Fungus

Tl;dr: Fix leaks, increase ventilation. Remove fungi/mold and badly affected material, clean with water and abrasive action, apply concentrated borate solution.

Type 1
- found in upper attics of 20 and 22
- fairly uniform distributed circular patches about 2.5 cm in diameter
- radiates out from central point
- composed of fragile white fibers, like cotton strands
- thicker towards center
- found on flat surfaces which aren't directly wetted
- numerous, perhaps covering 10 % of upper attic surface
- is it 'White spot mold'?

Type 2
- found in upper attic of 20
- only found in directly wetted areas, especially in cracks or at joints between beams
- irregular, protruding, compact form (sort of like foam expanding outwards)
- rust colored but white (and wispier) towards edges
- irregular polypore (i.e. not gilled and not closed-cell pores. More like coral)
- 'dry rot'/Serpula lacrymans?

Type 3
- found in some rooms in the ground floors of 20 and 22
- flat, black, radial
-...

General
- Bleach (Chlorine) is ineffective at killing stuff on porous surfaces like wood. (However, it is effective for killing most things on non-porous surfaces like glass, ceramic, metal, silicone, etc.)
- Hydrogen peroxide is ineffective at killing live mycelium as they produce strong peroxidases. (However, hydrogen peroxide is effective for killing fugal spores before they germinate.)
- Boric acid and borate salts are effective for killing fungi and insects. It is 'natural', non-volatile stable and largely non-toxic. MSDS: https://www.sciencelab.com/msds.php?msdsId=9927105 Application is done using concentrated aqueous solutions to the cleaned surfaces and, in more significant cases, by injection with or without drilling pilot holes.