Roof Truss Uplift Damage Cause & Cures
Arched roof trusses cause cracks at ceiling/wall juncture, causes & cures

Why does truss uplift damage appear at interior partitions in the center of a building?

The differences in temperature and perhaps humidity that we just described can cause the roof truss to arch upwards at its center, often seasonally as attic temperatures and moisture conditions vary.

Because the truss ends are secured to building exterior walls - a location that resists outward thrust, as the truss bottom chord wants to expand along its length, the force pushes it upwards into the attic space.

Therefore roof truss uplift is most likely to be observed at the ceiling-wall juncture of central interior wall partitions that run at right angles to the direction of the roof trusses, or in other words, interior partitions that are parallel to the house front and rear eaves.

That's where truss uplift cracks may occur (typically in the center of the truss).

Photo above:

this is the type of separation crack that you may see at the ceiling-to-wall drywall joint over a center partition that runs at right angles to the bottom chord of rising roof trusses.

Watch out: we have also had reports of roof and ceiling noise annoyances such as popping and snapping sounds and loose ceilings that may be due to roof truss uplift.

See POPPING SNAPPING NOISE DIAGNOSIS

Example of Drywall Ceiling Cracks Mapped to Roof Trusses

These photos and sketches, courtesy of an InspectApedia.com reader, illustrate bedroom ceiling damage, showing a range of cracks, bulges, and prior repairs.

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The owner found that each point of drywall damage corresponded to the exact point at which roof trusses passed over a non-load-bearing partition wall, suggesting that this may have been a rising roof truss problem.

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Below, annotated on a flipped-over architectural plan for the building, we see the red line marking the non-load-bearing wall over which the roof trusses pass and where cracks, bulges, and prior repairs were evident.

We think that there's a good chance that the damage above may well have been caused by roof truss uplift and improper fastening of drywall at the ceiling along that partition wall.

How to Avoid Roof Truss Uplift Damage to Drywall

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• Use uplift clips to install drywall:
  
  float the truss over the top of center wall partitions and at corners.
  
  Builders avoid truss uplift cracking or ceiling nail pops by using special truss uplift clips to connect the ceiling and wall drywall while avoiding nailing or screwing the ceiling to the bottom of the trusses within 24" of the building walls (typically in the center of the truss).

See the roof truss uplift remedial action sketch given here.

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The drawings of roof truss uplift and corrective measures for truss uplift shown here are provided courtesy of Carson Dunlop Associates and appears in their Illustrated Home.

• Reduce attic moisture:
  
  In addition to drywall installation details described here: avoiding fasteners in problem areas, using clips, allowing the truss to float above the drywall at the ceiling/wall juncture in center partitions, other experts emphasize the value of good attic ventilation and avoiding sending moisture into the roof space when avoiding rising or arching truss uplift problems in buildings.
• Proper attic ventilation:
  
  continuous air intake at eaves, outlet at ridge, will help prevent excessive attic moisture levels.
  
  See ROOF VENTILATION SPECIFICATIONS - home
• Avoid framing with wet lumber:
  
  use S-dry lumber that has 18% or lower moisture content during original construction. Keep framing materials dry during and after construction. If a roof or floor frame is wet during construction be sure it is allowed to dry below 18% before covering the material with sheathing or subflooring.
• Choose shorter truss spans when possible.
  
  Spanning the building width rather than length reduces the truss length and thus the arching of the lower truss chord.

How to Fix Ceiling/Wall Cracks Due to Truss Uplift

Reader question: 2018/03/09 Marsha said:

I think I may have this problem in my condo, how can it be fixed?

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Reply: Options for fixing drywall cracks due to arching trusses

First, Marsha, let's be sure we have the correct diagnosis of the cracks that you see in your condominium.

Use the "Add Image" button next to the Comment button on this page to send me photos of the damage and, if possible, photos of the framing in the attic above the area of cracking.

As I note in my photo (seen also in some other roof truss uplift articles where it was used without our permission), there are several possible causes of cracking that may appear at the top of walls at the ceiling

Particularly when the cracks are marked by the edge of drywall tape I'm not certain, without knowing how the building is framed, that these are caused by a roof truss uplift as opposed to poor taping - failure to adequately wet the tape bedding it into the drywall mud.

In contrast, if the crack is immediately at the juncture of ceiling to drywall, having torn through the tape, and particularly if we know that the ceiling overhead is fastened to the bottom of roof trusses, then we can be pretty sure that we're seeing a rising roof truss crack problem.

My photo above illustrates a ceiling framed with roof trusses - obviously before the drywall was installed.

In that case here are the repair options:

1. Live with the cracks:
   
   this is a cosmetic issue, not a structural one. I don't, however recommend just living with ugly interior ceiling-drywall gaps and cracks.
2. Cover the cracks:
   
   install crown molding along the ceiling / wall juncture around the entire room and paint to suit.
3. Sink, Tape, & Float:
   
   Along the areas where cracks appear at corners or near the center of wall partitions that are mid-span of the roof trusses above, use a hammer and nail-set or screw gun with appropriate bit to sink nails or to actually remove the existing drywall screws through the existing drywall and into the truss bottom chord.
   
   Patch the holes and re-tape the ceiling-wall connection, allowing the now-disconnected area of the ceiling to float. I [DF] have used this simple method in smaller buildings with complete success.
   
   Other writers instruct us to "cut the nails free from inside the attic" - a hellish job where access is limited. You might accomplish this with a sawzall but I think this is an armchair drywaller suggestion.
4. Fix attic venting & insulation:
   
   this "armchair-drywaller fix" [in my OPINION] recommended by some readers is appropriate IF on inspection you find signs of attic moisture or missing insulation.
   
   Really? Reducing attic moisture and assuring that attic insulation is complete are things that you should seek in any building where those problems exist. This "fix" might reduce future truss arching but it will not fix the existing cracks and gaps or tears at the ceiling/wall juncture.
   
   Also, I have seen truss uplift cracking in buildings where the attic was dry and well ventilated, simply because the bottom chord of an A-truss is covered in insulation while the rest of the truss is not. Temperature and moisture variations will certainly occur in that situation.

Truss Uplift Damage Prevention Products & Research

Examples of drywall clips that are installed during original (or replacement) drywall installation. Use of these drywall clips may not be practical for retrofit or minor repair work where the original drywall is left in place.

These products are used along problem areas at the top of center partition walls under trusses and at problem corners.

• Simpson STC/STCT/DTC Roof Truss Clips, (green circled-clip) Simpson Strong-Tie Company Inc., offices world-wide, Tel-US: 1-800-999-5099, Website: https://www2.strongtie.com
  
  Website excerpt: "Use STC or DTC depending on required loads. STC, installed with DS drywall stop, helps prevent fasteners tearing through the ceiling drywall "
  
  Simpson DS Drywall Stop, (red-circled clips) by Simpson Strong Tie,
  
  Website excerpt: "Eliminates costly blocking at top plate, end walls and corners. "
  
  Not shown: DBC13 R Drywall Clips, Simpson Strong Tie. and Moe-Tie Drywall Clips [apparently a generic term]

• Garrison, Tim, "Truss Uplift - Fact or Fiction?", [PDF], Builder News Magazine, April, 2006, retrieved 2018/03/09, original source: http://www.buildersengineer.com/assets/images/blog/truss%20uplift%202-14-06.pdf
• HOW TO AVOID TRUSS UPLIFT PROBLEMS [PDF] Accutruss, Technical Tips for Home Building, compiled by Ontario New Home Warranty Program, retrieved 2018/03/09, original source: http://www.acutruss.com/pdf/trussuplift1.pdf

Illustration: Trim-Tex Truss-Backing Angle used during drywall installation, cited below & discussed in this article.

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• Trim-Tex Truss-Backing-Angle, [illustrated above] Trim-Tex, 3700 W. Pratt Ave., Lincolnwood, IL 60712 USA, Tel: 800-874-2333 or 847-679-3000, Website: http://www.trim-tex.com/
  
  Excerpts: Eliminates inside ceiling corner cracking due to truss uplift of interior partition walls. Backing Angle may also be used where blocking is missing on inside corners. Thick vinyl flange helps screws start easier.
  
  Trim-Tex has a product called a “Truss Backing Angle” which is installed before the drywall is hung which helps prevent truss uplift.
• The idea is not really new; Trim-Tex is just trying to offer a better alternative that is also available at the numerous suppliers that carry their products.
  
  The backing angle is made out of vinyl, which is plenty strong enough. It just needs to hold the drywall edge in place along the top edge of the wall.
  
  It is attached the entire length of the walls being treated. This means that the drywall is backed for its entire length and can easily be fastened anywhere along the edge as long as the fasteners don’t go through the angle and into the truss. The screws start very easily in the vinyl engineered extrusions which speeds up production.