Fire Wall or Shear Wall?

In an email from Sheryl:

Hi Handyman Bob,

I listen to you regularly, but have not heard this question come up.

I recently moved into a townhome with an adjoining (firewall) wall with the neighbor.  Before hanging a large mirror, I drilled a small hole to see if I was on a stud.  It wasn’t, so I attempted to screw in a corkscrew shaped anchor.  It went part way in, then hit what I’m guessing is the firewall.  Do you have any suggestions on how to hang pictures on that wall?  Or does that side of the house need to remain empty?

Thanks so much,


And, my reply:

First of all, Cheryl, thanks for listening to the show.
What you describe sounds like a double layer of drywall. Multi-family construction requires that as a firewall between occupied units in many jurisdictions. If this is the case, then the drywall anchor you tried to use is the right style; you just need one made of metal. The plastic variety simply won’t withstand the torque of the screwdriver against the thickness of the two layers of drywall. To test this theory, try stabbing a fine tipped screwdriver or an ice pick through the wall. If it penetrates, it’s all drywall. If it won’t, it might be a shear wall, which means the drywall is against a layer of OSB (oriented strand board). Shear wall construction is used to keep a building from twisting in the event of an earthquake. If it turns out to be a shear wall, then a screw or a nail will work to hang your pictures. Hope this helps.
Handyman Bob

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