A Guide to the Repair of Historic Roofs - Dublin City Council

ROOFS A GUIDE TO THE REPAIR OF HISTORIC ROOFSRainwater goods of the more substantial or urbanhouses of the late-seventeenth and early-eighteenthcenturies were generally made of lead, with lead-linedoutlets through parapets or from eaves connecting tolead hopper heads and downpipes. However, therewas a general lack of understanding of lead’s tendencyto expand in heat and to tear when this expansion wasrestricted, or when the lead was used in sheets thatwere too long or too wide.Most vernacular roofs of this period were designed tothrow rainwater directly off the roof with no separatedrainage system. The stone slab, or flag, roofs found inthe west of Ireland demonstrate the use of local stoneto protect simple vernacular buildings against severeweather conditions.Eighteenth-century roofsSlate, which had been imported from Wales sincemedieval times, became increasingly popular in theeighteenth century. By 1778, the Reverend ThomasCampbell, in A Philosophical Survey of the South ofIreland, commented on the blue slating having a finereffect than you can imagine when seen in views acrossthe city from the steeples of Dublin. Welsh slate, withits typical blue-grey and purple colouring, is the mostpredominant surviving roofing material from theperiod, although some very beautiful examples of Irishslate still survive in situ from this time. Slate hasdistinguishing characteristics depending on thegeological seam from which it is quarried. Handextractedslate looks substantially different to themore regular, machine-harvested slate producedtoday. Original eighteenth-century slate roofs are raresurvivors, recognisable by the small, irregularly shapedsizes of the hand-dressed slate. As the centuryprogressed, the use of clay tile as a roofing materialgradually died out.Because of the increasing interest in classicalarchitecture from the early-eighteenth centuryonwards, the typical Georgian roof was designed to beconcealed behind masonry parapets to avoiddisrupting the proportions of the main façade. This ledto the use of shallower pitches and double roofs, allwith the aim of making the roofline lower and lessvisible. The use of dormer windows to the front slopeof the roof largely disappeared from Dublin buildingsas the century progressed, although their use lingeredon in other areas.The typical Georgian streetscape of the lateeighteenthcentury is characterised by thesuppression of the roof as an architectural element.Roof pitches were reduced to a minimum andarchitectural devices such as double roofs andparapet walls were used to ensure that the roofstayed out of sight from street levelNineteenth-century roofsIn the nineteenth century, the improved output of Irishquarries and the vastly increased supply of affordable,machine-manufactured slate from Wales facilitated theextensive use of slate as a roof covering, particularly inareas accessible by sea or canal. These Welsh slateswere generally of large size, were smoothly dressedand had more intense colour hues than the smallerslates quarried in the eighteenth century. Theintroduction of large slates allowed roofs of lowerpitch to be constructed. These roofs performeddifferently to their predecessors as the increasedoverlap between the larger slates afforded greaterwatertightness. ‘Gauged’ roofs, or roofs usingdecreasing slate sizes from eaves to ridge, becamepopular, as did slates shaped in fishscale or scallopedgedpatterns and slates laid on the diagonal tocreate a decorative geometrical effect. Colour was alsoemployed; polychromatic roofs used two or morecolours of slate in contrasting courses or patterns. TheVictorian taste was for complex and distinctive roofs,8