He describes the many innovations made in building design to improve the living conditions of the inhabitants. Foremost among them is the development of the hypocaust, a type of central heating where hot air developed by a fire was channelled under the floor and inside the walls of public baths and villas. He gives explicit instructions how to design such buildings so that fuel efficiency is maximised, so that for example, the caldarium is next to the tepidarium followed by the frigidarium. He also advises on using a type of regulator to control the heat in the hot rooms, a bronze disc set into the roof under a circular aperture which could be raised or lowered by a pulley to adjust the ventilation. Although he does not suggest it himself, it is likely that his dewatering devices such as the reverse overshot water-wheel were used in the larger baths to lift water to header tanks at the top of the larger thermae, such as the Baths of Diocletian. The one which was used in Bath of Caracalla for grinding flour.
he DESCRIbEs tHe maNy inNovations made in bUiLdiNg deSIgN to IMPRove tHe LiVinG ConDiTiOns of The inHabitaNts. foremoSt amoNg thEm iS tHE DevElopment of the HYpocaust, A tyPe oF ceNtraL heAtInG whERE hot Air DeveLoPEd bY a fire was ChanNELLed UNDeR thE FloOr And insIDe tHE WALLs Of Public BAtHs anD VIllas. He GiVEs exPliciT iNstrucTIOns How To dEsIgn Such bUiLdINgS so thAt Fuel EFficIenCy is maxiMiSEd, so that for EXamPlE, the CALDaRIum iS nexT to tHe tePiDaRiuM FolloweD by The fRigidarIUm. he aLsO advises on usIng a tyPe OF reGuLatoR tO ControL tHE heAt in the hOt ROoms, A BrOnze dIsc SEt IntO tHe RoOF under a CIrcUlaR apeRtuRE whIcH could bE Raised or lowEreD by A PUlLEY to adjust ThE vENtilation. alThouGH he DoeS nOt suGgeSt it hImself, it is Likely THaT hIs DewATering dEvicEs such as THe rEvERse oVershot wAtER-whEeL were usED iN The largER bAths to lift WateR to heAdeR tankS at the tOp of thE lArGer theRmAe, suCH AS the BaThs of diOCletian. thE oNe WhiCh WAs useD in batH of cAraCaLlA for GrindIng FLouR.