Podcast Episode 747: Lab-Grown Lumber, Controlling Humidity, and Exterior Insulation

This week's Fine Homebuilding podcast covers a mix of building topics, including one that touches climate and materials: a Netherlands startup called New Dawn Bio says it has grown wood in a lab that develops far faster than trees in a forest, without cutting any down. The company raised $2.4 million in early funding and says the process could cut wood costs by cutting waste from sawing and gluing. It's an early-stage technology, not something available for home projects yet, but it points to where building materials may be headed as the industry looks for ways to cut deforestation and emissions.

The episode also answers two listener questions relevant to anyone dealing with an older or humid house. One homeowner restoring a long-vacant Victorian house in Ontario is fighting high humidity, especially in a basement with a dirt floor. The hosts discuss whether covering the dirt with plastic sheeting (a vapor barrier) and insulating the basement walls would help dry things out, since a 50-pint dehumidifier alone hasn't gotten humidity below 60%.

The second question comes from a homeowner in North Carolina replacing windows and siding on a 50-year-old house, who's deciding between two types of rigid foam board, XPS or foil-faced polyiso, for a layer of continuous insulation outside the wall sheathing. The discussion centers on whether the foil facing on polyiso could trap moisture in a humid climate, versus using a foam that lets more moisture pass through. Anyone planning a similar siding or window replacement with added exterior insulation faces the same tradeoff, and the right choice depends on climate and how the wall is built.