There are four ventilation shafts and one intervention shaft in the tunnel across the Chilterns. These would also be used for emergency access during operation. The first of these is in Chesham Lane, Chalfont St Peter.

All the ventilation shafts used the same diaphragm wall construction method. Ventilation fans will be housed in a basement below a single storey headhouse. The construction compound will be in place for seven years. The shaft is 66 metres deep and is the deepest of the shafts. The tunnels are 47 metres below ground and the tunnel boring machines reached here in March 2022. The shaft is due to be completed early in 2026.

The access route to the compound is via a newly constructed temporary haul road directly to the A413 then to the A40 and the M40. All HGVs will turn left when leaving the haul road. The junction is controlled by temporary traffic lights.

PRoW (Public Right of Way) CSP 10 is diverted east around the construction compound before joining the existing footpath CSP 9 south of The Brow for the duration of construction and then reinstated along its original alignment.

Beyond the shaft the route continues towards Chalfont St Giles tunnelling under the River Misbourne for the first time. It passes under the Co-op store in the middle of the village and then on towards the Chalfont St Giles vent shaft.

The buildings that will be visible above ground are the headhouse, plenum (the shaft outlet) and three access hatches.