Derry City & Strabane - Considerations particular to vernacular buildings




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Considerations particular to vernacular buildings



Thatch represents one of the key traditional architectural features associated internationally with all of Ireland. However, today numbers have significantly decreased with less than 150 recorded thatch roofed buildings in Northern Ireland.

Thatch roofs have traditionally been constructed in materials local to the building’s setting, and often locally grown. Materials such as reed, straw and flax were, and remain, common, although now often imported. It is accepted that materials for thatching have a much shorter lifespan than slate or metal, and rot naturally over time. Thatch may also be susceptible to rodent, bird or insect inhabitation or infestation.

Overall, thatch must be recognised as higher maintenance than more common slate roofs. Look out for greening and vegetation, and thinning on thatch roofs. Look out for patches of damp on internal roof coverings, particularly around chimneys and ridges.

The longevity and approaches to repair of thatch vary depending on the selection and quality of materials, detailing, depth, and location and relative levels of rainfall. The requirements of adding new material to repair failing thatch should be carefully considered to not unnecessarily remove or replace existing fabric. Especially it is important to retain underlying intact layers of thatch and underlying original timber roof structures.

Thatch Under Tin

‘Thatch under tin’ (actually galvanized corrugated steel) is a hybrid roof type evolved out of need for a quick, affordable solution to failing thatch, and has preserved many examples of original roof construction that would have otherwise been lost.  Commonly found on modest vernacular buildings in Northern Ireland, what may appear to be a simple corrugated iron roof may often be found to conceal a much earlier thatch roof underneath.

While the resilience of a thatch may be extended due to the protection that a tin covering affords. However in some cases the addition of tin on top of a thatch may cause it to be poorly ventilated and lead the natural materials to ‘sweat’.

Such practice is generally discouraged nowadays, particularly with listed thatch buildings, where the addition of tin will detract from the historical and architectural character of a building.

With thatch under tin, make sure to check the integrity of the corrugated iron, look out for rusted edges or holes in the roof fabric. Repair or replace sections where necessary. Pay particular attention to junctions between the roof and walls and the roof and chimney. Corrugated roofs are often painted, and this may help with material longevity.

Look out for patches of damp or decay on internal roof coverings, as this may be evidence of moisture caught between internal and external roof coverings.


Mud Walls

Mud, earth or clay walls are predominantly found in rural, vernacular buildings. Usually mud walls are usually hand constructed from a mix of clay and natural occurring fibrous material such as stray or reed for binding. The clay and natural fibres are typically locally found materials and at times this may include turf or cut sod. The clay may have been moulded into sun/air dried bricks prior to construction, or laid up in wet layers with drying intervals. Sometimes a mud wall may be found to be encased in another material for example wattle or brick under render. Mud walls may exhibit variable quality of clay and addition and type of fibre in the walls, together with the skill, or lack of skill, applied to their construction.

Mud walls are, by necessity, traditionally rendered in lime. As with any rendered wall integrity of the render is seen to be key in enabling this material withstand weathering. If mud is exposed to the elements, its material qualities are not as strong as that of stone or brick and degradation may be rapid if render repairs are not carried out. In this case more than ever, the importance of keeping the walls dry is the secret of retaining these most sustainable of all historic buildings.