Guest article from Joe Malone BSc(Hons) ICIOB
'I have worked on a high number of complex building defect investigations over the last 6 months and most of my conclusions have proven that poor build quality and hidden latent defects are to blame'
My work as a consultant building pathologist has led to me forming a strong view that build quality simply isn't adequately managed anymore. I have worked on a high number of complex building defect investigations over the last 6 months and most of my conclusions have proven that poor build quality and hidden latent defects are to blame. Some might blame the demise of the traditional clerk of works role to oversee build quality but I have formed a view that clients are simply becoming too trusting. It costs money to run with a client side surveyor and why bother when you're working in 'partnership' or 'collaboratively' with your contractor? They allow contractors to self manage build quality or they trust to building control inspections and take further comfort in the fact that they purchased an NHBC guarantee. You may well be shocked at some of the things I encounter during my survey work so I thought I would give you a flavor by way of sample of some case studies on recent survey reports I carried out in London.
Case Study 1. Overflowing with Defects
You will notice the decorative spoiling to the underside of the balconies in figure 1. The square steel stanchion you see is also the rainwater downpipe that the balconies drain into. There is only one outlet for each balcony and the balcony is covered with timber decking that sits above the asphalt coating on a Harmer Uni-ring raised floor support system, as seen in figure 2 below. This was included in the build specification that I managed to get hold of. It was rather a shame that the clients quality control manager (if they had one) didn't also get hold of it because then the client might have seen that the system was completely omitted and replaced with larger timber battens directly screw fixed through the bituthene membrane on the balconies.
This Harmer system was meant to provide a dual role:
1. To raise the timber firrings off the balcony tray to allow rainwater crossflow to the single balcony outlet.
2. To provide a fixing system for the timber firrings, thereby preventing the bituthene membrane from being punctured.
Fig 2. Harmer Uni-ring system that was meant to be installed on balconies - Source: http://www.alumascroofing.co.uk
Screw fixing timbers directly through the bituthene membrane on the balconies was not a sensible thing to do but the second issue was that solid lengths of timber battens fixed to the floor meant that there was no crossflow of water to allow it to reach the single drain point. The net result was that rainwater spills over the edge of the balconies and tracks back underneath balcony ceilings causing the decorative spoiling that can be seen in figure one. This development is circa 10 years old and the problem has existed and remained undiagnosed from day one. I am still staggered that the developer managed to get away with this.
Case Study 2: The Lost Art of Parapet Walls
This case proved two things, one, that the high cost of property does not guarantee a better build quality and two, that no one seems to know how to build a correctly detailed parapet wall anymore.
I was appointed to investigate the cause of water ingress into a very expensive residential block overlooking the Millennium Dome. Water ingress was affecting one flat in particular below the top floor penthouse. As such most of investigation work was focused on the top floor (See figure 3 below).
A perimeter parapet wall surrounded the balcony and there were a couple of visual tell tales that made me suspect that all was not well with the parapet.
1. No visual sign of a dpc under the copings.
2. Cracked mortar joints between copings
3. No sign of weeps on either side of the parapet wall
4. Parapet stone drips were compromised on the outer ledge by the installation of fibreglass decorative cornice that was too wide for the application and therefore covered the coping stone drips causing significant water staining on the outer face of the parapet wall.
It was obvious to me that a coping would need removing to fully inspect the parapet and you can see in figure 4 below what I uncovered. This is as bad as it gets for parapet wall detailing. The dpc was too narrow for application, it was sagging into the cavity due to the lack of a hard support to bridge the cavity and there was no effective cavity tray or drip details installed in the parapet. I even found a couple of old joist hangers thrown into the cavity.
You may be able to see in figure 4 how the timber batten on the outer ledge compromises the drip detail on the underside of the parapet coping stone. The fibreglass decorative cornice was fixed to this.
I'll let you hypothesize what a very nice penthouse flat with this sort of view might cost but it had no relationship to build quality, which was quite shocking.
In next week's article I will provide some further examples of poor building practice which could have been avoided if the build quality was managed more effectively.
Joe Malone BSc(Hons)ICIOB
Malone Associates Ltd
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