g'day and welcome back to build some and this is video three in the four part
series on how to get the length of your hip and in this video we're going to
look at probably the least popular way which is actually calculating it so to
calculate that we need a few dimensions so obviously we need to know what the
roof pitch is and at least what our half span of the building is so in this case
we've put a 30-degree pitch roof and they're half span is 2.5 meters so that
information we can start to work out what we need so we need to know that the
riser a roof per meter is 577 millimeters okay so what we do is we go
10 times the picture of the roof will give us that answers her 10 times 30
will give us 0.577 so for every meter that the roof runs it rises 577 milk
that's alright for the rafters but we need to look at the actual hips so
closer detail every meter that way roof rises 577 mm
now for the hip itself if we have a square that's a meter by a meter then we
need to know for this distance here where the hips going to run 45 degrees
to the corner so bit of pythagoras meter squared plus a meter squared equals to
square root of two is one point four one four
so the plan length of the hip for every meter this way the planning for the hip
is one made out of 414 okay and at the same point it would rise the same
distance so the hip is obviously at a fraction different angle to our main
roof so it's not 30 degrees down here slotted less but the same rise at the
same point
so the formula there is so the true length of the hip for every meter this
way is one point five to seven on that angle up there
okay so what we've done there we've gone pythagoras again with our one point four
one four squared plus our rise squared gave us two point three three two square
root that gives us a distance of one point five to seven that means for every
meter of run we have one point five to seven meters of our hip so now we know
that formula we can transfer that into the whole roof and we know that our half
span was two point five so we can times that by one point five to seven and
gives us a hip length of three point eight one eight from the intersection of
the crown and after and the setting rafter down to a point in line with the
back of our plate it gives us three point eight one eight meters so that's
the centerline length we haven't made any duct deductions yet we now have to
make a couple of deductions so up at our intersection of our ridge our centering
rafters and our crowning rafter obviously this is where our central line
meets in the middle here we have to deduct this much off the length of our
hip but because we're really worried about our hospital we're going to deduct
this distance here offer half span so this rafter happens to be a 35 mil
rafter so half of 35 seventeen and a half so we're going to deduct seventeen
and a half off our half span to give us the true length of our
hip we also have to do the same at the bottom end because in a lot of cases we
cut the corner off our plate so now hip fits nicely with the bird's mouth so
we've got a 20 we're gonna say we've got a 20 millimeter hip that's going to go
in here so this little tab has been cut off 20 mil that means if we take half of
that distance it's 10 mil times 10 mil by our ratio of 1.4 one for gate gives
us zero point zero one four one four divide that by two it gives us seven mil
all right which is this distance here so we've got to take a further 7 mil off
the plate down here off the length so what we do this is our new plan length
we take our 2.5 which is our original half span we - the 7 mil for the
deduction down here at the plate and we minus 17 and a half mil for the
deduction up at the ridge so that gives us a total deduction of twenty four
point six mil or you can to round that up to 25 so 2.5 - 25 mil gives you a new
plane length of 2.4 75 take that times it by L length per meter for the hip and
we end up with a new length of our hip of three point seven seven nine meters
so far that's the new length allowing for a deductions
okay we can then work out the actual true length of the timber without
overhang as well so to work out our overhang we have to go back to add our
plate deduction back on and then add the width of the eave back on okay so we
take our four two point four seven five add our plate deduction back on which is
seven mil add our eave overhang back on or on not back on which is four hundred
and fifty gives us a new overall playing length of two point ninety three two
times that by L little factor of one point five to seven and it gives us a
total length of our heap of four point four seven seven meters so now we know
all the dimensions we need to know to mark out our actual hip so what we can
do is we can go over to our hip material mark and cut our hip end go back show
that I've marked it put the edge bevels on there and then from the very point of
our edgehill's we're going to measure down the timber we're going to measure
down our four point sorry a 3.779 put a mark draw in the
angle making sure we also draw any I'll stand up for our bird's mouth
that'll give us the position of our bird's mouth for a hip so we can cut
that out we can then add on for our plate deduction we don't need to add it
on we've already worked it out we can then measure a further four point four
seven seven to our point of our tail and we can cut the tail off
and then of course we can test fit it and yeah if it works well and good we
can check it for the other positions and then we can fit well all our hips so
there you go that's how we calculate the length of our hip and as you can see
that's probably why it's not such a popular method
you