water in cavity

[dean1984]

hi so i have recently had an extension built and the air bricks from the existing house were extended under the concrete slab with ducting the ducting enter the cavity at the other side of the extension below the lean mix infill. The groundworkers left the ducting open ended in the cavity with a gap in the lean mix at at each point where the ducting enters the cavity. an air brick is then in place (plastic with a sort of half periscope open at the bottom ) on the outer leaf.

the issue i have is that with the bad weather the cavity has filled with water where the gap in the infill are situated. after removing the water i can see it filling up again from the bottom through the outer leaf.

to add to the issues the water was high enough to run back up the ducting and track along the ducting to essential cause water to come up through the DPM (i think where it is joined)

my main questions are.
is the way the ducting is done standard practice or should it be joined to the air brick?
should there be a gap in the infill to accommodate the ducting?
i think i might but a french drain/land drain type setup in along the back of the property where the issue is to stop water pooling against the cavity outer leaf.

its all been signed off by buildings control but this extremley wet winter seems to be the cause f the issue, to be clear its the base slab that that im at the minute s there will be 200mm of insulation to go in and another dpm and screed going forward, so it got a long way to go before it would be in the actual room.

any help would be appreciated as i cant find info on this on any sites

 

[GoodDIYjob]

My feeling is that there is normally a periscope airbrick extension unit fitted in the wall, sort of Z shape that would connect directly to the ducting extension to prevent loss of air flow and anything entering the ducting run.

 

[dean1984]

i thought so too but that was signed off by building regs, i think the main issue i need to fix is the water entering the gap in the lean mix (basically creating a pocket full of water in the cavity), im thinking i may need to put a land drain along the back of the extension where the air bricks are so the gap doesnt fill with water.

i will try to post some photos tomorrow. i do think the issue was compounded as i haven't got any guttering up yet so the water isn't being taken away from the house. although the soakaway did fill up with last nights rain but that is another issue!

just to add water inst coming in through the air bricks its below as there is no lean mix below the air bricks

 

[Leofric]

is the way the ducting is done standard practice or should it be joined to the air brick?

Ducting should be connected to air brick.

 

[dean1984]

ok thanks i will connect the ducting to the air brick , but i still have the issue of the water entering the cavity as there is no lean mix concrete. i think the water tracked long the ouside of the ducting essentially along the channel underneath the concrete slab causing. if the cavity was full of lean mix i dont think the issue would exist but because the ducting enters the cavity lower than the level of the lean mix they have left a gap in the lean mix which is filling with water from the outside of the building.

can i build a land drain along the outer wall to keep the water away from the building?

 

[dean1984]

or potentially a weep hole below the air brick to allow the water out if it gets to high in severe weather. as i have mentioned i doubt it will get this high again as i think the lack guttering and taking water away from the hose has added to the issue. once that is sorted i expect the ground around the house to be a lot drier than it currently is.

 

[^woody^]

If the cavity is not filled in the ground then that would fail the building inspector's inspection - the probelm is it's not part of the statutory checks.

 

[dean1984]

its is filled except for where 5 ducting pipes enter the cavity (which i know was checked by BCO), can i fill the cavity in these areas retrospectively if i fit the periscope air bricks as mentioned above?