Do you recommend nailing trusses to the top plate of interior walls?

Q: Do you recommend nailing trusses to the top plate of interior walls or do you recommend 2×6 nailed to the top plate between the trusses? How would you secure the interior walls so they do not bow if they do not have another interior wall at 90 degrees to it?

A: Thank you for asking such an important question regarding attachment of roof trusses to interior walls. This is a topic that comes up time and time again and there are several ways to answer this.

Remember – trusses are made of organic material (wood) and because of this they will always be influenced by their environment. Because of the nice warm bottom chord nestled comfortably in the ceiling insulation and the top chord exposed to the cooler moist air in the attic space, the trusses will be under different conditions from top to bottom. These different conditions of moisture and temperature tend to cause the wood within the truss to move, shrink, bend or a combination of all. When this happens we have a condition called “Truss Uplift”. This term can make any contractor or truss company cringe.

The fact is… truss uplift is a very real condition and it will happen in areas where the temperature varies greatly from season to season. Truss uplift is with us for good but it’s how we deal with it that can make or break a good truss installation.

Back to your question about nailing a truss to the top plate of an interior wall. I would not recommend this because of what I have seen in the field and depending on how much truss uplift occurs, there can be quite a bit of separation at the drywall edges. I’ve gotten calls where the customer is upset that their drywall that was installed beautifully last summer is now cracking and there are all kinds of gaps in their ceiling at the interior walls.  I am often asked if maybe the trusses have been built too light or the girders are not strong enough and my response is, it’s difficult to explain the effect of truss uplift but this easily avoided problem occurs more often than you think.

So, truss uplift is just part of life.  How do we deal with it? Let the trusses do what they will do and find a better way to let it happen that will not cause any problems. If done correctly, trusses can move as they will, the drywall can move and bend with them and the homeowner never sees the effect.

There are a couple of ways to make this system happen. Simpson Strong Tie makes a truss clip that is basically an “L” bracket that has round holes that allow nailing to the interior wall and slotted holes that a nail is driven in most of the way. When the trusses lift up, the nails can slide in the slots while still keeping the walls plumb and in place. Drywall clips are required at the top of the wall to keep the drywall firmly attached to them.  If the nearest attachment point of drywall to the underside of the trusses is at least 16″ then the drywall will actually bend slightly as the trusses move and return to normal when the trusses settle again. No gaps!

Another option is to nail blocking to the top of the interior walls to secure the drywall to and again, start the first fastener for drywall at least 16″ from the interior wall.  This will work equally well for trusses that are parallel or perpendicular to the interior walls.

I hope this answers your question. Thanks!

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