What are they?

A picture or 2 would be more usefull. Could you not ask the current owners or the estate agent?

I am buying a two year old house and in the cornner of some rooms near the ceiling are plastic covers about 100mm x 30mm and circular ones about 60mm dia. on the oustside walls. My stupid question is what are they? many thanks for the answer!

Agreed.

But do you mean 100mm x 200mm by any chance? That would probably indicate a ventilation channel which has been blocked off (in which case, you might want to look into whether you still have adequate ventilation eg for a fire (incl gas) and to prevent condensation/damp in the property.

But if it's genuinely 20mm... dunno - sounds too small for a vent. Must be blanking off some form of channel through the wall though, surely.

David

If it was me I would take it off and see what is behind it. Also if it was me it would take a week or so to put back - not good for marital harmony......

No idea really - but how about covers for some kind of bolts through the wall (plates on the inside) - some some reason?

I imagine they would be access/inspection panels for access to the plumbing valves etc.

Mark.

They are prewire locations for a burglar alarm.

Steve