Underfloor drain channel through mid C18th house

[Anja]

We are repairing some rotten joist ends on suspended timber floor over earth.

We have freed up debris and damp earth bridging sleeper walls & cleared air bricks/vents to outside.

One of the 3 air bricks was at a lower level - about 150mm & sure enough we’ve found a brick built channel running back of house to front. It was filled with old & damp earth & brick rubble - now cleared. Old pitch (?) floor of channel in tact in some places.
The end is arched and runs under the next room floor - fully concreted eons ago.
Any thoughts on its age, use & what to do about the part that seems to run under the adjacent room with solid floor?
Thank you

 

[Cubist]

Can I get this right please? There an air-brick in the wall at one end of this channel/arch that runs completely under the house to emerge outdoors on its opposite side?

 

[Anja]

Almost - at the front of house a grille to outside - the arched opening is on the opposite wall of the front room - but it appears to travel through the wall and under the floor of the room behind - solid floor. The channel runs about 150mm from the base of the right hand wall.
This part of the house was previously a timber-framed building.
Here’s a terrible but very quick sketch
Thanks very much

 

[Kearn]

Was it jettied on that side when the frame was still in place?

If so… Could be a perimeter land drain, which was just outside the original wall, which has now been brought further out in line with the wall above meaning the drain is internal.

That said, it doesn’t look like formed clay cylindrical pipe, more pieces, or is it just broken?
I’ve dug up loads of clay land drains, situated about a foot from the outer wall of our place, but they’re Victorian insertions.

When was the frame replaced, and why?

For my theory to work, it would have been relatively recently (last century).

Odd to go to the effort of installing a grate though for what in the scenario be redundant!

Do done more digging and take some more pics of the pipe/drain!

 

[Anja]

Earlier timber frame possibly subsumed in classic Georgian rebuild 1750/60 (?)
Timber framed building evidence in upper floors only.

There’s no clay pipes etc just a channel about 300 wide made of bricks - lined with either pitch/tar or lime mortar.