Second DPC at external door openings

[WWilts]

"DPCs to be set at least 150mm above external ground level and second DPC to be set 150mm above this to 900mm either side of entrance door accesses."

Why is this second higher DPC specified on either side of external doors?

[Dave Jones]

a cavity tray must be provided on any oponing that breaches DPC

 

https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-1-external-masonry-walls/6-1-17-dpcs-and-cavity-trays/

 

[Brickie]

43 minutes ago, WWilts said:

"DPCs to be set at least 150mm above external ground level and second DPC to be set 150mm above this to 900mm either side of entrance door accesses."

Why is this second higher DPC specified on either side of external doors?

Because DPC should be at least 150mm above ground level & the assumption is made that your entrance will be a ‘level threshold’ (level-ish with your internal finished floor level to allow wheelchair access) and therefore a secondary DPC is required in this zone to prevent rainwater splash up saturating the superstructure wall. This secondary dpc should extend the specified distance past the raised ground level & then step down to lap into the lower dpc. 

[WWilts]

1 hour ago, Brickie said:

prevent rainwater splash up saturating the superstructure wall. This secondary dpc should extend the specified distance past the raised ground level & then step down to lap into the lower dpc. 

Is this second DPC on the outer leaf only?

[Dave Jones]

10 minutes ago, WWilts said:

Is this second DPC on the outer leaf only?

 

its a tray so weepers on the outside lapped up onto the inside skin. same over lintels, meter boxes ect

[Brickie]

33 minutes ago, WWilts said:

s this second DPC on the outer leaf only?

Yes. 
It’s only a cavity tray if it’s described as such,and would continue around the perimeter of the build,and would also normally lap out at at finished floor level (I.e. the standard DPC height.)

[WWilts]

17 hours ago, Brickie said:

would also normally lap out at at finished floor level

Something like this? Our brickie is not familiar with this, but it is included in the spec notes.

 

 

[Brickie]

That is a Cavity Tray,yes,though it would normally be lapped out FFL. Is this your own drawing or one you were supplied with?

[Dave Jones]

not unusual to have the tray couple blocks higher than FFL on inside skin, especially if a sloping site etc

[WWilts]

4 hours ago, Brickie said:

That is a Cavity Tray,yes,though it would normally be lapped out FFL. Is this your own drawing or one you were supplied with?

Own drawing, tweaked another.

 

Not familiar with the term lapped out. Does the pic now show lapping out? Sorry to be so ignorant.

[Brickie]

I’m referring to the positioning of the tray in terms of coursing,as you look at your drawing. The height of the lower (outer) part of the tray would usually be at DPC level (which is usually the same as FFL.) If it helps,visualise the substructure walls all built up to the height of the (as yet uninstalled) finished floor. Now,one course of blocks is laid on the inner skin, the tray is installed and lapped out & down so going from DPC plus 225mm internally to DPC height externally. 

[WWilts]

1 hour ago, Brickie said:

one course of blocks is laid on the inner skin, the tray is installed and lapped out & down so going from DPC plus 225mm internally to DPC height externally. 

Thanks, understood.

[Adsibob]

Anyone know if the recommended 150mm distance can be reduced when there is a french drain immediately next to the external face of the wall, such that rainwater shouldn't splash as high as 150mm because it is hitting gravel in the french drain?