‘How can my building still be damp after restoration?’ — public perception of historic buildings and physical realities

Scott Allan Orr | OCTOBER 12, 2015

It’s a common story: a private owner or public body responsible for a building pours resources and money into a historical property that needs a bit of TLC [tender love and care]. Work is completed, and everything looks wonderfully renewed and well-kept. A few months later — or seasonally — moisture appears or the interior is damp, or even more damp, then it was before work was undertaken. Inevitably, fingers are pointed at somebody: the contractor, the firm involved, the wider advisory body, or the city council — anybody that influenced the project’s direction.

The reality is that the project likely went exactly as planned. The discrepancy arises for a few reasons:

  • modern techniques and guidelines are applied in conjunction with historic constructions and materials
  • hygrothermal (water and temperature) performance of the building cannot meet modern expectations of the building fabric
  • there is a lack of understanding of the fundamental physical contrasts between historical and contemporary approaches to construction

Historic building materials such brick and stone are porous materials – they act exactly like sponges in the presence of moisture. When they’re used in buildings, physics dictates that they will absorb water from the atmosphere and rainfall, which can then either: evaporate out, or be transferred through the fabric. The latter of course, leads to damper interiors.

In many cases, recent renovations have removed or reversed modifications that took place in the 20th century that applied twentieth-century concepts of complete moisture blockage. Often, damp emergence in these constructions is a response to the removal of damp barriers that, if left in place, posed treats to the longevity of the historical materials.

This problem is exacerbated by a mid- to late-twentieth century trend for warmer — drier — interiors. Historical buildings were designed and operated with an understanding of the internal climate to be expected — acknowledging that there was a natural flow with the outdoor environment.

A modern interior in New York, proudly exhibiting exposed brick walls as an architectural feature. “My apartment” by “Michelle Spaulding”; no modifications made. Licensed under CC-BY2.0. Accessed 19 June 2013. https://www.flickr.com/photos/reconstructionist/2877943728/

A modern interior in New York, proudly exhibiting exposed brick walls as an architectural feature. “My apartment” by “Michelle Spaulding”; no modifications made. Licensed under CC-BY2.0. Accessed 19 June 2013. https://www.flickr.com/photos/reconstructionist/2877943728/

How do you explain that a building is supposed to be damp?

The public has specific perceptions of what it means to ‘restore’ or ‘conserve’ a building. Sometimes, emphasis is placed on ‘exposing’ history, proudly displaying bare stone and brick — internally and externally.

The historical reality is that these materials would rarely be left exposed, due to the rate of moisture transfer. On both sides of the building fabric, white lime washes (thin layers of calcium carbonate) would be applied to slow down this movement, and reapplied as necessary. Externally, especially in Scotland, harling (a layer of small pebbles or aggregate) would be applied in a similar manner.

The first impression of the White House in Newtownabbey leaves an elephant in the room: why isn’t it white? Historically, a rubble masonry construction like this would have been covered in a lime wash to protect the stones, but it was preferred to leave the stone uncovered for aesthetic reasons.

The White House is viewable here:

Before restoration: https://www.flickr.com/photos/uahs/6850334106/

After restoration: http://www.panoramio.com/photo/73065390

The challenge is put forth: how do you communicate to the public that a historical building was designed to operate in a certain way, and there is only so much that can be done to bring this in line with modern expectations of internal conditions? How do you explain that it’s only likely to get worse within a changing climate, but it’s impossible to say exactly how or when?

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