When embarking on a construction or renovation project, one of the most important decisions you’ll make is choosing who to entrust with the work. A good contractor is worth their weight in gold—a bad one can make your life miserable for years. And unfortunately, it’s not uncommon for so-called “professionals” to leave behind mistakes that are not only annoying but can also be dangerous.
In this article, I’ve compiled 10 questions worth asking any contractor—whether it’s for roofing, tiling, mechanical work, or even painting. These questions will help you make an informed decision and choose based on more than just likability or price.
1. Do You Have References for Similar Work That I Can View?
This is one of the most important questions you can ask a contractor before signing a contract. A reference isn’t just about “whether the house looks nice”—it’s also about how the professional works, how well they meet deadlines, how they communicate, and what their work quality is like.
What to Look for Regarding References?
Does it show similar type of work? If you’re building a family home, then an industrial warehouse isn’t relevant. Ask for a reference that’s similar to your project in size, style, and technology.
Can you view it in person? The best option is if you can visit a previous job and speak with the building owner there. This way, you’ll see not only the final result but also hear real experiences.
Request photos and documentation If a personal visit isn’t possible, ask for detailed photos, design documentation, and even excerpts from the construction diary. These reveal a lot.
Watch the reaction If the contractor is reluctant or evasive, that can be a warning sign. A reliable professional proudly shows what they’ve built.
Extra Tip: Ask the Previous Client!
If possible, speak with a building owner for whom the contractor has already worked. Ask:
- Did they meet deadlines?
- How did they handle mistakes?
- What was communication like with them?
- Would they recommend them again?
2. What Warranty Do You Offer on the Work Performed?
Colloquially, we often call it a “warranty,” but the official term is liability for defects. This is legally mandated and applies to two main areas:
- Material quality (e.g., manufacturer defect),
- And construction work (e.g., faulty installation, poor cutting, inaccurate fitting).
Example:
If a tile cracks, it could be a manufacturing defect—in which case the manufacturer is liable. However, if the tile is installed crookedly, or the joints are uneven, or the tile cracked/broke during installation, that’s a construction error—and the contractor’s responsibility.
The warranty period is typically 2 years, but for certain works (e.g., building structures) it can be 5 years. It’s important that the contractor not only verbally commits but also documents in writing how they’ll handle any potential defects.
The warranty isn’t just paper—it’s a safety net. A proper professional isn’t afraid to give a warranty because they’re confident in their work.
3. Do You Work with a Contract, and What Does It Include Exactly?
The contract isn’t just a formality—it’s the foundation of collaboration that protects both parties’ interests. A well-written contract clearly specifies:
The work’s start and completion dates This helps with planning, and if delays occur, there’s something to refer to.
The total cost of the work It’s important that it’s not just an estimated amount, but detailed: labour costs, material costs, possible delivery charges.
Payment schedule For example: 30% deposit, 40% midway through the work, 30% upon handover. This way, both parties are secure, and the “I paid but they never came back” situation is avoided.
What happens if construction is delayed The contract can specify that in case of delay, the contractor pays a penalty, or how the building owner will reimburse any additional costs (e.g., if work is postponed due to weather).
Handling additional work If during the work it becomes clear that something else needs to be done (e.g., extra floor levelling, additional insulation), the contract should specify how coordination occurs and at what price.
Material quality and responsibility It’s important to clarify who provides the materials: the contractor or the building owner. If the contractor provides them, they’re responsible for quality. If the building owner provides them, the contractor has the right to indicate if the material is unsuitable (e.g., timber too wet, poor-quality tiles).
Involvement of technical personnel The contract should specify who will be the Clerk of Works or Site Supervisor, who is responsible for the professional management of construction, and who will be the Building Surveyor or Construction Monitor, who represents the building owner’s interests. Both are authorised to make entries in the construction diary and play a key role in ensuring the work complies with regulations, plans, and quality expectations.
Example:
If the contractor uses substandard materials, the Building Surveyor can flag this and even halt the work. If the deadline slips, the Site Supervisor documents the reasons, so it can be traced back later what happened.
The contract, therefore, isn’t just a signed piece of paper—it’s the roadmap for safe collaboration. The more detailed it is, the fewer misunderstandings, and the smoother the construction.
4. Who Actually Performs the Work—You or Subcontractors?
This question is often omitted, yet it’s fundamentally important. When you choose a contractor, you often think they’ll perform the work themselves. However, in practice, the contracted professional sometimes sends subcontractors you know nothing about—not their names, experience, or whether they’re actually qualified professionals.
This isn’t necessarily a problem if the contractor takes responsibility for the subcontractors’ work and communication continues with them. However, if it’s not clarified who’s working on-site, it raises trust and quality questions.
Example:
You contract with a tiler who promises to do the work himself. Then two unknown people show up who don’t speak English, and you don’t know who’s directing them. If they leave behind mistakes, who do you turn to? The tiler who wasn’t there? Or the subcontractor you don’t even know?
That’s why it’s important that the contract specifies:
- Who actually performs the work
- Who directs the work on-site
- Who takes responsibility for mistakes
- Who communicates with the building owner on daily matters
If subcontractors work, that’s fine too—but it should be clear that the main contractor is responsible for them and maintains contact with the building owner. This avoids the “nobody knows anything” situation when work is abandoned or mistake corrections don’t happen.
5. What Materials Do You Use, and Do They Have Certification?
Material use isn’t merely a technical detail—it’s one of the most important foundations of construction quality. No matter how beautifully someone works, if they use poor materials, the result can deteriorate quickly. Therefore, it’s important to clarify from the beginning:
What types of materials does the contractor use? Ask what brands and manufacturers they prefer, and why. An experienced professional knows how products perform in practice—for example, which tile adhesive withstands underfloor heating, or which paint won’t peel off after a few months.
Is there certification or conformity declaration for the materials? Quality building materials have CE marking, manufacturer’s declaration of conformity, or Technical Assessment. These aren’t just papers—they’re proof that the material complies with regulations.
Who provides the materials—the contractor or the building owner? This is a key question. If the contractor provides the material, they’re responsible for quality. If the building owner does, the contractor has the right to indicate if it’s unsuitable and can even refuse installation.
Example:
If a tiler brings cheap, unknown brand tiles that were already cracked in the box, they won’t withstand the load. However, if the tile is good quality but the contractor cuts it poorly or uses improper adhesive, then the fault is in the work, not the material.
What happens if the material is defective or unsuitable? The contract should specify who bears the replacement cost in such cases and how complaints are handled. The contractor has a duty to indicate if material is unsuitable for installation—and the building owner has the right to request new material.
Material storage and handling It’s not enough for the material to be good quality—it must be stored properly too. For example, timber shouldn’t be placed on wet ground, paint shouldn’t be left in blazing sun, tiles can’t be exposed to frost. These should also be clarified in advance.
6. How Do You Handle Potential Mistakes or Complaints?
Mistakes can occur during construction—this isn’t necessarily a disaster in itself. The question is how the contractor reacts. A proper professional doesn’t deflect, doesn’t trivialise, but seeks a solution. That’s why it’s important to clarify from the beginning what procedure is followed for handling complaints.
What’s Worth Asking About?
What counts as a defect, and how can it be reported? Ask how defects can be reported: verbally, in writing, documented with photos? Is there a deadline within which to report?
Within what timeframe do you commit to repairs? A proper contractor doesn’t drag out repairs for weeks. It’s worth recording that they’re obliged to respond and take action within how many days following notification.
Who bears the repair cost? If the defect occurred due to the contractor’s fault (e.g., poorly laid tiles, improperly fixed roof elements), then naturally they bear the repair cost. However, if material provided by the building owner is defective, then responsibility is shared.
Is there a separate warranty procedure? Some contractors provide a separate warranty certificate or documentation describing what solutions they offer for what types of defects and within what timeframe.
Example from Practice:
Imagine a painter completes the work, but after a few weeks the wall starts peeling. If the paint wasn’t suitable and they provided it, it’s their responsibility. However, if the wall was damp and they didn’t indicate this in advance, they’re also at fault. A proper professional returns in such cases, fixes it, and doesn’t deflect responsibility.
Why Is This Important?
Because mistake handling isn’t just a technical matter but also a trust test. This is when the building owner truly sees whether the contractor works not just for money—but also accepts the consequences of their work.
7. What Work Process Do You Follow, and How Long Will Construction Take?
Construction isn’t just about “we’ll come and do it”—but a precisely planned work process that should be known in advance. This helps the building owner know when what happens, how long it takes, and when decisions or payments are needed.
Why Is Knowing the Work Process Important?
Planability: If you know when work begins, when materials arrive, when the electrician or tiler comes, you can adapt—whether with holiday from work or organising family life.
Transparency: A well-structured work process helps avoid surprises. You know when to pay, when to decide, when to be present.
Responsibility: If the contractor provides the steps in advance, they can’t later claim “there wasn’t time” or “nobody said anything.”
What’s Worth Asking About?
Is there a pre-written work plan or schedule? This can be a simple table or calendar showing what happens each week. For example:
- Monday: demolition
- Tuesday: floor levelling
- Wednesday: tiling begins
- Friday: grouting, cleaning
In what order do the works occur? This is especially important if multiple professionals work one after another. For example, you can’t paint until the electrician is finished, or you can’t tile until the floor is prepared.
How long will construction take? Ask what the optimal duration is and what might cause delays. The contract should include what counts as acceptable delay and what doesn’t.
When is payment due, and on what schedule? The payment schedule should align with the work process. For example:
- Deposit at start
- Part payment midway through work
- Final invoice upon handover
Is there a point where the building owner needs to make a decision? For example: tile selection, colour determination, lamp placement. These should be flagged in advance so work doesn’t stop because “we haven’t decided yet.”
Example from Practice:
For a bathroom renovation, the contractor says “it’ll be done in two weeks.” But if there’s no precise work plan, it could happen that the first week is only demolition, and the second week the tiler doesn’t come because they’re working elsewhere. However, if there’s a schedule, the building owner knows when to be there, when the plumber comes, and when the room can be used again.
8. Mandatory Insurance—But Is There Proof, and What Does It Cover?
Contractor liability insurance isn’t an optional choice but a legally mandated requirement. According to EU regulations and national construction laws, every construction contractor must have valid liability insurance covering damages they cause. However, this only provides real protection if:
The insurance is actually valid Request written proof, not just verbal references. The proof should contain the insurer’s name, policy number, coverage type, and validity period.
It’s clarified what the coverage includes Not all insurance is the same. Some only cover direct damages caused by the contractor (e.g., cracked wall, faulty roof structure), and some also cover damages to third parties (e.g., damage to neighbour’s house, accident on work site).
It includes risks related to the work site If they’re building a roof, for example, it’s important that insurance extends to work at height, damages from falling objects, or even weather-related accidents.
Example from Practice:
Imagine during roof construction, the contractor accidentally drops a beam that damages the neighbour’s car. If there’s valid liability insurance, the insurer compensates the damage. If not, the building owner can also find themselves in an unpleasant situation, as the neighbour will seek a solution from them.
What Else Is Worth Asking About?
Is there an excess that the contractor must pay? This helps understand how interested the contractor is in avoiding mistakes.
How quickly does the insurer handle claims? Some insurers respond quickly; with others, it can drag on for months. It’s worth clarifying in advance what the contractor’s experience is.
Does the insurance extend to subcontractors too? If not, separate insurance is needed for damages caused by subcontractors—or the main contractor must assume responsibility.
9. How Do You Maintain the Construction Diary, and Can I Access It?
The construction diary isn’t just a mandatory administrative tool—it’s the official documentation of construction that records every important event, decision, and work process. By law, it’s mandatory to maintain for all construction activities, and the building owner has the right to access and review it.
Why Is the Construction Diary Important?
Evidence: If a dispute arises, entries in the diary can be used to trace back what happened, when, and who was present.
Communication tool: Not only the contractor writes in the diary, but other professional participants too—for example, the Site Supervisor and the Building Surveyor.
Legal protection: If a mistake occurs during construction, the diary helps determine who’s responsible and how it can be remedied.
Who Writes in It?
Site Supervisor / Clerk of Works: They work on the contractor’s side and are responsible for ensuring work is done professionally, according to plans and regulations. They document work processes, check materials, and flag if something isn’t suitable.
Building Surveyor / Construction Monitor: They represent the building owner’s interests and verify that construction complies with the contract, technical specifications in plans, and regulations. If they detect a defect, they make an entry and can even halt work.
What’s Worth Asking About?
Who maintains the diary, and in what system? Electronic construction diaries are now used, which the building owner can also access. Ask if you’ll receive access credentials and how you can track entries.
How often are entries made? The diary should be maintained daily, especially when active work is ongoing. If the contractor only writes in it weekly, that’s already problematic.
Do they document material arrivals, work processes, defects? These are all important for later tracing what happened and who’s responsible.
Example from Practice:
If the contractor claims they completed a certain work section but the Building Surveyor doesn’t confirm it, the building owner can justifiably request clarification or correction. If the diary notes that roof battens were fitted at incorrect angles, it’s the Site Supervisor’s responsibility to have this corrected.
10. What Happens If the Deadline Slips or the Budget Changes?
Mistakes can occur—this isn’t necessarily a tragedy, but it’s important to detect, document, and handle them properly. The biggest mistake is letting them go without a word.
What Can You Do If You Notice a Defect?
Document immediately: Take photos, write down when you noticed it and exactly what the problem is. If possible, ask the Building Surveyor to examine it and make an entry in the construction diary.
Notify the contractor in writing: Don’t just mention it verbally! Send an email or official letter describing the defect and requesting correction. This leaves a trail and prevents later misunderstandings.
Involve an expert if needed: If the contractor doesn’t acknowledge the defect or doesn’t correct it properly, request an independent expert opinion. This could be a structural engineer, architect, or other specialist designer.
What Defects Occur Most Frequently?
- Inaccurate dimensioning (e.g., incorrect ceiling height, shifted walls)
- Improper material use (e.g., weaker insulation than specified in plans)
- Structural problems (e.g., inadequate concrete reinforcement, missing fixings)
- Aesthetic defects (e.g., cracked plaster, poorly fitted tiling)
What’s the Legal Background?
- The contractor has a warranty obligation: if they make a mistake, they’re obliged to correct it.
- The defect must be recorded in a protocol, and the correction deadline must also be recorded.
- If correction doesn’t occur, the building owner can seek legal remedy, even through legal channels.
Tip: Don’t Wait Until Technical Handover!
Many people only start looking for defects at handover, but by then it’s harder to prove when and how they occurred. Pay attention during construction too, and if something seems suspicious, speak up—even if it “seems like just a small crack.”
+1 Why Is It Important to Have a Building Surveyor on the Construction Site?
A Building Surveyor (or Construction Monitor) isn’t a luxury but the building owner’s line of defence. They’re the one who watches construction with a professional eye and helps ensure the building truly becomes what you dreamed—not just on paper, but in reality.
What Does the Building Surveyor Do?
Monitors construction: They check whether works comply with plans, regulations, and technical specifications.
Represents the building owner’s interests: They don’t stand on the contractor’s side, but on yours. If something’s not right, they’re the one who speaks up, documents, and can even halt work.
Makes entries in the construction diary: They record defects, observations, and suggestions in writing—these can later be important from a legal perspective too.
Assists with technical handover: They accompany the process and verify that everything is in order at handover.
Why Is It Good to Have One?
Reassuring: You don’t have to check every screw and concrete layer yourself—there’s someone who understands it and watches on your behalf.
You can save money: If they notice a defect in time, you don’t have to repair, demolish, and rebuild later.
Legally protects: If a dispute arises, the Building Surveyor’s documentation can help prove what happened.
When Is It Mandatory?
- If construction requires a building permit, then by law it’s mandatory to appoint a Building Surveyor.
- If it’s not mandatory, it’s still strongly recommended—especially if you’re not experienced in construction.
Final Thought—Your Home Isn’t a Testing Ground
Construction isn’t just bricks and concrete—but decisions, trust, and lots of questions. The more consciously you start, the less uncertainty and the more peace of mind. These questions aren’t meant to put the contractor in an uncomfortable position, but to help you choose well.
Because the most beautiful house doesn’t become a home because it’s finished—but because you didn’t lose your faith, patience, and sense of security along the way.
If this article helped you see a bit more clearly, it was worth writing. And if you feel it might be useful to someone else, don’t keep it to yourself—share it freely.
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