Open a ceiling in an old building and you tend to find the same things.
A lead pipe cut short and capped. Two generations of cable, one of them cloth-covered. A hole round a chimney breast where a flue used to run. Nobody closed any of it up.

What we expect to find
Thick masonry walls with pipes and conduit through them, and the gap round each one stuffed with newspaper, rag or crumbling mortar.
Ceiling voids that run across several rooms with no barrier, because the building was one house and is now six flats.
Timber floors with cables drilled through the joists. The floor is meant to hold a fire back for a set time and now it has a dozen holes in it.
Boxing round pipes that hides what is behind it. We open it up, look, and close it again.
The rating of the walls is often written nowhere. We record what we find, and your assessor or building control decides what it should be.
Listed buildings and conservation areas
Parts of the centre are in conservation areas and some buildings are listed. The Royal Borough of Windsor and Maidenhead is the local authority, so ask its planning team whether cutting an inspection hole in a historic ceiling needs consent. We would rather you asked before we start.
Closing a hole that is already there rarely changes how a building looks. Cutting new ones does, so we avoid it.

A worked example
A large old house split into five flats. Cellar, three floors, roof space.
The first visit is the cellar and the roof, because the pipes and flues start and end there. In the cellar we might find a 4 inch cast iron stack through a brick vault with its gap left open. In the roof space, a brick party wall that stops two courses short of the rafters.
Next the floors between flats. Joists have cable holes every metre or so, and lath and plaster ceilings below have been patched with board in places. Each flat's ceiling is checked for downlights.
The result is a numbered list, a floor sketch and photos. Sealing is then priced from that list.
Who enforces fire safety
Windsor is in Berkshire, so the fire and rescue service is Royal Berkshire. If it has sent you a letter, attach it to your enquiry, because it often names the compartments it is worried about.
We come from Luton and book visits in full days.
Questions we get asked
Can you seal gaps in a listed building?
Sealing existing gaps is often fine, but check with the council first.
Do old walls need different products?
Sometimes. The product has to be tested in a wall like yours, so we note what the wall is made of before choosing.
Send it over with the postcode. We will tell you what the work involves and roughly what it costs.
Get a price