Omission of Top Plate
Hi,
I would like to explore, for a new-build house, with the client, an option to run the finished ceiling into the widow bay. That is so that the ceiling is flush with the top window reveal.
There is a rim board, between floors, where headers will be installed as per R602.7.2. But the only way I can think of, to have this detail, is by removing the top plate(s) so the drywall runs into the window frame.
The rim board will be continuous, the header runs past the R.O. width 6″ either side (as per code article above), the wall fully sheathed, and there is the bottom plate of the wall above. My thought would be to fur out the header in line with top plate(s) and add strapping inside and out, along edge of the plates. Which all together would provide stiffness and continuity.
I do not see a code provision for this.
I wonder if anybody here has achieved this detail and can share their solution so that I can propose it to the engineer and not induce the blank stare?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Deleted
Cam,
If I'm understanding correctly, that's a pretty standard detail - maybe conceptualizing it differently will help. It's not an opening in the wall - rather the wall stops and starts at the bay, so no plates are necessary.
Interior load-bearing walls are routinely stopped at openings, and a flush beam substituted there to carry the floor joists above. The ceiling remains continuous through the two rooms. What you are suggesting is much the same: You stop the exterior wall for a certain distance, and carry the loads on a flush beam (which you could also call a beefed up rim-joist). No wall means no plates.
A similar detail has become popular with designs that want windows that extend right up to the ceiling. The floor joists - or if it's the top floor the trusses - are inset slightly and bear on hangers attached to a flush beam.
Hi Malcom,
This makes sense. I was overthinking it. I’m too caught up in CAD mode.
For some reason the idea of breaking the continuity of the top plate on the exterior load bearing wall was throwing me.
On interior walls I wouldn’t even think about it. And I fact I have it happening in multiple places already.
Thanks
Deleted
It’s unfortunate to see comments retracted as I think they can be interesting to learn how things are interpreted. Or perhaps, even more pertinently, how simple things are overlooked, certainly structurally, as I may still be doing. They certainly might teach me how to write more clearly.
I often retract my comments when I realize I have read the question wrong, or when I realize I am opening a can of worms I don't have the time or energy to follow through on, or when I post negatively just because I'm in a bad mood, or various other reasons. Perhaps it's more important in my case due to my "expert member" badge; I try to stay in my lane but sometimes veer out of it into elements of building that I am definitely not an expert on. Others have their own reasons for doing so.
Regarding your question, I don't have anything to add to Malcolm's response.
Mike,
I'm guilty (?) of all those too.
Hi Mike. Nice to see you commenting on my question. I appreciate your input. I’m not sure if you were a person to delete a comment, but I was not passing judgment or being critical of the act. I received an email notifying me of a reply and by the time I went to read it had gone. I was a bit disappointed as it appeared to be interesting and I was keen to read it all. Oh well. It doesn’t matter. Again, thanks for your input.
I deleted my comment, #4, because I realized after reading your post a second time, more carefully, that my comment wasn't relevant and might confuse the issue.
I had brought up a structural concern that was not relevant. I don't see any problems with your proposal.
For what it's worth I'll share my earlier thoughts. Normally the double top plate plays an important structural role in handling lateral loads. So for people living in high wind or seismic zones, it's important to provide an alternate load path when interrupting those plates. You've done that. So it's not a concern.
But for anyone having questions in their minds, it would be best to run the idea by a structural engineer familiar with standard wood frame construction.
For a single story building, or the upper floor of a multi-story building the intersection between the roof and wall line needs to be detailed to transfer lateral loads, the "sliding" of the roof parallel to the wall. Connecting the roof sheathing through to the wall framing below accomplishes this. The double top plate, which is continuous along the entire wall line, transfers this load to all the shear walls on that line.
For a multi-story building, the floor above needs to transfer its lateral loads into the wall lines below in a similar manner, and again the double top plate of the wall below serves that function.
So when the double top plate is interrupted, some alternate path needs to be in place. The rim joist can do this, IF it is continuous along the entire wall line. For long wall lines typically it is not, however. When it's not then a splice should be strapped to permit a tension transfer across the splice.
If you do have a reason to keep a continuous top plate, you can fur down or strap the ceiling with 2x material to compensate for the top plate thickness. There are various steel straps and tie plates that can serve the function of the (missing) second top plate, for example to splice the plates, or to tie a corner. This is done routinely in advanced framing, to eliminate unnecessary lumber (joists would be stacked over the studs).
I like the idea of just deleting the top plate because of the continuous header though.