How rotten do my windows have to be

before replacing them?


How our experienced Building Surveyors can help you ?


If you are buying a property and need help or advice with regards to any property issue an Independent Building Surveyor can help you. We can help with problems ranging from wet rot and dry rot to subsidence and heave.

We can give advice with regard to building surveys, structural surveys, engineers reports, independent valuations and defects reports. Please free phone 0800 298 5424 for a friendly chat with one of our surveyors. We always like to meet you at the property during the survey and are more than happy to talk about the report and discuss any concerns you may have.

Rotting window, can this be repaired?


Should rotten windows be replaced or repaired?

A building survey that we carried out recently revealed the windows to be so rotten that when it rained you literally did get wet inside. Having said that when we inspected the windows we found only a very small number of them needed full replacement and most were repairable due to the quality of the original timber. It is far more economical for them to be repaired than to be replaced.

Rotten timber

Timber sash window

This is where deterioration is likely to occur but it can be repaired

Wet rot in sash windows


Rotten timber, is this wet rot or dry rot?

Often we hear that windows are old and need replacing. Ironically if they are old the last thing they need is replacing as they would usually have been constructed with good quality timber. By this we mean heartwood rather than sapwood or soft wood.

Victorian sliding sash windows will have been made of good quality timber

If you have original older style sliding sash windows from the Georgian, Regency, Victorian or Edwardian period then they will be made of good quality timber. If these windows are not maintained we tend to find that the paint peels and exposes the timber beneath and if neglected for a long time the timber beneath (depending on the quality) starts to rot. However it does seem to be that with older, good quality timber that they can be left for a long time before the rot begins.

Victorian sliding sash window

Sapwood defined

This is the outer soft wood of the tree trunk that contains moisture and sap that keeps the tree alive.


Heartwood defined

This is the inner darker wood that does not contain as much moisture as sapwood and so is more suitable for woodworking. It is also less susceptible to fungus than sapwood.

Victorian sliding sash window with timber visible where paint has peeled off

Free phone 0800 298 5424

Can I change the windows if it is a Listed Building?

Are you aware that different buildings have different listings? These are Grade I, Grade II * and Grade II. Our general comment would be no, you cannot change them but for more detailed information we would refer you to our articles on Listed Buildings, older properties and conservation areas.

Listed Buildings

Property Eras and Common Problems

Leasing a Listed Building

What do I look for before I start to replace my windows?

When carrying out a building survey we carry a knife and screw driver with us to allow us to physically check how rotten the windows are. Generally the area of the window that will have rotted the most will be the window sill or the base of the window. This is where we carry out our knife test at ground level. We used to use our car keys but many years ago we actually bent the keys doing this and had trouble getting back into the car! We now recommend a knife or a screwdriver.

Casement window which has rotted to the base

Flaking paint to window sill but window is in reasonable condition

The corner of the window should also be checked for rot

Knife Test Defined

This is where we literally push the knife into the window to check for rot. It is not rocket science!

Knife going all the way into a rotten window


What do the ovals or circles in our building surveys mean?

Within our reports we utilise a system of ovals and circles to highlight problem areas or characteristics within a property to better explain the issues. If this does not explain the issue completely then we can also use one of our sketches that have been commissioned exclusively for us for use in the reports.

Georgian sliding sash windows

Georgian sliding sash window


Even where the window sill and the lower sash is rotting it is still often worth saving the window

You would be amazed at how a good carpenter can repair a window. Also, providing the building is not listed or in a conservation area, you may be able to make amendments to a sliding sash window such as adding draft excluders and seals. It is amazing how removing a draft can increase the comfort level of sitting near a window.

This window is starting to deteriorate


This windows looks perfectly ok but has been filled and redecorated

Yes we do carry out surveys in the snow!


Modern timber windows, do they need regular maintenance?

Timber windows are generally considered greener as they are a renewable source. Unfortunately the best quality timber used tends to be in the more expensive windows and more expensive furniture and certainly not in the types of windows that are used by modern developers and builders unless the properties are of a very prestigious nature. We do find that timber windows from the 1970's, 1980's, 1990's and 2000's do need regular redecoration and they do deteriorate rapidly if not maintained unlike the older style windows.

Modern timber window


Can a plastic double glazed window be more economical than a timber window?

We can look at the different windows on several levels. Over the years timber windows have proved time and time again that they are long lasting. This is of course if they are maintained. From a Building Surveyors point of view they also have good structural properties and can be mended and reused. However it is this factor of maintenance that is a difficulty as many people do not feel that they have the skills or the time to maintain the windows. It is recommended that you redecorate timber frames every four to five years dependent upon location and other factors.

Timber window frame stained six years ago with stain peeling off

These Timber window frames were stained three years ago


Maintenance free windows

Anything that is advertised as maintenance free, which plastic windows are, has a major selling point. In addition to this older timber sliding sash windows are known for being drafty and this to some extent has been the same thought for some modern timber windows but this is not the case if they are fitted correctly.

Care has to be taken even with new timber windows to make sure they fit properly to ensure they are draft free


Double glazing salespeople are excellent salespeople

The benefits of double glazed windows have been sold again, again and again by double glazing companies. Interestingly from what we understand research shows that the windows do not meet many of these claims.

Plastic window without trickle vents

Trickle vents

Trickle Vents Defined

Trickle vents allow a trickle of air through, therefore stopping/reducing the likelihood of condensation occurring within the property.

Plastic double glazed windows are often claimed to be maintenance free but we would argue that very few things are maintenance free. Over time moss can impregnate into the plastic of the double glazed windows.

We have recently been in a property that had been built in the 1960's with metal windows. These had been replaced in the 1970's or 1980's with plastic windows and it is now necessary to replace all the seals.

Perishing rubber seal on inside of window

Misted window caused by the seal breaking in a plastic double glazed window


If you replace timber windows with plastic windows make sure you get the style right!


Sliding sash windows

Original timber sliding sash window that needs redecoration

Plastic window that replaced a sliding sash window but looks nothing like it!


Sliding sash York Windows

Original timber York sash window

York window

Horizontal sliding sash

This plastic window replaced a timber sliding sash York window!


Feedback and Testimonials

We have been on the internet for a long, long time and know that there is a lot of choice out there and would emphasis you use your common sense and have a look at examples of Surveyors surveys before you buy. Double check the Surveyor has the right experience and knowledge of a structural survey and the property problems that you have.

Pattern staining above double glazed plastic windows


Here are some of our other surveying articles that we hope will be of help to you.

Building Surveys also known as Structural Surveys

Windows and the Great Fire of London

Roof Windows, Roof Lights, Sky Lights and Light Tunnels

Heat Loss in a Poorly Insulated House

Why are our surveys better than the competition



Metal or crittal windows as they are generically known

The metal or crittal windows were very popular in the 1960's/ 1970's and are still used today but not as often. They tend to have been replaced with aluminium or plastic.

Crittall window from the 1960's


First aluminium double glazing

The first double glazed windows were made from Aluminium. Although they were in favour for much of the 1960's, 1970's and 1980's they are not used as much now for residential properties but are still commonly used in shops with either an aluminium finish or a proprietary painted coat finish.

Aluminium window with double glazing



Shop front with aluminium windows

Aluminium shop window with a painted finish


Windows without window sills

Window without a sill

Window without a window sill

Close up of window without a sill


Flat window sills

Sometimes flat window sills will tip water back into the window

Classic timber casement window with flat window sill


Bay Windows

Bay window

Double bay window


Always look above the bay window as a flat roof can leak

This is what bay windows are all about. Lots of natural light to have a good read!


Independent Surveyors

If you truly do want an independent expert opinion from a Building Surveyor with regard to structural surveys, building surveys, structural reports, engineers reports, specific defects report, dilapidations or any property problems such as Asbestos please contact 0800 298 5424 and we will call you back.


Our Good, Bad & Ugly surveys!

If you are in the process of buying a new home we would like to tell you about what we call our good, bad and ugly survey. This is a Building Survey also sometimes known as a structural survey. We have developed this over many years, in fact several decades. We have listened to feedback from our clients and amended and altered our surveys to make them easy to read and describe issues clearly. The key factor we believe is our Independent Surveys are easy to understand and written in plain English.


Chartered Surveyors with thermal imaging cameras?

Let's have a look at a sliding sash window through a thermal imager. Yes we do have thermal imagers and yes it can be dangerous Chartered Surveyors using thermal imagers if they do not have enough experience working with them. We have developed knowledge of thermal image cameras over the many years we have now worked with them. We have even given lectures about them at some universities.

Thermal image of a sliding sash window

Sliding sash window


Compare our website articles and compare our surveys

Have a look around our website to see the quality of our articles, for example this one, and look at the quality of our surveys (we are more than happy to send you an example). We pride ourselves on our professional standard and easy to read reports which we have been carrying out for many years on every age, type and style of property across the UK.


Examples of our unique surveys

If you would like to see some examples of our building surveys we are more than happy to send you these via email. The surveys contain photos, sketches and definitions that help to explain the specific problems that we find within the property.


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Reviews from clients on Commercial Building Surveys

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