Although your question addresses only "lodging-houses," I will discuss all three London lodgings (lodging-houses, spikes, and Salvation Army shelters) together, as Orwell's nightly adventures in these chapters take him to all three, according to last-minute availability and as his frugal budget allows.
At the end of chapter 24, Orwell laments the conditions of the "doss-house" as cheap but not clean, and he leaves unwashed. His narration, taken from his notebook at the time, describes the inhabitants in oversimplified (even racially derogatory) terms. He mentions the eating habits of "Navvies" (slang for navigational engineer, or canal/construction worker) and a "Jew":
In a corner by himself a Jew, muzzle down in the plate, was guiltily wolfing bacon. (133)
There has been some criticism of the young Orwell here as being a latent anti-Semite. He later mentions the passive racism of others, too:
They were singing "Anybody here like sneaking Judas?" (136)
In chapter 25, Orwell moves from the lodging-house at Waterloo Road to the Pennyfields, which holds accommodations for between fifty to one hundred tramps nightly. He points out that such houses were owned by "rich men," highlighting his seeming distaste for how the wealthy profit from the suffering of their poor countrymen.
Despite the loathsome conditions of the lodging-houses, Orwell treats the tramps, even the owners, with dignity and sympathy:
It was a filthy place. Yet the deputy and his wife were friendly people, and ready to make a cup of tea at any hour of the day or night. (139)
Orwell does this often: he contrasts the horrid physical conditions of the people and of the living conditions of the country itself against the inner conditions of the poor people.
The Irishman was a friendly old man, but he smelt very unpleasant, which was not surprising when one learned how many diseases he suffered from. (141)
Orwell is at his best when describing kitchens, a place where the inhabitants eat together and share food. Most of the time, Orwell's narration focuses on two rituals: eating and sleeping. His thesis seems to be that basic survival and dignity depends on providing these two simple human needs and that these cities need to do a better job of it.
As an advocacy journalist, Orwell uses external conflict to show how Londoners treat tramps. He contrasts the horrid external conditions (horrible smells, bug-infested beds, rotten food) of the country with the inner human conditions of the inhabitants (their goodness, friendliness, and willingness to share).
His book is intended to be an eye-opening exposé about the horrible living conditions in these cities and an implicit call for reforms in public policy, working conditions, healthcare, and lodging practices. Though the young Orwell has a tendency to discuss the lodgers with stereotypical or racial descriptors, his role as an insider "embedded journalist" (as a part-time tramp himself) gives him the accrued perspective to denounce the profiteers and sympathize with the homeless. Most importantly, Orwell is able to build trust with his reader as a credible and reliable narrator about the poor treatment of tramps.
The eNotes study guide says it best:
His message at the end of the London episode (chapter 28) makes the same point—that the down-and-outers are human beings, not ciphers ....
He concludes by lecturing his readers not to think of all tramps as drunken scoundrels and not to expect a beggar to be grateful when he is offered a penny. The narrator's commentary is modest, muted, a plea rather than a screed; yet he has proved to the reader that he has earned the right, through brutal personal experience, to deliver this lecture.