Construction fail: See anything wrong with this blockwork wall with damp proof course?

Blog Post
Picture of a blockwork wall with faults

The above photograph was taken by one of our building control surveyors carrying out a site inspection, and shows how attention to detail (or a lack of!) can lead to future problems. This extension will suffer from moisture problems, but there is not one reason why – there are three.

Look closely at the DPC (damp proof course) arrangement

A membrane is built into the wall to be joined to the damp proof membrane in the floor slab at the junction between the wall and floor. As damp proof membranes are generally unsuitable for use as a DPC in loadbearing walls, the contractor has rightly built an additional DPC into the wall to protect the membrane. But the DPC spans the full width of the cavity and so all moisture within the cavity will pond on the DPC. The result? The blockwork above the DPC will become saturated and cause damp problems within the extension, the skirting boards will rot and the mould will occur on the plaster. This could have been avoided by building the membrane on to the inner leaf only and protecting it with a 100mm DPC, or by protecting the wide horizontal DPC with an additional cavity tray over.

Now look at the blockwork in the reveal for the door

The full picture shows that the contractor has built in a vertical DPC where the two wall leaves meet to prevent moisture tracking across. But in our ‘cropped’ part of the picture this is not visible – mortar has been smeared over the joint, making the vertical DPC useless at this junction.

The reveal has no insulation at all

Just solid masonry separated by a vertical DPC. This means that this part of the wall will be colder that the rest of the wall, resulting in condensation forming around this part of the structure – a case of ‘cold bridging’. Judging by the standards of workmanship, it’s quite likely that there is no insulation below the DPC either, meaning the same problems will happen around the skirting too. It’s important to think about cold bridging through any part of the structure but especially where junctions occur.

Further information

Use of an insulated cavity closer would have prevented these last 2 problems. For more information about preventing cold bridges, refer to our Registered Construction Details.

 

Please Note: Every care was taken to ensure the information was correct at the time of publication. Any written guidance provided does not replace the user’s professional judgement. It is the responsibility of the dutyholder or person carrying out the work to ensure compliance with relevant building regulations or applicable technical standards.

Comments

Damcor

Submitted 5 years 6 months ago

I tend to use Damcor insulated DPCs on jambs rather than Thermabate as this product makes fixings for window jambs difficult on site.

I assume this product is passed by BCOS?

(No subject)

Submitted 5 years 6 months ago

DPM not lapped at the reveal either. Cowboy!

(No subject)

Submitted 5 years 6 months ago

Very well spotted I am impressed by your man on the ground.

(No subject)

Submitted 5 years 6 months ago

Unbelievable that people still do not understand basics

(No subject)

Submitted 5 years 6 months ago

Nothing on the vertical part of the reveal below DPC level also. Taking the floor up to the outer skin is always a poor detail - extra insulation required and forces the installation of the frame into the outer skin with all the potential problems that brings at the reveals.

Webmaster note

Submitted 5 years 6 months ago

All comments posted at an earlier date to this one have been transferred from our old website.

DPC nightmare.

Submitted 3 years 9 months ago

I've started a bathroom refit for a customer but had to find the source of the damp issue first. Outside floor level too high so Im installing ACO channels, 2 vents had been cemented over so cleaned them out. I then find the DPC on the internal block work is 100mm HIGHER than FFL and I doubt the floor has DPM under it. Also I'd gamble on the DPC spanning the cavity and causing pooling. Any advice would be appreciated, cheers.

Reply

Submitted 3 years 8 months ago

Hello there

Sorry but to determine cause and solution for this problem requires a site inspection. We do not provide individual personal solutions and must recommend that you engage the services of a surveyor with suitable experience who can visit the site to advice further.

Kind regards
Barry, LABC

Cowboys

Submitted 3 years 8 months ago

The brickwork opening should be 15 ml bigger than the inside block work so there is a check for the door frame to but against

dpc

Submitted 3 years 5 months ago

My builder has installed 3 DPC`s One at correct ground level, one 8 foot high and another 20 foot high. Why have they installed 2 extra courses?

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