Architects and engineers have battled daylight in Houston’s Rothko Chapel from the moment it opened in 1971, trying to protect and illuminate the 14 monumental paintings the space was built to showcase.

They did not know until recently that the world-famous art and spiritual sanctuary was also susceptible to a potentially more dangerous issue: wind.

That problem surfaced this summer, adding four months and $1.1 million to a renovation project that has shuttered the chapel since March.

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The scene may seem familiar to anyone who has renovated an old building: Scary things often lurk behind walls that haven’t been opened up for decades. And when construction crews dismantled the chapel’s acoustical ceiling tiles this summer to prepare the building for a new skylight, they found the concrete support walls were built without steel reinforcement.

This was a common building practice in 1970, and the chapel is grandfathered from current codes written with an eye toward 130 mile-per-hour hurricane gusts, said executive director David Leslie. But the chapel’s leadership took no chances.

“This is a simple matter of stewardship,” Leslie said. “I don’t like to use double negatives, but we cannot not do it. … If a weather incident hit the walls at just the right angle, you could lose the chapel. A wall could collapse.”

Lead architect Stephen Cassell of the New York firm Architecture Research Office said visitors were never in danger of being inside a toppling building, because the chapel would be closed during a major hurricane event. But he and ARO partner Adam Yarinsky were also mindful of protecting Rothko’s priceless paintings.

Ahead of the chapel’s 50th anniversary in 2021, the renovations are a key element of a $30 million, multi-phase expansion across its 4-acre campus on Sul Ross, next to the Menil Collection grounds.

A new welcome center took shape this summer across the street from the chapel, which is on track to open in March. But the unexpected structural work has pushed the chapel’s reopening to next June.

The organization has raised $12.8 million of the funds it will need to finish all the elements of the plan, including another building and a meditation garden, Leslie said.

As part of the fix, crews are now removing plaster and cutting floor-to-ceiling channels in the masonry walls to insert skinny support columns of rebar that will be grouted into place, adding tensile strength to the building. Several inches wide, the columns will be cut at various intervals across the entire structure.

Linbeck project manager Allston Marble said the intervention is not “complicated or super-special” — he’s done it before on older buildings — but the scope of the chapel project makes it unique. With mechanical equipment butting up to the mezzanine level, crews must also dismantle the top portion of the building’s brick exterior to access the concrete wall there.

“It’s a big delay, but it’s the right thing to do,” Cassell said.

Despite the setback, the new skylight designed by George Sexton Associates was installed last week, slightly ahead of schedule. The steel framework and glass are the first elements of a new system that incorporates louvers (now being fabricated), digital projectors and mirrors to better modulate light and showcase the paintings.

Another new asset is buried outside: an underground stormwater capture system that slows runoff to the city’s bayous. “This is going to be a huge improvement to this area,” Marble said. “There were no detention requirements when the chapel was built, so whatever didn’t go into the soil just ran off into the street.”

New birch trees from North Carolina and shrubs from Georgia will arrive in a few weeks, beginning the transformation of the landscape around the chapel. Leslie hopes most of the grounds will be walkable again by March, to give visitors a sense of the Rothko’s magic again.

A sublime, bright glow infused the chapel’s interior on Monday. Although the floor was filled with a forest of scaffolding, the space felt larger and more open than it did a year ago because the black baffle that hovered over the room’s center has been permanently removed, adding about 10 feet of ceiling space.

“It has changed the quality of the space so much,” Cassell said. “The original space was more soaring, more appropriate for the scale of the Rothkos.”