Waterproof Envelope Snagging & How to Avoid Water Ingress Problems

Ask any warranty provider about the biggest area of claims with a new build house and the answer will be the same: the majority are due to penetrating damp through roofs and walls.

Frustratingly for self builders, these problems are eminently avoidable, as they’re usually caused by poor workmanship rather than actual failure of the components or materials.
Waterproof envelope snagging is, unfortunately, very rarely carried out.

If my experience of working with self builders and contractors has taught me one thing, it’s that it’s important to implement a robust, proactive regime, from the start of a project right through to completion. Here’s a closer look at the key areas to consider.

Rising damp & foundations

Instances of rising damp are rare these days, but it’s important to pay attention at the foundation stages to prevent problems.

A common issue is a lack of site investigation works. Normally this would provide a good insight into prevailing ground conditions. If it’s not done, you could end up with incorrect foundation depths, which will require design changes to rectify matters and incur substantial additional costs.

The positioning and installation of the damp proof course (DPC) is another major factor when it comes to rising damp. Some of the most frequent problems are:

• Incorrect use and cutting of the DPC, such as trimming it too short, cutting into awkward corners or trying to make good with offcuts.
• Poor lapping of the damp proof membrane (DPM) to the DPC.
• Use of low-level cavity trays.
• The DPC being fitted below the finished ground floor level.
• Access ramps bridging the DPC, allowing moisture to cross over.

Water penetration in cavity walls

The main external walls of your new home need to be designed and built to withstand water penetration; but it’s amazing how often mistakes are made. Issues that quite often need addressing include:

• Bridging of the cavity with mortar snots (lumps of cement).
• Insufficient cavity width.
• Poorly installed insulation (or use of the wrong material).
• Incorrectly positioned, missing or wrongly installed wall ties.
• Mistakes in the fixing of sundries such as cavity closures, movement joints, cavity trays and lintels.
• Changes in the characteristics and colour of the facing bricks.

There’s more to consider, too. While it may sound obvious, windows must be correctly installed, for instance. They need to be the right way up and facing in the right direction, which isn’t always the case! They should be properly sealed with good quality mastic, too, including under the cills.