Major League Soccer franchise the Portland Timbers has announced a more than $50m (€46m/£38.8m) expansion project for Providence Park, the club’s home ground that it shares with National Women’s Soccer League franchise the Portland Thorns.

The privately funded development would add four new levels and approximately 4,000 seats on the east side. Three of those levels were designed for reserved and group seating sections to help meet demand, while including a pedestrian-friendly public arcade along SW 18th Avenue.

Additionally, a 93-foot-high covered structure would be added on the same side, designed by Portland-based Allied Works Architecture. The vertical expansion design raises the stadium’s capacity to approximately 25,000.

The Timbers have a season-ticket waiting list of more than 13,000 fans and have sold out for every regular-season and play-off match at home since the club’s inaugural MLS season in 2011. Providence Park’s existing capacity of 21,144 for soccer currently ranks in the bottom half of the league in terms of size.

“We felt it was imperative to see how we could transform the stadium and add capacity to both meet the demand that we have for tickets and also position the club to be viable and competitive for years to come,” Timbers president of business, Mike Golub, said. “That has been the impetus for this process, which we hope is beginning to reach fruition.

“This proposed project is a win-win for everyone involved, and we’ve been very encouraged by the collaborative work that’s been put into this project to date.

“We still have some work to do, but we are actively working with the city and neighbourhood association, and everyone is excited by the prospect of an expanded Providence Park and ensuring the long-term viability of this unique stadium.”

The potential construction timeline would include two off-seasons, beginning either at the end of the 2017 or 2018 season, and conclude in time for either the beginning of the 2019 or 2020 MLS season.