Gambrel Roof Joist Heel Size

[Dennis Putnam]

Is there are standard for the heel dimensions for a gambrel roof joist? I'm using 2X6 joists on 2X12 rafters. What should the heel dimensions be? Thanks.

[Jerry Miner]

Not sure what you're asking. There are a lot of ways to frame a gambrel. Can you post a drawing of what you mean? Is this similar to what you want to do?

Gambrel (3-23-13).png

What are you calling the "heel" of the joist?

[peter gagliardi]

If above is where you mean, typically it is called the seat cut. That is the horizontal cut that sits on top of your wall plate.
Unless it won't give you enough rafter left over for a proper overhang, it is sized to the width of the plate. 2x4 plate is 3 1/2" nominal, and so would the seat cut be. If rafters are deep, you could do the same with 2x6 walls- 5 1/2" seat cut, or you might have to go less than 5 1/2" . In any event, I wouldn't go less than the 3 1/2". You do need enough for good toenailing without splitting the seat cut all up which defeats the purpose.

[Dennis Putnam]

Thanks for the replies and yes, it is the seat size I meant. Sorry but I got my sizes reversed too. The joists are 2X12 and rafters are 2X6. I also may be missing something. Are you saying I need a plate across the joists rather than aligning the rafters directly on the joists? That is beginning to make sense as I was wondering how to offset the gable ends for the wall studs. If that is the case than is obvious that the seat dimensions would match the plate. All the plans I have found for gambrel roofs are short on the deals of how to tie it in. I'm planning to build knee walls to make raising the rafters easier. I have that joint figured out and how to handle the peak but tying the lower rafters to the joists that is a bit fuzzy.

[peter gagliardi]

It will be easier and stronger to either plate the top of joists and nail directly thru plate into top of joists, then toenail rafter into plate. If you have to set rafter directly onto joist, it will be hard to get strength and good nailing between the two pieces, so 2 3/4 plywood gusset plates crossnailed on either vertical side of joist and rafter will help strengthen it. Go up the rafter the same depth as your joist, in this case 11-11 1/4"

[Dennis Putnam]

I'll be using a plate now. Thanks.

[Jim Andrew]

Add whatever the thickness of your boxing is to that seat cut, you don't want to have to notch your boxing around every rafter. It is easier to box your walls before putting up your rafters, and just pulling the rafters tight to the boxing.

[Jerry Miner]

So you're building a gambrel more like this?:

Gambrel (3-25-13).pngGambrel detail (3-25-13).pngGambrel detail 2 (3-25-13).png

As stated above, the seat cut is typically cut to fit the top of the wall or plate. If you need more "meat" in the rafter to carry the overhang, the seat cut is reduced (but always 2" at a minimum)---in your case, I think you can cut the seat cut to the centerline of your rafter, leaving half to carry the overhang and half to bear onto the wall or plate.

The rafter can land on top of the wall, with the joist sitting next to the rafter (as in the third drawing above), or on a plate attached on top of the joist (as in the second drawing. One method gives you more "headroom" above the joists; one gives you less room above, but more below the joist.

In the old days, these connections were toe-nailed. Nowadays they are more often connected with metal clips (the engineers really like the metal clips)---like a Simpson A-35 or something similar.

[Dennis Putnam]

Thanks, the middle image is what I have planned with Simpson ties.