Concrete floors and cavity

[Nick2847]

Hi, I am trying to better understand the flooring in my home and hope some expert advice will clear things up. I have dug down the side of my Edwardian house that was covered with pebbles and found the air bricks way below ground level. My internal floors are concrete and means I wouldn't necessarily have to have air bricks open and uncovered.

But what I don't understand is that inspecting in the air bricks is a void space. The air bricks are open and I can see earth and cobwebs through the air brick slats.

I know there are issues with high ground around my house and the driveway was built on top of the previous one by the last owner. See photo.

I am trying to prevent any damp or major problems from lack of ventilation or water ingress into the void under my house. Any advice appreciated.

 

[motorbiking]

Are all your internal floors concrete or has the house been extended? My guess is the concrete is not original and there should be ducting to an original floor space somewhere in the house.

 

[Nick2847]

Thanks for the reply. All the floors are concrete but I don't think they are original.

There are airbricks on the front and side of house serving this front lounge room only, but no ducting I can see going further into the the house

It is a long thin, semi-detatched house with a conservatory off the kitchen (also concrete floors).

Would this front room floor be classed as a floating concrete floor or just not been backfilled. I believe the house has had the concrete floors and raised driveway (ground height) for 15 years prior to us buying.

No real signs of damp other than some blistering on an internal, adjoining wall.

I am a but confused as to why there is a void in the sub floor area with concrete floors and where the DPC is. Thanks for any reply

 

[Mr Chibs]

The concrete floor was poured later than the house was built and they couldn't be bother to brick up the old vents.

DPC is usually just above the air vents, so you if you have a look in the mortar line you may see it somewhere on your house.
Ideally you want the ground level to be two courses of bricks lower than the DPC.

 

[Tigercubrider]

Those air ducts look younger than the house?

 

[Nick2847]

Thanks for the replies.

@Mr Chibs would a void or cavity between the internal concrete floor and ground level still be present if concrete floors were poured later? Would this not be backfilled or concrete poured from ground level up? I would be happy to brick up the air bricks to prevent moisture ingress if ventilation was not needed.

@Tigercubrider I believe the air bricks are original, should be black cast iron like the my neighbours, but have been weathered from being buried for so long.

Thanks for the help

 

[sxturbo]

Not read all the posts, but it's not unusual for rotten floors to be replaced by concrete

 

[Nick2847]

Thanks @sxturbo my main question is that why would there still be a cavity present between the replacement concrete floor and ground level under the house? It is only 1 course thick really. I'd just expect it to be filled in, but I am not a builder!

 

[Mr Chibs]

In 99% of replacement floors they leave the vent alone after relplacing with a Rotten wood with a concrete floor, if you took the vent off, you might be able to see the dpm membrane which is under the floor and up the sides (usually) to contain the concrete.

You won’t get any water ingress worth worrying about by leaving the vents alone.

 

[Nick2847]

But could I cover them @Mr Chibs ? As I plan to run aco guttering along the chanel pictured to reduce ground height and divert rain water to sewer rather than accumulate in a trench. This area was also badly hit by the 2020 christmas floods, another reason for the Aco.

 

[sxturbo]

Is there definitely a void space under the concrete?

I don't think it's likely, have you tried poking a rod through?

If you have concrete floors the blocking the air brick isn't an issue.

Are you walls solid brick or cavity construction?

 

[Nick2847]

Definitely a void space @sxturbo which can be seen through the airbrick (in the screenshot above).

Solid walls.

But yes, you echo what others have said that blocking air brick with concrete floors is not an issue. Thanks.

 

[Mr Chibs]

Are you saying there is a suspended concrete floor? Can’t see this being the case, think there will be just a brick hole where the air vent is.

If you poke a garden cane in the air vent from outside, how far in will it go?

 

[Nick2847]

@Mr Chibs it is difficult to push a garden cane in as the vent gaps are narrow and the ground is high so cannot get the angle. But a 15cm screwdriver goes all the way in. I would say a cane would. There is lots of earth in there and the void is only 1 course deep, so either poor backfilling or no backfilling?

Photos are difficult but you can see quite far back on the photo attached.

Carpet underlay is laid straight on top of concrete internally.

Thanks for bearing with me

 

[Mr Chibs]

If it’s not a void under the slab and only behind the air vent (Or inside skin)... don’t worry about it... no point in removing the vent, as you’ll need to find matching brick(s) and pointing it up nicely is not that easy when you want it to look good.