*
Rock ford,
The way I deal with problem is, after the common rafters are all set, measure from each corner to the end of the ridge. This will give you an idea of how much difference there is between sets of hip rafters. For real accuracy you can make up a dummy hip rafter tail and just take the dimension.
Now for the jacks. Lay out a common tail on stock long enough to get the longest jack. Then brace the hips straight. The next step would be to get the layout for the longest and shortest jacks on one side of the hip rafter. this is much easier with a helper. Now you can measure these, I usually just hook the top edge of the plate,but any point that you can locate on the birds mouth will work.
Now with these two numbers, count the number of on center spaces the long and short rafters. Mark both these lengths measuring from the birds mouth on the would be jack rafter diagonally to the top edge.
Next measure the difference, this has to be measured, not done as subtraction because of the way the lengths were marked diagonally. With that number in hand you can divide it by the number of on center spaces. This will give you the amount to add or subtract to or from the long or short jacks.
This method also works for unequal hips and valleys.
Hope this helps and don’t create confusion,
it’s easier than it sounds.
Ale
Replies
*
O.K., the out of square issue is a long story, but what I ended up with is parrallel walls all around, but racked; a parallelogram? It basically started where two steel columns were set in the front of the building and the offset over 44 feet length is about 2 1/2 inches.
Anyway, I decided I had to live with it since the columns were already set. Up until now it really hasn't been a problem. I framed the first-floor hip end, and not surprised, one hip was too long, while the other was too short. I cut the jacks according to the tables and was unable to maintain th 16" o.c. spacing at the hips; the difference was 1 1/2" near the ridge and slowly got better(almost perfect) torwards the corners.
The second-story section has two hips that will yield about 40 jacks.
Are there any adjustment that can be made while laying out the jacks? I really don't want to trial-and-error cut each jack.
Thanks!
*draw a roof framing plan and you will see that youhave 4 trig problems.. i don't think you can use a framing square because nothing is square..if you solve for two jack rafters in each triangle you will have determined the gain for each of the four triangles...maintain your 16 inch spacing along the plates and keep your rafters perpindicular to the plate line.. make up your error with blocking at the ridge or just one last irregular piece of plywood..or... forget the trig.. layout your plates.. get your hips in place and measure off a string line to get your gain for each of the four planes..b but hey, whadda i no ?
*Rockford, did you happen to notice that the sum of the theoretical two hips equal the sum of the two real hips?Theres a clue in there, I think.Anyways, if you know the length of the hip, the run of the longest common, and the number of units to the corner, it is a simple mathematical calculation to find the common difference. Each side of the hip will have it's own set of rafters, but there will also be two sets of each, for each end.The worst building that I've ever had the pleasure of building was 2' out of square! And it was a hip with trusses. Ironically, the footing contractor was held up because the owner wanted an engineer to lay out the building lines, so that they would be done RIGHT!After we brought the problem to the super's attention, he told us to do our best (it was a large commercial building). I wouldn't want to be the ceiling contractor in that one!blue
*Rock ford, The way I deal with problem is, after the common rafters are all set, measure from each corner to the end of the ridge. This will give you an idea of how much difference there is between sets of hip rafters. For real accuracy you can make up a dummy hip rafter tail and just take the dimension. Now for the jacks. Lay out a common tail on stock long enough to get the longest jack. Then brace the hips straight. The next step would be to get the layout for the longest and shortest jacks on one side of the hip rafter. this is much easier with a helper. Now you can measure these, I usually just hook the top edge of the plate,but any point that you can locate on the birds mouth will work. Now with these two numbers, count the number of on center spaces the long and short rafters. Mark both these lengths measuring from the birds mouth on the would be jack rafter diagonally to the top edge. Next measure the difference, this has to be measured, not done as subtraction because of the way the lengths were marked diagonally. With that number in hand you can divide it by the number of on center spaces. This will give you the amount to add or subtract to or from the long or short jacks. This method also works for unequal hips and valleys. Hope this helps and don't create confusion,it's easier than it sounds. Ale
*mike, blue and alex sound like their all over it, and I did my own "what am I gonna do here?" version. My column supporting the ridge and hips was about two feet from center of building ( couldn't move the water heater, you know?). I did my plate layout without consideration of the "bastard" column. I wanted tails even across the wall. Then I set and braced the two longest jacks. Then it was relatively easy to just pull layout off the jacks to the hip, and then tape the length of each jack. Neanderthal, I'm sure, but hey, werks fer mee.