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Truss uplift

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mudmixer

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neal -

You should know there are no statistics on the various situations, let alone any engineering calculations. Unfortunately there are few situations that are the same and could be due to different details/plans/conditions/climates.

The practice of keeping the nails or screws well away from the wall/ceiling joint has been a common practice for about 50 years around here.

I expected some problems with my own lake home (I held the ceiling sheet rock nailing away from the wall/ceiling joint) that had 9' walls and scissor trusses spanning 28', but the house had tremendous thermal storage. Maybe the height of the walls provided some "give". But it saw winter temps at up to -42F and then heating up to 70F before I got there for a week-end thanks to a programmable thermostat.

Despite being an engineer, I can only offer anecdotal observations that would not be adequate for requirements on the code committees is an active in.

Dick
 

nealtw

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neal -

You should know there are no statistics on the various situations, let alone any engineering calculations. Unfortunately there are few situations that are the same and could be due to different details/plans/conditions/climates.

The practice of keeping the nails or screws well away from the wall/ceiling joint has been a common practice for about 50 years around here.

I expected some problems with my own lake home (I held the ceiling sheet rock nailing away from the wall/ceiling joint) that had 9' walls and scissor trusses spanning 28', but the house had tremendous thermal storage. Maybe the height of the walls provided some "give". But it saw winter temps at up to -42F and then heating up to 70F before I got there for a week-end thanks to a programmable thermostat.

Despite being an engineer, I can only offer anecdotal observations that would not be adequate for requirements on the code committees is an active in.

Dick
Thanks Dick, I understand that and have been explaining it to home owners for years. I am just trying make it work in my head with what I have seen in the field. We see a vaulted ceiling with a full gable over the outside wall all the time. We often just added studs to the back of the gable that are notched out for the members in the truss. So in this case the wall and the truss are built together or tied together so much like the problem here.
I have never seen a problem with the gable lifting.
The gable has more upright members that the other trusses.
So is it the extra members, or the sheeting on the outside, or is it the proximity to the cold and moisture that keeps it down.

The truss company should be aware of what ever the problem is and should have shipped a gable and or called for sheeting or shipped an extra truss so that one didn't have to land on the wall.

I have never seen a house with concrete tile have an uplift problem so in my head, you could hold it down but with what force and how to attach to it.
 

oldognewtrick

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Neal, the dead load from a asphalt shingle is less than 300 lbs per square compared to sometimes 4-5 times that for most hard surface installations.
 

nealtw

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Neal, the dead load from a asphalt shingle is less than 300 lbs per square compared to sometimes 4-5 times that for most hard surface installations.
That's my point, they can be held down. I can't believe that all this theory is kicked around and there is no data to be had.
 

oldognewtrick

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Standards and building science are moving targets. What's gospel today is heresy tomorrow.
 

nealtw

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I would like to see a chart the says if member A has this moisture and B has this moisture it will lift X per foot of run. You can be sure someone tried to do that and when it doesn't add up they just shut up.
 

bud16415

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There is a plastic angle strip for normal wall to ceiling edges and you screw the drywall to the plastic angle a couple places between the truss. The plastic angle is attached to the truss. Gives a place to screw to but allows the movement. His is different because the wall extends up the truss. The way I would think that should be built is hold the truss back 4 or 5 inches and then frame a wall up to the ceiling height and then use the plastic angle for any movement at the ceiling.

What he has now is a problem as you cant easily move the truss. He could build a new wall out a few inches but that’s also a PITA with the fireplace and all.
 

bud16415

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As to the expansion with heat I found some numbers for wood. It was something like 1/3 steel but had a huge range by type of wood. I ran the number for a 40’ span and a temp range of 80 degrees and it came out to 1/8”
 

nealtw

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As to the expansion with heat I found some numbers for wood. It was something like 1/3 steel but had a huge range by type of wood. I ran the number for a 40’ span and a temp range of 80 degrees and it came out to 1/8”
They talk about wet and cold like they were added together.
But very dry to very wet for 40 ft is about 3/8.
Subtract your very warm to very cold 1/8.
Just does not compute.
There is a chart on page 4
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch12.pdf

EMC values were determined from the average of 30 or more years of relative humidity and temperature data
available from the National Climatic Data Center of the National Oceanic and Atmospheric Administration

dry lumber is between 6 and 8%, I don't think 15% is what you would call very
wet
 

Harvey Juric

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It does not look like truss uplift. It looks like they framed the wall in 2 sections, wrongly installed drywall (drywall joint at the same place as 2"x4" pony wall joint), and the wood dried out.

Another reason may be that the top part of the wall is nailed more securely to the truss than the bottom wall. The truss will actually lift the entire wall. This may account for the difference in width of the crack. It is larger towards the middle of the room.

In any case, it is all about the moisture in the wood framing components of the home.

I have posted an article on humidity in new homes here: http://buildersontario.com/humidity-new-home
 

arnoldat30

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I assume that is has to do with moisture in the wood. It closes back up in the summer. I know that it was not done correctly, just looking for advice on how to fix it without tearing the whole wall apart.
 

arnoldat30

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I also have an indoor wood furnace which dries the air out quite a bit. I installed an aprilaire steam humidifier this winter which keeps my humidity in check but still didn't help with the crack.
 

nealtw

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I also have an indoor wood furnace which dries the air out quite a bit. I installed an aprilaire steam humidifier this winter which keeps my humidity in check but still didn't help with the crack.
You likely have vapour bearier so moisture or lack of it in the house won't help or hurt the trusses.
Have you talked to the truss people?
Is that a barring wall below it?
 

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