Matt Springer has been giving presentations around San Francisco about home earthquake preparedness since 2008 (for more information about the presentation, go to his earthquake preparedness website). This blog is devoted to posts ranging from technical "how-to" articles to more philosophical "should-you" topics. New articles will be posted at most about once a month, so people who subscribe won't be subjected to lots of e-mail.

Wednesday, September 7, 2011

“Be sure to bolt your furniture bracing straps to a wall stud”…ok, now for the other 95% of the population who doesn’t know how to find a wall stud:

I have been meaning to post for the last few days and kept getting too busy, so then Colorado had its largest earthquake in 40 years, then the east coast of the US had its largest quake in 67 years*, and then that evening I myself felt a small tremor in San Francisco that was centered on the Hayward fault in the East Bay…ok, ok, I’m posting already!

*The last quake that large on the East Coast was…New York, 1944!  (See my earlier post, “Why the heck do you live in that place with earthquakes”)  Please remind your East Coast friends: DON’T run out of the building, DON’T believe that “Triangle of Life” e-mail spam, and DO drop, cover, and hold on.  Better yet, direct them to this blog!

In my talks, I always feel like my description of how to brace tall furniture to the wall is incomplete, because I say that you need to bolt straps to the wall studs, rather than drywall or plaster, but that I don’t have time to describe how to find wall studs and work with them.  That just gets too far away from the topic and there isn’t enough time in the talk; but really, if you want to brace your furniture safely, you need to know about the wall studs.  So, today let’s get around to that topic.

Most walls aren’t as solid as they feel.  In fact, in a modern building, you can probably get from one room to another without using the door (if you are so inclined) if armed with a reasonable sledgehammer.  Plaster and drywall (sheetrock) crumble and powderize, as you know if you have ever tried putting a short screw into a wall without a wall anchor. 

If you brace your tall furniture to the wall with straps or brackets and put the bolts directly into the drywall, then it won’t take much motion for the furniture to want to fall away from the wall hard enough to simply pull the screws right out of it.  There are various anchors and toggles that expand within the drywall or open up on the other side of it, but a heavy object like a book case or file cabinet pulling away from the wall still runs the risk of defeating the structural integrity of that drywall and turning it into dust (giving the term “anchors away!” another meaning).

Fortunately, every 16 or 24 inches (center to center) in decently modern buildings, and at various intervals in some older buildings, there are vertical structural supports called wall studs that are an integral part of the main structure of the building; they will not simply disintegrate under most imaginable circumstances.  They are typically wood beams (left photo below from www.woodaware.com) in shorter buildings, and metal struts (middle photo below from www.cdcbgreenhome.com) in taller buildings.  (In older buildings with lath and plaster walls, thin wooden slats called laths are nailed across the studs to support the plaster, shown in the right photo below from wikipedia.org, but these laths are not structurally sound.)  If you bolt something through the drywall or plaster and into the studs, it isn’t going anywhere.




This means you have to be able to do two things: find a wall stud, and bolt something into it.


Find your wall studs

The old-fashioned method that I used in college to find wall studs was to tap the wall with my finger or the butt end of a rubber-handled hammer.   Most often the sound will be hollow, and as you move sideways, the tapping sound will get less resonant and tighter until you reach the stud, where it sounds less like tapping a drum and more like tapping a brick; then will get more hollow again as you keep moving.  The least resonant part is where the wall stud is located.  If you find a few of these and they are at regular intervals, you are probably in good shape (note that some older buildings may not have a spacing of 16 or 24 inches, so assuming is dangerous).  This method of finding studs sometimes works, but frequently it is difficult to actually tell the difference between the sounds. 

A technological step up from this is to use a stud-finder consisting of a swinging rod magnet.  You can buy these cheaply in hardware stores.  The rod magnet will be flopping around as you slide the stud finder along the wall, but if you slide it past a metal nail in a wooden stud, or past a metal stud, the magnet jumps toward the wall and the other end of the rod sticks straight out as a result, showing you where the nail or metal stud is located.  This can work well but can also be frustrating, especially in wooden studs, because there are only nails in specific locations up and down the stud, and if you aren’t sliding the stud finder in the correct plane that contains the nails, you’ll sail right by that stud without noticing it.  The baseboard is a good place to start, but if it is not accessible, then you basically have to keep sliding the stud finder around at different vertical levels until you find a nail, then mark the horizontal location and search for others.  If you know your stud spacing, you can use it as a default, but it’s nice to confirm by actually finding a nail somewhere in the other studs.

After my last move, I found myself in a place with metal studs and decided that it was time to go high-tech.  Even though the magnetic stud finder works a bit better with metal studs,  I dropped a few more bucks on a better, electronic stud finder that somehow senses when an object is behind the wall and beeps when it is nearby.  It isn’t foolproof, and you cannot use it with lath and plaster walls, but it is way better than the magnetic kind if you have drywall.

Before we go on, here are some little hints.  You want the object into which you screw or drill to really be a wall stud, NOT a wire conduit, water pipe, or some random metal box put behind the wall for who-knows-what reason.  This is why it is nice to find a few studs and confirm that these objects are showing up at regular intervals.  If there’s an object where you would not expect to find a stud, better not drill into it!  Also, know what is on the other side of the wall from you.  I found a strange extra “stud” running vertically all the way up the wall where it shouldn't be, and then realized that the bathroom was on the other side of the wall and the shower head was right there, meaning that there were water pipes!  Lastly, rather than find the studs near the floor when planning to put bolts in higher up on the wall, it’s safest to confirm that the stud pattern is how you think it is on the approximate level where you want to put your bolts.


Bolt things to your wall studs

Now let’s say you know where your studs are.  Better know WHAT your studs are, as well, because there are different rules for bolting into wood or metal studs.

For wood studs, a nice long woodscrew or lag bolt of the sort normally supplied with earthquake bracing straps is just fine.  These are thick, sharp, and long (like 2 inches) so that they reach through the drywall and into the wooden stud for about an inch.  The threads of a screw may not seem like much, but all those threads carved into the wood and compressing it in the process hold extremely well when pulled upon.  Use a drill bit that is just slightly smaller than the solid part of the screw, so that the core of the screw will not need to displace very much wood but the threads will tightly cut spirally into the wood.  WHILE WEARING GLASSES OR GOGGLES, and preferably with work gloves, drill into the wall in front of the stud.  The drill will go through the drywall quite easily (proving why you shouldn’t just put your bolt into the drywall) and then will hit the stud and encounter more resistance; drill in all the way.  Then pull out the drill bit and screw in the screw.  A little resistance is good, but if it is too hard to screw in, you may have to take a larger drill bit and widen the hole a tiny bit.  A power screwdriver is nice here.

(Hint: it’s wise to have newspaper on the ground to catch the crumbled drywall and the wood sawdust.  What?  You read your newspaper on your iPad?  Well, I GUESS the iPad will catch the sawdust but probably not the best idea…  Actually, I also like to tape a small piece of foil sticking out from the wall under where I’m drilling to catch most of the dust.)

For metal studs, some sources say that you can just drill an appropriately sized hole in the metal stud and screw directly into that, but I would not suggest it; not for something heavy that may want to pull away from the wall.  Instead, you should really use a toggle bolt.  This is the metal contraption on a bolt that is spring loaded so that you can shove it through the hole in the metal and its two wings spring open on the other side, leaving the screw part of the bolt sticking out of the wall.  When you screw a nut onto that bolt, trapping the furniture bracing strap or anything else, you can tighten the nut so that it and the expanded wings squeeze together on the front and back of the metal stud.  Now your bolt is literally part of the main structure of the building and will be very sturdy. 

I’ve included a photo here of various anchors that you should NOT use for this purpose.  The three on the right are anchors designed to work directly with drywall and won’t work with metal studs.  The all-metal device 2nd from the left is a molly bolt, which works by the flexible part of the metal sleeve collapsing and spreading outwards on the far side of the wall as the bolt is tightened.  Theoretically this would work just fine with the metal stud, but I recommend against it unless you have experience with molly bolts because there is no obvious event that tells you that it has spread, unlike the toggle bolt that snaps into place with an obvious click.  The plastic blue variant on the far left also works by collapsing and spreading as the bolt is tightened but is meant for drywall; I fear that the sharp edges of the hole in the metal stud might gradually cut through the plastic.

The unavoidable disadvantages of doing this are that, first, the hole in the wall must be much larger than the bolt because the spring-loaded part is large when compressed.  So instead of using, say, a 1/8 inch drill bit to make the hole for a screw into a wooden stud, you might be making a 1/2 inch hole or more in the metal and, unfortunately, the wall.  The larger the toggle bolt needed, the wider the hole will need to be.  If you are not sure what size toggle bolt to use, tell the sales associate at your hardware store what kind of furniture you are trying to brace, and they’ll tell you which toggle bolt to use.  The second disadvantage is that once a toggle bolt expands on the far side of the stud, you’ll never get it back again.  If you later abandon that site and want to patch the hole in the wall, you won’t be able to pull it out but you can simply push it further in until it falls into the hollow part of the wall, never to be seen again.

Drilling into the metal stud is similar to drilling into wood, except that the metal stud is thin so you will encounter resistance for a while but then will punch through to the other side, unlike a wooden stud, in which case you just keep drilling until the bit can’t go any further.  Also, metal is hard!  Make sure that your drill bit is rated for metal, and be prepared to go through the metal extremely slowly.  You may actually think it is not working for a couple of minutes, until it punches through.  Be careful to prevent the bit from moving sideways as it starts the hole.  And it will be VERY LOUD and set up quite a vibration.  It can be easier to drill a smaller hole first, then follow up with a larger drill bit in the same place. 

It’s best to try to drill into the center of the stud rather than at one side, because the metal stud is shaped in cross section like a U with the “base” of the U being to one or the other side; you’ll be drilling into one of the two “arms” of the U.  That means if you are too far to one side, instead of punching through the metal layer, you’ll keep encountering more of the “base” and won’t make much progress; plus, you won’t have a complete hole into which the toggle blot can be secured.  Also, please keep in mind that rather than annoying sawdust, you will now be dealing with sharp metal shavings that can irritate your skin and should under no circumstances be allowed to fall down to where a child or pet can step on them or eat them.


Last word

All this hassle!  But it is worth it, as you know if you caught that funny episode of Modern Family on TV in which there was an earthquake and the book case fell over, almost hitting the kid, because the dad had been procrastinating while telling his wife that he had already braced the bookcase.  What a nice advertisement that episode was for earthquake safety!  But once you spend the half hour to do this and brace your bookcase, file cabinet, or whatever else you want to prevent from falling over, you can rest easy knowing that it simply is not going to fall unless the rest of the building is falling with it, in which case you probably have other things to worry about anyway!


(Thanks to the folks at Cole Hardware in San Francisco for checking this article for accuracy)


No comments:

Post a Comment

COMMENT POLICY: Comments on blog posts can be very useful, raising issues and adding helpful information. However, some people attempt to post generic comments with embedded links to irrelevant websites. Due to this comment spam, all submitted comments will be verified by me first so there will probably be a delay before legitimate comments get posted. If your comment is taking a while to show up, it probably just means that I have not checked my e-mail yet.