Uneven Rafters - Job in Progress HELP!

[Jeffery L. Haynes]

Originally Posted by Wayne Carlisle

It looks like when the decking was installed, the installer did not leave the required spacing between the edges of the plywood.

This type of problem is what you are seeing.

I have yet to see a stick roof where the "required" spacing between the sheathing is performed and yet they are fine..................what you have is simply bowed rafters....it is an aesthetic issue.

If every home was built to exact manufacturers specifications the price of a home would be through the roof (no pun intended)

Some installations instructions are simply worded to alleviate the manufacturer from ALL responsibilities regardless weather they are wrong.

Unless the sheathing states that it has been sized for spacing, I guarantee that the sheathing is 48" x 96".......now add 1/8" on each side for lets say a 75' single story home........... by the time you get to the other end your spacing is way off.........do you want to talk about how spacing will affect the drywall now...............you see what I mean.

In other words that 1/8 spacing is BS..........those that look for that are the same ones who want to measure that every nail is 6 inches apart on seams (actually had a friggin rookie B.I. check that on one of my jobs).

regards

Jeff

[Kenton H. Shepard, CMI]

Also, the crowns may have been installed upside down on the low rafters. Rafters with heavy crowns can vary more than an inch if the crowns on adjacent rafters are installed in opposite directions.

[Randy L. Mayo, PE]

Mitch

I have seen allot of stick built roofs with this type of sagging at the ridge line.

One or more of the following factors usually contributed in the cases I have inspected:

1.) Over spanning of the rafters.
2.) Lack of interior support walls typically in large rooms such as a living room or garage.
3.) Poor fitting joints where the rafters meet the ridge board.
4.) Non-uniform and/or unnecessary vertical braces supporting the ridge board. (overlaps with #2 above)
5.) Rafters placed 90 degrees to the rafters causing the exterior walls to spread.
6.) Sagging ridge line due to shortening of rafter caused by rafter sagging.

I have attached a few drawings to help visualize the issues.

[Randy L. Mayo, PE]

Mitch

#5 should have said "Ceiling joist placed 90 degrees to the rafters"

[Kenton H. Shepard, CMI]

Originally Posted by rmayo

Mitch

I have seen allot of stick built roofs with this type of sagging at the ridge line.

One or more of the following factors usually contributed in the cases I have inspected:

1.) Over spanning of the rafters.
2.) Lack of interior support walls typically in large rooms such as a living room or garage.
3.) Poor fitting joints where the rafters meet the ridge board.
4.) Non-uniform and/or unnecessary vertical braces supporting the ridge board. (overlaps with #2 above)
5.) Rafters placed 90 degrees to the rafters causing the exterior walls to spread.
6.) Sagging ridge line due to shortening of rafter caused by rafter sagging.

I have attached a few drawings to help visualize the issues.

I didn't see sagging of the ridge. I thought the problem was non-planing rafters along most of their length, not at the ridge or where they rest on the plate. A little clarification here, Mitch?

[Randy L. Mayo, PE]

Mitch

Kenton made a good point. My reply was geared toward the probable cause and did not address any possible solutions.

Without seeing the entire attic and support framework I cannot suggest a fix for your problem over the internet. If the problem is related to the issues I listed there will be no cheap solution. Long term sagging of lumber also involves plastic deformation of the wood fibers which cannot be totally reversed.

Sistering on both sides of an already over spanned rafter only adds more dead load to an overloaded rafter. Ideally you probably will need some additional support at mid-span of the sagged rafters. There are a few ways of doing that but each method is customized bases upon your framing situation and interior wall support locations. Sagging over large span areas like a garage may require a support beam in the attic to support the ceiling joist and any diagonal braces installed to support the rafters.

My main point is you need to identify the root cause of the problem before you spend money trying to fix the symptom.

[Jeffery L. Haynes]

Originally Posted by rmayo

Mitch

Sistering on both sides of an already over spanned rafter only adds more dead load to an overloaded rafter.

My engineer always insist that sistering be the whole length, from plate to ridge or wall to wall.......

Again, like most questions I see in this forum, the poster did not provide enough information about the roof system nor enough pictures.

[Randy L. Mayo, PE]

Jeffery

Sistering the whole length, from plate to ridge or wall to wall is the only way to do it without adding additional dead load to the sagged or damaged rafter. The only problem with that is the constructibility issues with getting a 16-foot or longer 2x6 into the attic and into place. In a case like this you will have to jack the bowed rafter back to it's original position in order to get the new rafter in place. Then with a considerable amount of sweat, sledge hammers and hydraulic jacks you may get it in. All to often the contractor or more likely the homeowner's brother-in-law takes a short cut and trims the end of the new rafter to make the installation easier which now no longer transfers the loads properly. On the plus side this particular house has what appears to be a fairly large attic area so there may be some room to work.

From the picture the ridge line has sagged which indicates the fix will involve multiple rafters and a significant amount of work. If you leave the ridge line "as is" any new full length rafter will be slightly shorter than the original. Jacking up the ridge line will cause the existing sagged rafters to pull away from the ridge board. Working in a confined space is very time consuming and any contractor who has been in the business for a few years has learned this the hard way. So in order to recoup his labor costs the bids will be high enough to make the home owner sit down and think twice about tackling this project. Again without actually looking at this house I am only guessing on the extent of the problem.

[ROBERT V. YOUNG]

I see upper and lower cord with no bracing. It might help to if you add gussets cord intersections to brace it all together.
Here is a photo.
Also Mr.Mayo they can bring even thing in through the gable end vents. If non make a hole at both ends to add ventilation if needed if not close it up after.
If you use jacks to straighten out the work many factors have to be taken into considerations.
You will be applying forces to the ceiling components ( joists, wall framing, plaster ) and you must set up jigs to compensate for the loads.
Also jig ( 8 foot ) to be seated and cup in place that rafter you single out to straighten. Then sister it in place, and gusset all cords together.
Its tricky as you mention.

[ROBERT V. YOUNG]

Mr Hetzel.
Cambers often form with the use of logs being handled wrong at the mill also. BUT
When trees grow on mountain sides, scientist have noted that those are the timbers that tend to curve during humid days, freezing conditions and fluctuations in temperature and weather drying out or lack of humidity,etc.
The word camber.
http://en.wikipedia.org/wiki/Camber

Just my 2 cents.

[Kenton H. Shepard, CMI]

Originally Posted by Wayne Carlisle

It looks like when the decking was installed, the installer did not leave the required spacing between the edges of the plywood.

This type of problem is what you are seeing.

Inadequate spacing between sheathing panels results in shingle buckling that looks like this...

[ROBERT V. YOUNG]

Originally Posted by kshepard

Inadequate spacing between sheathing panels results in shingle buckling that looks like this...

Sheeting looks inadequate also to K.
I see several variables at work in that photo.
You have inside photos of that home Kenton so we may see the interior rafter design ?