XOL PI — Architects
Architects excess-of-loss PI in the UK — a 2026 explainer
Excess-of-loss (XOL) professional indemnity sits above your primary layer and responds when a single claim, or the aggregate for the policy year, exhausts what the primary insurer will pay. For architects operating post Building Safety Act 2022, the case for understanding how excess layers behave is stronger than it has been in a decade.
What an excess-of-loss layer actually is
A professional indemnity programme for an architect’s practice has two possible shapes. The simpler is a single policy with one insurer for the whole limit — for example £2m any one claim and in the aggregate. The alternative, and the subject of this page, is a layered programme: a primary policy up to a stated limit, then one or more excess layers that sit above it. Each layer is a separate contract with its own wording, its own premium and (usually) its own insurer.
An excess-of-loss layer, sometimes shortened to XOL or written “£X m xs £Y m”, agrees to pay claims once the layer beneath has been exhausted or is treated as being exhausted under a “drop-down” provision. It does not respond independently to a claim that sits entirely within the primary. Because of this, the premium for each successive layer is normally cheaper than the layer beneath — the insurer is buying a lower probability of loss.
When architects hit the ceiling of a primary layer
There are four recurring patterns in which a primary PI programme designed for a mid-size architects’ practice can be tested to its limits:
- Building Safety Act 2022, section 135. Section 135 of the Building Safety Act 2022 amended section 1 of the Defective Premises Act 1972 to extend the limitation period for claims relating to dwellings to 30 years retrospectively and 15 years prospectively. Historic residential work an architect signed off in the 1990s or 2000s can now sit inside the actionable window. If several matters emerge in the same policy year, aggregate erosion is the risk.
- Cladding and facade concentration. A practice with several post-2000 residential blocks in its back-catalogue can, in the worst case, see multiple related notifications arriving in a compressed period. Whether the primary policy aggregates those depends on the aggregation language — see below.
- Design-and-build interfaces and net contribution. Where a net-contribution clause is absent or unenforceable, an architect can find themselves defending a claim for the whole loss even where responsibility is properly divided. Damages recoverable can run above practice-day-to-day cover.
- Client-required limits. Public-sector frameworks and large private-developer appointments increasingly specify £5m or £10m aggregate. Winning that work requires a limit the primary insurer will not always write on its own paper.
How a layered programme is structured
The generic anatomy of a layered PI programme for an architects’ practice looks like this:
| Layer | Typical role | Wording notes |
|---|---|---|
| Primary | First loss, from ground up. | Full policy conditions, exclusions, retroactive date, ARB Standard 8 compliance. |
| First excess | Sits above primary; attaches when primary is exhausted. | Usually “follow-form” to primary; may add drop-down for primary aggregate exhaustion. |
| Second excess (further XOL) | Higher tranche; only responds to very large single claims or once earlier layers are stripped. | Follow-form; premium far lower per £m of limit. |
The layered structure often costs less per £m of limit than a single tower placement, but the trade-off is co-ordination: three wordings must line up cleanly on aggregation, notification, ARB-mandated cover conditions and jurisdiction. A layered programme where the excess wording gives less protection than the primary can create a “difference-in-conditions” gap that only appears when the claim arrives.
Delegated authority vs traditional excess placement
Excess-of-loss capacity in the London market is placed one of two ways.
Traditional placement. A broker approaches individual excess insurers, presents the risk, negotiates terms and binds each layer separately. Each layer’s underwriter decides on the risk in front of them. This is the historic norm and remains how the majority of excess capacity is written.
Delegated authority. Certain brokers hold binding authority from a capacity provider to write pre-agreed excess layers within defined parameters — a book of business, an underwriting appetite and a wording specified up front. Where a firm meets the criteria, the broker can bind on the insurer’s behalf under those terms.
Delegated authority does not create cover the market cannot otherwise write; it can shorten the time to bind and provides a stable wording where the underwriting appetite is well-defined. Whether it is right for an individual practice depends on the exposure profile, retroactive-date position and the composition of the underlying primary layer.
Aggregation at the excess layer
Aggregation is the mechanism by which multiple related claims are treated as a single claim for the purposes of the limit of indemnity. It matters most at the excess layer because bad aggregation language can either exhaust the layer prematurely (many small claims counted separately) or, from the client’s perspective, leave them without cover because a single “unifying factor” caps recovery below what several individual claims would have delivered.
The Supreme Court’s reasoning in AIG Europe Ltd v Woodman [2017] UKSC 18 remains the guide for interpreting “a series of related matters” language. In practice, at the excess layer, three questions matter:
- Does the excess wording use the same aggregation trigger as the primary?
- Are notifications made under the primary automatically deemed made under the excess?
- Where the primary aggregates and the excess does not (or vice versa), which prevails?
Drop-down, follow-form and differences-in-conditions
Drop-down
A drop-down provision allows the excess layer to act as primary cover where the primary insurer becomes insolvent, refuses to pay, or where the primary aggregate is exhausted before the claim reaches the excess. Without one, an insolvent primary insurer leaves a hole in the tower.
Follow-form
“Follow-form” means the excess layer adopts the primary policy wording subject to its own limits and any specific endorsements. It is the default in modern layered PI. The important discipline is to check whether the excess actually follows the current primary wording — wording updates between renewals can leave layers on slightly different terms.
Differences in conditions
Where the excess wording does not mirror the primary, a difference-in-conditions (DIC) analysis is needed. This is not a fault in itself — some excess policies have deliberately narrower conditions — but the practice, and the broker, need to know where the gaps sit before a claim tests them.
Retroactive continuity and notification-attachment at the excess
Architects’ PI is written on a claims-made basis. Two features are especially important at the excess layer:
- Retroactive date continuity. The excess layer’s retroactive date should match the primary’s. If the excess has a later retroactive date, historic exposures — especially those brought into scope by section 135 BSA 2022 — may be uninsured at the excess even if the primary responds.
- Notification-attachment. Where a circumstance is notified during the current excess layer’s period, the excess should attach on the same terms as the primary. Some excess wordings attach only on formal claims; the difference can be material.
Common wording issues seen on renewal
On architect renewals with layered towers, the recurring wording issues are:
- Aggregate limits at the excess that read on their face as “each and every” but revert to “in the aggregate” in the schedule.
- Excess policies with narrower cladding, fire-safety or basement-conversion exclusions than the primary.
- Retroactive-date drift where a change of primary insurer has not been mirrored in the excess.
- Follow-form clauses that follow the primary as originally written, not as endorsed during the policy year.
- Jurisdiction clauses at the excess restricting cover to UK courts where the primary is worldwide.
None of these is inherently a defect. Each is a decision the practice needs to understand before it is priced.
Frequently asked questions
When does an architect’s practice typically need an excess-of-loss layer?
There is no universal threshold; the point at which excess capacity becomes relevant depends on the client contracts a practice takes on, the value of projects in its back-catalogue exposed by section 135 of the Building Safety Act 2022, and the exposure profile of any cladding, facade or high-rise residential work. As a general rule of thumb, practices being asked contractually for aggregate limits above what one insurer will comfortably underwrite on a single-policy basis will need to consider a layered programme.
Is excess PI cheaper per pound of cover than primary PI?
In most well-underwritten programmes, yes. The layer sits above a substantial retention (the primary limit), so the probability of a claim reaching it is lower. A well-placed second-excess layer is normally cheaper per million pounds of limit than the primary. Price is not the sole consideration — wording continuity and aggregation matter more than headline premium.
Can I have different insurers on each layer?
Yes, and it is common practice. The discipline required is to ensure the wordings align, particularly on aggregation, retroactive date, notification attachment and any policy-specific exclusions. A broker managing the placement should be able to produce a layer-by-layer schedule showing where the terms match and where they differ.
What is the difference between excess-of-loss and top-and-drop cover?
Traditional excess-of-loss sits above the primary and only responds once the layer beneath is exhausted. A ‘top-and-drop’ extension allows the excess policy to drop down and act as primary where the primary is exhausted or fails. It is a specific feature to negotiate; it is not automatic.
Do ARB Standard 8 ‘adequate cover’ requirements apply to excess layers?
The ARB’s Architects Code, Standard 8, requires architects to have adequate and appropriate insurance cover for their work. Adequacy is judged on the totality of the programme — primary and excess combined — against the risk profile of the practice. Where an architect relies on excess layers to reach the level of cover they need, those layers form part of the adequacy assessment.
How does section 135 of the Building Safety Act 2022 change the case for higher limits?
Section 135 amended the Defective Premises Act 1972 so that claims relating to dwellings can now be brought within 30 years retrospectively (for causes of action accruing before 28 June 2022) and 15 years prospectively. Historic residential work is therefore back inside the actionable window in a way it was not before. Where a practice has meaningful residential exposure in its back-catalogue, this is a direct reason to review aggregate limits.
How is a layered programme co-ordinated on notification of a claim?
Best practice is a single notification, made through the placing broker, that copies all layers simultaneously. The primary insurer takes the lead on claim management; excess insurers receive the notification for record and are involved once the loss is credibly likely to breach the layer beneath. The broker’s job is to ensure notifications are made in a form that meets the requirements of every layer. If you already have a live issue, notify a claim.
Is delegated authority the same as a ‘line slip’ or ‘binder’?
The terms are often used interchangeably but have technical differences. A delegated-authority arrangement gives the broker (or coverholder) the right to bind risks on the insurer’s behalf within pre-agreed underwriting parameters, using an agreed wording. A line slip is a facility to place risks with a panel of insurers on similar terms. A binder is a specific type of delegated-authority instrument. All three exist in the London PI market.
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