[Nealtw]

I know that Neal may have the term for it, but the bearing weight on your joists from the knee wall is minimized as that I'm advocating putting the knee wall as close to the outside wall as possible (in just far enough that you can get the longer rafter in). As an example, Think of houses that have a bump out (cantilevered) area out the back of the house and the bumped out area still has a wall built at the end of the bump out. This is possible because the load transfer (like for your knee wall) would be so close to the outer house wall that it wont deflect your floor joists.

As a matter of fact in very wide (deep) homes the rafters generally are not single pieces of wood as that dimensional lumber is only made so long. Instead they overlap rafters on knee walls and such. I would do a 2 x 8 down one side to the outside wall (would require cutting end of 2 x 8 at an angle). I would then do another one on opposite side with an angle so that it will meet the ridge board. The boards would of course overlap (on opposite sides of your existing 2 x 4) and the roof will be much stronger.

Lastly before you do this make sure the roof isnt sloped down (caved in) because of the broken 2 x 4. If they are (which mine were at my house) you can use a small bottle jack and from inside jack up each individual rafter until your roof is straight.

I am a truss guy mostly and anything else we did was under instruction by an engineer. So really the geometry of the stick built roof is above my pay grade. But as I understand it the knee wall is never structural unless it is over a bearing wall or the ceiling joists are span rated to take what ever load live and dead that would be applied.

 

[JWindmill]

Would 2x4s be acceptable as collar ties, or should I use 2x6? I have a lot of 2x4s from the demo is why I ask. If it’s important to use 2x6, I’ll pick some up.

 

[Nealtw]

Would 2x4s be acceptable as collar ties, or should I use 2x6? I have a lot of 2x4s from the demo is why I ask. If it’s important to use 2x6, I’ll pick some up.

I would use the 2x4s.

 

[NotYerUncleBob2]

I've done this exact project some years back where the rafters were 2x4 and 16 feet long. That roof was sagging in the middle like a Chinese pagoda! 5-6" of deflection in the middle. We ran some string lines to see how straight (or not straight) everything was and used string lines to make all the sistered 2x6 line up in plane. When it was all done and drywalled it was dead flat.
I don't think you'll need much more than the 2x6's sistered to the rafters. If you cut the angle into the ends first you should be able to fit them in there to run pretty close to the full length of the rafters. But in practice, they don't have to go the entire length to strengthen the roof if they're sistered and joined well. If you come up a couple inches short, what's that really going to do? A 2x4 isn't going to deflect over a 2 inch span in this scenario. The rest of the rafter will do the work with the 2x6 sistered to it.

 

[The Chairman]

The only way to get it perfect is to strip the roof and sheathing off. It looks from here that you are close enough to stop any further damage. Just remember to budget a more permanent fix the next time you need to re-roof.

 

[NotYerUncleBob2]

The only way to get it perfect is to strip the roof and sheathing off. It looks from here that you are close enough to stop any further damage. Just remember to budget a more permanent fix the next time you need to re-roof.

The only way to get it perfect is to strip the entire house and foundation off and start all over. ...but truly perfect is not necessary or even attainable in real life. This roof will be just fine with the new rafters sistered in.

 

[The Chairman]

...but truly perfect is not necessary or even attainable in real life.

You say that only because we haven't met!



I just put a new roof on my workshop and this is precisely what I did. Any cracking or suspect joist got replaced. They hadn't put decking under the entire roof, so I pulled off the old with all the water damage and put on new. Why not take advantage of almost full access when you can? That roof will last another 30+ years because I was so thorough. I just might be dead by then.

 

[ChuckF.]

If you remove some of the soffit material on the outside of the house, can you work your replacement material up and into the attic through the hole?