Thread: Truss Uplift Info needed

Received a call from a frustrated homeowner this afternoon. His question is how is truss uplift repaired. The home is 3 years old in a newer development. After being in the home 8 months they noticed the drywall separating at the seams in most of the 2nd floor bedrooms and bath. The developer came back, repaired the cracks and repainted. Six month later the same thing happened and the owner hired someone to make repairs but now same thing happened. Out of frustration they called me and asked if I would take a look at it.
I've never seem uplift but what they are describing that's what it sounds like, that's also what the painter told them. I haven't been to the house, I'll be looking at it Wednesday. The house id only 5 minutes from away so I offered to look at it and not charge them since it will be an education for me as well. I'll take pictures Wednesday and post them. Two questions, Is this repairable if truss uplift and is there any obvious things sign to look for. I'll post pictures after seeing the home.

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Cut the tape along the wall/ceiling joint, install cove molding around each room fastened *only to* the ceiling.

This will allow the trusses to uplift, which moves the ceiling up and down, which moves the molding up and down, however the molding just slides up and down next to the wall (it's not attached to the wall) and hides the crack behind the molding.

But ... I thought truss uplift was a cold weather phenomenon?

Jerry I appreciate the information. Now that you mentioned the solution I recall either reading or hearing the same thing when I went thru inspection class. I don't know if it's just a cold weather thing or not, as I said I have never seen it so I'll take a few pictures for you to look at. I'll be out of town for a few days so you won't see pictures until late next week.

Bill, I would look carefully to make sure that there was not some other cause, just for CYA purposes. Around here, we get seasonal movement due to expansive soils. Of course, we don't have basements or bedrock and almost all of our houses are monolithic slab on grade. Wet and dry seasons can easily move a slab around an inch or more.

On the subject of Truss uplift, I was under the impression that both temperature and humidity could cause this phenomenon. Also, don't forget that the "lift" has to "settle", so a 6 month or so cycle might make sense.
Good luck.
Jim

Truss uplift usually occurs during cold weather months and is most often caused by non-uniform cooling of the truss components. The top chords and web members contract slightly due to the low temperatures in the attic while the bottom chords, being covered with insulation and closer to room temperature, contract very little or none at all. This causes the bottom chords to be longer, relative to the rest of the truss, than they should be - and they bow up. When warm temperatures return to the attic (and all the parts of the trusses are close to the same temperature) all the components return to their "normal" lengths and the bottom chords return to their normal position.

Originally Posted by Jerry Peck

But ... I thought truss uplift was a cold weather phenomenon?

Originally Posted by Jim Luttrall

Also, don't forget that the "lift" has to "settle",

(slaps forehead with hand)

Duh!

So in the 'not cold weather' the trusses settle back down. Duh! (That guy Jerry must be an idiot. )

Truss uplift clips can be installed. I inspected a newer house in a neighborhood where this was occuring to many houses. The builders came back in and retro installed the truss clips and adjusted the nailing of the ceiling drywall around the perimeters of the ceiling using wooden blocks to attach the drywall to. It was not an easy task but was done. Supposedly this retro fix wil work if done proeprly and entirely but I am waiting until the next cold spell to hear from the client as to whether the uplift happens again.

Here is a simple article that explains about how the the clips function.

Truss Uplift and Ceiling Cracks

Eric.

I don't think the issue is heat/cold it is moisture change that causes truss uplift.

The coefficient of linear expansion of both softwoods and hardwoods is 0.0000017 to 0.0000025" per degree F. On a 30' truss that changes temperature 25 degrees the dimensional change of the 30' tension chord would only be 0.02". Not enough to explain the uplift.

Longitudinal dimensional change of soft wood is 0.1 to 0.2% and juvenile wood can shrink 2%. SYP is notorious for having juvenile wood. The same 30' truss that expands/contracts .2% moves nearly 3/4" and with ends restrained by attachment to the walls, could easily show uplift of up to 3"

In my world, forget heat/cold as a driver for wood movement and think MOISTURE CHANGE!

This is a link worth reading
CarsonDunlop and Associates - CDA Reports / Truss Uplift
Hope this helps

"Other causes":

"Most ceiling sheetrock cracking is caused by truss movement usually traced back to Wind, Thermal, or Installation. Here are some abbreviated conclusions which I have experienced first-hand during inspections:

1. Wind uplift due to negative pressure on roof sheathing and/or attic (balloon) pressure through vents is causing excessive truss movement which the brittle sheetrock joints cannot withstand. This is confirmed by truss calculations of the longspan truss showing an L/107 deflection of the 15' bottom chord panel lengths.

2. Wind exposure on the large porch ceiling is creating an uplift on the bottom chord and the toe-nailed connections have broken loose from the wall. Replace toe-nailed connection with hurricane ties at the exterior wall similar to those that were installed on the porch beam.

3. Ceiling sheetrock was installed on green lumber truss bottom chords with a moisture content in excess of 19% on a hot summer day. Sheetrock panel-butt splices have now telegraphed through showing an 1/8" ridge in a 4x8 pattern on the entire garage ceiling surface. The same sheetrock installer did both the house and garage, but the garage is not insulated and therefor subjected to more extreme with the 9 degree winter temperature.

4. The longspan scissor trusses at the great-room entrance will deflect (breathe) during snow and temperature changes. The same sheetrocker did both houses of the same model and only yours shows sheetrock cracking at the parallel interior wall and 4'oc cracks near centerline perpendicular to trusses. Because the other owner lives there year-round, and yours is a vacation home visited infrequently, the cracks are easily explained by thermal changes. When your heat is totally off while you are away, the attic/house temperature nears an ambient 25 degrees this week. When you arrive and heat the conditioned space to 75+ degrees, the truss bottom chord warms and expands causing a truss vertical deflection. This same deflection can happen when your roof snow load goes from zero to 3' of snow. The truss has been designed to carry the load, but deflects (breathes) when it is applied. This movement will break the sheetrock corner joint next to a stationary parallel wall.

5. When the truss was installed reversed, it caused an interior bearing to occur in a mid-panel instead of the designed-for truss joint. The dead load truss deflection created a crown in the bottom chord at that bearing which made an 'S' wave in the entire ceiling.

6. Cambered trusses were forced down 1/2" to interior bearings and toe-nailed to top plate in lieu of vertical slotted panel stabilizing clips. After 6 months, random sheetrock cracks occurred at interior walls where the truss returned upward and pulled some toe-nails out
.
7. Trusses were toe-nailed to interior wall top plates. The alluvial soil beneath the slab settled and so did SOME walls creating up to 1" gaps between the ceiling and top plate, or between the sole-plate and slab. The trusses were too-strong and pulled the interior walls off the slab and broke the sole-plate (red-head) slab connection."

TRUSS Engineering Design, Fabrication, & Useage - truss uplift

Originally Posted by Mike Drorbaugh

In my world, forget heat/cold as a driver for wood movement and think MOISTURE CHANGE!

Mike,

Wouldn't (or couldn't) the heat/cold be the driving force for the moisture change?

Heated interior, unheated attic, cold/wet/rainy/snowy outside = moisture changes in the trusses?

Originally Posted by Jerry Peck

Wouldn't (or couldn't) the heat/cold be the driving force for the moisture change?

Relative humidity. The warmer a substance is the more moisture it can hold. Conversely, the cooler a substance the less moisture it can hold. So when a truss top chord is cooled its relative humidity goes up.

Bill,
Lots of good educational info on truss uplift, but here are some suggestions if and when you go back to inspect the home (to help out the homeowners/clients with their problem).
1. Check attic for proper levels of insulation and most importantly check for uniformity (12 - 16 inches evenly distributed).
2. Make sure the attic is properly ventillated (are there air baffles in the soffit vents? ridge vent or pot vents OK?)
3. If all this looks OK, then suggest additional fasteners be installed in the trusses particularly into the top plate of all interior walls.

Hope this helps,
Bob Dalga
Home Analysts, Inc.
Kalamazoo, MI

Robert, not to argue with you, but why would you suggest more fasteners?
There is no way you are going to keep a truss from moving with a few nails or other fasteners, the science behind the phenomenon says it is going to move or break in the process. Securely fastening the truss to the top plate just means the truss will lift the entire wall. The truss is designed (over designed usually) to account for wind, snow, and all other loads; fastening it to a few measly 2x4's and Sheetrock is not going to stop anything.
Unless I missed something, more insulation and ventilation is going to promote uplift, not lessen the effect. It is the difference in the temperature and humidity between the top and bottom chord that creates the phenomenon. If you want to stop the movement, take out the insulation and allow the top and bottom chord to be the same temperature and humidity level.

Creating a slip joint effect as previously outlined is the accepted fix.
Jim

Originally Posted by Eric Shuman

Truss uplift clips can be installed.

Truss Uplift and Ceiling Cracks

Eric,

This is from that link: "The drywall hangers must cooperate as well. Do not allow them to nail or screw the drywall directly to the trusses within 16 inches of an interior wall."

Besides the fact that I'm not sure that only giving 16" for the drywall to flex will allow that flexing without the gypsum board breaking at the line of the nails/screws 16" out from the wall ...

... that violates all screw/nailing requirements for gypsum board that I've seen.

A quick question for anyone who's responded to this. Since the problem appears when the top chords absorb moisture when cold while the bottom chord covered with insulation stays warm; would moving the insulation away from the bottom chords do anything to reduce the truss uplift. I didn't see that in any of the replies but seems to make sense if the problem is caused by the bottom chord being warmer them the top.

Unless I missed something, more insulation and ventilation is going to promote uplift, not lessen the effect. It is the difference in the temperature and humidity between the top and bottom chord that creates the phenomenon. If you want to stop the movement, take out the insulation and allow the top and bottom chord to be the same temperature and humidity level.

Bill, removing the insulation would reduce the difference in temperature and humidity, but you can't do that and still comply with the building codes (or common sense).
I would think that moving the insulation from the attic floor to the bottom of the roof to create a conditioned attic space would have the same effect... but that would take some work on a completed structure.
Providing a slip joint as Jerry and others have mentioned is going to be the easiest long term fix.

Here are a few pictures I took in the home with the truss uplift problem. I probably cut the pictures too small to see all the detail, none the less you can see where the walls are cracked. Always along a wall/ceiling and all the rooms are on the same side of the house. The owner had an engineer coming out Saturday to review and recommend a solution. The owner said she would call and let me know what the outcome is and what the engineer recommends.

Speaking from my building experience, I have personal knowledge of attaching trusses to the interior walls with hurricane straps. In 1980 we did such a thing to try and defeat the dreaded uplift and the resulting drywall damage. It worked like a dream, no drywall damage, but it lifted the wall 3/4" off the floor and the resulting openings between the base shoe and hardwood were much worse than any drywall damage I've ever seen.

The method of not fastening within 16" of the walls has been the most effective fix in our area of the midwest. Leaving out that fastener allows truss to move and the drywall to bow with out any resulting damage. Simpson Strongtie actually makes a truss attachment plate that allows the truss to move vertically yet still be attached to the wall plates. The drywall clip method also works quite well.