Timber Framing and Roofing Technical Proposal: Structure and Weatherproofing in Public Contracts
Timber framing and roofing contracts combine structural calculation and roofing craftsmanship. The buyer expects a proposal that proves mastery of both dimensions: the structural resistance of the frame (Eurocodes) and the lasting weatherproofing of the roof covering (DTU 40 series).
Timber framing: calculations and material traceability
For timber framing, the evaluator verifies the structural calculation to Eurocode 5: permanent loads, imposed loads (snow by zone, wind), load combinations. The proposal must specify timber species and use class (treatment mandatory in class 2 and above), frame type (traditional or industrial trusses NF EN 14250), and timber certification (PEFC, FSC). For steel framing, NF EN 1090 applies with corresponding execution class and welding qualifications.
Roofing: DTUs and critical details
The roofing material choice must comply with the applicable DTU.
Material choice and layout
Depending on material (tiles DTU 40.21-24, slate DTU 40.11, zinc DTU 40.41, profiled steel DTU 40.44), the proposal must specify: product reference, format, minimum admissible pitch, and fixing method. A layout plan showing element arrangement and singular point positions is highly valued.
Critical details and ventilation
80% of leaks originate from critical details. Detail each type: ridge (ventilated or sealed), valleys (metal, zinc), verges, chimney flashings, ventilation outlets. Sub-roof ventilation (air gap, tile vents, ventilated ridge) is essential to prevent condensation.
Flashings and rainwater drainage
Flashings complete the roofing and must not be neglected. Detail gutters, eaves channels, and downpipes: material (zinc, copper, aluminium, PVC), cross-section sized for roof area and local rainfall intensity, fixing method, joints, and thermal expansion. DTU 40.5 governs rainwater drainage works.
Disqualifying errors
No structural calculation — Eurocode 5 (timber) or Eurocode 3 (steel) is essential.
Underlay membrane forgotten — In snow/wind zones, underlay is mandatory.
Critical details not treated — Valleys, verges, and roof penetrations are risk zones requiring detail drawings.
Timber treatment not mentioned — Preventive treatment is mandatory in use class 2 and above.
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