Damp,  Floors

Underfloor discoveries… 14/11/2016

Yesterday we made some plans for what timbers to use around the window, on the external corners of the bay and as batons for shelf support in the alcove.

We also decided to lift some floorboards to clear out the detritus & get a better sense of what’s going on under there! All boards were carefully numbered to ensure we can put them back in the same order and direction.

The single airbrick in the bay was blocked internally which means there has been no ventilation to the subfloor for a while. Additionally, no gap exists in the wall between the lounge/dining room which presumably prevents cross-ventilation from one side of the house to the other. The sleeper walls are of a solid construction rather than the ‘honeycomb’ pattern I have seen in other houses, which again probably impedes airflow under the floor.


Each alcove has a solid sleeper wall across it, only allowing airflow in the gap created by the joists between the sleeper wall and the floorboards. Curious attempts to improve airflow in the alcove next to the front wall have been made in the past, with a series of holes being drilled in the floorboards & an air vent being installed on top of the carpet!

The sleeper walls are higher than the surrounding stepped foundation, so in future we will level the floor. For now we are clearing out the old plaster and rotten wood debris, removing nails & temporarily supporting joists with bricks before relaying the floorboards to make things less treacherous whilst installing the hemp-lime bio-aggregate to the front wall.


The subfloor is completely covered with a bitumin damp proof layer – I think probably original to the property. There is also an original bitumen damp proof course in place to all of the stepped brick foundations and the sleeper walls. The wooden bearers that are sat on top of the sleeper walls (directly onto the bitumin layer) are very damp and have suffered the worst of the rot/woodworm along with the ends of the joists & floorboards. I guess this is where the wood is the coldest, so where moisture is likely to condense?


We also found a mysterious copper pipe covered in verdegris with what appears to be a damp patch in the dust underneath it. This pipe heads from the doorway towards the alcove, splitting into a smaller (10mm?) copper pipe that heads to the right side of the fireplace and another copper pipe that goes through the wall into the dining room. We are wondering if this might be an old gas pipe to supply previous gas fires in the property – hopefully it has been properly disconnected! I am guessing that the verdegris & damp patch underneath is most likely caused by moisture condensing on the outside of the cold pipe and dripping onto the subfloor below.



I only recently discovered that burning gas causes a lot of moisture to be released – somewhat counterintuitive since we tend to think of any and all heat purely having a drying effect. Although extra heat does allow the air to carry more moisture (relative humidity) if the source of heat is producing excessive moisture, then presumably this has to escape out of the house, be buffered by suitable, vapour permeable building materials, or it will condense somewhere.

The house would originally have had coal fires which burned without producing as much moisture, and I believe will also have created good airflow currents from the airbricks, through gaps in the floorboards, carrying excess water vapour from the home environment, up the chimney and out of the building. It definitely seems plausible that gas fire ‘upgrades’ may have contributed hugely to the damp issues in this property, with subsequent attempts to rectify things possibly making things worse.


The plan for today :

  • Take rubble bags of debris to the recycling centre,
  • Buy wood for the window, bay corners and alcove shelf baton
  • Start creating dochens/drilling holes for them.
  • Try to lift the other half of the floor and clear out the rest of the debris.

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