Window Installation Teams 2026: How to Vet Them [Guide]

Introduction: How poor installation ruins even the best windows

My name is Tom, and I've been installing windows for Wingedas for 18 years. Last week, I received a call from a client in London. They had purchased beautiful, triple-glazed windows with a premium profile for nearly €9,300. She called me heartbroken because mould had appeared on the wall in her living room, right by the new patio door. I went to take a look, and immediately knew what had happened. The "specialists" they hired, who were €350 cheaper than us, had installed the window using only foam. No tapes, no preparation of the reveal. They simply put the frame in, foamed around it, and left.

The result? A thermal bridge like a motorway, through which heat escaped and moisture infiltrated. All the water vapour from the house condensed in that one spot. The new, expensive windows performed worse than their old, wooden ones. The cost of repair? Hacking off plaster, drying the wall, removing the window, and performing a proper, layered installation. An additional €1,160 and two weeks of mess. They lost €815 on that "saving" and a lot of stress.

I'm writing this so you don't make the same mistake. The window is only half the battle. The other half, the more crucial one, is the installation. You can buy windows from NASA, but if an amateur installs them, you'll be throwing money down the drain. Literally. That's why I've prepared a list of 7 questions you must ask your installation team. These are questions from my experience, ones that immediately expose shoddy workmanship. Read on, make notes, and don't get duped.

Question 1: How exactly will the installation proceed? Please describe it step-by-step.

This is an absolute fundamental. If the installer starts to stammer, speaking in generalities like "well, you know, normally, we just put it in and foam it," then run. A professional will describe the entire process like a well-oiled machine. Look for specific terms and stages in their answer.

What to look for in the answer?

• Preparation of the window opening: Do they mention cleaning, levelling, and priming the reveal? This is crucial for tapes and foam to adhere properly. Nothing will be airtight on a dirty, dusty surface.
• Type of installation: Do they mention "warm installation" or "layered installation"? This is the standard in 2026. A correct installation must consist of three layers:
  • Internal layer (vapour barrier): A special tape on the inside that blocks the penetration of water vapour from the house into the insulation layer.
  • Middle layer (insulating): Installation foam that fills the gap and provides thermal insulation.
  • External layer (vapour permeable): A tape or EPDM flashing on the outside that protects the foam from rain and sun, but allows moisture from the wall to evaporate.
• Mechanical fixing: How will they secure the window? With frame anchors or mounting brackets? How many fixing points do they plan? From my observations, companies cutting costs use 30% fewer fasteners than they should. Then the window "sags," and adjustment problems begin.

A story from a building site: A few years ago, we rectified an installation in a new terraced house near Warsaw. The developer had saved money on the team. Patio doors, 4 metres wide, were fixed with only four anchors. Four! After six months, the frame bowed, and the doors stopped closing properly. This is not a joke; these are real problems resulting from a lack of knowledge and cost-cutting.

Question 2: Who will physically install my windows? Employed staff or subcontractors?

This is a question salespeople dread. Why? Because many companies, even those with attractive showrooms and expensive advertisements, don't employ their own installers. They sell you windows, and then outsource the installation to the cheapest team available on that date. It's a lottery. You might get excellent professionals or two students earning extra money during the holidays.

Why is this so important?

• Responsibility: When installers are directly employed, the company takes full responsibility for them. They train them, equip them with tools, and control the quality. In case of problems, you know who to call.
• Experience: Permanent employees are people who have been installing that specific company's windows for years. They know the product, its specifics, and what to pay attention to.
• Communication: The salesperson you sign the contract with knows their installers. They know how they work and can convey your comments to them. With a subcontractor, there's often no direct contact.

Industry secret: Companies that use subcontractors pay them per unit or per square metre of installed window. This leads to poor practices – speed is prioritised over quality. No one will bother with thorough reveal cleaning if they are paid "per window." Time is money, and precision costs.

Of course, not all subcontractors are bad. But if a company uses external teams, ask how long they have been working together and if you can see photos of their previous projects. Let them prove that they are trusted professionals.

Question 3: What is the warranty on the installation itself, and what does it cover?

Beware, a trap! Most companies boast about a "10-year warranty on windows." Great. But what good is that if the installation warranty is the statutory 2 years (under consumer protection laws) or not clearly defined at all? Installation defects most often emerge after the first winter, and sometimes even after 3-4 years. Leaks, draughts, cracking plaster – these are all due to poor installation, not the window profile.

What to look for in the contract?

• Separation of warranties: The contract must clearly state how many years of warranty apply to the product (windows) and how many to the installation service. Look for companies that readily provide a 5-year warranty on their work. This shows they are confident in their quality.
• Scope of installation warranty: What exactly does it cover? Only airtightness? Also, the correct functioning of the windows (adjustment)? What about plaster cracks around the window due to poor fitting? Ask for details.
• Service response time: Ask how quickly the service team will attend after a fault is reported. The market standard is 14 days. If the company avoids answering, that's a bad sign.

Remember, the window manufacturer will never accept a complaint if the product defect results from poor installation. You will be left with the problem, and the installation company will wash its hands, blaming "uneven walls" or "defective windows." A clearly defined, long warranty on installation is your insurance policy.

Question 4: Do you have experience installing windows in my type of building?

Installing windows in a large pre-fabricated concrete panel building from the 1980s is an entirely different story than installing them in a new house made of Porotherm blocks or a hundred-year-old tenement house with fragile walls. Each building type has its pitfalls and requires different technology.

• Old tenement buildings: Uneven, crumbling reveals, often with wooden lintels. Here, you need to know how to reinforce the opening, sometimes using special consoles and extensions. An installer without experience can damage the wall structure.
• Pre-fabricated concrete panel buildings: Very hard concrete, which makes anchoring difficult. There's often also a problem with unevenness and the need for extensive plastering work.
• New builds (e.g., Porotherm, aerated concrete): Very brittle materials. Over-tightening an anchor can damage a block. Special frame fixings or anchors for aerated concrete must be used and installed in appropriate locations.
• Timber-frame houses: A completely different technology, requiring the use of windproofing and special sealing flashings.

Ask for photos of completed projects in buildings similar to yours. Ask what specific materials they will use to handle the specifics of your walls. If you see that the installer treats all buildings the same, it means they have no idea about building physics. From my observations, 8 out of 10 problems with airtightness stem from a mismatch between the installation technique and the wall material.

Question 5: How do you protect the property before work, and what does post-installation cleanup entail?

This may seem like a minor detail, but it shows the company's professionalism. Removing old windows involves plaster, dust, and rubble. A professional team comes prepared. They have dust sheets, cardboard, and tape. They protect floors, furniture, and radiators. This is an absolute standard.

Red flags:

• "The client must prepare everything themselves."
• "We only install; cleaning is up to the client."
• No answer, avoiding the topic.

A good team will roughly clean up the workspace after finishing – sweep up larger debris, collect sheets, and remove old windows. Don't expect floor washing and carpet vacuuming, but basic tidiness is a must. Ask if they take the old windows with them. Some companies leave them for the client "to dispose of," which is a significant problem. A good company will take them away immediately.

From real life: Once, my client's neighbour was replacing windows. The team walked onto her white living room carpet in dirty boots because "they were just in for a moment." Dust from cutting concrete settled on all the furniture. After they left, the apartment looked like it had been bombed. The cost of professional cleaning exceeded the savings on installation. It's not worth it.

Question 6: What materials do you work with (foam, tapes, anchors)?

The devil is in the details, and in installation, those details are the materials. A company might talk about warm installation, but then use the cheapest foam from a DIY store, which will crumble and lose its insulating properties after two years. Or use tapes whose adhesive doesn't hold in the frost.

Ask about specific brands:

• Installation system: Do they use a complete system from a single manufacturer (e.g., Soudal, Illbruck, Tremco)? This is the best solution because all elements (tapes, adhesives, foam) are compatible and tested with each other.
• Installation foam: What foam do they use? Is it a low-expansion, flexible foam that "works" with the window? Cheap, high-expansion foams can warp delicate PVC profiles.
• Tapes: Do the tapes have appropriate certifications? Pay attention to whether the team brings special adhesives (primers) for difficult substrates. Without them, even the best tape won't stick to dusty concrete.

If the salesperson cannot answer this question and says that "the team has everything they need," it means the company has no standards. Each installer buys what they deem appropriate, which most often means whatever is on promotion at the wholesaler. And that's a direct path to disaster.

Question 7: What will you do if, during removal, it turns out the wall is crumbling or the lintel is damaged?

This is the ultimate test. It's about dealing with unforeseen problems. This is common in older buildings. You pull out old window frames, and half the wall comes with them. What then?

Answers that indicate professionalism:

• "We will stop work, inform you of the problem, and present possible solutions along with a quotation."
• "We carry materials for minor masonry repairs and are able to rebuild a damaged section of the reveal."
• "We collaborate with an associated structural engineer/mason who can quickly come for a consultation if there are more serious problems."

Answers that should raise a red flag:

• "We'll just foam it up somehow."
• "That's not our problem; we just install windows."
• "You'll have to get a bricklayer yourself."

An unprofessional installer in such a situation will shove the window into the hole, fill everything with foam, and cover it with plaster. The problem will emerge after a few months, and they will long be "unavailable." A true professional knows that a window cannot be installed in an unstable opening. First, the wall must be repaired, and only then can the window be fitted. This demonstrates responsibility and long-term thinking.

Conclusion: Don't buy windows, buy peace of mind

Choosing an installation team is one of the most important decisions when replacing windows. Remember, the contract you sign isn't just about a piece of plastic and glass. It's about the airtightness, warmth, and security of your home for the next 20 years. Ask these 7 questions. Listen carefully to the answers. Don't be afraid to be inquisitive.

It's better to spend two hours talking to a salesperson and choose a company that's 10% more expensive but reliable, than to struggle for years with mould, draughts, and unscrupulous contractors. From my 18 years of experience, one brutal truth emerges: 9 out of 10 problems with new windows are due to poor installation. Don't let your home become another statistic.

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