It didn’t take long for the owners of this suburban Cape Cod to want more space. The couple—who shared the home’s only upstairs bathroom with their two young children—envisioned an eco-friendly addition with more character than luxury. So together we set out to create a cost-efficient addition with both function and flair. The sizeable rear addition nearly doubled the home’s square footage while making a striking statement. An unusual choice for exterior cladding—standing seam roof material used here as siding—appealed to the couple’s modern sensibilities. The steel cladding’s blue jewel tone and vertical orientation contrast against the pop-out’s gray lap siding, a nod to the home’s traditional façade, where blue shudders tie back to the addition and a bright yellow door reflects the owners’ love of color.