Hey homeowners! I'm working on an exterior remodel for my 1960s home in Seattle. Currently, I've got old cedar siding, and I believe there's plywood underneath without any continuous insulation. I'm considering whether to tear down the plywood and install ZIP-R to meet the new WA state energy code requiring R20+5 levels of insulation. I'm curious if anyone has experience with ZIP-R in the PNW and if it's worth the investment. Also, why do many contractors recommend just replacing the siding without addressing the underlying insulation? Would love your insights before I decide! Thanks!
7 Answers
ZIP-R might not be ideal, especially in earthquake zones, since the insulation gap can weaken the structure. Instead, attaching exterior insulation with furring strips for siding might be a better route.
Think about what ZIP-R is—it’s mainly OSB with an outer layer meant for new builds to save labor. Since you've already got plywood, just adding exterior insulation might be smarter and more cost-effective.
I’d suggest filling the wall cavities with blown-in insulation instead of removing everything first. That way, you might save time and money while still improving insulation.
ZIP isn’t common because it’s not very profitable for builders. If you can see the sheathing, go ahead and replace it, but be aware it may only enhance that section’s performance. Contractors usually avoid it due to its complexity.
I’m curious about your priorities—are you mainly focused on fire safety by switching from cedar to HardiePlank? Also, have you been proactive about moisture issues around your foundation and siding? Meeting the R-value requirement is great, but consider why it matters to you.
Great questions! Our cedar is quite old and has some air leaks, plus we suspect rot behind the siding. We’re considering a full overhaul for peace of mind. We’re replacing old windows and the deck too, since we already fixed the roof last year.
If you decide to go for ZIP-R, it’s a lot safer to install it over the existing plywood. It doesn’t really downgrade your energy performance either.
ZIP-R can be pricey for R-value. If your existing sheathing is in good shape, consider adding a taped and sealed 1" foamboard under the new siding. It’s typically more economical.
Yes, you'll need to make sure to flash the windows and doors a bit further out with foamboard and furring strips. It’s pretty straightforward!
Good point! Which type of foamboard would you recommend for weatherproofing while also providing insulation?