Mixed-Sized Joists

[Greg Subick]

Been doing this for twelve years and saw something for the first time. While inspecting the roof structure from the attic I noticed the use of two different sized joists with no rhyme nor reason of a followed pattern and was just wondering if this is allowed? Several 2x6's used, intermingled with 2x8's with no recurring or noticealbe pattern, no specific locations (such as valleys) just randomed placed about.

Any thoughts?

[Lon Henderson]

If the 2X6s meet the requirements for span and load, then I don't see why it is wrong, even if weird and extra work to keep the top line of the rafters even. That doesn't look like professional work which might be a red flag, even if the rafters don't violate any structural requirements.

[Greg Subick]

Lon, thanks for the reply. Yes, I looked it up and found that span limitations, etc. and wrote it up accordingly. Sloppy job to say the least through! Thanks again.

[Chris McIntyre]

It's not perfect, but nothing is, I have seen a lot worse.
Most likely the framers ran out of 2x6's and finished up with the 2x8's. Typically you install rafters intermediately as needed to get the ridge in place, then fill in the remaining spaces which would explain the random placement.

[Rick Cantrell]

The ridge board should be =>1" larger than the rafter, even if the rafter is larger that required.

[Chris McIntyre]

The ridge board should be =>1" larger than the rafter, even if the rafter is larger that required.

What's so bad is, in the 1rst pic, you can see they nailed a 2x strip on the bottom of the ridge board to get it flush. :)

[John Kogel]

In custom built homes, I have seen similar for a reason - if the span for the rafters on one side of the roof is longer, they upsize the rafters.

In those pics, I see all 2X8 on one side, so I wouldn't call it random. But that's just what I see from these pics.

For odd-sized rafters meeting at the ridge, it would be better to lap them, IMO.

I thought I saw a cleat attached to the ridge board as well, but it could be a split that he wanted to repair with screws. Some of the cuts are a little off, but I don't see a significant structural defect.

[Corn Walker]

Since when is a 2x8 only 6-3/4" deep?


What's so bad is, in the 1rst pic, you can see they nailed a 2x strip on the bottom of the ridge board to get it flush. :)

But in the 3rd photo there's no evidence of that, which makes me curious about why those fasteners are there in the first photo.

[Ray Thornburg]

Sometimes framers just try to use the wood that's available to them.....sometimes there are other reasons.....making economical use of the wood that's there, insulation requirements, plan specifications or maybe that was the only wood on the job that was long enough. As long as it meets span and load requirements and is properly braced to prevent deflection it is no problem.

[David Bertrams]

It appears as though 2x8s or larger were ripped to the odd size of 6 7/8. Not a good idea.

[Thom Huggett]

How about the other end of the 2x8's? Did they over-notch the 2x8's at the top plate to even out the roof level with the 2x6's? The code allows a notch of 1/4 of the depth of the member at the top plate (IRC R802.7)

[Ray Thornburg]

How about the other end of the 2x8's? Did they over-notch the 2x8's at the top plate to even out the roof level with the 2x6's? The code allows a notch of 1/4 of the depth of the member at the top plate (IRC R802.7)

If 2x6's are sufficient for the load and are notched why would using a 2x8 not be ok for the same load provided there was adequate bearing at the plate .....even if the notch was slightly bigger?......there is an exception to 802.7 that permits the notching of the cantilevered portion of rafters down to 4".

[Thom Huggett]

If 2x6's are sufficient for the load and are notched why would using a 2x8 not be ok for the same load provided there was adequate bearing at the plate .....even if the notch was slightly bigger?......there is an exception to 802.7 that permits the notching of the cantilevered portion of rafters down to 4".

Over notching can cause splitting of the member, and not necessarily parallel to the length of the member, so you could end up with a smaller section than at the support. Each joist will split differently. If the joists are over-notched they can be evaluated by a structural engineer, or in some cases you can add skewed, top-flanged joist hangers to each joist to support the notched portion of the joist.

The exception in 802.7 is for the eave side of the rafter, not the main span.

[sara mcmains]

It appears as though 2x8s or larger were ripped to the odd size of 6 7/8. Not a good idea.

Yes, this is a VERY important point. One aspect of the grading of non-engineered lumber is knot location -- such as how far the knots are from the edges. Ripping it down you might now have a knot right on the edge, so a 2x8s ripped to 6 7/8 is NOT as good as a 2x6, even though a non-expert would think it would be better.

[Larry Morrison]

Most of the structural concerns have been hashed out. One situation where you may see something like this would be that 2x6 was all that was needed for structural but the 2x8s where used because of insulation requirements in rafters at the bottom end of the 2x8s. (hope you follow what I wrote:)