Hip, common rafter birdsmouth depth?

Joe Carola

John,

Read this post I made at Contractor Talk and check out the picture of the hip I marked and the drawing I made. This might clear up how you have to mark the hip HAP cut. Hope this helps.

http://www.contractortalk.com/f14/hi...06/#post720163

__________________
Joe Carola

Gary in WA

Yep. And simpler if you are older on page #33: http://books.google.com/books?id=Z8f...rafter&f=false

Be safe, Gary

__________________

johnd393

That's pretty much what I did except the rafter was not shortened at the top.

This might be more than you want to read so feel free to skip it.

The garage is 24X28 with a 6/12 slope.
I used a speed square for all the plumb lines.
Starting with the commons, I made the plumb cut at the top.
I measured down along the top edge, 161" and made the wall plumb line.
I moved the wall plumb line to shorten the rafter half the ridge or 3/4" 90deg to the plumb line. Than positioned the square to mark a 2" seat cut.
Than to fit over the sheathing I extended the seat cut 1/2" beyond the plumb line. Than cut it.
The ridge board is 49 1/2" or 1 rafter thickness longer then the lenght - width of the building.
I built a scaffold in the center so I could work at the ridge. I didn't do anything to set the height of the ridge except nailing 2 commons on one side and raising it till it was plumb with a small level.
The commons and ridge all fit together nicely.
For the hips I made the double cheek cut at the top.
Measured along the top edge from the point of the cheek cut, 216" and made the wall plumb line.
Moved the wall plumb line 1 1/16" to shorten 1/2 the 45 degree ridge thickness.
Marked the HAP along a line 3/4" in from the shortened plumb line.
Marked the seat at this HAP point and cut the seat to the shortened plumb line.
I trimmed the sheathing at the corners so I did not extend the hip seat cut to clear the sheathing like I did the commons.
The hips are or fit as if, they are too long.

Joe Carola

When pre-cutting the hips like that, you can run into this problem because if one wall isn't perfect the hips won't fit. You have to cut the hips at the top now in order for them to fit right because cutting the bottom at the HAP line would not be correct

__________________
Joe Carola

tpolk

same with rafters, sub tract ridge at top not at wall as wall cut changes vertical dimension at seat cut

__________________
The older I get the better I was

johnd393

Well, something went wrong and I don't know what it is. The diagonal corner to corner dimensions were very near equal before putting up the common rafters. Maybe a bunch of micro errors made the ridge too low. All 4 hips looked long by about the same amount. I didn't measure it.
As to my unorthadox shortening at the lower end. Lets create a sample rafter. Lets forget about the seat cut for a minute. Lets also eliminate any overhang and have the rafter end at the plate outside edge.
Now we cut plumb cuts top and bottom at the calculated rafter lenght. The rafter is too long because of the ridge thickness. I you put it up like it is, it will overhang the plate edge. It's also to high cus we didn't cut a seat cut yet. It's just a board with a angle cut at both ends. You could flip it around and turn it over and it would look the same. We could cut the extra off either end. We aren't screwing up the seat cut cus we didn't even lay it out yet. We can cut the seat for what ever amount of bearing and HAP we want.

tpolk

no, you have a triangle. top of ridge to top outside corner of plate, horizontal run to center line of ridge(run), vertical to top of ridge(rise). as you raise the triangle at the wall plate to give rafter plumb height you create a horizontal seat cut. depending on how much rafter you want left you can put a seat cut that is 3.5" to the bottom inside edge of the rafter at the inside of the wall plate. what ever you raise the rafter=triangle you have to raise the ridge the same. If the ridge is a fixed point as in it has to be at a certain elevation to meet other roof lines then sometimes you need to shorten the wall height. the hip will be , has to be whatever this common rafter has established in a standard hip roof hope this helps

__________________
The older I get the better I was

johnd393

I attached some pictures.
I pulled the nails out of the hip seats and trimmed them some to get the HAP right. Now I'm learning the an added benefit of cutting jack rafters, extra firewood.
I thought I would be better at this. I got 2 jacks to fit but it's not a fit to smile about.

Attached Thumbnails

         

 

tpolk

things are looking ok. i know how frustrating a hip can be and I'm sorry I'm not a better typer to get whats in my head out better. do you own a framing square? on the square it gives you lengths for your jack rafters based on the pitch of your roof. it will tell you how much to add to each based on your on center layout. hope this helps

__________________
The older I get the better I was

johnd393

I thought it would be fun to build the hip roof. The materials were $1000 cheaper than trusses. This old retired guy can lift rafters by himself. I won't have to do siding up to a high gable peak. I have a framing square, but mostly used a speed square. I used a calculator than checked it against the tables on the framing square. I started with the bottom jacks. For the first two corners, the calculated laid out lenghts weren't working so I trimmed and recut till they almost fit and nailed them in. One thing that was causing problem is, I was trying to layout on the hip exactly where the jacks would go. Then I read in the book to put them where the make a 45 degree angle with the hip. That was easier. The run of a jack is sposed to be the same as its distance from the corner. For 16" you get the same number as the Common Diff on the framing square. When I used 16 1/2 for the run I got a lenght that seemed to work. That extra 1/2 was the sheathing thickness. Three jacks in my discarded pile were close to that. One had the seat cut too deep so I stuck a shim under it. The last 2 bottom jacks went up the ladder once and got nailed in.
John D

tpolk

__________________
The older I get the better I was