With the exception of some brochs, few walls survive from Iron Age buildings to any height, but it is clear that various materials were used in wall construction. In some cases, such as the cARs, drystone walling up to one or more stories occurs. In a few cases timber lacing of walls has been proposed, particularly in vitrified duns such as Rahoy (MHG487; Childe and Thorneycroft 1938) and Langwell (MHG7371; Nisbet 1994) as well as at Dun Deardail hillfort (MHG4348; Ritchie 2018). There is also evidence of the use of turf, for example at Coille Gaireallach, Skye (MHG59524), Wester Rarichie, Easter Ross (MHG8465), and a large structure (c 19m internal diameter) at Bellfield, North Kessock (MHG53532; Hatherley and Scholma‑Mason forthcoming). One of the Early Iron Age structures at Culduthel (MHG49950), another large roundhouse with external diameter of 18m, may also have had turf walls with a timber revetting encasing the outer wall (Hatherley and Murray 2021).
Less evidence survives for timber exteriors (Romankiewicz 2009, 380). The ring-groove roundhouses may have had walls of planks or closely placed posts, but conclusive evidence is rare. However, evidence from the large roundhouses in the early years AD at Culduthel suggest that walls were made of closely set timber posts set with stones (Hatherley and Murray 2021). Such stone packing, together with voids likely to represent the rotted posts, also survived in the ring-groove of the roundhouse built into the earlier stone circle at Strichen, Aberdeenshire, there arguably in a non-domestic context (Phillips et al 2007; compare Romankiewicz 2018)
Good roofing evidence survived at the galleried dun at Langwell, where the burnt timbers even preserved beetle holes in the timber in many cases. The logs used in the roof were up to 18cm diameter, and up to 2m in length. Inside the house there was a ring of postholes which would have supported the roofing timbers. These large timbers were not found in the central area, suggesting to the excavator that this area was left open or covered by skins. It was also postulated a layer of branches, twigs, heather or even birch bark could have been used for roofing materials (Nisbet 1994, 62, 67). Roofing with turf that was supported by rafters springing from the rampart was proposed at the vitrified dun at Rahoy, Lochaber, where burnt timbers and sods survived (Childe 1946, 88–89). A destruction layer at Cyderhall, Sutherland (MHG11834), also preserved roofing timbers (Pollock 1992). Turf has also been tentatively suggested as a roofing material for the Late Iron Age houses at Culduthel based on environmental analysis (Timpany et al forthcoming 2021b).
There is little evidence of building interiors and what survives needs careful dating evidence as some material may be secondary. Most roundhouses had a central hearth, sometimes slab-lined. At Cnoc a’Leacachan, Easter Ross a roundhouse exposed during construction work had a wattle fence lining the inner wall which was radiocarbon-dated to 756–390 cal BC (MHG28205; Wordsworth 1997). At Dun Morangie, Tarlogie, the building shows evidence of internal modifications (MHG8706; Hatherley 2015), as indeed do many brochs. Postholes at the Culduthel roundhouses (MHG49950) hint at internal partitions (Hatherley and Murray 2021). Some roundhouses had upper stories or lofts (ScARF Iron Age section 8.1); at Culduthel, the size of the posts for the internal rings of the roundhouses from the early years AD suggest this possibility. The fill of the ring-ditches of the two large roundhouses from Culduthel included charred planks which may be the remnants of a wooden floor. Whereas ring-ditches at many other sites were thought to be formed by people and animals, at Culduthel they were deliberately cut features with stone and wooden partitions, floors and steps. The activities which would have occurred in these subterranean chambers are not known, but finds from the ring-ditches included the exotic objects which were deliberately deposited, suggesting they may have been used for the storage of the community’s most valued items (Hatherley and Murray 2021). The roundhouse at Cyderhall also had a sunken floor area in its earliest phase (Pollock 1992).