Waterproofing Technical Proposal: Guide for Public Sector Roofing and Waterproofing Contracts
Waterproofing contracts — flat roofs, basement tanking, expansion joint treatment, waterproofing system refurbishment — are among the most technically demanding in public procurement. The buyer knows that a waterproofing defect can cause considerable damage and costly litigation. Your technical proposal must demonstrate total mastery of systems, DTU standards, and water-related risk management.
What the buyer evaluates in a waterproofing proposal
Waterproofing is a high-liability trade: decennial guarantee mandatory, Veritas or Apave inspection common, specific insurance required. The buyer pays particular attention to: your knowledge of the waterproofing system suited to the substrate (concrete, metal deck, timber), compliance with DTU 43 series standards (DTU 43.1 concrete flat roofs, DTU 43.3 metal deck, DTU 43.4 timber), management of upstands, rainwater outlets, and detail points, and your manufacturer approval (Siplast, Soprema, IKO, Derbigum) that conditions the system guarantee.
Without manufacturer approval for the proposed system, your application will often be rejected — this is a frequent pass/fail criterion.
Recommended structure for a waterproofing proposal
A waterproofing technical proposal should cover:
Existing condition survey and strip-out
For refurbishment projects, describe your survey method: destructive probes, infrared thermography moisture detection, core samples to identify existing layers. Specify your strip-out protocol (partial or total) and waterproofing waste management (classification of asbestos-containing waste if pre-1997).
Proposed waterproofing system
Detail the complete build-up: vapour barrier, insulation (type, thickness, thermal resistance R), waterproofing membrane (single or double layer, bituminous or synthetic), heavy protection or self-protected. Justify each component against the applicable DTU and the CCTP's FIT classification (for flat roofs).
Detail points and junctions
Detail points (upstands, valleys, rainwater outlets, expansion joints, roof penetrations) are the source of 80% of waterproofing defects. Provide detail drawings for every junction identified in the CCTP. This is the most discriminating scoring criterion.
Guarantees and quality control
Specify: your decennial waterproofing insurance (certificate to be appended), the manufacturer system guarantee (10, 15 or 20 years depending on the build-up), waterproofing testing at handover (flood test, thermography), and your proposed maintenance contract.
Critical mistakes in waterproofing contracts
No manufacturer approval — Proposing a Soprema system without being Soprema-approved voids the manufacturer guarantee. The buyer knows this and will reject your bid.
Neglected detail points — A proposal that describes the field membrane without detailing upstands, valleys, and outlets will score very poorly.
Non-compliant thermal insulation — Failing to meet the thermal resistance R required by RE2020 or the CCTP is disqualifying.
No weather-dependent schedule — Waterproofing cannot be applied in rain. A schedule without weather constraints will be judged unrealistic.
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