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Can I Install New Windows after EWI?

Installing windows before or after EWI?

We receive many questions from customers about whether it is possible to install new windows at a later date than their EWI installation.

It’s a tricky question, because in an ideal world it’s best to leave the external wall insulation undisturbed by installing new windows first. However, for some homeowners this just isn’t possible for reasons pertaining to added costs, or simply because their current windows at the time of installation were in a good condition. It is possible to install new windows after your EWI installation, but we would really advise that extra care is taken.

When installing EWI, new windows are often installed before the insulation to ensure that the EWI is fit snug against the window panes. The best kind of windows to install ahead of your EWI installation are windows with trickle vents. This is because with the added insulation, gaps in the windows can be blocked up – which can increase the chances of condensation build up, so trickle vents are fairly necessary to alleviate this.

It does make sense to install new windows before you go ahead with an EWI installation, because it saves you having to bother with carefully removing the windows at a later date – at the risk of damaging the insulation. However, we are aware that often the windows may be perfectly okay at the time of installation, but for varying reasons may not outlive the 25 year life of the external wall insulation.

How do I install windows after EWI?

Unfortunately, replacing your windows after external wall insulation is not the easiest job and you will need to make sure that you choose a highly rated professional to carry out the task in order to avoid as much damage as possible.

If you are very lucky and your windows installer does a perfect job and measures the windows exactly right, then they can be easily fitted into the wall and then sealed up against the insulation. Unfortunately, it is really common for windows to be slightly under or over sized and that means either cutting back some of the insulation or adding insulation to fill out any gaps. In these situations it’s unlikely that you will get away with it without any marking or scarring of the external wall insulation, or having to repair it which is very difficult to do.

As you can imagine, this is all going to add an extra cost to the job. So it’s definitely worth thinking about how old your windows are and whether it’s viable to get them replaced before your external wall insulation installation.

The key thing is to ensure your installer is as careful as possible to not damage the rendering when taking the old windows out. We recommend removing them from the inside of the house to avoid knocking the render on the reveals. If any damage is done to the reveals, this is usually fairly easy and cheap to repair. Unfortunately if any damage is done to the main elevation, this can prove difficult to patch without leaving a scar on the wall. And it may be necessary to re-render the whole elevation.

If you have any further questions, then please comment below or call our technical team! Stay tuned for more content, we upload a new blog post every Tuesday and Thursday all about EWI; from answering customer queries to detailed product information.


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