22 May 2016
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United Kingdom
Hello all.
Please can I have your opinion(s):

I'm knocking down a leaking garden shed to gain some space, and building a new lean-to shed in my garden to allow a bit more space.

Try and picture this if you can: there's a 1.5m garden wall (we live in a Victorian terrace) at the end of the garden and behind that a back passage that allows rear access to our house (and our neighbours homes of course); the passage is soil and turf (weeds).

Question 1:
I'm going to use this rear wall to build a lean to shed against (replacing existing one) but I'm wondering if I can build the roof so that the pitch of the roof drops water over the wall into the passage rather than my garden. I'm anxious a, it might weaken the wall over time, b, its not legal/appropriate. (this is a bad idea isn't it?)

Question 2:
Can I simply use the wall as the rear wall of my shed? Should I use breathable membrane as the rear wall?

Question 3:
I'm thinking of using breathable membrane (or another suggestion?) and some featheredge board (with a gap between them) as I have a large pile of it and a very small pile off money. What do you think?

thanks in advance, Simon
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1. Directing a flow of water onto the top of a wall will almost certainly have an adverse effect on it in the medium-long term.

I do not however see any problem with falling the roof over the wall so that water drips into the alley. Its not really legal but who is going to care? This is assuming your talking about a smallish shed 8x6 or similar. A large 14'x10' shed will create a much bigger volume and would need dealt with.

Your main problem would be a busy-body neighbour who might object.

2. You can use the wall assuming you own it but as you say it will never be truely dry. If the wall is in good condition and especially if it's rendered and painted on the alley side then it'll probably be dry enough.

3. as above your choice, for a truely dry environment you should build a seperate structure. 2"x2" Battens or similar on the wall with your breather membrane over them would do fine (assuming you did roof right over the wall.)
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I'm going to direct the water into my garden. However, I'm now wondering if I can use a damp course membrane against the wall (with batons as you suggest) rather than breathable one £9 for 4mx3m). She'd will be about 3.6 X 1.5 metres with longest lens th against the wall.
Thanks. Simon.

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