A United Nations-affiliated nongovernmental organization said it will take 20 years for the Gaza Strip to rebuild in the wake of the July-August war between Israel and Hamas that either damaged or destroyed 17,000 housing units, the Associated Press reported. Palestinian officials estimated the rebuilding process could cost more than $6 billion.

The Shelter Cluster, which works with the U.N., Red Cross and Norwegian Refugee Council, said in a report it estimated the 20-year figure by looking at the capacity to move in construction materials legally across the Israel-Gaza border. Gaza is still reconstructing from more than a decade of near-annual conflicts between Israel and Hamas, the quasiterrorist political group in power in Gaza.

The 140-square-mile Gaza Strip is home to 1.8 million people and has a housing deficit of roughly 75,000 units. More than one-quarter of Gazans live in the strip’s largest city, Gaza City, described by the Washington Post as the 40th most densely populated urban area in the world with 42,600 people per square mile.

The rebuilding effort could be hindered by an Israeli blockade that impedes the movement of a slew of building materials, including concrete. Gazans get many of those materials via smugglers who illegally move materials through tunnels connecting Gaza to Egypt. As reported by Sky News, there is talk of easing the blockade, which has had widespread detrimental effects on the Gaza economy and garnered international condemnation.

More than 2,000 people were killed in the recent bout of fighting, about one-quarter of them children. The conflict began when tensions flared after three Israeli teenagers were kidnapped and murdered in the West Bank, but full-scale fighting began with Israel’s Operation Protective Edge that was undertaken to root out Hamas rocket systems and covert attack tunnels.

A documentary shot for Britain’s Channel 4 examined the Gaza housing market during what one developer called a “boom” in 2013:

Gaza's Property Ladder from Cookie Dought on Vimeo.