Knowledge
The design responsibility matrix: where waterproofing falls through the cracks
The architect assumes the engineer owns it, the engineer assumes the supplier. The waterproofing has no owner, and that is the defect.
For architects
Waterproofing guidance for architects.
Taking waterproofing design responsibility beyond your competence is a career risk. Here is what BS 8102:2022 actually asks of you, how to settle the grade question defensibly, and how to make sure the design has an owner who isn't you.
On most commercial basements, the waterproofing failure is designed in long before anyone reaches site - and the drawings it is designed into are usually the architect's. BS 8102:2022 does not make the architect the waterproofing designer. It expects a waterproofing specialist on the design team from the earliest stage. The exposure arises when no such specialist exists: the waterproofing gets assembled from supplier literature, drawn up under your signature, and the design responsibility quietly becomes yours.
Your job is not to become a waterproofing designer. It is to recognise where your competence ends, insist the role is filled by someone independent, and hold the record that shows you did. The guidance below is the reasoning we use on live schemes - free to use, with or without us.
BS 8102:2022
What grade does each space need?
The grade is a decision about the space's intended use, not the basement's depth and not the contractor's preferred system. It is the first waterproofing decision on your drawings, and it governs everything downstream.
G1A
Car parks, plant rooms, storage
Some seepage tolerated.
Read in depth
G1B
Ventilated storage; non-critical plant
No water penetration; damp tolerated.
Read in depth
G2
Workshops, back-of-house
No water penetration; some damp.
Read in depth
G3
Habitable, offices, retail, archives
Dry environment, controlled humidity.
Read in depth
The scope gap
Where do architects get exposed?
The same pattern produces most commercial basement defects: everyone on the design team assumes someone else owns the waterproofing. These four articles map the exposure and how to close it.
Knowledge
What is a waterproofing scope gap?
The absence of independent design responsibility, where most commercial basement defects originate.
Knowledge
Risks of placing waterproofing in the structural engineer's scope
When SE-led waterproofing design creates a scope gap rather than closing one.
Knowledge
Is basement waterproofing the structural engineer's job?
Where the structural engineer's responsibility genuinely sits on a basement, and where the waterproofing specialist's begins.
Responsibility
Who should design it, and when?
The short answer: an independent waterproofing design specialist, appointed at RIBA Stage 2, holding the waterproofing scope in writing. The longer answers, with the reasoning:
Waterproofing Wisdom Agent
Settle the grade question on your own scheme - today.
Pathway · Grade assessment
Get a grade-by-space read under BS 8102:2022.
Describe the scheme or upload the basement plans. The agent works through Table 2 space by space and lands on a defensible recommendation with the reasoning your design team can sign off.
Run a grade assessmentPathway · GA review
Have your GAs read for waterproofing risk.
Upload basement and ground-floor general arrangement drawings. The agent flags the junction concerns and detailing assumptions BS 8102 expects resolved by Stage 4 - before they reach tender.
Review your GAsFree to use · Built by CLW and grounded in BS 8102:2022
CPD
Bring the reasoning to your whole team.
We run a free 45-minute CPD on basement waterproofing risk for design teams, in-house. Real failure case studies, not slides about products - BS 8102:2022 in practice, including where design responsibility actually sits.
Request a CPD sessionWorked with architects on
Schemes where the waterproofing had an owner.
FAQ
What architects ask us.
Direct answers on responsibility, grades, supplier details and appointment timing.
Is the architect responsible for basement waterproofing design?
Not by default - but on many projects the responsibility lands there anyway, because nobody else has been given it. BS 8102:2022 expects a waterproofing specialist to be part of the design team from the earliest stage. Where no specialist is appointed, the waterproofing "design" is often assembled from supplier literature under the architect's signature, which places design responsibility with the architect without the specialist competence to discharge it. The defensible position is to recognise the limit of competence and ensure the role is properly filled. How responsibility falls through the cracks →
What grade of waterproofing does each basement space need?
The grade is a decision about the intended use of each space, made against Table 2 of BS 8102:2022 - not about the basement's depth or the contractor's preferred system. Habitable and office space needs Grade 3; plant and car parking can often accept Grade 1A or 1B; the grade drives everything downstream, including cost. The four grades, explained →
Can I rely on a waterproofing manufacturer's standard details?
Treat them as product information, not design. Supplier details and warranties routinely disclaim design liability, so specifying them does not transfer the design risk anywhere - it stays with whoever signed the drawings. An independent design, recorded against BS 8102:2022, is what closes that exposure. Supplier warranties vs independent design →
When should a waterproofing specialist join the design team?
RIBA Stage 2, when the waterproofing strategy can still shape the structural approach and the cost plan. By Stage 4 the key Type A/B/C decisions are often locked in, sometimes against best practice, and the specialist's role shifts from prevention to triage. When to appoint →
Got a basement on your drawings?
Tell us the stage you are at. We will tell you what a defensible waterproofing position looks like for your project - and take the design responsibility off your plate if that is what it needs.