At least three aspects of the roofs of vernacular houses are significant - roof shape, roofing materials and the structure which supports it.
In the late 16th and early 17th Century, the pictograms on the contemporary maps seem to show that the native Irish lived in dwellings with hipped roofs i.e. without gables. Only the houses of those who had arrived in the Plantations had gables. Only a small minority of houses in the north of Ireland are now hipped, and this change is believed to have become established by the 19th Century. However in parts of southern Ulster there remain both hipped and half-hipped roofs, although hipped roofs are in the minority. Surviving thatched hipped roofs have an even smaller range: a small area of Counties Fermanagh and Cavan. Gailey (1984) notes that occasional examples can be found out of this core area and the photograph here shows one such isolated example. Located in Muff, a small village in the southeast of Inishowen, this building was demolished in 2002. It is one of a very few examples of a hipped vernacular building in Inishowen.
Thatch - most houses in Ireland used thatch until early in the 20th Century and it remained relatively common in Inishowen until recently.
There still remains a considerable stock of thatched buildings in Inishowen, although they are disappearing at what appears to be an increasing rate. Wheat straw remains the most common material used in thatching, although modern varieties of wheat are bred with a short stem to minimise lodging (being flattened by wind and rain) and so are less suitable than older varieties. Straw from other cereals such as oats and barley was less favoured. Rushes were also used, but often these were confined to thatching outbuildings. Close to dunes marram grass was used, such as in the photograph here, an occupied farmhouse less than 1 kilometre from the sea. In the case of marram grass the thatch was tied to the roof by ropes and secured in this case to pegs in the gables and the top of the walls.
Tiles are uncommon in vernacular buildings in the north of Ireland but slate became increasingly common, especially in the houses of the wealthy. In some areas local slates could be obtained: in Donegal the sources included Saint Johnston in the east of the county. Gailey reports 'blues' for sale at 37 shillings per thousand and 'tops' for 28 shillings per thousand. However imported slate, mainly from north Wales (such as the ubiquitous Bangor Blues), became increasingly common. Many of those used in Inishowen houses were shipped into the port of Derry.
In most of the North of Ireland traditional houses support their roofs in one of two ways. One is the use of purlins which are beams stretched transversely along a building. Sometimes these extend the length of the building, but more often they rest on internal partition walls. More common is the use of tie beam trusses which are pairs of angled timbers extending from the head of the walls tied with horizontal bracers. It is likely that these trusses evolved from cruck trusses
Cruck trusses spring from ground level or from within the wall. Unlike tie beam trusses they are integral to the walls of the building. The cruck blades support most of or all the weight of the roof. There are two types of cruck blade - a continuous blade is made up of one piece of wood, while a composite blade is joined between the wall part of the cruck and the roof part. The use of crucks were necessary to support the roof when the walling materials was earth or sods, but the building technique was retained for a time as a relict building technique even in houses built of stone or brick. The oldest surviving houses seemed to use oak for the crucks. However, as oak forests were removed after the Plantation, bog oak and, eventually, softwood came to be used.
In County Donegal, a number of cruck trusses in buildings have been studied. Des McCourt (Some Cruck-framed buildings in Donegal and Derry Ulster Folklife 1965) reports that Pococke when travelling in Donegal in the mid-eighteenth Century, had commented on the composite cruck trusses around Letterkenny. McCourt says that the surviving examples of cruck trusses in the county are made of single pieces of timber. All of them are raised from the ground, starting not far from the wall head. They may therefore be residual features marking a stage between full crucks and beam trusses. McCourt argues that "...they represent the last lingering traces of a tradition which, in this country and probably elsewhere, died out much earlier when the problem arose of having to provide timber of appropriate size and shape for trusses". The cruck truss tradition lingered in Inishowen longer than elsewhere, perhaps because of its relatively isolated position and McCourt was able to study a number of buildings with cruck trusses. One was in Faglieran in north Inishowen, with bog timbers making up the crucks which are set in slots in the wall. Another cruck he describes from a building in Claggan, north of Moville again uses bog timber. In this case the blades of the cruck are very different in shape which indicates the increasing difficulty of obtaining timber for building purposes. Yet another building described by McCourt is in Ballynahowna in Glengad. McCourt speculates that links with the west of Scotland, where a similar form of cruck trusses have been described, may have contributed to the persistence of this form of roof construction in Inishowen. He also points out that houses of soil and mud were being built up to the early 19th Century and so the crucks remained an essential part of the construction process until relatively recently.