I'm more familiar at present with Kaupang, and the full details are available via Dagfinn Skre's academia page. I'd especially point you to Kaupang in Skiringssal, at pp. 214ff.

Plots of land were small, perhaps surrounded by a wattle fence and maybe a ditch for drainage. Buildings were similarly small. The best-excavated examples are typically only about 6x4 m (20x13 ft), or 24 m2 (260 ft2). I live in a small four-room city apartment that's about 3x that size. So the buildings at Kaupang were about the size of a modest modern living room.

Not much survives from these buildings, even where artifacts do survive. This indicates that construction was light, most likely consisting of simple planks placed either horizontally or vertically. Insulation, if any, was also light. Heavy textiles are the most likely option. There is little evidence to suggest wattle or daubing. There are occasional hints of inside partitions, although it is unclear whether these divided sleeping areas, storage areas, or even indoor animal pens (which would have been pigs, keeping in mind that premodern breeds sometimes looked more like stocky dogs than Porky the Pig).

The hearth consisted of an open fireplace, near the center but sometimes closer to one wall. This may, in part, have been done to keep sparks from hitting any textiles being made on a standing loom, which was a major feature in most Viking-Age houses.

I can't help as much with Hedeby at the moment. Although the research there is in some ways better regarding housing structures, the publications I'm familiar with are mostly in German and would take some time to go through. However, there are modern reconstructions standing on top of their excavated Viking-Age counterparts. You can get a sense of these online here (some photos at top, others nearer the bottom).

Note that here the walls are framed and daubed. This would provide better insulation than the buildings at Kaupang, and this may in part be a chronological change. Hedeby lasted a bit longer than Kaupang, which mostly dried up around 900. These buildings may represent a later and larger development. Alternatively, they may represent a somewhat wealthier neighborhood than the buildings excavated at Kaupang.

It's important to keep in mind that at both sites, we've only excavated about a half dozen of what must once have been hundreds of buildings. The populations are typically estimated at having been 600-1200 people, and buildings seem to have been replaced every 30 years or so. So at both sites, we've seen perhaps only 5% of the structures, and it's hard to know whether these are examples of or exceptions from the unexcavated majority. But at least by comparing the two sites, we can get a sense of the variety—humble though it may be—available to town-dwellers during the Viking Age.

I hope that helps! For good measure, you might also be interested in the model of Birka prepared by the Swedish History Museum in Stockholm.