Leak close to dormer

A friend of mine lives in a dormer house. There is a dark patch appearing during rain on the sloping ceiling about half way up along where the dormer protrudes out.

I had a look at the patch and it is about the size of a dinner plate. There are no other damp patches and there has been no recent storms to damage anything. I think his house is about 5 years old and he said it has never leaked before.

Could it possibly be something as simple as the guttering around the dormer being full of 'stuff'?

His roof has the standard concrete tiles construction.

I am just wondering if anyone has any knowledge of this area as he has no internet access and asked if I knew anyone who could help.

Is there a side attic that one can crawl into to investigate the source of the leak?

Houses need TLC and maintenance to function.
This includes cleaning the gutter and your surmise could well be correct.
However...
The dormers in houses are seldom detailed correctly for interstitial condensation.
The provisions of Part F can be dispensed with for small roofs and many people seem ot think this includes dormers.

"For the purposes of health and safety, it may not
always be necessary to provide ventilation to small
roofs such as those over porches and bay windows."

An argument can be made that a dormer is just a roof-level bay window, but in my opinion, this can prove unwise in practice, because as the most exposed windows in the house they are more prone to the effects of inclement weather.
That having been said, single dormers without extension flat roof elements normally serve well, and the problems are less likely to be interstitial than to be to do with how the junction of the dormer and roof is sealed and weathered.
The choice of concrete tiles may not be the best to give good sealing.
Sexy minimalist details work with slate or smaller plain tiles or shingles, but larger profiled concrete tiles can be difficult to work.
The profiled section needs to be cut to "fit" the angle of the roof junction and if the open ends are not sealed with mortar bedded on the lead valley gutter, rain can blow back up under the tiles.
Its a clumsy looking detail but it has been shown to work.

The junction between the dormer and roof is usually smaller and more fiddly to detail than a large gable roof abutment for exemple, and I'd check here for lack of sealing and correct installtion of flashing at the abutment.
All that having been said, dinner plate circular leaks usually betray a single drip feed, not a torrent.
Limited opening up from within or an attic visit should dertermine the cause and then you need to take advice on how best to repair it.
Opening up from outside by a good roofing specialist would be your best bet because this is difficult high level work and not to be undertaken by laypersons.

FWIW

ONQ.

Thanks for the replies.

It can't be accessed from inside. It is the ceiling, insulation and roof. It's on the sloping part.

If no access, only way to get at the leak is to break through at point of leak to see where its coming from, leak could be at a higher point and running down timber to drop point. Unfortunately this is the only way as trying to source it from outside would be more difficult. Will house insurance cover the costs, probably roofer, defo plasterer and painting.
Its a pain in the ass but fixable.

Secman

I believe the builder who built the house is sending someone to have a look at it for him.

OK,

We had a look on the roof and it appears that the cement pointing along the edge of the tiles at the gully on the dormer side of the roof is loose and has fallen out in patches. This is the only obvious source of the leak to two pairs of utrained eyes!

We used silicone to seal the holes as a temporary measure (heavy rain forecast), and will approach the builder with our findings. He has promised to look at it for him.

When we looked at the other dormer, the cement was also loose, and along some of the ridge tiles.

I suspect whoever done the initial job didn't mix the cement properly.

If the builder won't help him he said he could do the ob himself.

I am asking any roofers out there how to do this and what is the correct product/mix to use for re-doing it, to make it last longer.

I amaware that the old stuff would have to come out first.