Nailing roof trusses to interion non-load-bearing walls 1

[toomyw]

I'm hoping someone here can help.

I volunteer with Habitat for Humanity. I'm not a thoroughly experienced builder.

We're building a house. The exterior and interior walls were all built.

Then we put on the roof trusses.

Now my boss wants to nail the trusses to the interior, non-load-bearing walls. (of course, we nailed the trusses to the exterior walls and secured them with hurricane clips)

I've heard that this is not always a good idea, but I can't seem to find anything either right or wrong about it and would appreciate any feedback you may have.

Thank you.

 

[Focht3]

I'm not a structural engineer - so this would seem to be outside my area of expertise. But there is a potential problem if the Habitat house is located in an area with expansive clay soils, and the edges of the foundation are lifted (which can happen for a variety of reasons.)

If the interior partitions are fastened to the trusses and the edges of the slab lift the trusses, the partitions can be lifted, too! Sounds strange and unlikely, but it has happened here in San Antonio on some duplexes in a retirement community on the west side of town. Three to six inch high gaps formed at the bottom of these partitions - very strange looking. In retrospect, a gap at the wall/ceiling interface would have been preferable (but still undesirable given the size of the gap.)

Anyway, something else to use as fodder in your discussion -



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[jeffandmike]

There are a few factors that play into how much of an issue it will be.

Ceiling finish - is it a suspended ceiling (probably not in all rooms of the structure if it is a single family residence) or gyp board applied directly over the bottom chord of the trusses? With gyp board ceilings, large cracks can occur at the ceiling / wall interface due to vertical movement of the bottom chord of the truss. Simpson Strong-Tie (

http://www.strongtie.com)

manufactures a clip (DTC, STC or something like that) that attaches to the bottom chord and provides for vertical deflection. In their catalog, there is also a detail illustrating that the gyp board on the ceiling is not connected directly adjacent to the partition (to allow for the ceiling to slip by the wall). Crown molding can be installed to mask this, if necessary.

Truss spans - how long are the trusses spanning? Shorter span trusses will not have as much movement vertically at the bottom chord as longer span trusses (assuming they are designed and fabricated correctly). Now you may be asking what is considered short and what is considered long? For standard wood trusses for a single family residence, I would consider trusses spanning around 35 to 40 feet or so to be a long span.

One other attachment I've seen is created by providing 2x blocking laid flat attached perpendicular to the truss bottom chords (end nailed through the chord of the truss and each end of the blocking with 16d nails). Then another 16d nail is nailed vertically through the blocking into the top plate of the partition (interior, non-load bearing) walls. A gap of 3/4" or so should be provided between the blocking and the top of the partition wall. This creates a situation where the nails will be loaded in withdrawal so vertical movement can occur a lot more readily than if the nails were toenailed or somehow loaded in shear only. (I've never used this detail but have seen it recommended by some truss designers).


Sometimes the truss calculations (provided by the manufacturer or designer) will have details addressing these issues. If details have not been provided (common), maybe check with the manufacturer / designer and see what they recommend. Also, the calculations usually have the calculated deflection of each of the trusses (handy for determining how much vertical movement you will need to account for).

 

[SlideRuleEra]

I consider this to be a good idea IF the house and foundation are properly designed and well constructed (components are square, plumb, the right dimensions, etc.). Connecting trusses to the non-load bearing wall will help to tie the structure together. Most so called non-loadbearing walls really do have a measure of structural integrity. You may consider installing hurricane clips to these walls also. On a personal note - I did this to our own home (during construction) in 1986; took a direct hit from hurricane Hugo in 1989 - no damage. Maybe these extra connections helped, maybe not.

 

[Taro]

It is not generally a good idea to rigidly connect roof or floor members to partition walls. This is a load path issue. A few examples of problems that could arise:

- The partition wall may be damaged.

- Significant loads could be transferred through the "nonstructural" wall down the the floor that supports the partition. The floor probably was not designed for this extra load and could be damaged.

- The intermediate support will change the load distribution within the truss. Truss members that might have been designed for tension only could be put into compression and buckle.

 

[dik]

Another issue of concern is 'truss uplift'... due to differences in humidity between the top and bottom chords, the truss can 'bow' upwards and even lift the interior partition. It is a common cause of ceiling cracking in the vicinity of the partition.

 

[Trussdoc]

Truss uplift is the major cause for concern in attaching non-bearing partitions to roof trusses. Even the best designed trusses can undergo uplift if juvenile or compression wood finds its way into the plant that makes them.

A SINGLE toenail through the truss bottom chord into the top plate of the wall will allow some movement without damaging the surface finish too much. The clip is preferable and a small expense for reducing the possibility of callbacks and repairs.

 

[JAE]

I guess I don't agree that nailing to interior partitions is a bad idea. This is residential construction, folks, and I would bet that most ALL interior partitions have some nailing.

If the partition support (the floor below) is not designed to take the full tributary load from the truss then, guess what! The floor will deflect downward and redistribute the loads to the outer walls as originally intended.

If the partition support heaves (per my San Antonio friend above)- the interior partition will simply BEAR on the bottom chord of the truss and push upward on the truss whether it is nailed or not.

If you don't nail, then you must account for the lateral stability of the interior partition (most codes require 5 psf lateral as a minimum).

Most (I say most...not all) truss designs are based on the full wall to wall span and usually ignore the interior walls supports. So the truss doesn't need the interior wall's support, but it does happen in most residential construction anyway.

 

[boo1]

We alway toe-nail interior walls to the trusses. This will help keep the wall plum and allow lateral stability JAE indicated above.

 

[LPPE]

I agree with JAE. If you dont nail the partition walls to the structure above, you would probably topple the wall by leaning on it. And I've NEVER seen anyone install slide clips on interior partition walls so the structre above can deflect without imparting any reaction on the wall.
It seems that essentially all walls in residential construction become bearing walls when the floors are loaded.
Thats my $0.02.