Construction of a ridge raising — what happens structurally?

Step 1: demolition and preparation

Before the start:

• Asbestos inspection on old roof decking (houses before 1994). If found → specialized remediation is mandatory.
• Erecting scaffolding around the house.
• Temporary protection for the floor below (foil, plastic sheeting over ceilings).

Demolition:

• Removing roof tiles (often carefully, for reuse).
• Removing counter battens, roof battens and roof decking.
• Removing existing rafters or roof trusses — only where the structure allows it.
• Disconnecting gutters, lead and zinc work.

Step 2: new structure

The most commonly used methods for a ridge raising:

• Timber frame construction (HSB): prefab wall elements that are hoisted and assembled on site. Fast, clean and high insulation values. The most common choice.
• Traditional carpentry: new roof trusses and purlins made on site. More flexible with uneven geometry but slower.
• Steel structure: for large spans or heavy loads, for example with a roof terrace.

The structural engineer determines in advance:

• Whether existing walls and the joist layer can carry the extra weight.
• Which dimensions and wood quality are required.
• Possible wall reinforcement or a steel ring beam as a connecting element.

Step 3: insulation and airtightness

A new roof must comply with Bbl requirements (Dutch Building Decree): a minimum of Rc 6.3 m²K/W for roofs in new construction. For renovations, this is formally a guideline value, but most municipalities require this for newly installed roofs.

Standard build-up from inside to outside:

1. Plasterboard (later, during finishing). 2. Vapour barrier foil — prevents moisture from entering the insulation. 3. Insulation (PIR, glass wool, hemp or cellulose) — at least 16–20 cm for Rc 6.3. 4. Roof decking (plywood or OSB). 5. Vapour-permeable foil. 6. Counter battens and roof battens. 7. Roof tiles or alternative roofing.

Importance of airtightness: gaps around connections lose more heat than thin insulation. Good contractors work with tapes and grommets for airtight detailing.

Step 4: facade and connections

With a ridge raising, a part of the side facade often goes up as well. Points of attention:

• Can the existing brickwork be continued or is additional brickwork required?
• With timber framing (HSB): the top edge is often finished with lightweight cladding + plasterwork or wooden boarding.
• Connection to the neighbouring property in a terraced row: extra fire-resistant brickwork or a special fire-resistant board is mandatory (60 minutes WBDBO).
• Rainwater drainage must be at the new gutter height; the downpipe usually needs to be replaced as well.
• Plan the ducts for ventilation and mechanical extraction in advance.

Step 5: roofing and interior finishing

On the outside:

• Roof tiles in a colour that matches the old ones as closely as possible.
• Lead, zinc or lead replacement strips around chimneys and connections.
• Gutters re-hung at the new height.
• Skylights or a dormer are installed in this phase.

On the inside (often outside the basic quote):

• Plasterboard on the joists.
• Painting, skirting boards and finishing trims.
• Electricity, water and heating.

Calculate € 8,000 – € 20,000 on top of the structural shell (casco) price for a 'turnkey' habitable state.

Frequently asked questions

Short, honest answers to frequently asked questions.

How long does the construction itself take?

Demolition 1–3 days, structural shell assembly 1–2 weeks, roofing 3–5 days, interior finishing 1–3 weeks. Total 4–8 weeks.

Is my foundation suitable?

For terraced and intermediate houses usually yes, provided the structural engineer confirms this. For older houses or soft soil, foundation research is required.

What if I find asbestos?

Stop work immediately, call in a specialized remediator. Costs € 2,000 – € 8,000. Never start asbestos removal yourself — fines can reach thousands of euros.

Which insulation is best?

PIR is thin and has a high insulation value, but is synthetic. Cellulose or wood/hemp fibre is more sustainable and has better summer performance. Glass wool is cheap and acoustically strong.

How does my house stay dry during construction?

The contractor places weather-resistant tarpaulin over the entire house. During heavy rain, droplets can get through — ask about the working method and rain planning in advance.

Can I include skylights right away?

Yes, that is wise. Installing them during construction costs much less than building them in afterwards — often a saving of € 500–1,000 per skylight.

What is a 'thermal bridge'?

A point in the structure where heat easily escapes (e.g., a continuous steel beam). Good timber frame contractors design them out using double insulation layers.

Summary

A ridge raising can be divided into five steps: demolition, new structure (usually timber framing), insulation and airtightness, facade and connection work, and roofing + finishing. Ask your contractor about the construction method, the Rc-waarde of the new insulation and the working method in case of rain. Count on 4–8 weeks of construction time and interior finishing as a separate budget item.