COMPLEX roof - HELP! - Hip end with offset partial octagonal

[journeyman Mick]

.................That’s how my old man taught me originally. He was a cabinetmaker, turned carpenter after he migrated here. It’s not the easiest way though. You can get that little red roofing book that I’ve heard of, but it doesn’t give you any understanding, and I’m not sure if it covers bastard angles. Ditto for the roofing square method.
The most accurate way is through trigonometry. With a $10 calculator and a little bit of knowledge, you can calculate anything that you want, with any combination of dimensions and angles, to an accuracy of however many decimal places that your calculator goes to.............

John,
I've used trig to work roofs and other angle stuff but it's generally ages between goes so I tend to forget how and need to ring an engineer maths geek mate for a refresher. I also tend not to trust myself to get it right 100% of the time, I know I'd stuff it up quite badly in maths at school on occcasions. I understand how it works, just not confident in my own abilities I guess. But yeah, if I had to do a big, complex job I'd sit down with my mate for a refresher and whip out the old HSC calculator.

Mick

[journeyman Mick]

Just like John and Grant, I didn't do an apprenticeship. Learnt by watching and doing with a bit of reading thrown in. Would have done more reading, but there wasn't anything suitable. Never worked with anyone who pitched a roof so had to work it out myself. Used trig for the valley rafter on this job and managed to cut it about 100mm short (although looking back, perhaps it was the old tape measure trick)
Became really good friends with the owners of this place, there was only one page of plans, no details so we had a breakfast meeting once a week (hot chocolate, croissants, freshly laid eggs etc) to work out all the details for the week to come.

The building is "L" shaped, with a 3M wide verandah all around + 1M overhang. No internal doors, they all open onto the verandah. No privacy issues as it's on over 100 acres and the nearest neighbours are quite a distance. First pic is looking from the inside corner of the "L" out towards one end (ends are all hips)
pic 2 is looking down the valley framing
pic 3 is a general internal shot, before the internal walls went up or the stone cladding went onto the steel frames.
pic 4 is looking up one of the ridge posts (300 x 300 red stringy, cut on site) showing the hip rafter intersections. Tight enough that you couldn't get a bit of ciggy paper in there. The rafters line up with the geometric centre of the post, but because it was milled with a hagen saw they're a bit wonky.
Pic 5 is a view along the finished verandah, steelwork is clad with locally quarried stone. Doors and windows made on site in Jarrah, cladding under windows in brushbox, louvres next to doors (barely visible) in WRC.

Mick

[bricks]

This thread made me seriously think about my own ability to build and entire house by myself, trussed roof = no worries, this stuff= my house comes tumbling down, Good on you guys for having a go but im lost as of the first post.

[echnidna]

Its not that hard Bricks when you think about it,
You just got to get the ridges in place first then the hips and rafters fall into place from there on.
Maths is ok but drawing it out full scale on the floor is a good double check.

[AndrewPatrol]

One of the most interesting threads for a long time. Like was said before, no such thing as a dumb question, and if you dont challenge yourself then life gets a bit boring. Good on ya Chipperchip and best of luck. One thing I thought of ( may be a waste of time though ???) is - have you considering making a simple model? No need to reply ,you probably havnt got time. Just an idea.

[boban]

Impressive fellas

[ChipperChip]

Nearly finished the drawings! That was harder than I expected. Sorry about the delay Pawnhead, Mick and others.

OK, this should be a lot more info, although I've not flooded it with dims. I hope I got the balance between clutter and info right. It's worth noting that I'm not completely confident about the dims in the area of the NE and N walls of the octagonal roof, but it's kind of a moot point. We're talking principles here not five decimal places, and I know it's close to right. I'll be re-measuring everything before I actually put this up anyway.

There are a few changes to the look of this where I've cleaned up some approximations that didnt matter so much before. A-A' is still the line of the original hip end, and B-B' is the line of the section I'm still preparing, which I will try to get up in the next half hour. The ones I'm uploading now are:

1) A dimensioned plan showing all loadbearing elements in the roof except two hanging beams BR2 and void areas). Red beams are propping beams for the roof structure, and blue beams are those that take the perimeter roof load where it's not being taken by the wall. Note that the red beams are offset from the centre because they have to land above joists below, and I'll be honest I had so much on my plate back then I failed to think the joist placement through properly.

2) A plan showing the area over which the ceiling height is 190 higher than in the rest of the upper storey. The RL's for the floor show where the step is (E-W on the landing, at the SW corner of the stair void).

3) An elevation of the roofline. This is worth seeing to understand just how shallow the pitch of the long broken hip is. It calculates out to just over 9 degrees.

4) A plan view with a 'normal' hip-end superimposed over the octagonal roof to try to convey what I meant about treating the broken hip as if it was a ridge, and the two bastard hips as if they were common rafters. Of course, once this is up I wouldn't be looking at it like a hip end, but I hope you can see what I mean from...

5) A closeup of most of the timbers at the peak that would result from doing this. I didn't do the other rafters coz frankly it's midnight.

and lastly
6) A plan view of the proposed ceiling joist layout.

The tricky part about getting the octagonal section up correctly in this way is making sure the three bastard hips are cut right and that the west end of the broken hip is propped at the right height. That's why my main original question was about what to do around the (very short!) minor ridge. I guess I could just put a block in where the broken hip will eventually go just to let me get it all to the correct height to measure the broken hip and to stringline for the minor ridge.

Oh, and when I said I hadnt used any trig... obviously I did to get my expected pitches of the faces of the octagonal area. And I just extended the spreadsheet to give me the pitches of the bastard and broken hips.

I hope all that makes sense. I'm going to finish this last drawing then get some Z's and will check here in the morning before work (eek... in 6 1/2 hours) to see if there's anything anyone needs me to add... that's if you're all insomniacs.

[ChipperChip]

Oops, only lets me put 5 images up for some reason...

Here's the ceiling joist layout I'm proposing. This is just an indication of course - but it gives the idea of directions and so on. I'm thinking I'd tripl-grip all the angled joins.

[ChipperChip]

The section isnt going to happen tonight. My brain just switched off and I can't get it started again. Sorry folks, but the relevant bit is in there (crosshatched part of the siren). I couldn hear a thing!

[pawnhead]

Yes it is pretty much perfect. And you're right, it's not at 45 degrees. It's about 40 & 50. So this isnt just a regular octagon, it's a slightly squashed one. Dont you love renovations. Actually, architecturally it has to be squashed to make the courtyard below work.

That’s not a problem. You just have to check all your dimensions on site.

I'll do a much more thorough plan view with the internal walls, remaining propping beams, dims and R.L.'s. I'll try to knock up a section, and a ceiling joist plan sounds like a very good idea. I just need more detail than I can squeeze into a 100k jpg What I'll also try to do is something to demonstrate what I meant by treating those bastard hips as commons...

Don’t worry about any of that.

Once again, huge amounts of thanks to you Pawnhead - I hope you drink beer mate One of my side projects at the moment is building a microbrewery.

I don’t mind a beer occasionally, but I don’t expect a shout unless we bump into each other in a pub. Just buy yourself a foily.

OK, this should be a lot more info, although I've not flooded it with dims. I hope I got the balance between clutter and info right. It's worth noting that I'm not completely confident about the dims in the area of the NE and N walls of the octagonal roof, but it's kind of a moot point. We're talking principles here not five decimal places, and I know it's close to right. I'll be re-measuring everything before I actually put this up anyway.

All good. Those drawings look good (except for a couple). The offsets are critical, as are all the dimensions verified on site. You’ll have to measure/double check all of the offsets before you do any birdsmouth calculations. Check the RLs of all your pitching plates.

4) A plan view with a 'normal' hip-end superimposed over the octagonal roof to try to convey what I meant about treating the broken hip as if it was a ridge, and the two bastard hips as if they were common rafters. Of course, once this is up I wouldn't be looking at it like a hip end, but I hope you can see what I mean from...

5) A closeup of most of the timbers at the peak that would result from doing this. I didn't do the other rafters coz frankly it's midnight.

Forget about that. Throw all that junk away. It's not ridgey-didge, calling it a ridge.
Get hip. It’s a flying (broken) hip!

The tricky part about getting the octagonal section up correctly in this way is making sure the three bastard hips are cut right and that the west end of the broken hip is propped at the right height.

Of course. Verify dimensions before we start the calculations. Locating their position on site isn’t a problem. Plumb bob, tape measure, water level, Isaac Newton.

I hope all that makes sense. I'm going to finish this last drawing then get some Z's and will check here in the morning before work (eek... in 6 1/2 hours) to see if there's anything anyone needs me to add... that's if you're all insomniacs.

I keep very irregular hours.
For the past three years I’ve been a full time carer for my aged mother who suffers from bipolar disorder amongst other medical ailments. It gets very demanding mentally at times, but it’s not that big a workload, so I’m happy that I have time to spend renovating this house, and surfing the web. Life is pretty good at the moment, and I always look at the bright side.

I’ll explain how I’d pitch this hip, and deal with SohCahToa when you’ve checked your dimensions.

The section isnt going to happen tonight. My brain just switched off and I can't get it started again. Sorry folks, but the relevant bit is in there (crosshatched part of the siren). I couldn hear a thing!

Don't worry about it.

Just fill in that plan.

[ChipperChip]

The section isnt going to happen tonight. My brain just switched off and I can't get it started again. Sorry folks, but the relevant bit is in there (crosshatched part of the siren). I couldn hear a thing!

Where the HELL did THAT come from.... Crosshatched part of the siren?? Couldn't hear a thing?? OK, my brain really was fried...

Feeling better this morning.

Thanks Pawnhead, will get all that today. Dont fret about me calling that broken hip a ridge I KNOW it's a broken hip. I just meant that in terms of the construction of that joint in the octagonal section, the layout in plan looks a lot like a (slightly uneven) hip end IF the broken hip had been a ridge. If my dims are right and the spreadsheet gives me a length and angle, I feel I can trust it and build it as such. At this point I feel more comfortable with that way of achieving the octagonal area but I'm gonna get your measurements today and see how your plan works out. But I'll be honest I dont really think I should have rafters coming together there, from a load bearing point of view mainly. Surely it should be the (larger) hip rafters that are joining up? Rafters there also make it tighter to work in, but that's obviously less of a consideration. Did my enlarged view of how I thought that joint might work make sense?

You've already made me see the easy way to pitch the main roof's broken hip so I can stringline the minor ridge, for a start Still struggling with what to do around the east end of the minor ridge but perhaps that will have to go by spreadsheet and faith too. But at least I now understand exactly which dims are critical.

We're getting there. I'm due on site twenty five minutes ago tho and typing more isn't getting me THERE. Glad the boys have plenty to do. Later.

[pawnhead]

If my dims are right and the spreadsheet gives me a length and angle, I feel I can trust it and build it as such. At this point I feel more comfortable with that way of achieving the octagonal area but I'm gonna get your measurements today and see how your plan works out.

Fair enough. If you can plug your dimensions into a program and come up with the measurements then you don’t have to worry about trig, but I’ll keep going with my explanations for the benefit of anyone else who may be interested, and when I’m done I might give a run down on trig if anyone’s interested. There’s explanations on the web, but I think I can explain it a bit simpler, and also explain how to get compound angles for hips and valleys.

But I'll be honest I dont really think I should have rafters coming together there, from a load bearing point of view mainly. Surely it should be the (larger) hip rafters that are joining up? Rafters there also make it tighter to work in, but that's obviously less of a consideration. Did my enlarged view of how I thought that joint might work make sense?

That looks alright structurally. If your program can spit out all the dimensions and angles for that, then I can’t see anything wrong with it. I take it that you have deeper hips than your rafters. It was common in the old days to use 6” X 1” for hips and valleys, and of course you can still do it that way, but I just use 4X2 for everything. As I’ve said you could cut them all to a point, but that’s the most time consuming way.

You've already made me see the easy way to pitch the main roof's broken hip so I can stringline the minor ridge, for a start Still struggling with what to do around the east end of the minor ridge but perhaps that will have to go by spreadsheet and faith too. But at least I now understand exactly which dims are critical.

We're getting there. I'm due on site twenty five minutes ago tho and typing more isn't getting me THERE. Glad the boys have plenty to do. Later.

I’ve explained a bit more of my pitching process, but I haven’t got up to that Eastern point yet. From what I have done, you can see that it’s easy to set up stringlines to locate that point. As I’ve said, you could also sit down with a calc, and cut everything on the ground, and just put it together like a mechano set: -

I’ve amended the last drawing to explain a bit better how to set out the broken ridge.

Set up stringlines at the ceiling level in line with the two walls as shown. If there’s hangers or beams in the way, then off set the lines up, down, left or right, to wherever you can get a clear run. If your walls are a bit out of parallel it’s not a big deal. You just have to mark the centre on the ceiling joists, and pull a line under where the ridge is, and transfer it up to the rafters with a plumb bob or spirit level. Then you can run a line for the top of the ridge.



Next, nail a temporary prop to the ceiling, plumb it up, and brace it back. Hold your tape against the first creeper rafter on the South Western corner, and by eye, line it up with the Eastern roof plane of the main roof. Cut a piece of ridge 600mm longer than your measurement, then install the broken ridge, butted against the last creeper rafter, and nailed to the prop as shown here.



Next, run a stringline from the top of the main ridge, somewhere close to the southern end, down to the bottom of the last main roof rafter on the Eastern side.
Run another stringline from back on the Eastern roof somewhere (the position isn’t crucial), intersecting the first stringline, and extending past over the broken ridge stringline.
Now you have two fixed stringlines, and you’re holding a third one over your ridge. Adjust the position until it just touches the other two stringlines, and mark the ridge below.




Note in that second detail, the height of the South Western hip in relation to the height of the top of the main ridge. I'm working to centre lines all the time, and the central point at the top of that hip is the intersection of the three planes. It's outside edges are high and must be planed down, or it must be set at a specific lower height that can be calculated. That's why the creeper rafter is shown installed lower than the top edge of the hip. Planing the corners down gives better support for the roof battens. I've shown all the ridges installed low so they don't have to be planed down.

Drive in a nail in the centre of the broken ridge, on your pencil mark. Let it stick up so it just touches the stringline above. The top of this nail represents the intersection point of three roof planes. Drive a nail on an angle into the long point of the hip at the top. Hook your tape on this nail and extend it down to the nail in the broken hip. Sight the measurement plumb down to the Northern face of the broken ridge. Cut and install your broken hip.

From the drawing it looks like your valley rafter has no eaves overhang at the bottom. You can use trig to calculate its length, or you can measure it. I haven’t mentioned this yet, but check that the bow is up on all your timbers before you cut them. Cut and install your valley rafter, and it should look like this at the -



Bear in mind, that whilst your hips are high at the edges, your valley rafter will be low. After measuring your ‘cripple’ rafters (the ones that go from the valley to the hip), make sure that when you install them, you leave them down from the top edge of the hips, and up from the top edge of your valley. The top faces are supposed to line up with the centrelines. You can calculate the exact distance if you’re fussy, or you can just mark it on a scrap and measure it.

Now you should have a roof that looks something like this: -




BTW None of this is to scale. I'm just using a photo program with no scale capabilities and I'm just guessing the joist spacings.

To locate that point, you can use trig, but it’s just as easy to install your fascia board along the Southern end of the main roof first. Make it slightly longer than you need it on the Eastern side. If there is no rafter near the end, then make sure it’s straight, and brace it if you have to. Trim your South Western octagon hip rafter to length, if you haven’t already done that prior to installation. Run a stringline from its end, over to the fascia you’ve installed and check that it’s parallel to the pitching plate. Mark the back of the fascia, and cut it on an angle which is half of the overall angle between the two walls. Measure down the edge of the fascia and mark the top of the roof line. This is the centre-point for your next valley rafter.




Anyway. It's lunchtime and I'm going out back to lay some floor boards.

[pawnhead]

pic 4 is looking up one of the ridge posts (300 x 300 red stringy, cut on site) showing the hip rafter intersections. Tight enough that you couldn't get a bit of ciggy paper in there. The rafters line up with the geometric centre of the post, but because it was milled with a hagen saw they're a bit wonky.

That's where those fish plates come in handy eh? That's a nice looking house. You did a great job on that roof.
BTW what's a hagen saw?

I've never installed posts that big although I pitched a roof on a poll house built on exposed pine poles. I was foreman carpenter, but the builder already had the poles installed when I arrived on site. I think they were just concreted in but I can't remember.
I'll try to dig up the pics.

[journeyman Mick]

John,
a hagen saw is basically a carriage, usually a pair of holden wheels on an axle with a trailer jockey wheel to steady it. See sawing on top of this is a long pole, on the short end, just behind the carriage sits a motor, often a VW. The other end of the pole is a lot longer and carries a humungous saw blade, driven by a belt from the motor. There's usually a water reservoir and a pump top deliver a spray to the blade for cooling and lubrication. If it's really fancy there will be a few hessian bags hanging off the carriage to slow down any chunks that get thrown back at the operator.

Operator makes a few crayon marks at either end of the log and just eyeballs his cut from one end to the other. Suprisingly quick and accurate with the right operator. Bloody frightening contraption though. I posted a pic of one in a quiz thread here a while back and just did a search for it, but I've got a feeling it's old enough that it was archived and doesn't show up in a search.

Mick

[pawnhead]

Wow, that sounds like my kind of saw.

A big version of the table saws I used to set up on site from a slab of pineboard. No guard or anything.