Cavity Depth Below DPC

[self builder 123]

Hi

I understand from there should be 225mm of space in the cavity below the dpc. If not then in situ cavity trays should be used to direct any water to the outside via weep holes.

We have the following construction type - see diagram.

Untitled

• self builder 123
• 1 Feb 2009
• 2

Is there a serious risk of water penetrating through the inner leaf under the dpc ?

The outer leaf is concrete block which is to be wet harled.

 

[noseall]

in this instance a wide piece of dpc (450mm+) could be fitted beneath the timber frame sole plate, down the cavity and out across the outer leaf at dpc level.

this would give you the cavity tray plus a dpc under the sole plate, all in one go!

why didn't you save yourself the hassle and keep the trench blocks 225mm down from dpc level?

p.s. don't forget weep vents every 900mm or so.

 

[self builder 123]

Hi Noseall

Many thanks for your reply.

To be honest this only became apparent to me this weekend !

There was no mention of the need for the 225mm space ( which makes perfect sense ) on the drawing and the builder never made any comments when he was fitting the trench blocks.

The building is well underway. The cavity has been kept extremely clean by the builder. He has left gaps all around down at the dpc level and has been flushing out the cavity as he goes with a hose.

I applied the Aquaseal liquid DPM when I realised that any mortar that might fall down could bridge across the cavity - the builder said it would not hurt when I asked if I should do this.

As the building will have 2 coats of render which will contain waterproofer in both the scratch coat and the wet coat, plus there is good soil drainage around the building, do I have anything to be concerned about regarding moisture ( from driving rain ) finding its way into the inner wall ?


Look forward to hearing from you.

 

[noseall]

As the building will have 2 coats of render which will contain waterproofer in both the scratch coat and the wet coat, plus there is good soil drainage around the building, do I have anything to be concerned about regarding moisture ( from driving rain ) finding its way into the inner wall ?


Look forward to hearing from you.

you are highly unlikely to encounter any driving rain problems at least.

however, condensation is another matter. provided you construct the inner frame using robust building techniques then i would say you will have no worries.

 

[self builder 123]

Hi Noseall

Many thanks.