Raised Patio - DPC needed?

[chewymix]

Put this into 'In the garden' but i think this might apply more here and i cant delete the old post - sorry for the dupe.

Hi

We recently had a new kitchen extension completed and was signed off by BC and everything is present DPC wise for the new walls. Part of the build a patio was created, thats tiled, at the same height as the kitchen floor which is around 10 inches about ground level and so above the DPC of the building. The kitchen has bi-folds onto the patio and in front of the bi-folds is a drain sunk into the patio but on either side of the bi-folds there are the brick walls, reclaimed old stock if it makes a difference, and this in total is the full width of the patio.

Everything seems(ed) fine but with all this recent rain i have noticed that the lowest 2 or 3 courses of the bricks either side of the bi-folds looks like water could be wicking up the brick ad it looks a darker colour that the rest of the wall. Is this an issue and should another DPC have been put in place at the height of where the patio is for this wall that faces onto the patio as in my mind the DPC on this wall is too low for the new 'ground' level.

Thanks for any advice

cheers

 

[Blagard]

The patio should have been a full 150mm below internal floor level and the DPC would likewise be 150mm above ground. The bottom two courses above ground should also be frost resistant bricks as they always get saturated by splashing water - hence the name splash course.

Certainly the way you have it is not right and the brickwork either side of the bi-fold doors should have a DPC 150mm above the ground/tiles. You are fortunate that other parts of ground are low enough for the DPC to work properly there and for the cavity to be able to drain out of the low level weep holes.

 

[chewymix]

thanks for this - the whole extension has been built with the first 2 or 3 courses, i dont remember exactly, in red brick which i presume is frost protected and on top of this is the DPC - The issue seems to be that as the patio has raised the ground level on the back elevation then the patio could act as a bridge between the DPC and the ground? Thats what i am thinking anyhow and i wonder if this is actually an issue or will the cavity stop anything leaching into the inside wall and if it is an issue what would the remedy be, chase out just about the patio on the outer layer retro fit a DPC??

cheers

 

[Blagard]

the whole extension has been built with the first 2 or 3 courses, i dont remember exactly, in red brick which i presume is frost protected and on top of this is the DPC

They could be an engineering brick and that would be fine. Your above DPC facing bricks may also be frost resistant, only time will tell. If they are not, the lower saturated ones will start to perish with frost action.

The issue seems to be that as the patio has raised the ground level on the back elevation then the patio could act as a bridge between the DPC and the ground? Thats what i am thinking anyhow and i wonder if this is actually an issue or will the cavity stop anything leaching into the inside wall and if it is an issue what would the remedy be, chase out just about the patio on the outer layer retro fit a DPC?

With a drain in front of the Bi-fold doors that area will hopefully be OK with no bricks to get saturated. As long as the DPC can be seen above ground it is not bridged externally, but it is too low to stop the saturation by splashing. When water does get into the cavity it will usually escape via the lower weep holes. If they are not present then water could build up in the cavity and bridge the DPC. If that happened the only real answer is to lower the patio as a higher DPC would not help get rid of the water. Personally I would wait and see how it all performs and if for instance the bricks above the low DPC start to perish then chop them out and replace with an engineering brick or known frost resistant facing brick (Some are as good as engineering bricks)

 

[chewymix]

I'll post a picture on the weekend as its a bit dark to see anything when i get home. This was all in place before final BC sign off so they were happy enough with it so maybe i am being a little paranoid but there is certainly dampness on the external layer of bricks either side of the bi-folds for 2 or 3 courses, but maybe its just superficial.

 

[Blagard]

This was all in place before final BC sign off so they were happy enough with it so maybe i am being a little paranoid but there is certainly dampness on the external layer of bricks either side of the bi-folds for 2 or 3 courses, but maybe its just superficial.

I bet the patio was not in place when BC inspected the work at DPC level. And the added patio is not being inspected. Basically as I said before, it is the patio that is wrong as it is set too high.

 

[chewymix]

correct for the BC inspection regarding the DPC but it was in place for the final BC signoff -

I'd be interested to hear of what the potential fix(es) could be that did not involve removing the patio if indeed there turns out to be an issue.

 

[themiddleagedun]

I wouldn't worry about it. If you had a DPC 150mm above your patio the bottom two bricks would still get wet by rain splash anyway...

 

[chewymix]

OK so here are a couple of pics - apologies about them needing to be rotated. I presume that this will just dry over time and that its the excessive rain we've had recently thats mainly caused this as there is no 'pooling' of water on the patio, it drains pretty quick.

View media item 71709
View media item 71710
cheers

 

[Blagard]

Very smart but extremely poor (IMO unacceptable) with regard to the arrangement of the DPC.

Is the DPC in one of the brick bed joints above ground ? Certainly it must be buried below the patio door, so I think all below ground!

The only thing saving you from serious damp problems is that channel drain. Apparently no where for the cavity to drain and so at some point don't be surprised to get a damp inside.

Solution - drop the patio

 

[chewymix]

The DPC is below the ground level of the patio but that is in fact now about 12 inches above the soil level and in fact the cavity goes down to the origional ground level. In other words, as its hard to explain, DPC was put in on top of engineering bricks then the kitchen floor level, and so also the patio, was RAISED by about a foot. So i dont think water will pool at the kitchen floor level but it could collect at the bottom of the cavity, which is below the patio level.

I hope that makes some type of sense.

 

[trowlerman]

if the damp is not going inside the house then there is no issues , however if your that woried its quite easy just to insert a dpc in the bed joint 150 mm above the patio.

ps if its a tiled patio do not go on it while its wet !!!!

 

[Blagard]

If the cavity ever floods and there is no where for the water to go, it will bridge the below ground level DPC on the inner leaf and there will be a damp issues.

 

[mandm65]

unable to comment on your prob, sorry. Wondering if like to share your exprience with bi-fold doors? We are also considering bi-folds for our extension.
cheers

 

[maltaron]

As the patio is unlikely to have a DPC under it there should have been a vertical DPC from below the house DPC level to the patio level. As it stands the patio bridges the DPC and damp is inevitable.