Americans are coughing up $4,600 more on average to buy their dream home than six months ago — thanks to a record run-up in prices for a once-cheap plywood substitute.

Prices are on a tear for those bonded wood-chip sheets commonly used as sheathing for walls, floors and roofs in new home construction. Oriented Strand Board, or OSB, has long been used as a low-cost alternative to plywood, but the product now fetches a higher price as increased demand and tight supplies lead to delivery delays and elevated construction costs in the U.S. and Canada.