Setting Out A Bastard Hip Roof (Part 1)

This is the first of two animated videos that will show you how to set out all members of a Bastard / Mixed Pitched / Dual Pitched Hipped Roof prior to erecting the roof. It will focus on a situation where the wall plate has scope to be positioned laterally so as to give an equal overhang all round.
The second video-Setting Out A Bastard Hip Roof- (Part 2)- on this subject will focus on a scenario whereby the wall plates can only be positioned/moved vertically in relation to each other. in order to give an equal overhang all round.

[@user-xi4cy4np1f]

Your video is done quite nicely. I like the terminology of crown rafter for your single common rafter and the criss-cross diagonal lines representing the horizontal run of the irregular Hip rafter underneath the it's slant length travel.

[@darraghcrosbie527]

Great insight Mike as usual, thanks for all the help on n phase too hope all is well Darragh Crosbie

[@eugeneflynn4211]

yet again supberb tutorial on complicated roofs well done mike great animations

[@michaeldownes516]

Glad you liked it

[@ciaransavage6683]

Great video, would like to see more about rafters and hips

[@michaeldownes516]

thanks...did you check out other videos on this channel re hips and common rafters?

[@gavincollins9376]

Many thanks

[@michaeldownes516]

You are welcome

[@oreallyoreilly6576]

Brilliant

[@michaeldownes516]

Glad you liked it...have a look at part 2 if you havent done so already..it will focus on a senario where the wall plates can only be repositioned verticaly to each other as opposed to this example where they were adjusted horizontally to each other...

[@eimhink]

Good stuff Mike, great to update myself. Eimhin K

[@michaeldownes516]

Thanks 👍

[@Sherlockly]

So the dihedral angle is the edge cut when looking down at the hip from a birds eye view but what about finding out the two different plumb cuts for each side of the hip ?

[@michaeldownes516]

...at 11 mins into video you will see the deductions to make for the Hip Plumb Cut....note the initial plumb line shown at this point in the video....draw this plumb line first at each side of the hip, square accros from each other. next measure the distance from this initial line to the actual hip plumb cut shown on both side of the hip.....now of course the plumb cut lines are no longer square accross from each other. Dont forget all those deductions/adjustments are measured square off the the initial plumb line on the side of the hip (i.e. off-set measurement)

[@harperd8255]

So in this case were the wallplates are set level, do you think that the width of our cavity walls for different roof pitch scenarios would need to be firstly taken into consideration in order to suit the load bearing positions of the 2 wallplates ?

[@michaeldownes516]

If there are concerns re wall plate positions/support on a cavity wall consider the following...at the 9th minute of this video the position of the BM (birds mouth) on the lower pitch roof was found by sliding the wall plate horizontally from the first BM on the steeper pitched rafter to the second rafter. .....but instead of moving the wall plate horizontally at this point in the video,,, move it on a vertical plane downwards until it gives the BM on the lower pitched rafter (keep upstands the same for both rafters). Now you can measure the height difference between both wall plates...and you can have the wall plate at the same point all around on the wall. This approach would be needed where there is no scope to move the wall plate position horizontally but only vertically, This would be the case in a basic timber frame wall.. Do not forget, if you are using the Site/Builders Square to mark the commons. the difference in plate levels will increase by that amount the rise of this lower pitch rafter. By the way, you would have to redraw the position of this lower wall plate on the plan view on the setting out sheet....this will mean that the hip will now not be in line with corner of the wall plates.....the distance from the new corner of the wall plate to the hip position can then measured off the setting out sheet. Also, the Hip will be birds mouthed over the upper wall plate.. .

[@ciaranosullivan9605]

Hi Michael, a quick question. If I have a hipped roof with say major span a 50* and minor span 30* pitch what angle on plan view would the hip be at. Thanks again.

[@michaeldownes516]

Hi Ciaran, if you draw a rectangle that represents the common run by the crown run, the diaagonal of that rectangle represents the hip run. Spliting that rectangle diagonaly has produced 2 right angled triangles. Assuming you have the run distance of the common and crown then the following formula will give you the angle on plan of the hip run line.........crown run divided by the common run=answer. .......then answer shift TAN = angle of hip line on plan have a look at the following video on using TAN etc... kzbin.info/www/bejne/iWikZYx4a6h-hqc to get crown run use the following formula: crown rise divided by TAN of crown pitch= crown run ...check against the following example below to confirm that you are using the above formula correctly...... .... a crown that is pitched at 60°, its rise is 1.732m, .......will have a run of 1m.

[@jmsteele5149]

Surely the centre line of the hip changes due to the different pitches? It’s gotta be offset at the top no?

[@michaeldownes516]

The center line stays centered on the Hip...before we include the hip, think of the roof surfaces only, starting with 2 differing pitched surfaces meeting at a hip ridge line. Then visualise a thin vertical surface (of zero+ mm)droping from that hip ridge line (drops to a distance equal to hip depth}. Next, increase the thickness of that thin surface to now match hip thickness....but keep that thickness centred on the first vertical thin surface as it were. The surface will then meet mid way across the top of the hip, after the dihedral angle/backing bevel is applied. Hope that clears it up a bit more assuming i interpreted the question correctly.

[@jomcvelia5224]

So if I have a 35* one side and 45* the other how do I calculate the hip degree

[@michaeldownes516]

Using a scientific calcularor....Take the Rise and divided it by the Hip Run......then hit = sign.....then hit Shift Button...hit Tan button...hit = to give your pitch. Example .....Rise of 1 metre divided by a Hip Run of 1.732 should give pitch of 30° if you are applying the above formula correctly Here is a link that you may find usefull for roof formulas on this channel kzbin.info/www/bejne/iWikZYx4a6h-hqc

[@Brandon-no3vc]

what is a bastard hip and valley?

[@michaeldownes516]

if the pitch° on the hipped end and side of the roof are the same then the hip line, on plan view, will be at 45°. This a regular hip. If the hip line on plan is not 45° on plan , the that means the pitch at the hipped end and side of the roof are different....this is a bastard hip. ( assuming that both roof surfaces meet at 90° to each other on plan view) This is shown in thumbnail image for this video. Another way of looking at it is that the run distance for the common and crown rafter are the same o a regular hip roof.......if the run distance is different (before deductions) for the crown and common, then you are looking at a bastard hip. For a typical valley, if the pitch of the 2 intersecting roof surfaces are the same that meet on a valley line on plan, then this valley line will be 45° on plan (assuming that both roof surfaces meet at 90° to each other on plan view...which would be typical). Bastard Valley will occur If the 2 intersecting roof surface pitchs° are not the same, then the valley line will not be 45° on Plan View (again....assuming that both roof surfaces meet at 90° to each other on plan view...which would be typical). note: "45° on plan" refers to angle between hip line and wall plate line ...on plan view.

[@Brandon-no3vc]

@@michaeldownes516 what