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Posted: Tue Jun 12, 2007 8:14 am
by Maximus
Just about to lay a 25m2 patio, i can't work out how to create the required fall away from the house, can anyone advise as to the correct method.
Posted: Tue Jun 12, 2007 4:54 pm
by lutonlagerlout
well 1:60 is advised
so say the patio is 6M long ,divide 6m by 60 = 100mm or 4 inches
if the patio is 4 m long the fall will be 66mm
3 m it will be 50 mm fall and on
cheers LLL 
Posted: Tue Jun 12, 2007 10:39 pm
by Tony McC
17mm per metre is a handy way to remember how much fall to allow. 17 ÷ 1000 = 1:58.8
Posted: Wed Jun 13, 2007 4:45 pm
by cm233lh
On the subject of fall, I'm doing a similar sized patio. I'm planning to put the drainage gulley half way along the side furthest from the house - so I'll have falls in 3 different directions towards the drain - away from the house in the middle, and towards the drain at either side. What I can't work out is how the flags will fit together on the diagonals, where the slopes meet with each other. Is there a technique for handling this, or do you just have to fudge it as best you can?
Posted: Wed Jun 13, 2007 5:55 pm
by lutonlagerlout
that sort of system involves a lot of cutting flags into triangles etc etc
better to put a linear drain down one side and have the fall going one way
you dont even notice 1:60 unless it rains
cheers LLL
Posted: Thu Jun 14, 2007 10:30 am
by squire
lutonlagerlout wrote:you dont even notice 1:60 unless it rains
cheers LLL
Or unless you are a two year old trying to pedal your tractor back up. "Daddy, PUSH ME!" 
Posted: Thu Jun 14, 2007 5:42 pm
by cm233lh
lutonlagerlout wrote:that sort of system involves a lot of cutting flags into triangles etc etc
better to put a linear drain down one side and have the fall going one way
you dont even notice 1:60 unless it rains
cheers LLL
Thanks for the recommendation LLL. Unfortunately the missus aint too happy about having a steel or plastic grille all the way along one edge of her nice new patio. Is there a reasonably priced slot drain, or perhaps a kerb drain that a DIYer could use on this kind of project. (The patio in question is at between the house and a flight of steps going up, so it's got vertical walls on all 4 sides - and none of them are parallel.)
Posted: Fri Jun 15, 2007 4:00 pm
by Tony McC
When you have a pavement with twisting falls, flags can often be the wrong type of paving to use, because their larger plan size makes twisting that much more difficult, so you end up with diagonal cuts, as LLL suggested, or with bloody huge lips between adjacent flags.
In situations such as this, my preferred option is to switch to a paving type that accommodates twists more readily, namely block paving, or to ensure there are 12mm joints between the flags that will accommodate more of the twist than would be possible with butt-jointed flags.
One of my pet hates is the use of diagonal cuts on flags. If you have an area of paving that requires a good number of the flags to be diagonally cut to accommodate the twist in falls and levels, then YOU'RE USING THE WRONG BLOODY PAVING! The area should be paved with 'small elements' rather than 'large elements'.
And who is primarily responsible for this bollix? Bloody architects who insist that flags are their preferred option. Knobheads! 
Posted: Fri Jun 15, 2007 4:31 pm
by lutonlagerlout
i'll second that
LLL
Posted: Sun Jun 17, 2007 9:57 pm
by cm233lh
Tony McC wrote:In situations such as this, my preferred option is to switch to a paving type that accommodates twists more readily, namely block paving,
...
And who is primarily responsible for this bollix? Bloody architects who insist that flags are their preferred option.
...
Tony, Thanks for confirming my suspicions - I had favoured block paving. However, even with your post to back me up I'm still having a problem convincing the bloody architect (= wife) that she wants a driveway in the back garden.
Sounds like I'll have to fudge it with wide joints. I'll let you know how I get on in a few weeks times.
Thanks for all the help so far fellas. I've found your web site a fantastic resource.
Posted: Mon Jun 18, 2007 11:34 am
by TheVictorianCobbleCo
the twisted flags will look cr*p, what about sloping to one side and putting a drain point in the 2 bottom corners and pipe the water away beneath the flags.
Posted: Mon Jun 18, 2007 5:04 pm
by lutonlagerlout
"you can lead a horse to water bill,but you cant make him drink it"
LLL :;):
Posted: Tue Jun 19, 2007 2:47 pm
by cm233lh
Right, we've worked out a compromise, and wondered if any of you guys would care to comment on the wisdom of doing it this way.
I'm now planning to keep the fall all in the same direction, so no twisted flags. I'll put a linear drain across the entire length of the house (6 m), and create a 1:60 fall towards the house. The drain will be 150 mm below dpc. That way the drain is not so obvious to the eye, and it also solves some other issues with surrounding walls, underground drain runs.
Is it a good idea to arrange it thus? (the house is at the bottom of a hill), and is it likely to atract the attention of a buyer's surveyor? Anything specific to take into account when you drain towards a house.
Also is 1:60 required for natural stone flags, or could I get away with 1:80?
Thanks for any help you can give me.
Posted: Wed Jun 20, 2007 12:53 pm
by Rich H
No problem that I can see with what you've described. If you are 150mm below DPC you're fine. As a tip, lay the channel a few mm below the paving to ensure that there aren't even minor water traps in the adjacent paving.
As for the fall, you really should have 1:60, but I've seen 1:100 laid before, although you can expect standing water on some of the more riven slabs (but still no puddling between, provided the pointing is even). In reality, most landscapers I've employed generally use the 'bubble-to-the-line' method, where the spirit level bubble is touching the line on one side and there is therefore a gap between the bubble and the line on the other side.
Happy to stand corrected but I think this gives you 1" over the length of a 6' Stabila level or 1:72.
Posted: Wed Jun 20, 2007 1:13 pm
by Tony McC
Rich is spot on. The recommendation is that any drainage fiting should be at a level that is 6mm below that of the adjacent paving or surfacing. this ensures that, if/when there's a touch of settlement in the paving, there is almost no risk of the drainage fitting being higher than the paving.
