Urban centers around the world are facing a critical challenge. Populations are growing rapidly, yet the supply of housing and essential amenities is falling behind. In large, established cities around the world, a shortage of affordable homes is compounded by a lack of space for schools, clinics, and community infrastructure. The pressure to densify is immense, but traditional approaches to development are proving too slow, too disruptive and too carbon intensive.

In New York City alone, the public housing system serves over 400,000 residents across more than 2,500 buildings. Many of these structures are aging and in need of repair, with a deferred maintenance deficit exceeding $25 billion. Yet despite their condition, these buildings often sit on underutilized land and contain untapped structural capacity. The opportunity to do more with what we already have is enormous.

This is the moment to rethink how and what we choose to build.

For too long, the default response to aging buildings has been demolition and replacement. This ‘fast architecture’ mindset mirrors the disposable culture of fast fashion. It prioritizes short-term gains over long-term sustainability, discarding viable structures and replacing them with new builds made from materials with high embodied carbon. The process is not only environmentally damaging but also economically inefficient and socially disruptive.

Sidara companies advocate for a different approach. Through adaptive reuse and vertical extension, particularly using mass timber, we can unlock the latent potential of existing buildings. This strategy allows us to add capacity without tearing down what is already there, preserving communities and reducing environmental impact.

The Case for Mass Timber Overbuilds

Despite growing awareness, climate resilience remains a blind spot in many urban strategies. Unlike carbon emissions, which can be measured, benchmarked, and regulated, resilience lacks a universal metric. There is no ‘resilience rating’ akin to a LEED certification. This makes it harder for investors, tenants, and developers to prioritize—and even harder to demand.

To increase the capacity of existing buildings without the need to tear them down or undertake major structural work, mass timber extensions on roofs are a rapid, environmentally friendly way of adding existing floorspace. This means residents can remain in situ while works are carried out and new housing, commercial or community space added with minimal disruption.

Mass timber is an ideal material for this purpose as it is renewable and lightweight, with a significantly lower carbon footprint than conventional materials. It is prefabricated and can be assembled quickly and quietly. Its strength-to-weight ratio makes it ideal for vertical additions, especially on buildings with unused structural capacity.

Through our extensive experience of evaluating buildings of all sizes and types, we understand that those that were constructed in generations past is often capable of carrying greater load capacity – that is to say that extra stories can be extended without the need to make major adjustments to the structure and foundations.

TYLin’s work at Amherst College is a prime example. Instead of fully demolishing an outdated concrete structure, the team added three stories of mass timber, creating a vibrant new student center while preserving the original building. The project is now topped out and nearing completion, demonstrating how thoughtful engineering can deliver both sustainability and speed.

Scaling the Solution: NYCHA and Beyond

In 2021, TYLin also partnered with Peterson Rich Office on a pro bono study for the New York City Housing Authority. NYCHA’s portfolio includes thousands of mid-rise brick buildings, most of which were built in the decades following World War II. These buildings are structurally sound but underutilized, with vast reserves of untapped floor area.

The study showed that by adding a single mass timber story to each building, NYCHA could:

• Increase housing capacity without displacing residents
• Protect failing roofs, reducing long-term maintenance costs
• Support rooftop solar power generation
• Avoid costly foundation work and minimize embodied carbon

While one additional story may seem modest, the cumulative impact across thousands of buildings would be transformative. It is a scalable, low-disruption strategy that addresses housing shortages while aligning with New York’s ambitious carbon reduction goals.

A New Mindset for Urban Growth

This is not just about engineering. It is about shifting the way we think about buildings. Instead of viewing them as single-use, single-generation assets, we must design for flexibility, longevity and evolution. Cities change. Industrial zones become residential neighborhoods. Cultural districts emerge. Demographics shift. Our buildings must be able to change with them.

Adaptive reuse and vertical extension offer a way to densify cities intelligently. They preserve community ties, reduce environmental impact, and unlock economic value. TYLin have been doing this work for decades – long before the notion of adapting a building or changing its use was seen as a viable solution to the pressures of a growing urban environment.

What Comes Next

If we are serious about improving living standards in cities, and doing so sustainably, it is up to city planners, architects, engineers, designers, housing authorities and developers to adopt a reuse-first mentality. Before demolishing, we should be asking whether a structure has the potential to serve a new purpose through with extension of adaptation.

Mass timber overbuilding is not a niche solution – they are a fundamental solution to a growing problem in cities around the world. What is needed is proactive engagement with city officials to include mass timber overbuild within our building codes.

With the right tools, data and mindset, we can transform our cities without tearing them apart.

All Renderings Courtesy of PRO

Find out more about Sidara at Climate Week NYC 2025