"John Rumm" wrote in message
o.uk...
On 06/11/2012 15:06, David WE Roberts wrote:

"John Rumm" wrote in message
o.uk...
On 06/11/2012 11:50, David WE Roberts wrote:
We are building a veranda across the back of the new extension, and a
car port up the side of the house to link with the veranda and provide
a
covered walkway from the front to the back of the house.

The main veranda and car port are pretty straightforward but the corner
where the two meet requires a bit more thought.

The solution appears to be a hip, joining the two roofs sloping in
different directions.

The triangle calculator suggests the hip will be 5.3m long.

Working from
http://www.bsw.co.uk/uploads/files/b..._4pp240810.pdf


seems to suggest that 72*220 (3*9) C16 might do the job.
However this is for floor joist sizes on a ground floor.

You have missed the one bit of information that would be needed to
make sense of this - the type of roof you are expecting them to carry...


Ooops - 10mm polycarbonate using glazing bars supported by wood.

That makes it a tad simpler ;-)

The roof itself will weigh practically nothing (i.e. 100N/m^2) in the
grand scheme of things. So the biggest forces you need deal with are snow
loading (about 0.6kN/m^2), wind uplift (depends on where you are - but
could account for another 0.4kN/m^2), and access (i.e. it needs to be
strong enough to support the weight of someone building it).

A 5.3 m hip suggests about 3.7m rafter span.... What were you planning on
using for those? What is holding up the far end?

I would have thought 5x2 would be fairly conservative. Then the hips could
be a tad deeper say 6x2 (or deeper and slimmer 7x1.5).

It will also depend a bit on what rafter spacing you go for. The poly
sheets are available in a range of widths.

The area to be covered is approximately 4.7m long by 2.4m wide, joining two
other structures.
The long side is the 3m roof of the extension plus the 1.7m veranda.
The short side is the carport.


The car port side will be 2.5m long sheets at 720mm centres - each sheet is
just under 700mm wide and the rest is expansion and glazing bars.
Along the hip these will reduce from 2.5m down to zero along the angle of
the hip over 4.7m.
If the plastic is reversible (some have one UV resistant side only) then
hopefully one 2.5m sheet will cut to fit two rows.
The rafters will be probably 2 * 5 apart from the last few.

The veranda side is a bit different.
This side will go down from 5.3m to zero over 2.4m.
Again I plan to use 720mm centres but the first couple of rafter will have
to be a bit more meaty as they are spanning a significant part of the 5.3m.
The last few can be a bit more modest.
The builders will iron out the fine detail - I am trying to do the design
and procurement of the roofing whilst they are fitting the kitchen and
finishing off various bits inside.

It should be simple but is taking far longer than I expected.

Cheers

Dave R
--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

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