge raising take?

Count on four to eight weeks.

Do I need a structural engineer?

Yes, almost always. The existing load-bearing structure needs to be assessed.

Will it fit in with the neighbors?

For terraced houses, often only if the neighbors also agree to the new roofline.

Can I combine a dormer with a ridge raising?

Yes, this happens. The combination provides maximum daylight and headroom.

Which roofing material should I choose?

Often the same roof tiles as the rest of the house, to keep the appearance perfectly aligned.

What about rainwater drainage?

The gutters must be adapted to the new roof shape and drainage capacity.

Does the WOZ-waarde (property valuation) change?

Almost always yes, but this depends on the municipality and the housing market.

Summary

A ridge raising elevates the ridge of the existing pitched roof, resulting in more headroom in the attic. Single-sided and double-sided are the main variants. The procedure almost always requires planning permission and demands a structural assessment. For terraced houses, alignment with neighbors and the aesthetics committee is essential.

Conclusion

A ridge raising provides more space than a dormer, while retaining the original roof shape. It is a serious intervention — especially with terraced houses — that is only successful with proper consultation with the municipality, neighbors, and an experienced structural engineer. Those who arrange this properly get an attic that can be used as a fully fledged floor.