Thread: roof framing, irregular hips

Theres only 2 things I don't miss about not building houses anymore.
Digging stump holes.
Working out weird hips.

For 30 degrees (Unless I'm mistaken, which is quite possible), I believe it would be: -

{tan 30 / (1 / cos 16 ) } tan ^ - 1 = 29.0296044403471

For 60 degrees it would be 59.0102500875002



I take it that these are irregular 'bastard' hips. Why don't you just cut your 30 X 16 degree cuts on your CMS (or with a protractor and power saw), then just use your power saw set at 90 degrees off the first cut, to give you your 60 degree cut. Finish it with a handsaw if it doesn't cut deep enough. Then fit it with a planer.

Are you sure that your hip is 16 degrees?

What are the constraints that you're working with?

Haven't pitched that many roofs and it's been more than ten years since the last one, so I'm next to no help at all. Whenever I was stumped I would resort to drawing it out as large a scale as possible on a sheet of ply or on the concrete slab to work the angles out. I trust my drawing skills over my maths any day. Like Pawnhead says, you should be able to set one angle with your circular saw bevel and cut the other freehand with it, finishing off with a handsaw if neccesary.

Mick

thanks for the various thoughts, i will go away and think on it some more

pawnhead, im embarreresd to say that your calculation seems remarkably similar to my calc for the hip pitch. i didnt think of that

Originally Posted by dirtydeeds

i have a roof framing job (maybe) comming up with irregular hips

the ridge/common junction cuts are my problem. it HAS has to be cut by hand because the roof timbers are going to be exposed from below and my crosscut mitre saw cant cut 60 degrees


Details

the main roof pitch is 30 degrees
the cheek angle is 60 degrees
the hips are going to be regularised 2inchx6inch timber so they end up 44mm x 145mm finished size

the hip pitch is a tad over 16 degrees, using the usual calculation
--> hip pitch tangent = tan roof pitch divided by (1 / cos cheek angle)


Problem

I know how to set out the off centre starting point for the cut

MY QUESTION IS....

what is the calculation to give me the correct cut angles (ie 30 and 60 degree cuts adjusted for a 16 degree pitch)

I'm new to the forum and i know this thread is old but i can answer your question.

Main Roof = 30.25°
Minor Roof = 45.29°
Hip=26.796°


Your hip angle is wrong the formula you are using should be sin(60&#176 instead of cos(60&#176
Tan-1(tan(30.25&#176/(1/sin(60&#176=26.796° you can simplify this formula by multiplying by the reciprocal so are formula would look like this Tan-1(tan(30.25&#176xsin(60&#176=26.796°

The reason i know that the minor side is a 45.29° is simple heres a formula

Tan-1(tan(30.25)/(sin(30)x(1/sin(60)=45.29°


I think your question is referring to the backing angle?

To get the backing angle the formula would be
Tan-1(sin(26.796&#176/tan(60&#176=14.59°

the other side would be

Tan-1(sin(26.796&#176/tan(30&#176=37.98°

To get your sheathing angle use this formula

Cos-1(cos(60&#176xcos(26.796&#176=63.49°

Cos-1(cos(30&#176xcos(26.796&#176=39.37°



Also you can get your hip unit run for any roof using this formula
12/sin(plan angle)

12/sin(60&#176=13.86

Hip angle=Tan-1(7/13.86)=26.796°

Originally Posted by pawnhead

For 30 degrees (Unless I'm mistaken, which is quite possible), I believe it would be: -

{tan 30 / (1 / cos 16 ) } tan ^ - 1 = 29.0296044403471

For 60 degrees it would be 59.0102500875002

Looks like your trying to figure the sheathing angle

Cos-1(cos(30) / (1/cos(26.746)=39.34

Cos-1(cos(30) x cos(26.746)=39.34

Well, this thread was started January 29th, 2007 ... I guess the roof must be pretty well finshed by now.

DD, not sure I understand your question. If the Hip rafter is already backed you need what is commonly referred to (over here on the other side of this planet, anyway) as the Sheathing Angle. This is layed out on the backed upper surface of the Hip, in conjunction with the pitch angle of the Hip on the side (plumb) face of the rafter.

If your Hip is not backed you need the Hip Rafter Side Cut Angles on the upper shoulder (Hip Pitch Angle again on the plumb face). These side cut angles are different at the foot and peak of your rafter. The side cut angles are seen on the bottom shoulders of some of the log Valley rafters as they intersect the wall.

This is a link to my web based Roof Framing and Joinery Angle Calculator. I dislike posting only a calculator as it doesn't lead to an understanding of why the angles work the way they do. Besides, you'll have to supply the trigonometry to finish laying out the compound angle.

This is a link to a page with the calculators, formulas and diagrams of the angles commonly used in complex roof framing.

Hope this helps you out.