Lean to shed design


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12 Dec 2022
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Dear all

My brother is helping with my planning application for a lean to shed to the side of my corner plot. There is a garden wall which I want to use as the side walls of the shed to maximise space. Beyond the wall is a hedge that I own so there is 310mm between outside face of the wall and my boundary. I sketched designs which had PIR side panels against the wall with T n G cladding between the top of wall and the PIR roof.
I planned to extend the roof to overhang the outer face of the wall by 100mm or so. My brother has drawn up designs that show the roof to finish flush with the inside face of the wall with guttering directly above the brickline. He feels that would be more acceptable for the planning officer. My concern would be water ingress from rain coming at an angle or blowing off top of brickwork and dripping down the cladding face.
The wall is around 1.8m and the roof would sit around 30cm above that to give an idea of the dimensions.
Any suggestions/thoughts?
Oak cladding to side edge of wall - would a sealent along the edge work?

Attached photos show my initial pencil sketch and my brother CAD design

Thanking you in advance




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In both designs you will I expect get water ingress at the corner between brick wall and cladding, your design has a lower risk due to the overhang but with the correct wind direction it would still be likely.

You would need a flashing from behind your cladding that extends over the top of the wall. The alternative is to somehow plan for water ingress at this point, although I can’t think how you’d do that without some kind of ventilated cavity.

The alternative would be to build on top of the wall and have your cladding extend down past the interface at the brick wall.

In all situations you are using a single skin brick wall with no damp proof course as your wall so it will wick moisture from the ground and from the outside during persistent wet periods. Ventilating the cavity on the inside behind the insulation would likely manage this.

Sorry all rather negative.


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