Hip rafter height above wall plate.

[Ash10010]

Hi, I have a question regarding hip rafters and the height above the wall plate. I think it's called the up stand?
Am I right in thinking that the plumb cut height (corner of birds mouth to top of timber) should be the same for hip rafters and common rafters?
Am I only allowed to take 1 3rd plumb cut out of the timber on hip rafters like I've done on the commons?
If I follow this rule it makes my hip rafter too high at the bottom.

 

[noseall]

Hi, I have a question regarding hip rafters and the height above the wall plate. I think it's called the up stand?
Am I right in thinking that the plumb cut height (corner of birds mouth to top of timber) should be the same for hip rafters and common rafters?
Am I only allowed to take 1 3rd plumb cut out of the timber on hip rafters like I've done on the commons?
If I follow this rule it makes my hip rafter too high at the bottom.

Hip rafters are quirky as is their seat and plumb cut as well as the fact that their angle (pitch) is different to the rest of the commons and jacks. We do all our hips by trial and error with the blade physically offered up in place. We sometimes mock up and fix a couple of pairs of jacks (top and bottom of hip) and put them in place so that their compound cuts actually touch. We then lie the hip blade on top of these to get the lie angle and then strike a pencil plumb line onto the blade, so that we can bevel the plum angle.

Never cut too much out and don't forget the dragon ties.

 

[Ash10010]

Would it be acceptable to notch about 20mm off the wall plate where the hip sits? Rather than cut more than a third off the hip? It's a side extension and I'm following what has been done on the existing building. The existing buildings hip has been cut beyond the 1/3.

 

[noseall]

Would it be acceptable to notch about 20mm off the wall plate where the hip sits? Rather than cut more than a third off the hip? It's a side extension and I'm following what has been done on the existing building. The existing buildings hip has been cut beyond the 1/3.

Technically, you could cut the entire thing through (horizontally) as long as you collect the whole seat cut with the wall plate and a dragon tie.

 

[noseall]

Would it be acceptable to notch about 20mm off the wall plate where the hip sits? Rather than cut more than a third off the hip? It's a side extension and I'm following what has been done on the existing building. The existing buildings hip has been cut beyond the 1/3.

Notching the plate will mean the hip blade sits lower (bottom plane) than the rest of the rafters.

However thick the hip blade is (45mm?) cut this much off the pointy corner of the wall plate, so that your plumb cut sits better. You will likely have to trim a bit of the back of the blocks too.

Seems to me that you may have positioned the new wall plate too high in relation to your new roof timbers v's the old roof timbers. If it was a ceiling marry issue, you could have added thickening strips to the joists etc.

 

[Ash10010]

Thanks. It should all the the same height, I'm running the ceiling joists on top of the original wall plate to the new plate, level.
I'm going to give it another go today with some offcuts. I'm thinking attaching offcuts at the bottom and top of the hip then running a line across the commons.

 

[John D v2.0]

Hi, I have a question regarding hip rafters and the height above the wall plate. I think it's called the up stand?
Am I right in thinking that the plumb cut height (corner of birds mouth to top of timber) should be the same for hip rafters and common rafters?
Am I only allowed to take 1 3rd plumb cut out of the timber on hip rafters like I've done on the commons?
If I follow this rule it makes my hip rafter too high at the bottom.

No you do have to cut a lot more due to the reason you mention.
If you imagine the standard rafter only has to go as far as the outer edge of the wall plate, whereas the hip rafter has to make it all the way to the corner. Even with the lower pitch to the wall plate, it's still going a lot further after the inside of the wall plate. With a round building you wouldn't have that issue (although good luck building a round roof)
However it doesn't matter because the load is being taken by the seat cut, there's not much on the overhang.