The Insurance Council says owners of commercial buildings built before 1935 are finding it difficult to get insurance, forcing some to look overseas for cover.
Following the Napier earthquake in 1935, a building code was introduced requiring masonry to be firmly reinforced.
The Insurance Council said insurers are reluctant to renew pre-1935 buildings, which tend to be mainly made of brick, because they did not stand up well to the Christchurch earthquakes.
Chief executive Tim Grafton said building owners are unlikely to obtain renewed cover unless strengthening work has been done.
He said it's likely more people will be looking for insurance offshore as it's difficult to get here.