Condensation Issue


Legendary Member
We live in an 1845 stone built terraced cottage which stands directly on solid clay. There is 12" between the clay and floor joists. The front door opens into a 3' wide, 4' deep internal porch which in turn opens into the front room. Usually we keep the internal door closed and a draft excluder along the base.

Two years ago we had the front path relaid to ensure it slopes and drains away from the door. It does. Our front door is a bespoke frame and door designed for the doorway and professionally fitted. The doorstep is a piece of York stone set on concrete. The wooden floor butts leaves a 1.5cm gap where it meets the doorstep to aid ventilation in the area.

The clay is dry. The joists are solid.

A week ago Mrs P her foot through the floor! The floor has rotted from underneath. This seems to be due to the condensation which forms on the doorstep and runs down into the floor cavity and is also absorbed by the flooring ¾" flooring board in the porch.

Short-term fix is to keep the internal door open. Long term I need something else. Any suggestions?

Meanwhile I'm off to buy some flooring!!


I'm assuming the condensation forms internally and then weeps into the flooring which then absorbs.

You need to find a way to draw the moisture away from the doorstep to drain underneath the joists, I'm thinking something like a bit of plastic sheeting in a V with holes in the bottom so that the condensation beads downwards and away from the flooring. Someone else is bound to be along to point out the flaw in that though.


Yes @si_c it's internal. Interesting idea. Thank you.

I would have suggested some kind of seal but I'm guessing the problem is that the doorstep condenses on the inside as it's cooled from outside so I'd expect some form of insulation with a vapour barrier could also work.


You need to stop moisture getting to the timbers and flooring. Also ventilation under the floor is absolutely critical to prevent rotting. Ensure all airbricks are clear and even add more around the porch to eliminate damp. Next would be a damp proof membrane .

If floor is rotten, rip it all up now, examining moisture location and source. Place temporary floor whilst you plan the full repairs


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Leafy Surrey
Human activity provides most of the humidity that creates condensation.
Reduce it with simple steps:
  • Washing: if you must hang clothes to dry indoors, spin dry them at the highest speed first
  • Bathroom: use extractor fans with bath or shower. Check the over-run timer is set appropriately. Shut the door!
  • Cooking: Turn the gas down, simmer don't boil. Use lids on pans. Use the extractor hood. Shut the door!
  • Spillages: mop up promptly
  • Wet glazing: wipe dry or use a window vac
  • Bedroom: crack open a window overnight, or at least give the room an airing each morning
And if any room ever feels damp , crack open the window and .... Shut the door!

TLDR: reduce and localise sources of humidity, ventilate it away .
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