SIG Hydrostop AH25+

Part of SIG Hydrostop AH15+

Manufacturer: AccuRoof 

Materials: Polyurethane 

The Hydrostop AH25+ Roof Waterproofing System is a modified polyurethane liquid-applied roof waterproofing
system which comprises:

  • Hydrostop AH25+ Waterproof Coating — a single-part, moisture-triggered, modified polyurethane waterproof coating, mid-grey in colour
  • Hydrostop AH25+ Premium Reinforcing Fabric — a 165 g∙m–2 non-woven polyester fabric reinforcement
  • Hydrostop AH+ Blocker Primer — for the preparation of bitumen membranes and asphalt prior to the application of the system
  • Hydrostop AH+ WP Primer — for the preparation of timber substrates prior to the application of the system
  • SIG Approved Carrier Membrane — a heat-activated, polyester-reinforced, SBS modified bitumen membrane for use as a carrier membrane over insulation boards
  • Hydrostop AH+ Standard Quartz Sand — anti-skid additive with a granule size of 0.4 to 0.8mm for use in areas of pedestrian traffic
  • Hydrostop AH+ Transparent — used to seal the Hydrostop AH+ standard Quartz.

The coating has the following nominal characteristics:
Specific gravity (g·cm-3) 1.44
Colour mid grey.

BBA logo

Number: 19/5705 PS1 Issue 2
Issue date: 27/02/2024

Approved for use on

Flat Roofs Pitched Roofs 

For use as a roof waterproofing system on new and existing flat and pitched roofs with limited pedestrian access.

The system, when used in combination with Hydrostop AH+ Standard Quartz Sand, is satisfactory for use on flat roofs with limited pedestrian access.


Concrete Insulation Boards Mastic Asphalt Metal Reinforced Bituminous Membranes Timber 

The system is for use on the following substrates:

  • concrete
  • mastic asphalt
  • metal
  • reinforced bitumen membranes (including mineral surfaced)
  • wood
  • SIG-approved glass faced insulation boards
  • insulation boards in conjunction with an approved carrier membrane


25 Years 

The system will achieve an initial life expectancy of at least 25 years.

Installation Requirements

The system should only be installed by contractors who have been trained and approved by the Certificate holder.

Fire Safety

In the opinion of the BBA, a system comprising an 18 mm plywood substrate primed with SA bitumen primer, bituminous self-adhesive VCL layer, a polyurethane adhesive, 120 mm thickpolyisocyanurate insulation board, bituminous self-adhesive carrier membrane primed with Hydrostop AH+ Primer, and the Hydrostop AH25+ Roof Waterproofing System with Hydrostop AH25+ Premium Reinforcing Fabric, can be classified as BROOF(t4) in accordance with BS EN 13501-5 : 2016.

The designation of other specifications should be confirmed by reference to the requirements of the documents supporting the national Building Regulations.

Certified Products

The following products are also covered by the same certification:

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Unit 31F, Gelders Hall Road
LE12 9NH

T : 01509 505714

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