UKH

I had a bathroom window replaced with a double glazed unit and noticed there was no trickle vent. The installers said they would put one in but that’d mean drilling the frame which I’m not keen on. I know they are required by building regs but how much value are they in a bathroom? My view is that when having a shower or bath they’ll be overwhelmed and I’ll still have to open a window and the rest of the time they just make the house more drafty. 
Should I bother getting the vent retro fitted? The house is big relative to the number of people in it and is by no means air tight anyway?

Don't worry about drilling the frame, as that's how they are all done. (I have done it)

Trickle vents do give important ventilation, but if you care about your house then you will do this anyway. The expectation is less so in rented houses.

Personally, I would make sure you have a decent extractor fan at the highest point above the shower.  Ideally through the ceiling and linked to a roof tile vent, to allow for passive ventilation as the wind passes over the roof.

Good extractors are centrifugal,  cheap ones are axial.

Thanks Steve, that’s rather thrown the cat among the pigeons as I was just after affirmation that trickle vents in bathrooms don’t add much! Now I have to rethink!

Not sure when you had the new window installed, but my understanding is a window now 'must' have a trickle vent in when replaced/installed. We are just having a new window in and have been informed by the installer that it has to have one (we considered not for cosmetic reasons, but now think its crucial anyway for some air flow etc). 

Don't modern units effectively have a trickle vent, by allowing them to be locked shut with a slight air gap around the frame?

Yes, but in theory you also need a full time passive vent for when the window is full 'closed'. Which of course can still be manually closed to stop the trickle function, so they really don't make much sense!

We have a dMEV fan in out bathroom which constantly draws out a small amount of air. For this to work properly you need to ahve the bathroom trickle vent perminantly closed. Most new builds have these fitted now. You can also get these with a heat exchanger on them now a days too (ie heat excahnger just on the fan not a house wide solution)

My understanding is that, at least in Scotland, Building Regs dictate only a ventilation cross section area for any give room size - I think its volume of room from memory, rather than floor area. Locating this in a window frame is often most convenient, but it can be located anywhere else that is convenient/ appropriate.  At least that's my experience based on dealing with our building control officer when we built an extension 10 years ago. We have a timber clad / timber framed extension so it was vey easy to cut a hole in the wall an put the vent somewhere less obtrusive than in all window frames.

Surely you still need a trickle vent somewhere to allow air into the house, or does it assume most houses are inherently 'leaky' and allows the slight negative pressure to draw air into the house?

the idea is it very slowly pulls air from the house in to the bathroom and extracts it, as the bathroom is often wet this helps to lower humidty throughpout the house. Idealy there should be trickle vents in the other rooms open. If the bathroom one is open it just pulls it from there so does not even properly vent the bathroom.

I've just refreshed myself on Part F of the building regs and I have to say it contains conflicting guidance. The general principle when doing work on an existing dwelling, such as replacing a window, is to make the ventilation no worse than it was before. If the old window had a trickle vent, the new one must have one. However if a bathroom has a continuous background extract fan, the window must not have a trickle vent. Air infiltration in leakier buildings contributes to the ventilation required, so you may not need one anyway. I'm paraphrasing, but as ever there is more than one way to meet the requirement. Personally I think that trickle vents are nearly always poorly designed and cause cold draughts so I would avoid drilling holes in your new window if you think you have another option. Did your window installer provide a FENSA certificate?

Well the die is cast and tomorrow I’ll have a new trickle vent based on this thread but I must say I’m still cynical for the reasons I outlined in my first post, mainly the house is not short of draughty and when the bathroom is in use a trickle vent is not going to cut it especially as during the months it is most required humidity outside will be pretty high. I can see their point in bedrooms

Personally, I went for a Kair Heat Recovery Room Ventilator in the bathroom. It continually extracts and brings in air through a heat exchanger and only cost me 100 quid used. It has made a massive difference to both humidity and the actual temperature of the bathroom, it used to have a vent that was plenty good enough to lose most heat and not remotely good enough to stop mould.

Definitely the right choice!

( been building for over three decades)

I'll weigh in on this one. I run a small window installation business and I'm Certass registered so here is the current guidance.

All replacement windows must have trickle vents to improve the air quality.

Here's the view of the industry generally speaking. Trickle vents ruin the A rating of the window and we feel the homeowner will lock the window down in the night vent position if they feel the need for venting the room. The current rules specifically state that a locking night vent does not qualify as ventilation and that trickle vents must be installed with the window. I think that is a load of rubbish but I fit trickle vents to all my windows because it is the rules. The consumer can't sign a disclaimer removing the responsibility of the installer, this situation was clarified in writing to all installers via the regulators.

Expanding foam I'm told can seal up trickle vents, just heard like.

We had double glazing fitted several years ago.  Non of the windows have trickle vents.  Where necessary, such as the bathroom, the window is left ajar.  There's also a fan, which when windy blows in reverse.  

We also have a fireplace.  This involves venting the whole of the room with a great big hole up to the chimney.

We have no damp or condensation issues and as neither Mrs Billhook, myself or any visitor has collapsed due to poor air quality I cannot say its on my list of things to worry about.