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WATERPROOF ENVELOPE SNAGGING – Rising and Penetrating Damp.

May 1, 2019

WATERPROOF ENVELOPE SNAGGING – Rising and Penetrating Damp.
 

Now is the time for change because the problems do not.

 

Most warranty providers will tell you that the majority of claims are as a result of penetrating damp through roofs and walls - usually as a result of poor workmanship rather than the  actual failure of components / materials. 

 

 

 

By understanding the issues over many years through dealing with Selfbuilders and Contractors (including as a Loss Adjuster) it is clear that Waterproof Envelope Snagging should not only be carried out pre-completion, but it should form part of a robust pro-active regime from the start.

With the use of competent contractors, properly trained trades people together with capable and experienced PM’s (project managers) you can control or at least minimise these common defects in buildings. At the end of the day no-one wants to have to deal with claims and suffer the inconvenience of rectifying problems part way through.

 

Rising Damp - Foundations – fortunately these days situations of rising damp problems are rare but of course it is important  to pay attention at this stage to ensure the building is properly founded.

Common issues are a lack of site investigation works being carried out which would normally provide an insight as to the prevailing ground conditions -- leading to potential problems with incorrect foundation depths, changes in design resulting in substantial additional costs to rectify matters.

The correct positioning and fitting of the dpc (damp proof course) can be a major contributing factor to Rising Damp. Some  of the common problems being:-

  • the incorrect use and cutting of the dpc ( damp proof course) cutting it too short or cutting it into awkward corners or making good with offcuts.

  • the poor lapping of the dpm (damp-proof membrane) to the dpc (damp-proof course)

  • the use of low-level cavity trays

  • the finished ground floor level where the dpc is too low

  • ramps and access for the disabled bridging the dpc

 

Water Penetration – Cavity Walls

 

One of the major problems is water penetration through the walls themselves and attention needs to be paid in particular to the construction of the walls.  

Problems that quite often need addressing include:-

  • the bridging of the cavity with mortar “snots”

  • insufficient cavity width

  • insulation not installed correctly or using the wrong material

  • incorrect positioning, missing or wrongly installed wall ties

  • correct fixing of cavity closures, movement joints, cavity trays and lintels

  • change in the characteristics and colour of the bricks

  • correct window installation –

  • Make sure the windows are sealed with a good quality mastic – under the Cills or better still consider building the windows and doors into the structure if possible

  • Render: make sure you follow the manufacturers instructions &/or use a proven system and skilled tradespeople. Where necessary use expansion joints particularly if you are facing South - to allow for expansion and contraction due to thermal movement. If you live in an highly exposed area then consider using concrete blocks to achieve a better key for the Render (as is commonly done in Ireland for obvious reasons!).

 

Water Penetration through Roofs is the biggest problem. It is true to say that this has been helped in recent times by a change in the British Standards with regards to roofing.

However common defects that are still found include:-

  • the accurate setting out of slates and tiles to allow expansion, movement and the correct overlap into guttering

  • incorrect fixings of the roof ‘finish’

  • incorrect mortar strength – sometimes you will see the same mortar used on the ridge as is used on the gable ends………and then the mortar just drops out leaving gaping holes!

  • installation problems with stepped cavity trays, lead flashings, chimneys and flashing kits for Velux windows

  • lack of bracing and restraint of timber trusses

  • incorrect insulation positioning causing cold bridging and condensation

  • wrong or incorrect fitting under felt to pitched roofs

  • incorrect positioning of gutters and down pipes

  • build-up in flat roofs causing interstitial condensation

  • flat roof finishes and waterproof make up, drainage outfalls, parapet construction etc.,

 

More information

 

Andy Butchers is a Building Surveyor with over 30 years’ experience in the construction and Loss Adjusting industry and regularly shares his knowledge to help self-builders and renovators avoid and overcome issues on their projects.  He is a Director of Build-Zone Survey Services Ltd, the technical company for Build-Zone and Self Build Zone.  Call 01732 744186 or visit www.bzss.co.uk to find out more.

 

 

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