Condensation Problems

Have you checked Trickle Vents in your windows?

This article looks at a specific defect that we come across quite often which is condensation in properties. We also carry out building surveys, structural surveys, and structural reports together with engineer's reports, specific defect reports and dilapidations on commercial properties.

If you need help and advice with regard to any property problems please feel free to call us on free phone 0800 298 5424 for a friendly chat regarding anything property related.


The importance of the trickle vent

When conducting residential building surveys, structural surveys and commercial building surveys we as Independent Surveyors we are always pleased to see properties that have trickle vents. We are aware that you may not even know what a trickle vent is.


Trickle vent – sometimes you have to look very hard to see a trickle vent

What is a trickle vent?

A trickle vent allows a trickle of air into a property which then gives the room air movement. The trickle vents that we are discussing here are situated in windows and sometimes they also have an operating device that allows them to be opened and shut.


Trickle vents to top of window

Adjustable trickle vents

Adjustable trickle vents can, as the name suggests, be adjusted to allow a trickle of air to ventilate a room. The trickle vents are opened and closed by hand and can be found at the top of a window.


External view of window with
adjustable trickle vent


Open adjustable trickle vent


Closed adjustable trickle vent

Trickle Vents Defined

Small vents to the windows to allow air movement inside the property to stop a build up of fumes or humidity.


Trickle vents in a house
Sketch shows cross section of house

Added on trickle vents

Sometimes condensation can be such a problem and air movement is required to help resolve it that we see trickle vents have been added onto windows.

For example on this converted building that has been divided into many apartments there are condensation problems. To help to resolve this trickle vents have been added to the old sliding sash windows which is ironic as sliding sash windows are renowned for being drafty. However when this property was refurbished and the sliding sash windows improved then they were no longer drafty and there was a problem with lack of air movement and condensation occurred.


Added on trickle vent on a sliding
sash window

Close up view of added on trickle
vent to sliding sash window

Hidden Trickle vents

Interestingly enough you will probably walk past windows which have hidden trickle vents present which is an everyday occurrence in more modern properties.


Hidden trickle vent Can you see a trickle vent on this window?


May be this is a better photograph to see a hidden trickle vent – you have to look very closely at the top of the window to see the trickle vent


Closer view of hidden trickle vent

Why is it important to have trickle vents?

It is important to have trickle vents because trickle vents give ventilation into a property which is a constant trickle of air which does help to create air movement. We often see properties where trickle vents have been blocked up and this is not recommended as it means that condensation is much more likely.

Trickle vents are not the complete solution to condensation but they do help.

Why is it important to ventilate a room?

Airflow is important in a property to prevent condensation and dampness from occurring this can be helped with the presence of trickle vents when they are used regularly. In the winter months when windows and doors are often kept closed for long periods the small trickle vents allow air in and out of a property ensuring airflow and thereby helping to prevent condensation issues.


Trickle vent

A bit more about condensation

Condensation is where humid air from kitchens, bathrooms and drying areas then transfers to colder areas and ultimately meets a cold surface which it then condenses on.
Trickle vents help to cool the air and add less humid air in.


Sketch shows cross section of house with
air movement

Windows without trickle vents

We frequently come across during the course of carrying out independent structural building surveys of properties without trickle vents.


Window without trickle vent

Take care when dealing with double glazing companies

Often replacement window companies selling double glazed windows from what we would term the cheaper end of the market install windows without trickle vents. When it comes down to cost every penny counts and if they can reduce the number of things they do by not having trickle vents for example then they can lower the cost.

Whilst we do not know, the actual cost of a trickle vent is it has to be relatively inexpensive as it is such a small element in the window as a whole. However our experience is that often double glazing window companies do not include trickle vents making the replacement windows without trickle vents cheaper for the customer and thereby securing an order but giving little thought to the future of the property, ventilation and the possible condensation that can occur.

Please see our surveying articles on buying property

Structural Survey
Buying a house

Add trickle vents to your windows and doors

We always recommend having trickle vents in windows particularly as today we like to heat our houses to almost the point where we wear T shirts all year round and very rarely open windows to vent a house. Trickle vents allow a trickle of air into a property although as you can see from the vents sizes this can be very minimal.

Back in the 1960s

Back in the 1960s we used to have far bigger vents and these were termed as room vents. As we understand these were actually a legal requirement by Building Regulations.


1960s room vent

High level air vents

High level air vents allow airflow to ventilate a property


High level vent added to a Georgian property Can you see them?


High level vent added to a Listed Building is unusual we would normally see a square vent


High level vent

Independent Surveyors

If you truly do want an independent expert opinion from an Independent Surveyor with regard to building surveys, structural surveys, structural reports, engineers reports, specific defects report, dilapidations or any other property matters please contact 0800 298 5424 for a friendly chat with a surveyor.

Commercial Property Surveyors

If you have a commercial property, be it leasehold or freehold, then you may wish to look at our Dilapidations Website at and for Disputes go to our Disputes Help site .

We hope you found the article of use and if you have any experiences that you feel should be added to this article that would benefit others, or you feel that some of the information that we have put is wrong then please do not hesitate to contact us (we are only human).

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