Over many years, one of the recurring frustrations we see is how often clients are left with waterproofing “designs” that offer little more than broad narrative, lacking the detail a contractor needs in the trench. That gap between design intent and site execution is where risk, shortcuts and failures lurk.

Here’s what too many waterproofing reports get wrong, and how the industry standards expect better.

The problem? Words without usable drawings

Designers often bury generic descriptions, product data sheets, or typical details in 50 pages of narrative, leaving installers to hunt for critical information and frequently find it missing.

As a result, on site people must “fill in the blanks” by guesswork. How do membranes interface at service penetrations, around slab edges, beneath raised slabs, in internal box-outs, or at expansion joints? Which layer laps over which? What tolerances/movements are permitted?

That ambiguity leads to shortcuts, improvisation, and, ultimately, failure.

In contrast, a proper waterproofing design isn’t just a report. It must be followed by a project-specific package of drawings including but not limited to layout plans, cross-sections, and detail interfaces showing exactly how the waterproofing system, its ancillaries, and structure interrelate.

What the standards demand (and what’s being ignored)

BS 8102:2022

The revised standard reinforces that a waterproofing specialist should be part of the design team from the early stages. The scope is expanded: ingress from sources beyond groundwater (e.g. flood, surface water, through openings) must be considered.

It continues to define three protection types Type A (barrier), Type B (structurally integral), Type C (drained) and allows combinations thereof, subject to compatibility, to meet the project’s environmental grade.

The standard explicitly recognises that defects are inevitable. Repairability and maintainability must be built into the system from the outset. Importantly, BS 8102:2022 places greater emphasis on the construction phase and expects designers and contractors to maintain communication as changes occur.

Yet I often see “BS 8102-compliant” design reports that lack the very drawings and interface clarity that the standard presumes will exist.

NHBC Chapter 5.4 – “Waterproofing of basements and other below ground structures”

Chapter 5.4 is NHBC’s go-to when assessing waterproofing in warranty projects.

It sets out that waterproofing design must be rigorous and capable of preventing ingress from ground water and other sources, for all elements (walls, slabs, foundations).  The chapter emphasises provision of information. Design documents, drawings and specifications must be clear, coordinated, and communicated to all relevant parties (site teams, sub-contractors, suppliers).

NHBC also expects continuity of waterproofing across junctions (e.g. between DPC, DPM, tanking) and that details of penetrations, insulation, junctions, trench fill, service entries etc. are included in the design.

I’ve lost count of the times a client asked, “where in the design does it show the detail of the seal at the pipe penetration, or how the slab membrane laps to the wall membrane?” and the answer is, nowhere. That’s a major red flag under NHBC scrutiny.

PCA / Industry Guidance

The Property Care Association’s guidance and codes (especially for existing structures) call for full system design, specification of interfaces and risk assessment.

Best-practice publications (e.g. on Type C systems) emphasise that continuity, detailing and coordination of ancillary products are as critical as the membrane itself.

What good looks like (and what we at EPG demand)

When we accept a waterproofing design commission or take over a responsibility, our minimum requirements are:

• Full design drawings
• Plan showing waterproofing extents and transitions
• Sections and details showing all interfaces (membrane to structural elements, membranes to penetrations, to insulation, junctions and terminations either at DPC level or between alternate graded areas)
• Layouts showing drainage routing, sump, pumps, falls, access points
• If a dual or hybrid system is used, the sequencing and mechanical compatibility must be explicit
• Clear hierarchy of laps, overlaps, tolerances, movement joints

Maintainability / repair strategy

Where water might reach the void, how it will be collected and removed (particularly in Type C systems)

• How repairs or diagnostic measures would be carried out mid-life
• Coordination package
• Interfaces with structural, services, drainage, insulation designers
• Site reference levels, levels of fittings, site tolerances
• Design responsibility and warranty
• A named designer with accountability
• A design warranty (or retrospective assumption when called in)

If you’re a client or project lead, ask your waterproofing ‘designer’ if their deliverables include the above. If their answer is “we’ll leave that to the contractor,” you’re walking into risk.

Why these matter

Without proper drawings, contractors are forced to guess or improvise. That’s where weak spots go unnoticed until water finds them.

Defects in waterproofing are expensive, disruptive, and often hidden until long after handover.

Clients often assume the original designer holds responsibility; but too often they discover there is no one accountable, and then we (EPG) are asked to salvage design and liability post installation.

The industry must raise the bar. We should call out, not people but deficient practices. We need to flush out those who advertise themselves as “experts” or “specialists” but don’t deliver real, installable design.

If you’re in the waterproofing supply, contracting, or client side, demand clarity, demand drawings, demand accountability. Let’s quit tolerating “report-only” designs that leave the site to fend for itself.

Find out more about our structural waterproofing service HERE

Introduction

Imagine a proposal for a new infiltration test method that comprises filling a deep pit, of roughly estimated dimensions, with water, taking no account of wall collapse and spalling during the test, analysing the results without consideration of soil stratigraphy in the pit, is wasteful in resources such as water and gravel to fill pits and is a method considered dangerous. It would not be considered acceptable, so why does the drainage industry and Lead Local Flood Authorities continue to think that BRE 365 infiltration tests are an acceptable approach when much safer and reliable methods of infiltration tests are available? These other test methods are also especially suitable for infiltration via sustainable drainage systems?

Recent articles in AGS newsletters (AGS 2021 and 2024) have discussed the concerns of the AGS safety working group about the safety of general trial pitting methods and BRE 365 infiltration tests. In order to overcome the safety concerns tests are increasingly carried out using coarse gravel to fill the pit. This provides practical problems and also introduces concerns about the sustainability of waste gravel (in addition to the existing one of water use).

The current BRE 365 test method was first published in 1991 (BRE 1991) and the infiltration test method it describes has not changed since then (despite revisions to the document in 2003 and 2016). CIRIA Report 156 (CIRIA 1996) did propose some amendments to the test (for example it recommends that the depth of water should be comparable to that likely to occur in the infiltration system and also if soil conditions vary across a site the tests should be undertaken at 10m spacings) but this document is rarely referred to.

At the time BRE 365 was first published infiltration systems were essentially limited to soakaways that cover a small area and are relatively deep. They were also only normally used to drain small areas.

Properly designed SuDS require shallow infiltration devices dispersed around a site rather than a single large soakaway at the end of a piped drainage system. For these types of system the BRE 365 test is not suitable. Even for small single soakaways managing runoff from small roof catchments there are better ways than BRE365 to assess infiltration rates. There are often significant issues with the application of the test method and analysis of the results, as well as no assessment of surrounding ground conditions.

The industry should move from infiltration “testing” to infiltration “assessment”, because determining an infiltration rate is more than just pouring water into a hole. The ground model needs careful consideration and a full assessment using other test methods will give a better overall indication of the infiltration rate of the soil than a BRE 365 test on its own. In the ideal SuDS scenario many small tests in conjunction with good understanding of the ground model are better than a few large scale BRE tests used in isolation.

A further concern is the unnecessary and unreasonable requirement from some Lead Local Flood Authorities (LLFAs) for infiltration tests to be completed to demonstrate infiltration is not possible.

The BRE 365 test

The BRE365 test is not particularly accurate for a number of reasons (See Figure 1). There is also often scant regard paid to ground conditions when interpreting results. The dimensions of trial pits in practice are rarely, if ever, perfectly rectilinear and where gravel infill is used the porosity is often assumed rather than measured. However, such theoretical issues and the resulting variations in infiltration rate are not normally the cause of soakaway or infiltration system failure.

The most common cause of failure is that little, if any, attention has been paid to the overall ground model when designing an infiltration test programme and interpretating the results. Tests are often carried out by unqualified staff without any understanding of the ground model and there are often no robust soil descriptions provided.

Figure 1. Infiltration testing – theory and practice

The importance of the ground model is recognised in BRE 365 which requires “Examining site data to ensure that variations in soil conditions, areas of filled land, preferential underground seepage routes, variations in the level of groundwater, and any geotechnical and geological factors likely to affect the long-term percolation and stability of the area surrounding the soakaway”. Unfortunately, this aspect of the design and testing is often ignored.

The main causes of soakaway failures that are ground related (rather than poor construction or other non-ground related design issues) are all related to poor understanding of ground conditions, poor design of the testing or poor analysis of the test results as shown in Figure 2. One very serious issue that is all too common is the analysis of infiltration results in layered ground that follows the method in BRE 365. The BRE solution assumes that the infiltration out of the pit occurs evenly over the whole surface area. It is not appropriate where water only leaves the pit via a discrete stratum (figure 2a). This can underestimate the infiltration rate, leading to larger than necessary infiltration systems. However a more significant issue is where the permeable stratum is of limited extent and the ground is not suitable for soakaways, despite the test indicting it is (Figure 2b). In these cases the analysis method should be amended to take account of the strata in the test pit.

Excessive extrapolation of results where the water does not fully soak away over a working day is also an issue which generally leads to over estimation of infiltration rates (Figure 2c).

Figure 2. Issues with BRE 365 test results

There is a perception with infiltration testing that “more water and bigger pits” are better. The reason for this is the idea that soils around and below infiltration devices become saturated because of the large volumes of water entering the ground and that the bigger test takes account of the macro structure of the soil and rock and associated variations in permeability.

However, for infiltration SuDS features such as rain gardens, permeable pavements and infiltration basins there is a significant element of “interception” that occurs in the surface layers of the SuDS. This means that for the majority of rainfall events there will be no infiltration to the ground. Rainfall simply soaks into the surface layers and evaporates later.

Fully saturated conditions rarely occur in the soils around and below these types of infiltration systems. During infiltration events a field-saturated condition develops (which is not full saturation – ASTM 2016). True saturation does not occur due to entrapped air which prevents water from moving in air-filled pores. This may reduce the hydraulic conductivity in the field by as much as a factor of two compared to conditions when trapped air is not present (ASTM 2016). Field test methods should simulate the field saturated condition.

Macro structure will normally only be relevant in strata such as rock or fissured clay (and clay will not be suitable for infiltration.). The influence of macro structure or variations in permeability can be allowed for by using a greater number of smaller tests and, more importantly, by robust assessment of the ground conditions by qualified geotechnical engineers or geologists.

Good soil and rock descriptions to BS 5930: 2015 + A1: 2020 (which incorporates descriptions to BS EN ISO 14688 and 14689) are a vital part of infiltration testing. They can be used in two ways.

The first is that initial permeability assessments can be made by designers based on the soil descriptions and published permeability values.

The second is that they are required to allow designers to undertake a sense check on infiltration results, understand whether the normal analysis of the results needs to be amended (eg if all the water lost in the test has gone into a base layer of rock and all the walls are clay) and to provide information for the wider ground model.

Another important consideration is the cut and fill profile of a site. This can result in ground levels increasing or decreasing from those at the time of any site investigations. This needs to be considered when assessing the locations for infiltration tests and the design of infiltration systems.

Water companies

Water and Sewerage Companies (WaSC) are now able to adopt some SuDS including some types of infiltration system. Training to WaSC delivered by Water UK has emphasised the importance of the conceptual ground model for infiltration design and the fact that infiltration assessment is more than infiltration tests. The training also recommended that WaSC require the following to be supplied with any infiltration design:

• Reasonable assessment of geology and infiltration capacity of each stratum by a qualified geotechnical or geology professional;
• Advice from qualified geotechnical or geology professional on suitable depths and infiltration rates (with the stratum to which the rates apply identified);
• Review of final infiltration design by geotechnical or geology professional to make sure it meets the advice provided in the site investigation report; and
• Completed infiltration Checklist – SuDS Manual, Table B.6.

It also advised that there are acceptable alternatives to the BRE 365 infiltration tests such as permeability tests in boreholes.

Alternatives test and assessment methods

Is it time to reassess the use of BRE 365 and allow alternative methods of infiltration testing combined with wider assessment of the ground model? Other infiltration test methods are used successfully in other countries and there is no reason why those cannot be used in the UK. A larger number of alternative tests combined with an assessment of the overall ground model and other data will provide a much better indication of infiltration rates than a limited number of BRE tests.

The SuDS manual includes falling head tests to ISO 22282-2:2012 (completed and analysed as a test in the unsaturated zone) as an acceptable alternative to BRE365 tests. In practice they provide a reasonable alternative to testing in trial pits, providing the results are assessed in the context of the wider ground model by an experience ground engineering professional.

The borehole tests in the unsaturated zone require the ground to be pre saturated before the test, which is similar to the “test three times” approach in BBRE 365.

The AGS article in 2021 suggests that use of boreholes as a device for obtaining infiltration data is a natural ambition for AGS members seeking compliance with standards and health and safety. There is no reason why simpler and safer methods using boreholes, permeameters and ring infiltrometers cannot be used. Indeed, the design of site investigations must comply with the Construction (Design and Management) Regulations 2015. A fundamental principle of the regulations is that of elimination of hazards where possible using less hazardous alternatives. Given that there are acceptable and safer methods of infiltration testing than BRE tests then a site investigation designer is legally obliged to use the alternatives. This should be recognised by LLFAs and Water Companies.

Boreholes tests have been used successfully to assess infiltration rates for retrofit SuDS in streets where BRE tests are not practical.

For permeable paving and infiltration basins the head of water in the infiltration test should be kept low and therefore the use of the alternative methods is more suitable and reliable, which will removes the hazards associated with infiltration tests in deep trial pits.

Existing standards that may be used as guidance are:

• BS EN ISO 22282-5:2012 Geotechnical investigation and testing – Geohydraulic testing – Part 5: Infiltrometer tests), which describes various types of ring infiltrometer test; single or double ring, open and closed. These are used in other countries to assess infiltration from shallow SuDS features such as infiltration basins, permeable pavements and rain gardens (see below). They are generally suitable for testing at shallow depths and would need to be undertaken at the base of a stable and safe pit.
• ISO 22282-2:2012 Geotechnical investigation and testing – Geohydraulic testing – Part 2: Water permeability tests in a borehole using open systems. The ground around the well should be pre saturated and the results analysed as a test in the unsaturated zone. These can be undertaken to any reasonably expected depth for an infiltration device
• ASTM D5126-16 Standard guide for comparison of field methods for determining hydraulic conductivity in vadose zone. Permeameters can be used in boreholes with the common diameters typical of UK site investigations and some are available that can test at depths that can be reasonably expected for infiltration devices.

A summary of examples of infiltration testing used in various countries is provided in Table 1. It is of particular interest that the Scottish Building Standards already allow the use of constant head permeameter tests. There is no justifiable reason why this cannot also apply in the rest of the UK.

In summary all other countries determine infiltration rates using borehole, permeameter or infiltrometer tests.

When should infiltration testing be used?

A further issue is the unreasonable and unnecessary requirement from many LLFAs for infiltration tests to be completed to show that a site is not suitable for infiltration. On many sites it is often not necessary to fill a trial pit with water and sit watching it go nowhere for eight hours, just to show infiltration is not possible. A robust desk based assessment of the geology and ground conditions by a suitably qualified ground engineering professional can often be sufficient to show that infiltration is not viable. At the site investigation stage if the ground below the site is shown to comprise low permeability strata such as clay there should be no need for tests to show infiltration is not viable.

From a health and safety perspective not requiring infiltration tests in the first place, where they are not necessary is a good step forward (and follows the accepted CDM hierarchy that the first option to be chosen should be to eliminate the hazard by design if possible).

However, the consultant involved should provide a site specific, robust and well reasoned argument why infiltration is not possible. Examples of situation where this may apply are:

• Some (not all) sites where ground contamination is present. An example could be where residual hydrocarbon contamination is present that could be mobilised by infiltration drainage. Another example is where a development is located over old landfill material.
• Sites underlain by a significant thickness of clay that does not include more permeable layers (eg Lias Clay in some parts of Northamptonshire).

Permeametre tests

Constant or falling head permeameter tests can be undertaken over the same depths that BRE365 tests are normally completed. The tests are completed in boreholes which can be drilled by hand or power auger, windowless samplers, cable percussion, etc. More than one test at different depths may be necessary in layered soils (Gill et al 2023).

The test requires significantly less water than a BRE test and is more practical.

Various permeameters are available. The Guelph permeameter and similar instruments maintain a constant head of water above the bottom of the hole and rate of water flow into the soil is recorded at short intervals until it reaches a steady state. The field saturated hydraulic conductivity (K_fs) of the soil can then be calculated (Amoozegar 2020). Falling head instruments repeat falling head tests over a short length until a steady state is reached.

A photo of a permeameter is provided in Figure 3. Advantages of using permeameters are:

• The test equipment is relatively lightweight / easy to set up;
• Small volumes of water are required for each test; and
• Tests can be undertaken during drilling or windowless sampling or can undertaken separately from the main site investigation in auger holes, depending on required depth.

Figure 3. Permeameter (EPG Ltd)

A study by Bockhorn et al (2014) compared the infiltration rates obtained using a double ring infiltrometer, a Guelph permeameter and a trial pit test. Details of the tests are shown in Figure 4. All the tests were in Glacial Till comprising clay.

Figure 4. Comparison of saturated hydraulic conductivity from various tests (redrawn after Bockhorn et al 2014)

The trial pit tests were not repeated three times as per BRE 365. The pits were filled with water until a steady state outflow was attained and the infiltration recorded. The time to achieve this is not stated. The infiltrometer gave the lowest results followed by the Guelph permeameter and the highest results were from the infiltration pit. Two of the permeameter tests gave no infiltration at all which may have been due to compaction of the soils by machinery or just inherent variations in the Till across the site.

The possible reasons for the trends observed were considered to be smearing on the sides of the hole, compaction of the soils close to the surface and the fact that the pit would include infiltration via fissures in the clay and variations in soil grading.

However, it was also considered that the pit had not fully saturated the ground around it whereas the infiltrometer and permeameter tests had. It is known that typically in a BRE 365 tests the infiltration rate reduces from initial to third repeat of the test, typically by one order of magnitude. This would make the pit test results comparable to the Guelph permeameter results.

The infiltration rate of soils can show spatial variability due to the inherent heterogeneity. However this can be managed by using a suitable number of tests. The authors concluded that use of infiltrometer or permeameter tests alone would not provide a reliable indicator of infiltration rates. They concluded that data from pits gave more representative results but that the pits are highly invasive. However probably the most significant reason for the variations that was not discussed is the limited number of pits (four) in one area of the site compared to the number of permeameter and infiltrometer tests (19 and 18 respectively spread over a much wider area of the site).

The authors concluded that the most appropriate infiltration test method was to use the tests in conjunction with borehole soil descriptions and geological assessment of the ground. This requirement already applies to BRE365 tests (but is often not followed). Given the small difference between the permeameter tests and the pit tests and also accounting for saturation, it is considered that the results show that a larger number of permeameter tests and a robust assessment of ground conditions by a ground engineering professional is a reasonable alternative to BRE 365 tests. In any event, as discussed earlier, even BRE tests should be accompanied by a robust assessment of ground conditions.

The Irish Environmental Protection Agency (EPA – Government of Ireland, 2023) has conducted research on alternatives to percolation tests for waste water infiltration systems. The research included a comprehensive literature review of soil

permeability testing and design standards for onsite waste water treatment systems. The study involved assessment of a database of falling head tests in pits (over 900 tests), modelling and field tests to compare the different methods at 17 sites. In summary it was conclude that falling head infiltration tests in pits (a version of the BRE365 test, but in smaller pits) is not an ideal method and should be replaced. Constant head tests using permeameters are considered more reliable and practicable. It also emphasised that international guidance indicates that insitu permeability tests should only be used as a complement to detailed site assessments. Permeability test results should not be the main factor in assessing suitability for infiltration and there is a need for the results of the tests to be placed in the context of an accompanying assessment of the soil texture and structure.

Conclusion

The BRE 365 infiltration test has significant health and safety, practicality and sustainability issues. There are suitable alternative methods that are used by some in the UK and that are also widely used in other countries. Large scale pit infiltration tests are rarely, if ever, used in other countries to determine infiltration rates for SuDS.

The key to successful infiltration testing and design is to include a suitably qualified ground engineering professional in the SuDS design team to advise on the appropriate test methods and to interpret the results. They should also review the final design with reference to the site ground model.

The way forward to support a sustainable agenda, reduce waste of valuable natural resources and improve health and safety is to:

• Promote wider use of understanding ground models at the initial design stage and not to preferentially rely on limited study and a small data set of BRE365 infiltration tests.
• Avoid doing infiltration tests where the desk study information and preliminary assessment shows it is not viable (from a CDM perspective design out the hazard, which should be the priority);
• Use borehole, permeameter or infiltrometer tests as appropriate, if possible (design out the hazard from the testing).
• Even for larger systems consider the use of a greater number of borehole tests rather than limited BRE tests. Consider the benefits of a good geological characterisation and what benefits could be gained from having high quality data rather than the adoption of worst-case values because of limited data.
• Only use BRE tests when absolutely necessary and infill the pit with gravel to remove the hazard. Use data loggers for water level recording.

Furthermore, the analysis of infiltration test results should not blindly follow the assessment in BRE 365. If layered soils are present where water preferentially infiltrates into one layer this should be allowed for and stated. Infiltration test results should state which stratum they are applicable to. The tests should also be related to an ordnance datum level so that designers can take account of changes in ground level due to cut and fill.

Introduction

BS 8102:2022 identifies three types of structural waterproofing: Type A (barrier or membrane protection), Type B (structurally integral systems, typically using watertight concrete), and Type C (internal cavity drainage systems). For basements requiring a Grade 3 (habitable) environment, two lines of defence are typically specified, usually a combination of Type A and B, or Type B and C, where the choice is between Type A or C for the secondary system. There has been a marked industry shift toward Type C systems in basement construction in recent years. While Type C solutions are effective when correctly designed, installed, and maintained, this growing preference appears driven more by construction convenience than long-term client benefit. The challenge is balancing what works best for the program and buildability with what serves the structure best over its lifetime.

The Appeal of Type C for Contractors

Contractors increasingly favour Type C systems for their flexibility and sequencing advantages. These systems can be installed after the structural shell is complete, which reduces coordination issues during the early build stages. They require minimal substrate preparation, which helps streamline the program, and are more tolerant of minor installation defects that typically do not lead to water ingress, unlike Type A systems, where such defects can be critical.
Furthermore, Type C systems are not reliant on dry weather conditions. As the structural shell is typically complete before installation begins, the work is usually carried out under cover. This makes Type C particularly appealing from a programming perspective, helping to avoid delays and ensuring progress can continue during the winter months.

Why Type A Is Often Better for the Client

Despite its installation demands, Type A waterproofing is a robust and often more appropriate solution from a long-term performance perspective.

Firstly, Type A systems protect the reinforcement in concrete by preventing water ingress, enhancing the durability of the structure. They also act as a barrier to contaminants and harmful ground gases such as radon, carbon dioxide and methane.

Unlike Type C systems, which rely on pumps requiring replacement every 10 years and annual maintenance to prevent blockage from free lime deposits, Type A systems are passive once installed and correctly detailed. While Type C is often the most cost-effective option during construction, the long-term maintenance cost is rarely considered. Over a typical 50-year design life, maintenance costs can run into tens of thousands of pounds.

Furthermore, Type C systems require the client to obtain annual discharge licenses for water pumped from the system. This adds an administrative burden and ongoing costs typically not factored into the initial construction budget.

Type C systems can be impractical for large developments with complex foundation details. Details such as intermediate slabs on two storey basements, column penetrations, or slip-formed lift cores adjacent to retaining walls (common in cut-and-carve projects) can compromise the continuity and effectiveness of internal drainage membranes.

Other limitations include achieving the required 150mm termination above external ground level. Since the ground floor slab typically sits below this level, this is normally achieved with additional external membrane work. Type C systems also rely on sufficient water to direct water toward sumps and outlets; however, in many cases, the system experiences minimal water ingress, which can lead to stagnant water over the building’s lifetime.

Finally, some waterproofing contractors will only install the cavity membrane once the basement is demonstrably dry, meaning that the Type C system is either underused or not engaged at all during most of the building’s life. This raises questions about its long-term value and appropriateness for certain applications.

The Practical Challenges of Type A

Type A systems require careful planning and execution. Installers must be on-site at various stages of the build, usually to install beneath the slab, behind retaining walls, and at termination details. These visits may be broken down into multiple sub-visits, depending on the complexity of the detailing.

Type A systems are less forgiving, as minor errors in detailing or workmanship can lead to water ingress. In high-risk areas, such as the underside of capping beams, construction joints, or termination details, membrane defects can coincide with structural issues like honeycombing, cracks, or voids, resulting in water penetration. Additionally, when the membrane is installed below the slab, contractors must take care to avoid damage from reinforcement. The substrate can also be difficult to work over, as it can become slippery when wet.

Type A membranes also require skilled labour, either approved contractors or installers trained by the product manufacturer. The installation requires more time, greater attention to detail, and suitable weather conditions. These factors are challenging to overcome on live construction sites, which is why some contractors avoid them.

However, these are not reasons to disregard Type A systems. Instead, they highlight the need for proper planning and site preparation, challenges that are manageable through good construction practices, as BS 8102:2022 suggests.

Striking a Balance

While buildability is a crucial factor in design development, it should not come at the expense of quality and suitability. Designers and clients should be more assertive in resisting convenience-led design decisions that may not serve the project in the long term.

Independent waterproofing specialists should be engaged from the design stage to ensure that solutions are appropriate for the structure and end user, not just for site convenience. When the waterproofing design is supplier or installer-led and provided as a complimentary service, there is a risk that design decisions may be influenced by commercial reasons. This can lead to designs that technically comply with BS 8102:2022 but aren’t necessarily the best option for the client.

Contractors may favour short-term program efficiency, but a more holistic approach considering design-life should be encouraged. Proper training and planning make Type A systems the most robust solution. In most cases, failures in Type A waterproofing are not due to flaws in the system itself, but in the quality of execution.

Conclusion

Type A waterproofing should not be dismissed solely because of installation complexity. Design decisions must be based on what is best for the structure over its lifespan, not just on construction convenience or build cost.

As independent waterproofing designers, we advocate for technical solutions that serve the long-term performance of the structure, not just the short-term needs of the contractor’s program. Type A may be more demanding to install, but it delivers better long-term value and protection for the client when executed correctly.