Classic Truss Uplift

I thought I would repeat a thread I posted just minutes ago titled, ‘Classic truss uplift.’

Truss uplift phenomenon, is common among homes built with roof trusses as opposed to rafters, and should be narrated as such.
When a house suffers from truss uplift, the top floor ceilings assembly literally lifts, rises, off interior walls in the winter, and settles again when warmer conditions prevail.

At first glance, during a home inspection, one may hypothesize, the floors have settled. Actually the ceiling has risen sometimes creating ‘a gap’ at the ceiling, wall intersection, as much as (2") two inches at times, where an ‘interior wall’ meets the ceilings.
In this case, lift above a doorway, in a wall in the center of the second floor of a house. As well, this particular home had very wide eaves. Over 36" inches, or 3’ foot eaves overhangs on all sides.

Cause of Truss Uplift. Attics of newer homes have lots of insulation and ventilation, as in the case of this 1985 home that added 8" inch dense glass fiber batt insulation burying the bottom cord beneath the insulation allowing the chord to remain warm and dry.
The top chords, on the other hand, are above the insulation, exposed to cold winter environments in a well ventilated attic.
Cold winter air, as we have experienced, combined with very high relative humidity, as exists in Southern Quebec, Montreal, Canada, allows an upper chords to absorb moisture from the air, causing them to elongate, creating a bow at the bottom of the chord, enabling classic truss uplift.

Recommendation. Redecorating the ceiling wall intersection is an easy fix. Molding attached to the wall only.

I experienced truss uplift in a rental property that I own which eventually resulted in the detachment of the ceiling drywall from the trusses. Bit of a mess. And yes, I had added about 6" of insulation on top of the bottom chords of the trusses.

I purchased a home to flip about ten years ago that exhibited similar symptoms to those shown in the photos presented by the OP, along with other symptoms of foundation movement. The inspector I hired postulated that it was a result of heaving and settling of the structure, and recommended I have the plumbing tested. Indeed, there were numerous plumbing leaks. That inspector saved my bacon and became the only inspector I referred from that point on.

Not to say that what the OP is presenting is not 100% correct, but that, at least in my case, it seemed that a similar symptom might have a different cause. The house had rafters, BTW.

Molding attached to the wall only. (quote)

I would suggest:

Crown moulding should be attached to the ceiling only.

Install and paint in the winter when up lift is noticeable.

Paint line in the summer will show in the winter when the truss uplift happens once again.

Hi Bryce!

Totally agree: Moulding should be attached to the ceiling only.

Best regards,

Hey Guys I agree trim installed to ceiling only is the way to go. Installed in the winter when ceiling is at it highest!
Its too bad there is no real final solution to truss uplift!! Has anyone heard what the effects of installing a king post in the truss system? would this help the problem or would it create more issues?

Would it work to sister the bottom chord with 2x6 or 2x8 lumber, or would that just transfer the stress (and distortion) to the other members?

Ummmmm I don’t really think it is a home inspector’s job to make suggestions for repair like that. Don’t really know if it will work. An engineer would be the one to make that decision.


I am just curious? Where is the originator of this post defending his opinion?

On the other thread he started with the same title.
Classic truss uplift

Just to be clear, I was asking for my own edification, not to make suggestions to a client. As I mentioned earlier, I have a property where I encountered truss uplift.

If I were looking for a definitive answer, I would ask an engineer. I was hoping that, given the breadth of knowledge at this forum, that I might receive a helpful, informed opinion here.

You got one;)



Sistering onto the bottom chord, would not help, the truss works as as system. Since the mechanism that causes the truss to rise and fall is due to the coefficient of linear thermal expansion (CLTE) combined with shrink/swell due to changes in moisture content. One other factor you must consider is temperature and moisture content of the truss changes constantly, so you have to guess what the temperature and moisture content of the truss members where when the ceiling/wall drywall joint was taped. For the examples below I will assume at the time of construction the temperature was 70° and the moisture content was 15%. On the winter day we see the crack the temperature was 0° and the moisture content was 5%, i.e. lower humidity dries out the lumber.

The CLTE for pine is approximately 0.0000028 in/in/°F, so a 96" 2x4 that measured 96" at 70° would be how long at 0°?

The answer is 96 + [0.0000028] x 96 x (-70°) = 95.98"

Now to adjust for moisture. Pine will expand as the moisture content rises and shrinks as the wood dries out, however wood shrinks/swells differently in all three directions. Changes in length (96" direction) is very small and can be ignored. The coefficient for changes in the width (4" direction) is 0.00259. The coefficient for changes in the thickness (2" direction) can be ignored since changes in this direction does not effect what we are trying to solve.

The change in the width of a 2x4 due to a 10% reduction in moisture would be?

The answer is 3.5 - 3.5 x [0.00259 x (15 - 5)] = 3.41"

Now a computer program is needed to calculate the amount of truss uplift based on the shorter member lengths and widths. The geometry of the truss also has an impact, therefore a 24’ scissor truss will move differently than a 24’ standard truss.

I know this is probably more than you wanted to know, but I hope it gives you some idea of the complexity of this issue.

You see why I suggested that you speak with an enginer? :wink:

Thanks for the explanation Randy:cool:


Morning, William. Hope you are well and in good health today.
I posted Classic Truss Uplift on the open forum to express to other inspectors, what you sometimes come across during a home inspection maybe more than meets the eye. Look closely at things out of the ordinary. Ask questions to anyone present during the evaluation.

You can follow more of what I had to say on classic truss up on the closed for member only forum.

You could have addressed the truss uplift or decorated around the symptom.

Truss Uplift | This Is Drywall

May I ask, did you purchase the home? And if so, what was done to correct the structural defects?

Real estate agents refer to purchasing homes undervalued, due to structural defects mostly, as Flips. Not a choice word.

Rater spread and truss uplift exhibit different systems.
Rater spread exhibits a force being applied on the rafter, thus bowing the rafter inwards causing with the walls to be pushed outwards, or rolled over, from/at the top.

Doug I concur. I do not refer repairs.

As well truss uplift is superficial. There appears to be a consistences, truss uplift is a cosmetic issue.