Accoya® wood restores historic windows in Minnesota State Capitol

The majestic state capitol building in St. Paul, Minn., was in a state of deterioration: on the outside, the regal marble exterior designer Cass Gilbert envisioned when the building was completed in 1905 was crumbling while antiquated mechanicals and inefficient public spaces plagued the interior.

The state embarked on a $272 million, four-phase restoration plan in 2013, with tasks including replacing plumbing and electrical systems, boosting energy efficiency, improving access, replacing the roof and repairing the crumbling stone.

Another major part of the project was restoring the building’s original wood windows, which had been covered over with aluminum windows 30 years ago. The aging units—242 in total—had seriously suffered from fogging, failing glass, air leakage, and broken balances that rendered them inoperable, says Brooks Gentleman, owner of window replacement manufacturer Re-View, who were selected to restore the windows.

“They were boxy, and they didn’t look like the originals as they didn’t have the same kind of detailing as the previous windows,” Gentleman recalls. “Plus, the glass was failing and the windows were leaking air because the weather stripping had failed.”

Re-View removed the aluminum replacements, revealing the original wood window frames, which were then restored using restoration epoxies and replicated wood parts. Gentleman and company used an original complete wood window that still remained in the building as the basis of design for replicating all the new sashes with Accoya wood.

On the interior surface, recovered pine—older than a century—from the Idaho Lakes was laminated so the interior surfaces of the windows would match the existing woodwork in the building. Sashes were glazed with laminated insulated glass (IG) units with low-E coatings to improve the energy efficiency, security, and sound transmission.

Since some of the individual double-hung windows are about 2 meters (6 feet) wide by 4 meters (13 feet) tall, the sashes weigh in excess of 115 kilograms (250 pounds). Gentleman’s team engineered a system of weights and pulleys to make the massive windows easy to open.

The team also incorporated a combination of historic metal and modern weatherstripping in order to seal the operating windows, which produced an impressive outcome. After an independent agency tested many of the installed windows for air and water infiltration, they were shown to be twice as tight as the published ratings for modern replacement windows.

Gentleman credits use of Accoya wood for much of these results.

“Accoya wood as the base material is a very stable wood that doesn’t warp and bend like a lot of other woods,” he said. “That allows for more consistency and therefore a much better performance.”

As predicted at the start of construction in 2013, the work will be completed this June 2017.

Project details (management, design and construction firms worked collaboratively to restore the Minnesota State Capitol):
Project Owner – Department of Administration, State of Minnesota
Contract Administrator – CPMI (Cost, Planning and Management International)
Program Manager – MOCA Systems
Design Team – HGA Architects and Engineers
Construction Manager – JE Dunn Construction
Governing Body – Minnesota State Capitol Preservation Commission