DIY Home Improvement Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
32 Posts
Discussion Starter · #1 · (Edited)
Will these sistered garage rafters hold? (picture included)

Hello all,

I recently had some work done on my garage to help add support for a slowly sagging garage roof (from weight of snow in the winter). The scope of work was as follows (note, this is from a licensed/insured contractor who came recommended):

Resupport garage rafters
- sister 4 sections with 2x8s to existing 2x6 rafter supports, screwed together
- attempt to jack up sagging roof line
- install additional vertical support to ridge peak
- anchor all rafter to wall attachments

I went to inspect the work and my initial reaction is that the work didn't look good aesthetically. Instead, everything looks a bit sloppy.

However, I'm willing to put aesthetics aside if the work was done in a proper structural manner. I expected one long rafter sistered to each of the 4 existing rafters in the middle of the garage. Instead, for each existing rafter he used two separated 2x8s and then joined them in the middle using another board and 4 structural wood screws (the screws are 3" long, and appear to be FastenMaster brand). And the two separate pieces don't even touch each other, there is a gap on each. I'm not sure if he did it this way because it would have been difficult to get the full-length pieces in place (I'm guessing about 20 feet long?), with obstructions being in the way. I'm concerned that the sistered rafters will start to sag in the middle just like the existing rafters (because they aren't one solid piece of lumber. Do you think the 4 structural wood screws would hold the 2 pieces together well? If so, shouldn't they be 4" long rather than 3"?

In case you're wondering, a post underneath was not possible as it would obstruct vehicle access to the garage. I wanted to get other informed opinions before speaking to him.

Please see the picture below to see how the sistering was done:
 

·
Registered
Joined
·
5,975 Posts
Those are not rafters.
They are ceiling joists, or collar ties, depending where you are located.
Their purpose is to stop the walls from being pushed out by the forces (weight) acting on the roof rafters.
Sistering them will help, but sistering the actual rafters would be better.
One of the problems with fixing a sagging roof is getting things back to flat or level.
It likely has taken years to develop the sag, and it won't go back to straight overnight.
Depending on the age and value of the garage, you might look at replacing the entire roof the next time you need to re-shingle.
 

·
Registered
Joined
·
32 Posts
Discussion Starter · #3 · (Edited)
Thanks, and sorry about the wrong terminology.

There is a new post (vertical support) going from the 4 sistered ceiling joists to the ridge board. However, I'm afraid that sistering method used on the ceiling joists will result in them sagging further, and thus the post would also drop lower and not provide support.
 

·
Registered
Joined
·
3,275 Posts
Just a quick note, if you are looking at a PULL situation....eg boards trying to keep the walls from PULLING apart, a two bye four could likely do the trick! You'll would be very surprised at how much pressure it takes to pull apart a piece of wood....as opposed to how much it takes to break it by putting a load in the center of the span. Ront
 

·
Registered
Joined
·
37,460 Posts
That's not going to do a thing.
No way would I even pay someone that did what they did.
Jlhaslip has the best suggestion to make the roof flat again.
If they had of used full length wider lumber and used nails and diagonal bracing it may have helped stopped further sagging but it's sure not going to get the old sagging out.
 

·
Registered
Joined
·
1,991 Posts
Are the walls bowing out? what is allowing the sag to happen?
Its not sagging because of snow load its sagging because of a construction failure. Otherwise it should support snow load.
As to terminology in my world a collar tie would be in the upper 1/3 of the roof and could be a 1x6. A rafter tie would be in the lower 1/3 and be at least a 2x4. Joists can often double as rafter ties but not all rafter ties qualify as joists.
 

·
Registered
Joined
·
7,885 Posts
No matter where you see the sag, it may not straighten out. Only the long lengths that still have some spring can be jacked relatively straight then reinforced with new lumber. If you force it, the connections (where there are nails) will break first, then you have whole new problem.
I would forget trying to straighten the roof. Just to prevent further sag, and without an engineer, cheapest is that you have the time on your side. That is, the sag may continue or may not. The rafters and the joists took decades to move. But is it still moving? The way you added the lumber, you may have just made the problem worse by adding more load on the joists that were undersized to begin with. The correct fix would be removing the sagging joists and replace with span rated lumber. If you move the ceiling joists up, as collar ties, the span decreases as well and reforces undersized rafters.
 

·
Registered
Joined
·
32 Posts
Discussion Starter · #11 ·
So the point was not to reverse the sag, but to prevent further sag.

The sistered lumber sits slightly higher than the existing ceiling joists. Then there is a perpendicular piece of lumber that sits across the 4 sistered sections. From that perpendicular piece of lumber there is then a vertical post that goes to the top and supports the middle of the ridge.
 

·
Registered
Joined
·
32 Posts
Discussion Starter · #12 · (Edited)
Just a quick note, if you are looking at a PULL situation....eg boards trying to keep the walls from PULLING apart, a two bye four could likely do the trick! You'll would be very surprised at how much pressure it takes to pull apart a piece of wood....as opposed to how much it takes to break it by putting a load in the center of the span. Ront
This is a good point- do the outside walls naturally pull on the ceiling joists, versus the ceiling joists being pushed down?

If so, I might be more comfortable with the way this sistering was done (with two pieces bridged together in the middle- as shown in the pic, versus one full-length piece).
 
1 - 12 of 12 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top