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Dry rot windows – causes, symptoms and treatment

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Dry rot is a serious problem for timber frame windows and doors and can be extremely damaging to your property. It is caused by water ingress, a lack of ventilation and high relative humidity. It is vital to immediately tackle a dry rot problem once diagnosed as it can spread rapidly and quickly cause significant damage to your home and your wallet!

This quick guide will help you identify the signs that you might have a dry rot problem and provide advice as to what to next.

How to spot signs of dry rot:

  • Dried out shrunken wood – dry rot removes moisture from wood, as such if there is a dry rot problem, wood will appear dried out, brittle and warped. Commonly the wood will crack in a ‘cuboidal’ manner.
  • The growth of mycelium – a whitish/grey substance that resembles cotton wool. Mycelium usually occurs within the later stages of dry rot development.
  • A musty damp odour – although a damp musty odour may not indicate an issue with dry rot, it does indicate an issue with dampness, which then can be a precursor for dry rot if not treated.
  • Sporophore/fruiting bodies – easily recognisable as a distinctive fungus appearance that resemble pancakes with a rusty deep red colour (the spores).

What’s the difference between wet and dry rot?

It is important to understand the different between dry rot and wet rot. Wet rot requires a higher moisture content to grow on timber; around 50% moisture compared to dry rot which only needs around 20%. Therefore, it is much easier for dry rot to germinate on timber window frames at lower levels of humidity that are standard in the home. In addition, dry rot is more of risk as it can spread from the initial germination spot and attack other areas of the property, whereas wet rot tends to be localised and affects timber at the damp source.

If you think you might have rotting window frames but are unsure whether the cause is from wet or dry rot, don’t hesitate to get in touch with one of our experts who can run tests to determine the issue and suggest the best treatment.

What are the impacts of not treating dry rot quickly?

If you don’t act quickly, dry rot can easily spread to other areas of your home causing damage to other timber frames as well as potentially to structural timber. If left too long, damage can mean whole windows will need replacing, which is much more costly than catching and fixing the problem early.

How to treat dry rot in timber window frames

It is possible to treat dry rot yourself however it is not recommended due to the high level of skill required to ensure all of the dry rot is removed and to prevent further spreading, whilst also ensuring a perfect finish, with limited damage to the rest of the window, and prevent devaluing your home.

At IWP Dansk we have over 35 years’ experience restoring and replacing timber framed windows to ensure beautiful results that maintain the quality of your windows for years to come.

If you suspect a dry rot is present in your window or door frames it is first important to first have a specialist rot survey. We provide a full rot survey to confirm that dry rot is in-fact the problem (and not wet rot or another issue), identify the cause of the problem, and establish a suitable treatment programme.

We will then replace the badly affected timbers and treat any timber that can be retained with a fungicide to eliminate the wood rot problem. We will then use our specialist resin repair products which last as long as the substrate.

If you’d like any more information about the detection, prevention or treatment of a suspected dry rot problem with your timber windows or doors, please don’t hesitate to contact our support team at

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