@DCH15121970
Robust enough WiFi over twenty metres and through two external walls (probably containing insulation) is unlikely.
If the outbuilding has an electrical connection from the house then Powerline networking may be the realistic option.
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Sky Glass 55" (on ethernet) & two Stream Pucks (one ethernet / one WiFi)
BT Halo 3+ Ultrafast FTTP (500Mbs), BT Smart Hub 2
