Truss uplift -- maybe, maybe not

[JBB2B]

The non-weight bearing walls on one end of the second floor separated from the ceiling this winter. Paid one engineer who came, examined, and explained it as standard truss uplift -- roof joists kept warm in insulation stay dry while roof swells and expands, causing joists to arch and pull ceiling up with them.

Separate inspector believes high winds in conjunction with minimally overlapped joists to blame. Roof possibly started lifting.

Facts:

All ceilings lifted within days of each other, perhaps on the same day.

Ceilings only lifted on one end of house -- the gable end receiving high winds.

Ceilings have not begun to sink with onset of spring, but it is early....

One end of house (unaffected) has center tie beam. Affected end has joists meeting on top of center weight bearing wall. Only 3" overlap of joists. Not clear how well nailed to wall below. Traditional joist framing -- no prefab trusses.

Archway below windward gable wall developed shear cracks at similar time. Cracks indicate outside walls shifted down with respect to archway (or archway up with respect to outside walls.) Archway is to attached family room with separate roof line than affected area.


Possibly related/unrelated: All cracks found days after an early morning "sound" -- sound of something hitting/shaking the house or something cracking. No cracked beams found. Stairwell between first floor and basement now has buckled drywall and corner pieces. Stairwell between first and second floors is normal -- no separations, cracks, etc.

I'm an electrical engineer. This is beyond me. 7 year old house, I've owned for 8 months. I've paid two professionals and have two very different answers. I want to stabilize/correct any problems before dealing with cosmetics. Not many more professionals in the area to call. Any experience/advice?

 

[dlew]

JBB2B,

You have shown a lot of good information, but not enough.

Some questions that come to mind are:

1) Is the separation between the ceiling and the non-bearing wall uniforme, or arched? If arched, what line is level, the ceiling or the top of the wall?
2) Where is the building located?
3) There were high wind reported at the site around the time the cracks were found?
4) What type of foundations and subsoil is supporting the building?
5) You said that a noise, as something hitting or shaking the house, was heard one morning. Has been any minor seismic activity reported at the site?
6) How could the buckled drywall in the starway between the first floor and the basement be related to roof uplift?

 

[dik]

You may want to look at this link for a brief blurb on truss uplift.

http://irc.nrc-cnrc.gc.ca/cbd/cbd244e.html

If you can sketch a floor plan and try to locate where the maxumum movement has occurred. Maxumum uplift generally occurs at mid span of the truss and this may correlate to where maximum movement has occurred.

 

[JBB2B]

Additional info.

1.) Is separation arched or uniform? Slightly arched. A trip around the upstairs with plumb line and levels didn't reveal which was out of alignment, ceiling or wall -- only that there are no square or level surfaces anywhere in the house!

2.) House is located in Groton, Massachusetts (30-40 miles from coast).

3.) Extremely cold and windy winter this year. Can't pinpoint when the separation occurred so I can't pinpoint the weather. Occurred in the midst of 4 consecutive weeks of continuously below freezing temps and frequent high winds.

4.) Poured concrete foundation, full basement, on gently sloped lot. Walkout basement to the back. Former farm land -- not clay, not sandy, not gravelly, a bit low and wet 30 yards down and away in the backyard.

5.) No seismic activity recently.

6.) Common sense tells me the buckled stairwell is not related to uplifting. It's a good candidate as the source of the "sound". Seems too far away from the problem. However, given the proximity in time, I thought I'd mention it. Perhaps there's a connection that I haven't seen but someone else does.


Regarding article on trusses and uplifting -- they seem to describe the problem. However, every article on trusses and uplifting assume the more rigid trusses and not the more traditional joists and rafters forming a simple triangle like we have. Also, wouldn't it be seasonal? While this is our first winter in the house, there was no indication of previous cracking/splitting even though the house is 7 years old. We painted the bathroom in the fall. It had original paint and had never been patched.

 

[Trussdoc]

Truss uplift, as a documented phenomenon, usually occurs in the first two years of use, before the lumber and moisture levels have time to fully stabilize.

A suggestion... check how tight the sheatjing is against the rafters.Gaps could indicate that there was an upward force on the sheathing.

 

[bylar]

I live in NC and i have found a similar Phonenim. I believe in my case it is truss creep. I have had it in 3 houses. Truss creep is suppose to be a lack of adequate ventilation but i aasure that is not the case in this house. I tried tieing down the mid span of the trusses to a center wall and etc.

My take on the situation is that there is two actions. One is the cold air on the top chord verses a warmer air on the bottom chord and secondly a moisture diference. in the top and bottom chords.

I have lookled a many many houses in the area all with roof trusses and have found a simialar pattern.

The truss bows up in winter and settles down in summer.

Thats just my take.

Good Luck.

 

[19651969]

Based on the description you have provided, my opinion of the cause would be truss uplift. The metal plate connected wood truss industry has information on this subject and methods to control it. Unfortunately, after everything is constructed it is much more difficult to do. They say that truss uplift occurs in about 20 percent of truss installation cases. I do not agree that this usually occurs in the first couple of years. A lot depends on the outside weather and enviromental conditions within the house. An option would be to install crown molding that will float up and down with the truss and thus hide the cracks that develop at the wall/ceiling joint.

 

[JBB2B]

Question 1: All documentation I've found on truss uplift comes from the metal plate connected wood truss industry, or refers to those trusses. Does the same principal apply to traditional joists and rafters like I have? I *do not* have what I consider to be trusses. I have joists meeting in the middle and nailed to a center weight bearing wall below.

Question 2: Would putting in a plywood floor buy me anything? Or cause any additional headaches? If it's a matter of framing and the joists not being overlapped and nailed correctly, would plywood stabilize the joists with respect to each other? If it's environmental, would putting plywood cross grain across add another source of resistance to uplift?