Roofing Inspection

Per DTU 40.21 (tiles) and DTU 40.11 (slates), the roof structure (charpente) must provide adequate support and ventilation space for the chosen covering. Timber battens must be correctly sized and spaced per DTU requirements. For flat roofs per DTU 43.1, the concrete or timber deck must achieve specified flatness and falls.

1. Verify that the roof structure (rafters, purlins) matches the structural design and is in sound condition with no defects

2. Check batten size and spacing — must match the tile/slate manufacturer's requirements and DTU 40.21/40.11 specifications

3. Verify that counter-battens are installed over the underlay to provide a ventilation gap per DTU 40.21

4. For flat roofs, confirm that the deck achieves minimum 1.5% fall to drainage outlets per DTU 43.1

5. Check that all timber elements are treated against insects and fungal decay per DTU 31.1

- Batten spacing not matching tile gauge, causing tiles to sit incorrectly

- Missing counter-battens eliminating the ventilation gap and causing condensation

- Flat roof deck without adequate falls, leading to ponding water

- Untreated timber battens susceptible to rot and insect damage

Per DTU 40.21 and DTU 40.11, a breathable underlay (écran de sous-toiture) must be installed beneath the roof covering to provide secondary weather protection. The roof must be ventilated per DTU requirements — typically a minimum 20 mm ventilated gap above insulation and continuous eaves-to-ridge ventilation.

1. Verify that the underlay type (HPV breathable or non-breathable) matches the ventilation strategy per DTU 40.21

2. Check that the underlay is continuous with minimum 100 mm overlaps at horizontal joints and 150 mm at vertical joints

3. Confirm that a ventilated gap of minimum 20 mm is maintained between the underlay and the insulation per DTU 40.21

4. Verify eaves ventilation — continuous strip vent or equivalent providing minimum 10 mm continuous opening per DTU 40.21

5. Check ridge ventilation — dry ridge or ventilated ridge providing matching ventilation area to eaves

- Non-breathable underlay used without adequate ventilation gap, causing condensation in the roof space

- Underlay overlaps insufficient, allowing wind-driven rain to bypass the secondary barrier

- Eaves ventilation blocked by insulation or debris, preventing airflow through the roof space

- Ridge ventilation inadequate or missing, creating a stagnant air pocket under the covering

Per DTU 40.21 (clay tiles) and DTU 40.11 (natural slates), roof coverings must be installed with the correct headlap, sidelap, and fixing pattern for the roof pitch and exposure zone. French wind exposure zones (zones de vent 1-4) and site exposure categories determine the fixing requirements.

1. Verify that tile/slate headlap matches DTU requirements for the roof pitch — typically minimum 75 mm for pitches above 35° per DTU 40.21

2. Check that the fixing pattern (nailing, clipping, or hooking) corresponds to the wind zone and site exposure per DTU 40.21

3. Confirm that every tile/slate is mechanically fixed in high-wind zones (zones 3 and 4) and at perimeters per DTU 40.21

4. Verify that tiles/slates are laid in straight courses with consistent gauge and alignment

5. Check for cracked, chipped, or damaged tiles/slates and confirm replacement before handover

- Insufficient headlap for the roof pitch, allowing wind-driven rain to penetrate the covering

- Inadequate fixing pattern for the wind exposure zone, risking tile/slate loss in storms

- Perimeter tiles at verges, ridges, and eaves not mechanically fixed per DTU requirements

- Damaged tiles/slates not replaced, creating points of weakness in the roof covering

Per DTU 40.21 and DTU 40.35, all roof junctions (valleys, abutments, chimneys, dormers, pipes) must be weathered with correctly installed flashings. Lead, zinc, or aluminium flashings must comply with the relevant material DTU. Flashings must be dressed into the covering with adequate upstands and overlaps.

1. Check valley flashings for correct width (minimum 250 mm each side of valley centre) and overlap at joints per DTU 40.21

2. Verify abutment flashings — minimum 150 mm upstand under the upper covering and 75 mm step into the wall per DTU 40.21

3. Inspect chimney flashings for continuous back gutter, stepped side flashings, and front apron per DTU 40.21

4. Check pipe penetration flashings for correct collar size, tight seal, and overlap with surrounding tiles/slates

5. Verify that all flashing materials are compatible with adjacent metals (no galvanic corrosion risk)

- Valley flashings too narrow, allowing water to overflow in heavy rain

- Abutment flashings not stepped into the wall, relying only on surface sealant which fails over time

- Chimney back gutter too small or missing, causing water to pond behind the chimney stack

- Incompatible metals in contact (e.g. copper flashings on zinc roofing), causing galvanic corrosion

Per DTU 40.5 and NF EN 12056-3, rainwater gutters and downpipes must be correctly sized for the roof area and rainfall intensity. Gutter falls must be minimum 5 mm per metre towards outlets. Materials must be compatible with the roof covering and fixed at specified centres.

1. Verify gutter sizing against the roof catchment area and local rainfall intensity per NF EN 12056-3

2. Check gutter fall — minimum 5 mm per metre towards outlets, verified with spirit level per DTU 40.5

3. Confirm that gutter brackets are at maximum 600 mm centres for half-round gutters per DTU 40.5

4. Verify that downpipes are correctly sized (minimum 80 mm diameter for standard roofs) and connected to the stormwater drainage

5. Check that gutter joints are sealed and that expansion joints are provided on runs exceeding 10 m

- Undersized gutters overflowing during heavy rainfall

- Insufficient gutter fall causing standing water and debris accumulation

- Downpipes not connected to stormwater drainage, causing water pooling at foundations

- Missing expansion joints on long gutter runs, causing buckling in summer heat

Per RE 2020, the roof assembly must achieve a maximum thermal transmittance (U-value) typically ≤ 0.16 W/m²K for new buildings. Insulation must be continuous with no gaps, and vapour barriers must be correctly positioned on the warm side of the insulation to prevent interstitial condensation per DTU 45.10.

1. Verify insulation type and thickness against the RE 2020 thermal calculation — typically minimum 300 mm mineral wool or equivalent per DTU 45.10

2. Check that insulation is continuous with no gaps, compression, or missing sections, especially at eaves, ridges, and around penetrations

3. Confirm that a vapour barrier (Sd ≥ 18 m) is installed on the warm side of the insulation per DTU 45.10

4. Verify vapour barrier continuity — all joints taped, sealed at perimeter, and around penetrations

5. Use thermal imaging to identify insulation gaps, cold bridges, or missing vapour barrier areas

6. Check that the ventilated gap above insulation is maintained and not obstructed by insulation material

- Insulation gaps at eaves or around rafters creating cold bridges and heat loss

- Vapour barrier missing or discontinuous, leading to interstitial condensation and timber decay

- Insulation compressed by storage or services, reducing thermal performance

- Ventilation gap blocked by insulation, causing moisture build-up in the roof structure

Per French Code du travail and DTU 43.1 (flat roofs), roofs must incorporate safety features for future maintenance access. Flat roofs require permanent edge protection or anchor points for harness systems. Pitched roofs must have provision for safe access (roof hooks, walkway systems) per DTU 40.21 and Code du travail R4323 series.

1. For flat roofs, verify that permanent edge protection (acrotères minimum 1 m height or guardrails) is installed per Code du travail

2. Check that roof access hatches or doors are correctly sized (minimum 800 x 800 mm) and include ladder fixings

3. Confirm that safety anchor points or lifeline systems are installed and certified for fall arrest per NF EN 795

4. For pitched roofs, check that roof hooks or walkway tiles are installed along maintenance routes to equipment

5. Verify that all safety features are documented in the maintenance plan (carnet d'entretien)

- Flat roof without adequate edge protection, creating fall risk for maintenance personnel

- Missing or uncertified anchor points for harness attachment

- Roof access hatch too small or difficult to reach, discouraging safe maintenance access

- No maintenance plan documenting safety features and inspection intervals