Nina Liebskind, the wife and business partner of Daniel Libeskind, the architect designing the replacement for the twin towers in New York, has admitted the building could be delayed by up to eight months because of design changes to improve security.

Mrs Libeskind told Building the decision by New York governor George Pataki to recall the replacement for the World Trade Center, which was destroyed in the 9/11 attacks, would mean it was ready in September 2009 rather than January, as first thought.

She said the delay showed “how resilient the masterplan is”. She added: “Because of increased security criteria, the tower will have to be more slender than it was. It will be made in a different way. This is the beginning of a new design.”

Pataki demanded design changes after the New York police department questioned the building’s safety. The symbolic height of the tower – 1776 ft, marking the date of the declaration of independence – will remain.

In an interview, published in Building this week, Daniel Libeskind dismissed criticism of the design, which some say is overly patriotic.

He said: “We’re building something to last 100, 200 years. Think about how much has been accomplished to bring consensus, feasibility and spirituality to the site. We’ve accomplished a lot.”