does anybody know this conundrum?

Learn a good cad program. Sketchup is a good start. It will allow the what if's and the how do I do that, without cutting the first piece and without wasting any time or money.

yes, i know it well. but i try to work it out on the computer before sending it to the shop...

what are the:

building width
building length
pitch along width
pitch along length

(and if you don't know the pitches, what pitch are you targeting?)

i'll throw it into my roof module on HSB program and post a few images...

why not forget about the center pin and do 2 king post trusses, keeping the pitches the same, overhangs the same, etc.?

Mo,

I once asked a compagnon how they dealt with making equal overhangs on irregular roofs, and he said they just design the roof, and then move the walls to make equal overhangs. I like it--it's a simple approach when you're designing new stuff.

The other way is to to do a drawing to figure out how much to offset the hip or valley.

the wrestler

its possible to solve this graphically. i just did a quick sketch - with a 12x24 plan you'll need a 9/12 on the long side and a 5.25/12 on the short side, assuming 2' overhangs all around.

this does not put your hip over the corner post - which may or may not work structurally.

you'll also need a tension connection to keep the corners from spreading away from each other - or build a truss into the center pin idea.

with the hip offset from the corners it might make sense to do this as a common purlin system on top of primary hips and a few primary rafters.

and you'll have an odd shaped boss pin as things don't hit at right angles to each other.

and if you plan to attach a gutter board, your plumb cuts on the ends of the rafters will be different from side to side - so you can design around this with a unique end detail.

Some of the software I've used permits, even encourages, a uniform elevation for the gutter line as a place to begin. Then locate the ridge and specify a single height. All else follows, almost magically.

While it must seem more difficult at first, I believe that there are fewer hoops to leap through if you force the hip to land on a building corner (yielding unequal pitches on adjacent roof planes) than going the other route.

This topic is the subject of my next When Roofs Collide article in the June Timber Framing. With an irregular roof it's impossible to have the hip cross the corner of the building and have equal width and equal height overhangs, at least in my universe. You must offset the hip from the corner, and if there are irregular pitches, raise the plate on one wall or have different HAPs.

mo,

For a rectangular pyramidal hip roof with equal overhangs and a level fascia, you need to work from the gutter line


Start by drawing a line drawing in plan view. Remember to work from the gutter line. I add in the plates as a faint or dashed line just for reference at this point.

Usually I let the main pitch and the size of the building (including the OH's) determine the pitch of the adjacent side. Connect the corners and you have the hip lines. The hip line will not cross the corner of the plates as mike mentioned.

You will also want to shift the hip so the backing cut is not centered, but rather leaves equal depth on each face of the hip (you posted a graphical solution to this a while back that I still refer to).

Last thing you do to the plan drawing is add the jacks. If you use the same spacing on both sides, they will be staggered along the hip. alternatively , you can change the spacing to make them hit the hip in pairs.

To get the pitch of the adjacent side, determine total rise from gutter line to peak on the main side. Solve for pitch using total rise and adjacent run including OH.

Now you have everything you need except the HAPs. You have to choose one side's hap and let it dictate the other sides hap. It can be give and take between the two sides so that you don't take too much out of one or too little out of the other. I start by assigning the tallest HAP i can live with to the higher pitch side. then, using the runs of the jacks to the plate and the pitches, i see what that gives me for the shallow side. If it isn't too deep a notch out of it and I can come down a little, I may do that. The alternative for different HAPs is different plate heights, but that is a tough one to make look right in exposed framing. In stick framing it's common to raise the plate level on the steep side to make the HAPS the same.


One place to keep an eye on is the Hip where it crosses the plate(s) and forms the overhang. You will probably want to reduce it's depth after it crosses the plate line because you will be taking a good bit out of it to meet your two HAPs (assuming the hip is deeper than the jacks). this area can look funny if you aren't careful.

Sketchup is a good way to model this to avoid funny looking stuff.

that is what i found in my sketch... no matter how you push, you'll end up with an offset hip from the corner, if you want irregular, you get, well, irregular.

sure is. a bit tricky to do compound stuff the first few times - but certainly manageable.

good post gabel. essentially what i did in the sketch, but i had the magic of HSB in the background to connect all the lines for me.