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.
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:
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:
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.
Render is another common weak point. Go for a proven system and make sure to use skilled tradespeople, as well as follow the manufacturer’s instructions. Where necessary, in particular on south-facing elevations, expansion joints should be included to allow for expansion and contraction due to thermal movement.
If your property is in a highly exposed area, then consider using concrete blocks to achieve a good key for the render.
A change in British Standards has helped reduce the number of issues with roofing in recent years, but it remains the biggest problem area for waterproofing a house shell. Common defects include:
Inaccurate setting out of slates and tiles. The installation must allow for movement and the correct overlap into guttering.
The best way to control the risk of these common defects appearing is to be aware of the main flashpoints.
You should also use competent contractors, properly trained trades and capable project managers (PMs) who will take the care and attention to ensure the quality of work is up to scratch.
At the end of the day, nobody wants to have to deal with claims or suffer the inconvenience of rectifying problems part-way through a build.
Andy Butchers is a building surveyor with over 25 years’ experience in the construction industry. He 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, the technical company for Build-Zone and Self-Build Zone.