The solution favoured by eighteenth-century Irish estates was the icehouse: a thick-walled, partially buried structure, carefully insulated, designed to store blocks of ice cut from frozen ponds during winter and keep them usable well into the warmer months. At Tristernagh Demesne in County Westmeath, there are not one but two of these structures, built around 1790 and still standing on the grounds of what was once a substantial country house.

The pair sit roughly a hundred metres to the south-east of Tristernagh House itself, which is now ruinous. Each is built on a polygonal plan, and despite their shared purpose they differ noticeably in construction. The southern icehouse has a brick barrel-vaulted interior, a form of curved ceiling built from brick without the need for a central keystone, though its rubble stone porch has since collapsed and its entrance is now blocked. The northern one is more elaborate: its interior is finished with a domed brick ceiling, and it retains a rubble stone porch with a segmental-headed doorcase, meaning an entrance framed by a shallow arch. Unusually, this doorcase opens into the upper half of the chamber rather than at ground level, a detail that points to how these buildings were managed: access through a restricted, elevated opening would have helped limit the exchange of warm air when ice was being retrieved. The rubble stone facings and brick surrounds visible on both structures are typical of utilitarian estate buildings of the period, functional but not without a certain considered quality.