Date posted: 22nd May 2015

Trickle Vents

What are trickle vents?

A trickle vent is a small slot/opening in a window or building envelope component, that allows small amounts of ventilation (trickle ventilation) through a window and/or door when its is closed. They will help avoid problems associated with poor ventilation, like condensation. Well, this is the reason we are told we should use them!

My personal opinion on trickle vents is well known with KJM's staff. I really don't like them. For years and years we have been trying to improve the thermal performance of windows, with the introduction of low e glass, argon filled units and today... triple glazing, In my 35 years within the industry we were originally selling double glazing where the glass had a U-value, no better than 3, today that measure has dropped to 0.6 with triple glazing, so about 5 times better thermal performance than back in 1982, a considerable gain. 

Why do we have trickle vents?

This increase in thermal performance is where the problem began. When I was a child I don't remember words like loft insulation, cavity wall insulation and double glazing. I do remember single glazed windows with ice on the inside, draughty floor boards and a howling gale coming through the windows and doors, our central heating was a fire place. As time has moved on, we have tried to become more energy efficient and this has meant better insulation, draught-proof windows, doors and floors. So in this time, we have sealed up our houses and made them warm with central heating. Modern living can also mean more people in smaller spaces,tumble dryers, radiators, house plants and more showers/baths, all examples of how to add moisture (warm - water ladened air) to your home. Couple that with the fact that some of us don't open windows so much now, for security and insulation reasons, we then have a problem with condensation, moldy walls etc.

This is the reason trickle ventilators were specified in the 90's. They were required to meet Building Regulations on all new properties and extensions. The law today is that we must put them back if they were specified in the original specification, so most housing that has been built in the last 20 odd years will need them. So if you are thinking about replacing your old windows which already have trickle vents, your new windows will need to have them too (assuming they were required under the original building regulation requirement when they were installed) The new vents should offer at least the same capacity as the existing outgoing vents. If you are not sure about the size of your existing vents, remember that all habitable rooms (bedrooms, living rooms etc) should have a minimum of 5000mm2 of free area ventilation and all wet rooms (Bathrooms, W/C etc) should have a minimum of 2500mm2 of free area ventilation. To give you an idea, one trickle vent usually provides 4000 sq mm of ventilation. 

What I don't like about trickle vents

Well firstly trickle vents are normally fitted to the head of the frame or the top of the sash, this means they clear for all to see! They are in my opinion ugly. Secondly, although they are supposed to provide controlled ventilation, they are generally made of thin PVC and are not that great at holding back the worst of the UK's wind and winter weather. Finally, they are a major source of noise intrusion. In general they are not great quality!

Do people use trickle vents?

In my time in the industry, I have seen a lot of tricks, including trickle vents being filled with mastic, expanding foam used and the routed hole through the frame taped up to stop these problems. In general they don't seem to be popular. With almost all our window systems, we have as standard a secure night vent facility that customers can use and, of course, the obvious thing is to open your windows. I still recommend to customers that they keep rooms with a high moisture content (like bathrooms and kitchens) the internal doors are shut while using them (so the warm moist air stays in one place). When the family has finished using the bathroom, keep the door shut and open all windows in that room to provide a maximum air change for as long as possible. This should reduce condensation problems. Remembering that wet towels left on warm towel rails/radiators will "pump" the moisture from the towels back into that room.

Trickle vents conclusion

So trickle vents are terrible for noise intrusion, look ugly and let the heat out. We as an industry have been encouraged to make our products as thermally efficient as possible, trickle vents seem to do the exact opposite to that. Kitchen and Bathrooms are good locations for the use of trickle vents because of the condensation problems, but nothing beats opening your windows! That said ground floor or easily accessible windows, that are open are a security risk. I do believe the choice should be with the homeowner, unfortunately, I am not a UK law maker.

The Glass & Glazing Federation has a publication on Trickle Vents - You can download  this free Guide to trickle vents

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