There are at least one hundred place names, ruins, memories or surviving buildings linked with Haa houses or their locations. Of these at least forty buildings, some ruinous, display the typical characteristics of the building type. There were certainly others, and some may remain unknown, either incorporated in later buildings or as unrecognised ruins.

The Haa House developed from the seventeenth Century as the residence of lairds and merchants. After Earl Patrick Stewart was executed in 1612, the Northern Isles of Orkney and Shetland came under the effective control of the Scottish Crown, and soon after the building of laird's houses began. These early houses reflected more peaceful times with none of the defensive features found on the earlier castles of the Stewart era. The earliest houses remaining in anything like their original appearance are one and a half or two storeys, and are thick walled and rectangular in plan with irregular deepset windows, often with crowstepped gables and attendant outbuildings and courtyards. The Old Haa of Brough (Burravoe, Yell) is typical, dating from 1672; it was built for Robert Tyrie, a merchant, and retains fragments of its former courtyard including an arched gateway surmounted by an armorial panel. The flanking buildings which formed the opposite side of the courtyard, and can be seen in early photographs, have gone. Later forms of the building type developed as taller and more formal buildings with regular fenestration. This form of building reached its apogee around 1730-1750 by which time the largest were three storey buildings, generally only one room deep. The Haa of Sand (West Mainland) of 1754 and the Old Haa at Scalloway, c.1750, illustrate the Haa at its most advanced state of development. Later houses, such as the 19th century factor's house of Maryfield (Bressay) continued to display the typical tall, narrow, gabled form, often with a pronounced garret, until well into the nineteenth century.

These tall buildings are unusually prominant in the open Shetland landscape, and seem to be unsuited to such an exposed and harsh climate. The earliest Haa builders were immigrants from Scotland or their descendants, either merchants, landowners or the like, and it is possible that these incomers brought with them the tall laird's towerhouse tradition of mainland Scotland. There are other, similar house forms in the North East of Scotland: Fourdoun House, 1712, in Kincardineshire and Gallery in Angus have similar tall, cliff like, facades with relatively small windows. Shetland, in common with Scotland at the time, was lacking in timber resources, and wood was scarce and presumably expensive. The lengths of timber necessary for spanning floors and for roof construction would have been imported. The timber used for the earlier Haas is likely to have been pine originating from the Baltic area (by the end of the seventeenth century large quantities of timber were being imported into Scotland from that area). Nineteenth century imports are more likely to be pine from North America. In some cases drift or wreck wood was used. To economise, timber floor spans between walls were kept to a minimum and the extent of the roof area was reduced. The tall Haa form maximised internal accommodation by expanding upwards, with no increase in floor spans or roof area.

Apart from imported timber, local materials were used in the structure of the Haa. Stone is Shetland's most plentiful building material, and that available to builders included the horizontally bedded sandstones of the South Mainland, Mousa and Bressay; hard limestones from the fertile valleys of the Central Mainland; and various granites, schists and even serpentine from throughout the Islands. Brick only features as an oddity, its occasional appearance is traditionally attributed to ballast carried by ships. Until the late seventeenth century, lime for mortar and harling was obtained from shells burned over peat. Lime-kilns for this purpose still exist at Fladdabister and other locations in Shetland. Before the nineteenth century, most roofs were finished in turf or thatch, and only grander buildings were finished in local stone slabs or imported slate. It is probable that at least some of the early Haas were thatched. Some smaller Haa buildings retain felt roofs, which were probably formerly thatched. An example is the Haa of Aywick (Yell), said to be from 1650, now a one and a half storey crofthouse, with thick walls and window proportions and positioning which suggest the early date. The flat section at the apex of the felt roof is usually indicative of thatch at some point in the building's history. Slates began to be exported from Easdale on Scotland's west coast from the eighteenth century, and from Ballachulish on a large scale during the nineteenth century. Most Haas have or appeared to have had, timber partitions; floors spanning the depth of the house from front to back walls needed little additional internal support. The empty shells of many derelict examples show no trace of internal stone walls. The Haa of Sand retains all its internal timber partitions. The re-use of materials has always been a Shetland tradition and no more so than with timber where even today beaches are dragged for wood for possible reuse. The Haa in Fair Isle is said to have roof timbers obtained from wrecks, and the Haa at Gossabrough (Yell), once a shop, has partitions lined with sections of the packing cases of biscuits and golden syrup.

Classicism began to appear in Shetland in the early eighteenth century and around this time the first of the Forbes family of masons is said to have arrived from Aberdeenshire to work on Gardie House (Bressay), 1724. This is itself not a Haa but a sophisticated piended roofed box in the Scottish tradition of Sir William Bruce and James Smith. John Forbes was responsible for a number of classical funeral monuments and armorial panels between 1730 and 1750, and his sons were working on the Lerwick Tolbooth in 1767-70. John Forbes may have been instrumental in bringing classical ideas to Shetland. Initially only appearing in details such as door architraves, moulded window openings and armorial panels, classical influences became more sophisticated as at the Haa of Sand (West Mainland), 1754, which has a five bay frontage with a 2/1/2 arrangement. At The Old Haa, Scalloway, c.1750, the windows of the secondary rooms on the second floor are smaller than those below; again there is a five bay frontage, arranged 1/3/1. Around 1820, the whole frontage of North Haa (West Sandwick, Yell) was refaced, in a showy arrangement of pedimented porch and flanking pavilions with Venetian and tripartite windows. Quendale House (Lerwick), 1865, is a tall three storey town house with a formal arrangement of bipartite, tripartite and round headed windows. Smithfield (Fetlar), 1816, is typical of a number of rural Haa houses with flanking outbuildings and grounds set in a symmetrical arrangement.

Haas were sited to suit the activities of their occupiers. Those of merchants, like their böds, were located near harbours, sheltered voes or trading locations for the benefit of import and export. Landowners sited their houses in locations convenient for overseeing their estates, usually near a suitable landing place at a time when communication was principally by boat. Many of these merchants were also operators of fishing stations and their Haas were near beaches suitable for the drying and curing of fish. At Grobsness (West Mainland), eighteenth century, the Haa is located in an elevated position at one end of the beach, where it would have commanded a view of the activities below. A number of natural beaches were 'improved' by extending the area available for drying fish with flat stones forming platforms at the head of the natural beach. The earlier Haas served as both the residence and workplace with storage or shop in the ground floor and living accommodation in the floor or floors above. As the building type developed trade was forced out, either to outbuildings in the vicinity of the Haa, or to Böds and stores near the landing places or beaches. Later the Haa was largely residential although still serving a business interest in overseeing the estate. Town houses, often built in the same style as the Haa, served as a base from which to conduct business, and allowed Lairds to escape from the confines of their rural existence to experience the urban sophistication of Lerwick or Scalloway. Quendale House (South Mainland), c.1800, is a tall gaunt Haa of two storeys and an attic, three bays wide. The town house of the laird in Lerwick, again Quendale House, 1865, is grander, with a full three storeys, and has an elaborate arrangement of windows. Some of the last buildings in the Haa style are nineteenth century manses, factor's houses or farmhouses, such as The Haa, Watsness (West Mainland), nineteenth century; Maryfield, (Bressay), nineteenth century; and Kergord House, formerly Flemington, (Weisdale), 1850s. Although these houses continue to have tall Haa features, these are tempered by contemporary styling appearing from outwith Shetland.

Most Haas have been changed, extended and adapted over the years and few survive without alteration. A notable exception is the Haa of Sand which is almost unaltered except for changes to the side wings and to the internal layout of the ground floor. All rooms on the upper floors retain their fielded timber panelling, that in the drawing room being elaborate with arcaded sections, panelled columns and doors with shouldered architraves. Some examples of timber panelled interiors survive in other Haas and houses of the period. Gardie (Bressay) has panelling in its drawing room to the same pattern to the Haa of Sand. Other examples remain elsewhere, including the Old Haa of Brough (Yell).