I am currently getting quotes for windows and doors to our new extension (one room to be used for living/dining and as a kitchen ca 6m by 8m)

Trying to spec for the most energy efficient windows/doors, but does the U-value not rise when a hole is then punched through the window to insert a trickle vent?

Building control said I need 8,000mm² for trickle ventilation but that I did not have to place this in the windows. Has anybody tried putting trickle vents in the wall? Are the trickle vents even that big a problem for heat loss? What is the best way to do this? And if I have to include trickle vents in the windows is there a best way of doing it?

Thanks for the info, squowse, I'll just have to accept the trickle vents in the windows then. At the moment the old part of the house is as air porous as it can be without actually being drafty - if you ignore the odd one through the living room floor but we are planning on insulating the bungalow and getting it as airtight as possible. Without having the money for mech HRV, condensation could, of course, become a problem but I honestly struggle in understanding the reasoning behind this. What's wrong with opening my windows every morning and ventilating that way?

Our friends in Germany had to install MHRV as their house is so airtight apparently that opening the windows in the traditional way would not provide enough ventilation but trickle vents would not be sufficient there either (besides sabotaging their efforts to keep heat loss to an extreme minimum). Anyway, ours is a 1930's bungalow - no hope of reaching that level of insulation/draft proofing!

Trickle vents in windows are not compulsory. I've made a great many windows and none has a trickle vent. What is required under the Buildings Regulations is adequate ventilation. Trickle vents is just one of the alternative means of achieving it. Airbricks, passive stacks etc....

Never live in a completely sealed houe - you will die.

Trickle vents are usually put in the head of the window so can be hard to reach. And yes it does seem ridiculous in insulation terms to make a hole through a frame. They can be semi-concealed by venting them into the gap between sash & frame on the outside.

Many window fastener systems have a 'night vent' position where the sash can be locked when open a small amount - in my experience some bco's have accepted this for statutary background ventilation and some haven't.

Thanks all for the comments

ali.gill - read that doc, very informative, thanks. Now I know what passive stacks are.

squowse - will ask the suppliers about the trickle vents on their windows. Apart from the heat loss, I think they are ugly and impossible to keep clean, turning fairly mucky inside very quickly and looking especially bad from the outside on the white frames (which is what we'll have again probably)

biffvernon - I have decided to look into airbricks and passive stacks. I had a larder cupboard in the kitchen in my first house which had only three walls, on the fourth were two airbricks. Absolutely brilliant for keeping food stuffs cool, increased lifetime for my not-in-the-fridge fruit and veg quite a lot. Thinking about fitting airbricks and then build a larder over it. I know this defeats the purpose of the trickle vents but I open the windows every morning after getting up - trickle vents or not, religiously, I might add. There isn't a single house with air vents on the windows in Germany where I spend a lot of time and they do not have any undue problems with condensation. Everyone just opens their windows first thing in the morning for 5 to 15 min (whatever the weather). PassivHaus buildings and anything close to zero energy level, however, have mechanical ventilation with heat recovery.

rogerwhit - have asked my BCO officer, they will not accept the night vent position in lieu of trickle vents but I don't have to put them on the windows.

fostertom - thanks for the link, I didn't want to clutter the quote/cost and supplier thread any further. I don't know how to move my comment from one thread to a new one but after reading your original thread which is now running at 230 comments, I wanted to try to keep that one to a single issue thread.

fostertom: well, I agree with you on principle but I have a friendly and reasonable BCO who showed himself quite interested in and understanding of trying to build a lot greener than is considered normal locally, so can I join after we're done, please?

I thought that night-latching windows were specifically allowed? I'll see if I can remember where I read that.

As another alternative, a friend lives in a modern flat with no trickle vents in the windows. Instead there's a hole in the wall (about 150 mm dia, I think) covered with an adjustable plastic stopper. This has always struck me as a better idea, not least because it's easier to do a neat job of blocking it up!

Why dont you introduce your BCO to this and other related threads on the forum and then persuade him that you are well aware of the neccesity for ventilation and the dangers of inadequate ventilation. If he feels you understand the issues and realises that his coleagues around the country are happy to follow an alternative path, he may relent.