Replies

1. GBA Editor
   Martin Holladay | Mar 26, 2019 06:01am | #1

   Giles,
   My gut tells me that any thermal benefit will be relatively minor, and therefore not worth the expense. But I haven't done any calculations.

   Here's a more important point: If you don't use the same type of fasteners required by Huber's fastening schedule, you'll have to talk to an engineer to see if your substitution is equivalent or better from an engineering standpoint. Stainless-steel nails have a smaller diameter than steel nails, and perform differently.

1. 
   davisgk | Mar 26, 2019 07:09am | #2

   Thanks Martin, your gut seems to be correct, I found a relevant study that indicates less than 5% difference in degradation of the sheathing R value between galvanized steel and stainless steel. I also found a study of the withdrawal strength of SS nails vs galvanized that concluded SS has 20% lower withdrawal strength.
   https://www.cascadiawindows.com/database/files/product_documents/NAPHC_2014___Thermal_Bridging_Through_Exterior_Insulation___Higgins_Shane_Finch_.pdf

2. Expert Member
   BILL WICHERS | Mar 26, 2019 02:35pm | #3

   You’ll never see a difference in thermal performance between plain steel and stainless steel nails. Any difference won’t even be measurable when the rest of the structure is taken into account.

   Assuming 1/8” diameter nails, which is close but not perfect since nails have oddball diameters, 84 nails is only a little over 1 square inch of total area. The 4x8 foot panel is 4,032 square inches. Yes, the nails are far more thermally conductive than the zip sheathing or the wood of the studs, but the nails are also essentially insulated in the wood studs so they aren’t directly exposed on both ends which means they aren’t really thermal bridges through the entire wall in the way studs are in batt-insulated walls.

   The R value for a mid range carbon steel is about R0.17. Zip R6 sheathing is actually R6.6. A simple weighted average gives an overall R value for the panel of R6.59841. If you use a fastener that is twice as good a thermal insulator, your overall panel R value becomes R6.59845. That’s a 0.000008% improvement if I’m counting all my zeroes correctly :-)

   A 5% improvement in the fasters insulating value will give a tenth of the improvement I showed in my example. It’s miniscule. Also, when I looked up the thermal conductivity values for steel, it turns out the thermal conductivity is GREATLY affected by the actual alloy used. Even different stainless steel alloys like 303, 304 and 316 had surprisingly different thermal conductivities.

   Bill