Heather Nelson, of Boxford, Mass., sets a nail as Catherine Atwood of Falls-Village, Conn., holds a sheet of plywood while lending a hand at 921 Ward. A group of 30 bicyclists trekking across the U.S. stopped in Lawrence to help in building a Habitat for Humanity Home on Wednesday.

It’s close to 100 degrees with suffocating humidity, but that is not stopping one group of volunteers from getting their work done.

Wednesday was the first day of construction for the 30 cyclists who pedaled into Lawrence to help build a home with Habitat for Humanity. The cyclists, ranging in age from 18 to 25, are part of the group “Bike and Build.” Some are taking a break after recently graduating while others just needed something to do for the summer. Together, the group is traveling more than 4,000 miles across the U.S. to donate time to community service. Lawrence is just the sixth stop on their 72-day journey, which started in Providence, R.I., and will end in San Francisco.

The group has helped in a variety of ways so far, from sawing boards and wielding hammers to demolition and renovation. However, Chris Klapheke from Louisville, Ky., said the work is not the hardest part of the trip.

“The ride itself is the most challenging part,” Klapheke said. “The days when we are working six or eight hours — these are our days off.”

In Lawrence, the group is helping construct the Abdelbanat-Abduljabbar home in conjunction with Lawrence Habitat for Humanity. Originally from the Darfur region of Sudan, Karim Abdelbanat, his wife and their four sons have made Lawrence their home since 1990. For Stephanie McBride, a cyclist from Columbus, Ohio, working with the homeowners is the most rewarding part of the experience.

“It’s really nice to meet them and get to hear their stories,” McBride said. “It’s incredible to know we’re making their lives better.”

For Mr. Abdelbanat and his family, the experience is just as rewarding. One word seemed to sum up the family’s feelings: gratitude.

“Young people around the country traveling here to help us — I was not expecting that kind of help, but I’m grateful, very grateful,” Abdelbanat said.

The cyclists plan to finish their Lawrence work Thursday. They will commemorate their half-way mark with a celebration dinner before continuing for the West Coast. It will be a summer to remember for many of the riders.

“I might need a break after it’s done, but it’s the summer of a life; that’s the only way I can put it,” Klapheke said.