Mystery damp problem in Buxton

Matlock building surveys
I have been asked to look at the damage caused to internal plasterwork by damp within the bay window areas at both ground and 1st floor levels of a grand Buxton residence. The owner had considered many sources of the water but none were making any sense. I narrowed down the damp sources and showed the owner the best course of action. An extract from the report follows. I cannot disclose the property for obvious privacy reasons.
The bay corner pillars, 2 on each bay rising full height of the property have stone window heads
spanning between them which support a large mass of masonry below the 1st floor window sills.
The pattern of damp is focused around these 2 pillars, is worst on the ground floor but also rises to
within a metre below the 1st floor window head level and then above that level the pillars and
ceilings are dry and undamaged. The moisture indications at ground floor level are again focused
around the pillars. Moisture indications within the wall between the base of the pillars underneath
the ground floor sills reduces further away from the pillar bases. The damage in the left-hand bay
(looking from inside) is caused by the direct window head leak. Note there is no damage on the
right-hand bay. The dew point meter showed the columns at risk of condensation. Moisture
reading were high over the full height of the columns and their was no clear pattern showing any
source of water penetration. Surface damage is worse towards ground floor level and there is least
damage towards roof level.

In the absence of any direct common water entry point common to both bays the cold stone mass of the pillar and window head stonework appears to be causing condensation. Previous minor repairs such as adding window head drips indicated the problem has been around for a long time. This type of condensation is common in solid walled stone properties and the pillars will have particularly cold surfaces due to their slender sections and exposed surfaces.

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