Delta AT 800 is a Type C drained protection membrane that Delta says can provide below-ground waterproofing and protection against methane, carbon dioxide and radon. Delta cites BS 8102:2022 for waterproofing and BS 8485:2015+A1:2019, Table 7, for gas protection. That combined product description does not remove the need for a site investigation, a project-specific design, carefully detailed interfaces, controlled installation and independent verification. Water ingress and ground-gas risk remain separate design objectives, even when one membrane is used in the system.
What Delta AT 800 is designed to do
Delta AT 800 is identified by Delta Membrane Systems Limited as a Type C drainage membrane. In a Type C arrangement, water that reaches the internal face of the below-ground construction is managed by a drained cavity and directed to a suitable drainage or pumping arrangement. The membrane is therefore part of a maintainable water-management system rather than a stand-alone claim that a basement can never get wet.
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Delta also presents AT 800 as protection against methane, carbon dioxide and radon. Its product information references BS 8102:2022 for below-ground waterproofing and BS 8485:2015+A1:2019, Table 7, for gas protection. Those references indicate the standards and design framework Delta associates with the product; they are not a project certificate. The designer still has to establish the site’s gas regime, water conditions, building use and acceptable risk, then specify the complete build-up.
A useful way to describe the system is “combination waterproofing and ground-gas protection”: one membrane contributes to both objectives, while drainage, joints, penetrations, ventilation and verification make the design work in practice.
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Why waterproofing and ground-gas protection must be assessed separately
Water and gas can enter through many of the same weaknesses, but they behave differently and are controlled by different acceptance criteria. A membrane may resist gas diffusion while still requiring a cavity drain to manage liquid water. Conversely, a waterproofing detail that appears watertight may contain a discontinuity, unsealed service penetration or poorly welded joint that compromises gas protection.
- Waterproofing objective: classify the required internal environment and control liquid water, dampness, condensation and drainage performance in accordance with the project’s interpretation of BS 8102:2022.
- Gas objective: identify the gases present, assess their characteristic situation and provide the barriers, joints, ventilation and monitoring needed for the building type under the applicable gas-protection design approach.
- Durability objective: ensure that materials, drainage components, access points and maintainable pumps remain suitable for the intended life and future use of the structure.
Delta’s September 2024 Technical Guidance Note 002 describes selection by the site’s characteristic gas assessment and the building type. It advises using a conceptual site model and/or gas-monitoring data to establish a characteristic score from CS1 (very low) through CS6 (very high). The score is an input to design, not a label that can be assigned from the product name alone.
How to decide whether a combined system is suitable
1. Establish the site gas situation
Start with the environmental and geotechnical information: historic land use, made ground, landfill or fill, hydrocarbons, mine workings and other potential gas sources. The project’s competent assessor should develop a conceptual site model and obtain monitoring data where required. Delta’s guidance uses the resulting characteristic gas situation (CS1–CS6) to inform the protective measures.
2. Define the building and its consequence of failure
Building type matters because a dwelling, occupied basement, plant room, storage area and sensitive commercial space do not have identical tolerances for gas entry or water damage. Occupancy, ventilation, access for inspection, future maintenance and the consequences of an unavailable pump should be recorded before selecting the system.
3. Set the waterproofing strategy
Decide whether a drained Type C strategy is appropriate, whether another waterproofing type is needed, and how water will be removed during a power failure or pump fault. The drainage channel, sump, pump duty, alarms, backup power and maintenance access are design items, not optional accessories.
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4. Resolve every interface
Before installation, detail wall-to-floor junctions, construction joints, movement joints, columns, steps, service penetrations, drainage channels and ventilation routes. Delta’s published drawing index includes arrangements for these conditions. The relevant drawing for a project must be selected and adapted by the design team; a generic membrane layout cannot replace interface design.
5. Agree verification and acceptance criteria
Specify who will verify the gas-protection measures, when inspections occur, what installation records are required and how membrane integrity will be tested. Delta’s guidance calls for independent third-party verification, monitoring of installation and integrity testing. Include these activities in the programme before the membrane is covered.
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Delta AT 800: manufacturer-published data
The following figures are Delta’s current product-page data (accessed in 2026). They describe the product under the stated test methods and conditions; they are not independent comparative test results or a guarantee for a particular project.
| Item | Published information | How to use it in a specification |
|---|---|---|
| Product and code | Delta AT 800, DMS 026 | Identify the exact membrane and revision of its data sheet in the project specification. |
| Roll dimensions | 20 m × 2.0 m | Use for take-off and joint planning; allow for laps, detailing and waste rather than dividing floor area by roll area alone. |
| Methane permeability | Less than 31 ml/m²/day/atm, tested under EN ISO 15105-1 | Check that the test method, pressure basis, joints and project acceptance criteria are applicable to the designed assembly. |
| Durability statement | 100 years in natural soil where pH is 4–9 and soil temperature is no more than 25°C | Treat this as Delta’s condition-dependent manufacturer claim, not a general warranty or independently established service life. |
| Pressure resistance | Approximately 650 kPa under EN ISO 25619-2 | Compare the stated test result with the project’s temporary and permanent loads, substrate and protection layers. |
Do not transfer any of these numbers to a different membrane, joint detail or installed assembly without checking the relevant technical documentation. In particular, a sheet result does not automatically describe a welded lap, a penetration, a corner or a repaired area.
Details that determine whether the system remains continuous
Wall and floor transitions
The wall-to-floor junction is a common route for both water and gas if the cavity, seals and drainage channel are interrupted. Set out the membrane, channel and any ancillary waterbars or sealants so that the transition is continuous and remains inspectable where the design requires it.
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Service penetrations
Pipes, ducts, cables and sleeves need proprietary or project-designed seals compatible with the membrane. A hole cut on site and filled with a general-purpose sealant should not be treated as an engineered gas detail. Record each penetration and inspect it before concealment.
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Columns, pilasters, upstands, ramps and movement joints create folds, changes of direction and potential stress points. Use the project drawings and installation instructions to maintain the drainage path and gas barrier around each obstruction.
Drainage and ventilation
A Type C membrane relies on a functioning drainage route. Channels must discharge to a sump or other designed outlet, while pumps, alarms, access covers and backup arrangements must match the building’s maintenance plan. Where the gas assessment requires ventilation, show the ventilation path, terminals and protection from blockage on the coordinated design; do not assume that a drainage cavity is automatically a gas-ventilation system.
Installation, monitoring and verification workflow
- Freeze the design information. Issue the gas assessment, waterproofing strategy, coordinated drawings, membrane data sheet, joint details, drainage layout and inspection-and-test plan to the installer.
- Check the substrate and sequence. Confirm that surfaces are suitable, clean and free from projections that could damage the membrane. Coordinate concrete pours, curing, temporary works and access so the membrane is not installed into an unsuitable or contaminated area.
- Brief trained installers. Delta’s guidance says installers should be trained and work to the product installation instructions and data sheets. Keep training records and identify who is authorised to make joints and repairs.
- Install the membrane and drainage components. Follow the specified orientation, laps, fixings, corner treatments, channels and terminations. Protect the membrane from site traffic and later trades.
- Seal and record interfaces. Inspect wall/floor transitions, penetrations, columns, joints, channels and any repair. Photograph and log each critical detail before it is covered.
- Monitor installation independently. Arrange the independent third-party verifier’s visits at the stages defined in the inspection plan, not only at practical completion.
- Carry out integrity testing. Test the installed gas-protection elements using the agreed method and acceptance criteria. Resolve defects, retest repairs and retain the records in the handover file.
- Commission drainage and maintenance. Test pumps, alarms, sumps, discharge routes and access. Give the building operator inspection intervals, cleaning requirements, spare-parts information and emergency procedures.
AT 800 compared with a bonded Type A barrier
Delta also describes MemTech Pro Titan Bond (product code DMS 437) as a pre-applied bonded Type A barrier membrane. That is a different design role from AT 800’s Type C drained protection. The choice should follow the site investigation and the project’s waterproofing and gas strategy, not a headline permeability number.
| Design consideration | Delta AT 800 | MemTech Pro Titan Bond |
|---|---|---|
| System role | Type C drained protection membrane | Pre-applied bonded Type A barrier membrane |
| Product code | DMS 026 | DMS 437 |
| Published methane result | Less than 31 ml/m²/day/atm under EN ISO 15105-1 | 0.13 ml/m²/day/atm; welded-joint result 1.00 ml/m²/day/atm |
| Drainage dependency | Designed as part of a drained cavity system, so drainage, pumping and maintenance must be engineered | Bonded barrier role; project drainage and other waterproofing provisions still depend on the complete design |
| Selection questions | Can the project provide reliable drainage, access and maintenance, and can all interfaces be detailed? | Can the substrate, pre-application sequence, bond and construction joints be controlled for the project? |
The two methane figures must not be read as a league table. Delta publishes them for different products, and those published results do not establish that the test assemblies, joint configurations, exposure conditions or acceptance criteria are identical. Ask the designer and verifier to compare the applicable test evidence for the actual system being specified.
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What the documented project example shows—and what it does not
In a Delta case study, hydrocarbons were identified during site investigations. The reported sequence used Koster NB 1 as primary waterproofing, followed by three coats of spray-applied Pro Liquid Gas Barrier. A third party verified the work against the project’s BS 8485 characteristic-score requirements; Delta AT 800 was then incorporated, with joints double sealed. The case study reports that the system passed verification in accordance with CIRIA 735.
This is a manufacturer-reported example of one site’s sequence and risk profile. It demonstrates the importance of investigation, layered protection, third-party checking and joint detailing; it does not establish that the same products or order of work are suitable for every site.
Common specification and site mistakes
- Treating “combination” as a complete design. Correct it by documenting the gas score, building type, water strategy, drainage and verification plan.
- Using a generic CS rating. Obtain the project’s conceptual site model and monitoring information; do not infer the rating from neighbouring sites or from the membrane selected.
- Ignoring the drainage burden of Type C. Provide pumps, alarms, backup arrangements, access and a maintenance schedule, then test them before handover.
- Leaving penetrations until after membrane installation. Coordinate sleeves and service routes early, and use approved details for every penetration.
- Comparing isolated permeability numbers. Check method, units, pressure, specimen, joints, standard edition and project acceptance criteria before drawing conclusions.
- Covering work before inspection. Schedule independent monitoring and integrity testing while details remain visible; repair and retest defects rather than relying on photographic evidence alone.
- Assuming durability is unconditional. Delta’s 100-year statement is limited to natural soil with pH 4–9 and temperature up to 25°C. Confirm that the project environment falls within those conditions or obtain suitable design advice.
Support, documentation and handover
Delta says it has technical consultants and a nationwide network of registered installers. Their involvement can help with product-specific detailing and workmanship, but the project designer remains responsible for the overall design and the verifier remains responsible for independent checking. Request the current product data sheet, installation instructions, drawings, training evidence, inspection records, integrity-test results and maintenance information for the exact product and revision used.
Delta’s Technical Guidance Note 002 describes itself as a quick guide and directs specifiers to the full current standards and related guidance for complete design, specification, installation, verification and monitoring. For a live project, consult the current editions of those standards, the site investigation team, the waterproofing designer and the independent verifier before procurement or construction.
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