The Numbers That Changed My Mind About Construction

I spent fifteen years in the home improvement industry believing that on-site construction was simply how things got done. Then I saw the data.

According to a 2025 industry report, 95% of UK construction projects are now experiencing delays, with the median delay stretching beyond 200 days. That is not a typo. Two hundred days late, on average.

A Cornerstone Projects survey found that 91% of construction professionals have been involved in delayed projects in recent years, up from 85% in 2016. Even more troubling, the most common delay has shifted from “less than 10%” of the original timeline in 2016 to “21-30%” today. Projects that should take eight weeks are routinely taking twelve. Those promised for Christmas are finishing in March.

If you have lived through a traditional building project, none of this will surprise you. The scaffolding that outstays its welcome. The skip that becomes a permanent fixture in your drive. The builder who promises “another two weeks” for the fifth time running.

But here is what did surprise me: it does not have to be this way.

The factory-built extension, once dismissed as the poor relation of “proper” construction, has quietly evolved into something quite different. The UK prefabricated construction market is projected to reach £20.78 billion by 2028, growing at 5.2% annually. Major housebuilders are investing millions. The NHS has expanded its modular buildings framework to £3.6 billion over four years. Something has shifted.

At Room Outside, we have been part of this shift. Our modular construction process is not a compromise or a shortcut. It is, genuinely, a better way to build. Let me explain why.

The Construction Industry’s Uncomfortable Truth

The UK construction sector has a productivity problem that nobody wants to talk about honestly.

Research from Smart Infrastructure Magazine found that up to 30% of all work on typical UK construction projects involves rework. That means nearly a third of what gets built has to be fixed, adjusted, or redone entirely.

Think about that for a moment. If you hired a chef who had to remake 30% of the dishes they served, you would find a different restaurant. If your mechanic had to redo 30% of their repairs, you would find a different garage. Yet in construction, we have somehow accepted this as normal.

BCG’s Centre for Growth found that the UK’s pre-construction phase is the slowest across comparable developed nations: 65 months compared to an average of 50. For rail projects, we are 50% slower than average. For roads and social infrastructure, 25% slower. This is not about British workers being less capable. It is about systems and methods that have not kept pace with what is now possible.

According to McKinsey, 98% of megaprojects experience cost overruns or delays. The average cost increase is 80% above the original estimate. Now, your orangery or garden room is not a megaproject. But the same fundamental issues—weather delays, coordination problems, quality inconsistencies—affect projects at every scale.

Why Traditional Building Methods Persist

The honest answer is inertia. Traditional building developed when on-site construction was genuinely the only option. Craftsmen worked with locally available materials, adapting their techniques to weather and circumstances. There was skill and artistry in this approach, and I do not want to diminish that.

But modern manufacturing has moved on. When Rolls-Royce builds an engine, they do not assemble it in a field, hoping it does not rain. When pharmaceutical companies produce medicines, they do not mix compounds in a garden shed. Precision work demands controlled environments.

The construction industry, particularly for residential work, has been slow to absorb this lesson. But that is changing. Modern Methods of Construction are now expanding at a 10.0% CAGR in the UK, compared to traditional methods which still hold 91.2% market share but are losing ground. The Ministry of Housing, Communities & Local Government reports that volumetric modular projects can cut programme durations by 20% while reducing waste by 45%.

What Factory Construction Actually Looks Like (It Is Not What You Think)

When most people hear “factory-built,” they picture cheap prefab housing from the 1960s. Flimsy panels, dodgy insulation, buildings that looked temporary even when they were meant to be permanent. That association is understandable, but it is thirty years out of date.

A modern factory-built extension is precision-engineered in conditions that would be impossible to replicate on site. Temperature controlled. Humidity managed. Skilled craftspeople working with tools and jigs that allow tolerances measured in millimetres rather than centimetres.

The Quality Advantage Is Measurable

This is not marketing spin. The differences show up in hard data.

Research published in the Journal of Building Engineering found that modular construction uses up to 67% less energy during the building phase compared to traditional methods. Factory-built structures can also be up to 15% more energy-efficient in operation, thanks to superior insulation and airtightness.

Why? Because when you assemble a structure in a climate-controlled factory, materials behave predictably. Timber does not absorb excess moisture and then shrink as it dries. Adhesives cure at optimal temperatures. Seals form properly. Insulation goes in exactly as specified, without gaps or compression.

The Construction Industry Training Board reports that modular projects achieve an 80% reduction in on-site labour. That is not because corners are being cut. It is because the work has already been done, properly, in conditions where quality control is actually possible.

Quality Control That Actually Works

Here is a practical example. On a traditional building site, a quality inspection happens at the end. Once the extension is complete, someone checks whether it meets standards. By that point, problems are expensive and disruptive to fix. Walls need to be opened up. Work needs to be redone.

In factory production, inspection happens at every stage. Materials are checked on arrival. Components are tested after cutting. Assemblies are verified before final integration. A deviation from specification gets caught and corrected before it becomes embedded in the structure.

The Environmental Case (With Actual Numbers)

If you care about environmental impact, and many of the homeowners we work with do, the data here is striking.

According to the Waste & Resources Action Programme (WRAP), modular construction can reduce waste materials by up to 90% compared to traditional construction. A University of New South Wales study found waste reductions of 81-83% by weight.

To put this in context, the average new-build project produces approximately 3.9 pounds of waste per square foot. A 50,000 square foot building generates around 100 tonnes of waste, only about 20% of which gets recycled. Most ends up in landfill.

Factory construction changes this equation dramatically. Materials can be ordered precisely because cutting is computer-controlled. Off-cuts from one project become components for the next. Recycling infrastructure is built into the facility rather than improvised on site.

Transport and Carbon Footprint

Traditional construction involves dozens of deliveries: materials arriving incrementally, waste being removed in batches, tradespeople driving back and forth. Each journey adds to traffic and emissions.

A factory-built extension arrives substantially complete in a single delivery, with minimal follow-up visits for final connections. One study estimated a 30% reduction in total greenhouse gas emissions from modular construction compared to traditional methods. The reduction in vehicle movements also benefits your neighbours, which matters if you value good relationships with the people living next door.

Long-Term Performance

The environmental case extends beyond construction. A precision-built structure performs better thermally over its lifetime, reducing ongoing energy consumption. Make UK Modular reports that their members’ products operate at 55% lower heating costs compared to equivalent traditional builds. Over twenty or thirty years of ownership, that represents significant carbon savings as well as lower bills.

What This Actually Means If You Are Extending Your Home

Statistics are useful, but what matters is your experience. Here is what changes when you choose factory-built construction.

Timeline: Days Rather Than Months

Traditional conservatory or orangery construction typically takes 12 to 16 weeks on site. That is three to four months of your garden being inaccessible, your home covered in dust, builders arriving early and leaving late.

Factory-built extensions can be installed 50% faster than traditional builds, with on-site time often reduced to days rather than weeks. The CITB reports an 80% reduction in on-site labour for modular projects.

The majority of construction happens elsewhere, while your life continues normally. Foundations are prepared (this still requires on-site work, typically a week or two). Then your extension arrives, substantially complete, and is installed rapidly. The transformation from building site to finished space happens with remarkable speed.

Cost Certainty (Or Lack Of It)

The 2022 Cornerstone Projects survey found that 47.56% of respondents estimated their delayed projects had cost overruns of more than 20%, up from 27.7% in 2016. Nearly half of projects are now running significantly over budget.

Factory construction reduces this uncertainty. When work happens in controlled conditions according to established processes, variables shrink. There are fewer weather delays, fewer unexpected complications, fewer moments when a builder sucks air through his teeth and mentions additional costs.

This matters especially for premium projects. If you are investing £30,000 to £100,000+ in an orangery or high-specification glass extension, you want confidence that the quoted price will be the actual price. Factory methods make that confidence realistic rather than hopeful.

Living Through The Build

Anyone who has lived through traditional construction knows what disruption actually means. The constant noise. Dust that infiltrates every room despite plastic sheeting. Strangers wandering through your home for months on end. The psychological weight of living in a building site.

Factory-built construction compresses this disruption dramatically. The on-site phase is brief enough that you can plan around it. Perhaps you take a short break while installation happens. Perhaps you simply tolerate a few days of activity knowing it will end soon. Either way, the experience is fundamentally different from enduring months of construction chaos.

For families with young children, those working from home, or anyone who values their domestic peace, this difference alone can justify the choice.

The Questions People Actually Ask

Having discussed factory-built extensions with hundreds of homeowners, I know which concerns come up repeatedly. Let me address them directly.

Where This Is All Heading

The UK construction industry is changing, slowly but definitively.

The global modular construction market is projected to reach $207.82 billion by 2033, growing at 8.2% annually. Europe holds 45% market share, with the UK as a leading adopter. The UK government’s target of 1.5 million new homes by 2029 is driving significant investment in modern methods of construction.

The NHS is expanding its modular buildings framework. Homes England has launched a £2.5 billion modular housing scheme. Major housebuilders are investing in factory capacity. The direction of travel is clear.

For individual homeowners, this means factory-built construction is no longer an outlier choice. It is increasingly the informed choice, backed by data, driven by genuine advantages, and delivered by specialists who have refined their processes over years of development.

Making Your Decision

I am not suggesting that factory-built construction is right for every project or every homeowner. Traditional building has its place, particularly for complex renovations integrated deeply into existing structures.

But for a new orangery, conservatory, or garden room? For homeowners who value quality, want predictable timelines and costs, and prefer not to live in chaos for months? The case for factory construction has become compelling.

The industry is moving towards it. And the experience of actually living through the process favours it dramatically.

At Room Outside, we have built our modular construction process over years, refining methods, investing in precision, and learning what actually matters to the homeowners across London and the South East who trust us with their projects. We would be happy to discuss whether this approach might suit what you have in mind.

No obligation. No pressure. Just an honest conversation about whether a factory-engineered extension might be the better way to add the space you are looking for.