Should I Get External Wall Insulation When Re-Rendering?

A houses render is the covering that gives the building its external look. Over time, render cracks, flakes, and needs to be replaced. Increasingly, people are realising that this is the ideal time to add insulation to their properties to minimise costs and maximise the efficiency of their homes.


What are the benefits of EWI over re-rendering?

  • If your home requires re-rendering, then it’s the perfect time to insulate to save money. Combining the two projects significantly reduces the total cost.
  • When just rerendering, it’s necessary to remove the previous render before putting on a new coat. That can be pretty labour intensive as it’s designed to stick hard to the wall, as well as being a lot of materials that need to be disposed of.
    One of the benefits of an external wall insulation system is that it can be mounted on old render, regardless of the state of disrepair. That’s because the adhesive and mechanical fixings work in tandem. The mechanical fixings are long enough to penetrate the wall through the old render, meaning that you can avoid the expensive removal procedure.
  • As well as avoiding the need to remove the old render before rerendering, it also holds it in place for the lifetime of the insulation system. That means you don’t have to worry about it flacking, cracking or failing, as the EWI system over the top will ensure it stays in tact.


What kinds of insulation systems are suitable for re-rendering projects?

External wall insulation comes in many different varieties and buildups, each with its own unique properties:

  • EPS (expanded polystyrene) is one of the best value external insulation products on the market. It looks like large, lightweight grey boards. EPS is poular because it’s efficient, cost effective, and simple to install (though you shoulld still always use a professional).
  • Mineral wool is completely different. It’s a fibre made from spun rock, creating a dense wool that is mounted in compacted boards. Although it has a lower thermal performance than EPS and is therefore more expensive to get the same thermal results, it has grown in popularity in recent years owing to its non-combustible and A1 fire rating composition.
  • Kooltherm K5 is a newer and more expensive external wall ensulation product than either mineral wool or EPS. It’s thermal performance is among the best around,meaning that you need a lot less of it to get the same insulsation value as with other materials. This is ideal if you’re trying avoid builking up your property when insulation and re-rendering, but it does come with a sigificant price tag.
  • The most expensive external wall insulation product on our list is wood fibre insulation boards. Although it’s not as efficient at insulating as EPS, wood fibre insulation has some of the best ecological credentials around. Made from wood and wood byproducts, the materials used to create wood fibre boards are carbon neautral, plus the energy savings the insulation makes.


What render can I use for an external wall insulation system?

When adding insulation to your re-render job, you should be looking at thin-coat renders to seal the system. Thick-coat renders like Monocouche or sand and cement are not only too heavy, but also don’t have the flexibility of the thin coat renders. While some manufacturers do have moncouche systems that can sit on EPS / mineral wool we would strongly advise to stay well clear!