Anyone know what this is (in fireplace opening)?

[Lithgae]

Hi,
Pic too large to upload so at link - https://www.dropbox.com/s/yd3avl02du562l4/2018-03-17 16.08.41.jpg?dl=0

Its a slope coming off the right hand side of the fireplace opening about 30cm in height, sloping forward to the front of the fireplace. Chipping away at it reveals that it is brick underneath, with something black on top, but there is a hole underneath maybe 30 cm deep, that appears to reach through to under the floor. It looks designed, but I can't think what it would be for, and what the purpose of the hole underneath would be.

Any ideas?

 

[Lithgae]

I chipped away a bit more and found out. Its not anything historic at all. It appears to be a concrete slab. This is a weird one. It appears that the vent on the outside comes in above the fireplace hearth, and that the hearth at that side has been chipped away and the slab added to direct the airflow to under the floor. I suspect that this vent was added at some point after the fireplace was made redundant. Problem is that I would ideally need to remove this before putting a stove in, but then I lose an underfloor vent, which was probably put there for a reason. I'll need to think about this one!

 

[Feltwell]

Bit hard to tell from your description, but sometimes vents from the sub-floors were incorporated to feed the fire with air - my house has one, alas the hearth has long since been butchered so you can't see it from above, but in the sub-floor space there is an iron pipe about 2" in diameter sticking out of the base of the stack that goes back into it horizontally, round a 90 degree bend and up to below where the back of the original fire grate would have sat.

 

[Lithgae]

I've had a think about this. It's a bit of a long story but...

The house was down on the home report as being about 1885, however I think this has been guessed based on the bay window which would have become fashionable about then. Having been in a year, looking at old town maps, and the stone mason pointing out that the bay section was a different grain of sandstone from the rest, I am now fairly certain that the house is older and the bay section was added around 1885. Removing the cement render on the sides of the house revealed the marking of an old door, which strangely would have opened into the middle of an internal stone wall. The rear of the house is solid floor, the front is suspended timber and there are also some signs that the front floor has been lowered, possibly at the same time as the bay window extension was added, to meet the fashion of high ceiling front formal living room with bay window etc.

The house has signs of long term dampness in the corner to the right of the fireplace in the pic. Thank for the suggestion Feltwell, but this isn't actually a vent from the sub floor its coming from the back of the fireplace. I suspect that this has been added at the time the fireplace was blocked up as an extra vent to try and deal with the dampness in that corner as there wouldn't have been very good ventilation with only vents to the front of the house and a solid floor at a higher level to the rear. The vent on the outside is a semi modern alloy, unlike the vents at the front which are old cast iron. This also shows up the fact that the ground level to the side of the house is higher than the floor level on the inside, which is why the vent has to come in at about 20cm above the hearth at the back of the fireplace, and be directed down through the chipped away hearth to the underside. When I moved in at first this vent was blocked by paint, so it looks like someone has added this to deal with the damp/ventilation issue, then someone later has painted it closed!!

The mysteries of old houses!