How to hire a builder for a larger job

Hiring a builder for an extension or a full renovation is not a bigger version of hiring someone to fix a leak. The job runs for months, other trades come and go under the builder’s control, money moves in stages, and several legal obligations land on you personally whether you know about them or not. Almost everything that goes badly wrong on a domestic build was decided before anyone lifted a tool.

This guide assumes you have already read what a written quote should include and are past comparing numbers. That guide covers scope, quotes versus estimates, and how to get three prices into a comparable shape. What follows is what a larger job adds on top.

Nothing works without a defined job

On a small job the quote is the specification. On a larger one it is not, and a builder pricing off a conversation is guessing. Before you seek prices you need drawings and a written specification that says what the materials and finishes are, so that every builder is pricing the same building. If you do not have that, the first thing to buy is the design, not the build.

This also fixes the most common source of conflict later. When there is a drawing and a specification, a change is visible as a change. When there is not, every disagreement becomes one person’s memory against another’s.

The contract

The CCPC’s position is direct: a written contract signed by both parties protects you if things go wrong, and you should have a clear written agreement before the contractor starts. On a job of any size that means a real contract rather than an accepted quote.

What it needs to settle:

The drawings and specification it is built on, listed and dated, so there is no argument later about which revision was priced
The start date and the expected duration, and what happens if the job runs materially past it
The payment schedule, tied to identifiable stages
How variations are priced and approved, in writing, before they are carried out
Provisional sums for anything not yet chosen, and how the difference is settled
Which parts are subcontracted, and to whom
What happens when something unexpected is found once things are opened up
Retention: a percentage held back for a defined period after completion for snagging

For a substantial project it is worth using a standard published building contract rather than something drafted from scratch, and having whoever is administering the project on your behalf handle it.

Staged payments

The CCPC advises agreeing a payment schedule that sets out the amount to be paid at each stage, the work covered by each payment, and the total number of payments. On a long job that is not just prudent, it is the main mechanism you have.

The principle is simple: at every point in the job, the value of the work completed should be at least the value of what you have paid. Payments tied to calendar dates break that. Payments tied to completed stages, inspected before release, hold it.

A deposit against materials on a large job is normal. A large proportion of the total before work starts is not, and it inverts the only leverage you have. Keep a meaningful final payment, plus retention, until the work is finished, snagged and certified.

Pay traceably, and use a bank card for any large deposit. The CCPC notes that where a deposit is paid by card, the card provider may be able to reverse the transaction through a chargeback if the business goes out of business. Cash with no receipt leaves you with no record and no VAT invoice.

Insurance

Ask for the certificates, read the dates, and check the policies are current for the period of your job rather than expired last spring.

Public liability. The CCPC’s advice is to always check that someone working on your home has their own public liability insurance, because if they damage your home it might not be covered by your own policy. Check the level of cover is proportionate to the value of your house, not just that a policy exists.
Employer’s liability, where the builder has employees. A builder running a team without it is exposing you to arguments you do not want to be part of.
Contract works or all-risks cover for the works themselves while they are under construction, and a clear answer on who carries it, you or the builder.
Your own home insurance. Tell your insurer what is happening before it starts. Policies frequently restrict or exclude cover during building works or while a house is unoccupied, and finding that out afterwards is a bad way to find it out. You will also need to increase your rebuild cover once the house is bigger.

Certificates: establish who is responsible before work starts

On a larger job the builder brings in other trades, and certain work carries a legal certification requirement attached to the person doing it, not to the main contractor.

Electrical work on the fuse board, new circuits and rewiring must be done by a Safe Electric Registered Electrical Contractor, who issues a Completion Certificate. Any gas work must be done by a Registered Gas Installer, who must issue a Declaration of Conformance. Both documents belong to you and to the house, and both are the sort of thing a solicitor asks for years later. See what a Completion Certificate is and why your solicitor asks for it for what happens when one is missing.

Write into the contract that these certificates are provided to you before the final payment is released, and get the name and registration of the subcontractor rather than an assurance that “our electrician is registered”.

Building control, and your own duties

Two things become your responsibility on a larger job, and neither is the builder’s to solve for you.

Building control. A commencement notice goes to the local building control authority before work starts, generally not less than 14 and not more than 28 days beforehand. For an extension to a dwelling with a total floor area greater than 40 square metres, additional documentation is required with it, including general arrangement drawings, a schedule of design documents, a preliminary inspection plan and a Certificate of Compliance (Design), with a builder and assigned certifier named, unless the owner instead opts out of statutory certification. Opting out does not remove the obligation to comply with the Building Regulations. Confirm the position for your job with your local authority’s building control section.

Health and safety. This one surprises people. The Construction Regulations bring domestic homeowners within the definition of the “client” for construction work you pay to have done in your home. In broad terms that means taking reasonable steps to satisfy yourself that the designers and contractors you appoint directly are competent, appointing project supervisors in writing where the project involves more than one contractor, involves a particular risk, or is planned to last longer than 30 working days, notifying the Health and Safety Authority where the work is likely to exceed 30 working days or 500 person days, and keeping the safety file afterwards and making it available to anyone doing work on the house in future. The HSA publishes a guide for homeowners setting out what applies to a given project, and it is worth twenty minutes before you sign anything.

The safety file is also one of those documents that turns up in a future sale, so it is worth having somewhere sensible.

Registers, and what they currently tell you

There is no equivalent for general building of the statutory registration that governs gas and electrical work. The Construction Industry Register Ireland is the register intended to fill that gap, put on a statutory footing by legislation in 2022 and administered by the Construction Industry Federation, but as of August 2026 registration is still voluntary and the mandatory divisions are being phased in, beginning with larger residential providers rather than the builder doing your extension.

The practical consequence: a CIRI listing is a positive signal and not a licence, and its absence currently tells you very little. For now, the checks that actually discriminate between builders are insurance certificates, a tax clearance access number, a VAT number, and recent addresses you can go and look at.

What a good builder asks you

This is the most reliable signal available to you, and it is free. Interview them by noticing what they want to know. A builder who is going to be good to work with asks things like:

Who did the drawings, and can I have the specification?
Is this exempted development or is there a grant of permission, and can I see it?
Who is the designer and who is the assigned certifier, or are you opting out?
What are the ground conditions, and where do the existing drains run?
Where can I get materials in and where can waste go? Where do I put the site toilet?
Will you be living in the house while this is going on?
Which decisions are still open, and when will you make them?
What are you doing about the parts of the house we are not touching?
What is your contingency, and what do you want me to do if we open the floor and find something?

A builder who asks nothing beyond the size and the start date has not thought about your job.

Warning signs

Pressure to decide today, or a price that expires
A deposit requested before there is a written scope and a signed contract
Cash only, or reluctance to give a VAT number or a tax clearance access number
No fixed address, and a mobile number as the only contact
Unwillingness to name subcontractors or to provide their registrations
Insurance certificates that never quite arrive, or that are out of date
References that cannot be visited, or that are all very recent
A price well below the others with no explanation of what is different in scope
Resistance to putting variations in writing
Starting the job and then disappearing to another site for a fortnight

Once it starts

Keep a written trail. Confirm variations by email before they happen, photograph everything before it is covered up, especially services in walls and floors, and keep certificates and invoices in one place from day one rather than assembling them under pressure in three years’ time when you are selling.

If a dispute does arise, everything above becomes evidence. That, more than anything, is why the paperwork is worth the effort at the start, when nobody thinks they will need it.