Damp/Rotten Conservatory Floor - But Under Internal Door

Hi All,

I am looking at fixing my mother in laws conservatory floor, I only have a little bit of time to expose the problem today before going back next weekend to start working on it properly.
Stupidly I didn't take photos but after some general thoughts if possible before I head back, so I can rule things out or have an idea what to look for etc


The conservatory itself looked/smelled absolutely fine, no condensation on the windows at all (never has been during any season), no mould - nothing untoward that I could see or think to look for.

The issue is however, the floor directly in front of the internal door of the conservatory (patio doors from home into the conservatory) has rotted away by moisture/damp.
The problem has been slowly getting worse over the last couple of years, so not a quick thing apparently.

I took the lino up from in front of the door and the plywood subfloor it lays on is damp to the touch with green/black mould on the wood and underside of the lino. About half a meter or so away from the door the wood is fine, the wood along the house wall next to door looks fine - it seems to be just directly in front of the internal door.

I’m no expert believe me … so treat me like a moron … to me it would make sense if the floor was damp in front of the external conservatory door leading out to the garden, but internally with the rest of the conservatory above the floor looking fine I don’t immediately understand how they happens.
Especially as I say, unless someone hadn’t stepped on this spot and put their foot through the floor, you wouldn’t know there was a problem

Any ideas?
Thanks for your time it’s much appreciated.

Any pipes under there? Should be easier to have a look now there's a hole in the floor!
What about outside? Any signs of dampness on the brickwork? Are the air bricks [if any] clear?

No pipes around/under the doorway where the rotten dam wood is located.
Didn't check the outside when I was there, but will add those checks to the list when I return.

Just confused why in a metre or so squared space, nowhere near the external wall, is where the damp is located

Check roof above doorway, most likely entry point .

Bev Dawson said:

No pipes around/under the doorway where the rotten dam wood is located.
Didn't check the outside when I was there, but will add those checks to the list when I return.

Just confused why in a metre or so squared space, nowhere near the external wall, is where the damp is located

Click to expand...

Hi Bev, did you find out what was going on? As I have exactly the same problem as you and I'm also trying to make sense of it!

I’d say a breach in your damp proof membrane under the concrete so moisture from outside.

thanks Daz - in my case, the floor isnt concrete, it's a metal frame base with chipboard laid over it (like a Durabase installation). I have discovered a small hole in the damp proof membrane under the metal frame though, near the internal door, so maybe that's the cause of the problem in my situation.