Damp exterior wall

Delambre

Hi, we’ve recently moved into a property which was extended shortly before our purchase. I’ve noticed that the exterior wall of the extension seems to have a patch of damp brickwork (to the right hand side of the window in the picture) - it’s particularly obvious during heavy rain, but even during dry periods the brickwork is darker. There seems to be quite a sharp dividing line between ‘damp’ and ‘dry’ along the mortar joints below the window. The brickwork isn’t noticeably wet to the touch, but it does feel slightly damp compared to the ‘dry’ section. There are no signs of damp on the interior (it’s a cavity wall).

I can’t find an obvious source for this issue, unless water could be bridging from the garden wall (the wall with the trellis panel to the right side of the picture)? The soil at the bottom of the wall is definitely below the DPC. The extension wall is north-facing if relevant.

Is this something that merits further attention / corrective action, or best ignored? (I know money can be easily wasted on unnecessary damp treatments). And is there a simple way to get rid of the white marks along the ‘dividing line’ beneath the window? 

Many thanks in advance!

stuart45

It won't be getting as much sun in that corner to help dry it. Also the cill is giving some protection to the brickwork below. 
Try brushing the salts off.

FreeBear

Check the roof line and make sure the gutters catch all the water coming off the roof. Also make sure they are free of debris and the downpipes are in good order.

Delambre

FreeBear said:

Check the roof line and make sure the gutters catch all the water coming off the roof. Also make sure they are free of debris and the downpipes are in good order.

Thanks - I’ve checked this in the rain and everything is flowing where it should be. I can’t see any water leaking or overflowing from the gutters, and there’s no obvious sign of anything coming from the top of the wall down - the damp patch is confined to the lower half or so of the wall.

Would it be worth trying to force some kind of damp proof membrane vertically  between the extension wall and the garden wall, or would that just create a bigger problem?