Security
What is a collateral warranty, and should I sign the one on my desk?
Your contract is with the developer, but the bank funding them, the company buying the building and the tenant moving in all want a piece of paper from you personally. That paper is the collateral warranty, and the version on your desk was drafted by their solicitor, not yours.
QScope Team·4 May 2026·5 min read
The problem warranties solve is called privity: only the parties to a contract can normally sue on it. Your building contract is with the client, so the client’s funder, a buyer of the building, or a tenant has no direct contractual route against you if the roof you built fails after the client has sold up and moved on. A collateral warranty manufactures that route: a short direct contract in which you promise the beneficiary you performed the building contract properly, giving them someone to sue in their own name.
What you are actually promising, and to whom
The core promise is usually modest on its face, that you have complied with the building contract, and the danger is in the surroundings. Three clauses decide how heavy yours is:
- Step-in rights. Funder warranties typically let the funder step into the client’s shoes if the client fails: the job continues with the bank as your employer. Two things to check: that step-in comes with the obligation to pay you (including arrears), and how long the funder can sit deciding while you are obliged to wait.
- Net contribution and liability caps. A net contribution clause limits you to the share of loss that is fairly yours where others (the architect, the engineer) share blame, without one, a beneficiary can pursue you for the lot and leave you chasing the others. Caps, exclusions of consequential loss, and a liability period mirroring the main contract’s limitation period all belong on your side of the negotiation.
- Assignment. Warranties are built to travel, that is their point, but uncontrolled assignment means unknown future beneficiaries; the usual compromise is a limited number of assignments without consent. Also check the insurance clause: a promise to maintain professional indemnity cover for twelve years is a promise with an annual premium attached, only sensible where you carry design liability at all.
The ones nobody executes, and why that cuts both ways
The old title of this page survives as a fact of life: warranties are agreed in the contract (“the contractor shall provide warranties in the form annexed”) and then never actually signed, chased years later by a buyer’s solicitor mid-transaction. Know your position in that phone call: if the building contract obliged you to give them, refusing is a breach, and using the moment for leverage on unrelated grievances reads badly; but the warranty you owe is the annexed form, not the longer one that arrives “updated” by the buyer’s solicitors, and comparing the two before signing is exactly the check that pays. If no form was ever annexed, what you owe is negotiable, and this time your solicitor drafts.
On a small and domestic scale
Homeowner jobs rarely involve warranties, a buyer of the house relies on surveys and, for newer structural work, insurance-backed guarantees, and a warranty request on a domestic job usually means a developer-style adviser at work: apply the proportion test before financing the paperwork. Where you are the subcontractor asked to warrant to the employer above your main contractor, the same three clauses apply with one addition: your warranty should not outflank the payment protections of your subcontract.
What to do this week
1. If a warranty is on your desk, run the three clauses, step-in, net contribution and caps, assignment, and compare it against whatever form the building contract annexed.
2. Check the insurance promise against your actual cover, term and level, before you promise to maintain it for a decade.
3. At tender stage, ask for the warranty forms up front and price the obligations, because “forms to be agreed” is a negotiation you will have at your weakest moment.
Where the information stops
Warranties are the most solicitor-shaped documents a small builder signs: long-tail liability, insurance promises and step-in mechanics interact in ways this page can map but not clear. Any warranty on a job that matters goes past your solicitor and your PI broker before signature, and the cost of that read is trivial against a twelve-year promise.