Showing posts from July, 2019

Discrepancies between Internal and external DPC (damp proof course)

In a cavity wall construction, one would expect that the damp proof membrane to be at the same level on both walls. It turns out this is not always the case and my house is a good example where the internal wall's DPC is more than a brick lower than the external wall DPC.
I didn't even think to check this before reading the CIGA Technical note 14. This clearly states that if the distance between DPC and ground level is within a brick (as was the case with my property at time of install) then 'numerous other factors' must be assessed before declaring the dwelling as being suitable for CWI.

One of the factors is the relative level of the inner and outer leaf DPC.

This is exactly what I found in my property. Ive used a floorboard to show the position of the internal floor. The DPC is clearly a brick below the floorboard and less than brick above the block paving.

At least the cavity is clear of rubble as CIGA have said is so vital?

So the answers are

 Does the inner leaf …

DPC Bridges

In my previous posting Unable To locate DPC I discussed the integrity of the DPC(damp proof course) and how making blind assumptions can lead to violations of the Agrément certificate and thus and thus building regulations.  This post deals with bridges and what installers and CIGA inspectors should check.
A damp-proof course is a barrier, usually formed by a waterproof membrane such as bitumen or a non porous stone such as slate. Without a DPC, water can travel up through mortar beds and porous bricks from the ground through capillary action. The effect varies depending on the type of brick and mortar, soil type and drainage,  rate of evaporation from the walls and anything that might hinder evaporation (impermeable paints or cementinous renders). During the building of a dwelling a lot of care is taken to ensure that no structures accidentally create a connection between the ground and the wall above the DPC (known as a bridge. It's usually some well meaning and/or incompetent …

Unable to locate DPC

The BBA Cerficate for our CWI Agrément Certificate No 01/3789 states that the bottom row of drill holes should be maximum 800mm above the damp proof course (DPC).

The DPC is quite tricky to spot because the bottom row of bricks are undrendered but painted black. The home buyer surveyor was not able to identify the DPC and two CIGA inspectors did not look or document it despite concluding that the installation was done to system designer's specification.
It's not possible to assertain if the installation was correctly done to industry standards without locating the DPC. CIGA have stated that drill hole patterns were the key factor in their conclusion of conformity but  have told me it would be unreasonable for me to have that information (I was present for both inspections and no measurements of drill holes were done).
For my property one might ask which DPC?  The 1960s extension has a brick external leaf which has been tied into the original back wall but the DPC is a full br…