I’ve had a lot of inquiries over the past few years asking whether installing wood sheathing, like OSB or plywood, under James Hardie siding is a worth while purchase. Well, this answer depends on what the homeowner is actually trying to achieve.
If the goal is to increase the home’s energy efficiency, don’t look to wood sheathing! You’ll only get about .63 R-value. (This is about equivalent to putting another layer of drywall up–obviously not very efficient and certainly not worth the additional cost to buy and install.
Now if the goal is to shore up the integrity of the home, paying for wood sheathing is money well spent. Wood sheathing adds a significant amount of structural integrity to any home, particularly older, neglected or historic homes. Specifically, I like gravitating toward OSB sheathing for its increased strength over plywood, and (surprise, surprise) it costs less than plywood, too!
So, when you’re considering a wood sheathing, ask yourself why you really want it. Is it for energy efficiency or structural integrity?
