a problem-solving website that teaches you to think like an engineer.

We've been hearing about it for years.

The 21st century is the era of urbanization.

In almost every country around the world,

people are packing their bags, and moving into cities at record rates.

This is a global phenomenon,

across the spectrum of developed and developing economies.

Approximately 54% of people worldwide

now live in cities,

30% more than in 1950.

And projections show that urbanization,

combined with the overall growth of the worlds population,

could add another 2.5 billion people to urban populations by 2050.

In many countries, the largest cities are growing faster than their smaller counterparts.

Rural cities, towns and villages are being cannabalized

to facilitate the demand for jobs in these urban centres.

For better or worse,

we are increasingly becoming an urban world.

Thus, it's no surprise that the demand for city housing is skyrocketing.

Prices to rent or to buy are reaching, for many,

unobtainable heights.

Savos, a global property firm,

published its list of cities with the highest cost of accomodation around the world,

with the usual suspects ranking high.

New York, Hong Kong, London, Tokyo, and Paris

all consistently in the top 5.

But even smaller cities, like Dublin, are experiencing serious housing crisis,

with many people unable to afford to live

near their places of work.

With jobs flooding back into Dublin after years of recession

there is an incredibly high demand on urban housing.

In Ireland capital, housing prices has risen

by average of almost 50% in 5 years

and the number of listings are at a record low.

Some attribute Dublin housing price increases to a lack of housing supply

due to investors hoarding property,

and increased AirBnb, or vacant land not being developed.

while these are all definately factors

even if they were resolved, Dublin would still be falling short

of the 25,000 new units needed every year to meet

the current demand.

In recent years, construction in the city has increased significantly

but the return of cranes to the skyline, but many are

commercial units and apartment buildings are simply not being built

fast enough, and in enough numbers to make a dent in the demand,

causing rent prices to rise to the point that many

young Irish are once again having to consider

whether Ireland is a place they can build a future.

Continuing the ritual brain drain of

our country's youth to not so green pastures.

The government has responded to this problem unsuccessfully,

with ridiculous attempts to ban rents from rising,

a solution akin to banning a sick patient's temperature from rising.

The only cure for this fever

will be to increase the supply of housing,

that is, increase the supply of housing while minimizing cost.

Let's first focus on optimum height.

While some are calling for high rise buildings to Dublin

with the idea that it while increase density and greater supply,

buildings that are too tall don't translate into

affordability as they cost too much to build.

In theory, taller buildings reduce square meter costs of floor space

the higher you build, and increase the overall

returnable revenue from a single plot of land.

However, the cost increases as you build higher and higher.

Lift systems, fire prevention measures, water supplies

and pressurization and heating and cooling systems

all add to the cost of high rises.

Costs like these lead to a U-curve in regards to the cost per square meter

and height, where the cost per square meter initially decreases

with an increase in height, and then starts to increase

after the height reaches a certain point

due to the increased engineering demands.

Every curve therefore has a bottom-out point.

This bottom-out point is different in every city

and varies widely even within the city. But on

average the lowest cost per square meter in Shanghai

and in the Netherlands for example, is around 8 stories.

In Hong Kong, thanks to the limited land area increasing

land costs, it's around 12 stories.

The additional cost of engineering can be marginalized

by high costs of land, making in worth while to build higher.

Take the extreme example of 432 Park Avenue,

the tallest residential building in the world.

Built on the site, the historic Drake Hotel once occupied,

centrally located with Central Park views, the site became one

of the most valuable plots of land in the world at

$520 million. Now it goes without saying

this building was not constructed for the average man.

It has over 85 floors with 38,000 square meters of usable floor space,

but only 104 units

for people to live in, each costing millions of dollars each.

But the point stands

where there is exceptionally high demand, you can build higher.

The cost of land in Dublin doesn't come close to those of Manhattan

or Hong Kong though. So in most cases,

the bottom of our U-curve, ie. the cost effective height to build to,

will be between 6 and 8 stories.

With a recent Irish government report even suggesting

as high as 12 stories in some areas.

Let's next focus on minimizing the building costs

of these buildings. One of the primary causes of

increase costs with increased construction height

is the necessity of using floor space

for the structurally integral building core, which keeps the building

standing and houses elevators and other services.

While there are many ways to design the shape of the building,

certain floor plate designs end up being more desirable

than others to maximize usable space. Say that the

net area of the floor plate of this building is 1400 square meters

The core of the building of this shape

and size would need to be around 335 square meters

This gives a gross area of usable area

of 1,065 square meters

and thus a net to gross ratio of 1.31.

So a design like this is stylish, but when you analyze the

space efficiency, it's not great for maximizing floor space

A building like this

seems like it might have a bit more usable space

but the building core is still taking quite a bit of space

compared to the livable floor area. This design's

net to gross ratio is around 1.26.

And a building with this shape may not be as exciting,

but it's core area is minimized compared to the usable space.

Its net to gross ratio is only 1.14.

Which is about as good as it gets and is exactly

the floor plan of 432 Park Avenue.

While variety and expression of building design are important,

these elements invariably add costs and require

careful design consideration.

When affordability is an issue, simpler designs are better.

Wall to floor ratio is also a critical

measure of cost efficiency. It expresses the perimeter length

of the wall that has to be constructed for every unit of floor area.

So from a cost perspective,

the lower the ratio, the better.

Using simple geometry, we can see that a 3x3 square

has a total perimeter of 12 meters.

This would have a wall to floor ratio of 0.33.

A cross shape with the same area of 9 square meters,

has a perimeter of 20 meters. This would have a wall to

floor ratio of 0.45.

When constructing buildings, this simple principal is the same.

The more perimeter wall needed per floor area,

the more expensive things get.

A comparison of Asian and London towers provides an interesting

contrast in approaches wall to floor ratios.

Tall Asian buildings score between 0.30 and 0.35,

while London buildings score between

0.35 and 0.60

with the majority above 0.45.

This is because the Asian buildings have larger, more regular floor plates

with centrally located cores. So the design

of our tower has huge effects on our cost

but so does construction techniques.

Traditionally, towers are built using repeating floor design

with molds called formwork, being used

to cast the concrete structure. Despite this

essentially being an automated assembly line,

it can still be labor intensive and slow,

and is exposed to variabilities of site and weather conditions.

Prefabrication and offsite construction is

increasingly becoming an appealing option, but this can offer

high precision solutions created in factory conditions

and often reduce on site delays and help progress construction

even in a market with a skills shortage

On some construction projects in Dublin, already

concrete products and timber frames are being fabricated offsite

and assembled onsite. An extreme example of

this idea of prefabrication is being used in China

where a company called Broad Sustainable Building

built a 30 story building in 15 days

for a cost of $1000 per square meter.

and later built another 57 story building

in 19 days.

The building pieces are fabricated

in sections at two factories in Hunan.

From there, the modules complete with pre-installed

ducts and plumbing for electricity,

water, and other infrastructure are shipped to the site

and assembled like Legos, or flat-pack IKEA furniture

The company is in the process of franchising this technology

to partners in India, Brazil, and Russia.

What it's selling is the world's first standardized skyscraper.

One of the primary cost drivers for skyscraper

are the labor costs for specialized workers.

By outsourcing much of the construction work to

safer, controllable environments like this, we can reduce

the costs. In a country like Ireland, where many of its skilled construction workers

were forced to immigrate to Australia, New Zealand, and Canada

during the economic crisis, many of which have not come home.

This may well be a solution that can help with construction.

Regardless of building techniques,

policies need to change in cities like Dublin to facilitate

quicker cost effective builds. While not being completely blind

to future implications of relaxing regulations.

Currently, 1 car parking space per unit is required

for every apartment. In a city center location,

where we would hope to move toward public transport solutions,

this is a completely unreasonable regulation to have in place.

Especially when you consider the impact of costs

it has, with some reports estimating that this adds

30,000 euro per car parking spot to any building.

With our city populations growing more rapidly every year,

we cannot hold onto past ideals. While the optimum

height for minimizing the cost of apartments

may be 6 to 8 stories, we've discussed the benefits of building higher

beyond just the minimization of cost and how other

cities have transformed themselves in a past video.

Building higher facilitates cost effective public transport,

reduced commute times, and creates a more livable city.

We simply cannot continue allowing urban sprawl

to be our solution. It is an unsustainable

solution to a problem growing faster than we can keep up.

We simply need to look at the ever growing

rate of homelessness in cities like Dublin for proof of this problem

In a city that lost hosting for the largest

tech conference in the world, due to a severe lack

of infrastructure, the Dublin city council deemed it

sensible to refuse planning permission

to this 22 story hotel

on Tara Street, on the grounds that it would have a

"significant and detrimental visual impact on the city skyline"

A skyline dominated by two industrial chimney stacks

while functional, modern building that are

desperately needed in the city, are continually blocked.

This isn't a problem exclusive to Dublin.

San Francisco. A city

notorious for skyrocketing costs of accommodation has

an average building height of just 3 stories.

Mostly due to similar restrictions in building heights.

Washington D.C. has some of the worst traffic in the U.S.

and it has height restrictions blocking anything taller than its national monuments.

In larger cities with restrictive height regulations,

you can almost be garunteed

socioeconomic problems will follow.

In all reality, this problem has so many fascets beyond