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Wolfen 02-22-2011 12:24 AM

HELP reinforce a cracked rafter
1 Attachment(s)
Help DIYers...!

I'm a first time home owner in Southern California, total newbie in home repairs but I'm very motivated to learn..

Pls help me figure out how to reinforce my sagging garage roof. I noticed a huge crack in one of the rafters, and another 1 is starting to appear on a second one. Im thinking of sistering the rafter... and I need suggestions how to properly do it. You may also have other additional tips or suggestions how to accomplish the task, other than sistering... I really would appreciate your help.

Pls see image below:

bluebird5 02-22-2011 01:39 AM

cut some 3/4 plywood and glue screw it to the rafters

jklingel 02-22-2011 01:44 AM

Wolf: Wood cracks. A crack is different, in my mind, from a split. A split is where the board has been stressed beyond its strength limit and is failing. Are any of the boards you see severely bent? Ends broken, and splitting/tearing apart? If the ends of the boards are solid (not going anywhere), then you probably have nothing to worry about. However, keep an eye on them, and if you see signs of complete failure, like pulling apart or tearing, then get excited. I am not an engineer; just a DIY guy.

Just Bill 02-22-2011 07:35 AM

Not sure what I am looking at in the pic. I see 6 boards coming together at one point and nothing supporting that point, or am I wrong?? Is the 2x6 a single board??? Is the roof sagging at this point??? I also agree with the above, a split is not necessarily a crack.

mrgins 02-22-2011 09:34 AM

I believe the reason it cracked is because it is such a low pitch. From your pics it looks like a 3:12 or even 2:12. I'd turn your last set of common rafters into a truss with a vertical support to support the end of the ridge. Once
you've fixed the cause, then you can fix the resulting damage

Wolfen 02-22-2011 10:02 AM

seems more like a "split", not a crack
jklingel & Just Bil - The opposite ends of those rafters rest on the garage wall. The opposite end of the main joist (the one i captioned "2 x 8 JOIST") rests on the main wall of the house. Only the main joist is in perfect horizontal position, the rafters are angled down to the garage walls. i'll try to upload some more images later..

so yes, it seems more of an end split because it spans about 3 feet from one end of the rafter. Does that mean it is more serious?

mrgins - yes, it does seem to have a low pitch (my understanding of that is that the angle of the rafters is not acute enough). Also, it seems like the splitting was caused at one time when the previous owners had a huge airconditioning unit placed on top of the garage roof - maybe too many men on the roof at the same time. The part where the arconditioning unit rests seems stable though and is far from the meeting point of these rafters.

Wolfen 02-22-2011 10:19 AM

here's one perspective of the garage roof... sorry about the poor drawing

pyper 02-22-2011 10:29 AM

looks to me like that board is split from that point to the end.

If that's the case, then the best thing is to probably cut a new one to fit right next to it, jack it up a little more than necessary to remove the sag, and glue (with construction adhesive) and screw the two together.

Wolfen 02-22-2011 11:27 AM

Hi, I noticed some of you suggested "screwing" the rafter instead of just nailing.. Why and What type of screw should I use?

WillK 02-22-2011 01:01 PM

With a 3 foot span, if that's what I'm reading, it probably doesn't matter one way or the other, but putting in a ridge support isn't necessarily a good idea because you may have different expansion rates going on with rafters than joists, and tieing a ridge to a joist can create loading under certain conditions:

Another point to make... where you've pointed to a 2x8 "joist" actually that would be a ridge board I think.

I'd tend to suggest nailing if you have an air nailer you can get in there. Otherwise screwing might be easier due to the ergonomics - not much space to swing a hammer. But a nail will tend to be better able to handle shear stresses whereas screws are better for tensile loading. Note how much easier it is to break off a screw by bending it while a nail will tend to bend without breaking.

mrgins 02-22-2011 02:38 PM


Originally Posted by Wolfen (Post 595675)
Hi, I noticed some of you suggested "screwing" the rafter instead of just nailing.. Why and What type of screw should I use?

As a remodeler, I screw more than I hammer, if you'll excuse the expression. Less pounding and shaking, easier to set a screw with an impact driver than trying to swing a hammer, better gripping power. Use an exterior decking screw, 2 1/2" long

pyper 02-22-2011 03:21 PM


Originally Posted by WillK (Post 595729)
stresses whereas screws are better for tensile loading. Note how much easier it is to break off a screw by bending it while a nail will tend to bend without breaking.

Depends how many of each you use :thumbsup:

I tend to use screws for stuff like this because they resist pulling out a lot better than nails, and because it's easy to get out a cordless drill/driver than it is to get out and put away an air compressor. I definitely wouldn't pound nails into a broken board with a hammer.

Looking at the photo, I think I see a problem.

The "2x8 rafter" is not supported at the end. It's actually a structural element (a beam), not a ridge board (if I'm understanding the photo and the drawing correctly) because there are no ceiling joists to resist the lateral forces created by the roof pressing down -- over time the roof will sag and the walls will lean out at the top.

Or is there something not shown?

Gary in WA 02-22-2011 03:57 PM

The 2x8 "joist" is actually your ridge board. The last set of common rafters before your hip rafters (at corners) join should have a horizontal rafter tie (or ceiling joist) to keep the walls from spreading and the hip rafters from sagging at the top union.
I see the 2x holding up the back-hang for the garage door track, and a stiffener strut of metal for shear resistance.
Plywood on the sides will probably work, glue and screws or nails.

I am concerned for wall spreading, could you post another picture of the same, from laying on the floor looking up at the union, please?


Steeler99 02-22-2011 04:40 PM

I agree with GBR, and I'd suggest measuring the room dimensions at the floor and at rafter bearing height. Measure from the house to the outside wall, at the floor and ceiling. If the upper dimensions are larger than the lower dimensions, then you have a bigger issue than the "split" rafter.

I believe this is splitting because of two reasons

First, the low pitch is causing alot of lateral force on the top of the wall, causing the roof to sag at this particular point. It's minimal sag now, but I believe it will just get worse with time.

Second, the rafters are topping out...anyone see the space at the bottom where they all come together. This would cause natural weakness IMO...This gap may have been caused by the wall moving outward.

Wolfen 02-22-2011 04:52 PM

4 Attachment(s)
Ok, yeah the main 2 x 8 is a ridge board not a joist - Ive just googled it :)

Gary - I'll take another photo from laying on d ground later, here below are some that I took before leaving earlier, I hope I can provide u guys better info. The last image with multiple rafters altogether is the spot where the aircondition unit is sitting. There are no other weight on d roof other than maybe the pull force of my garage opener..

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