As luck would have it (or my lack of design experience), the kitchen extractor fan comes out in a bad place, close to the soffit vents into the cold roof at about head height. 

 

This might sound daft, but can the pipe be reduced in diameter and run down the wall outside the building, to make the water condense and run into the gutter?

 

Failing this are there dehumidifying cooker hoods? I think there are commercial ones. Is this practical in a normal kitchen?

 

Opening the window or running the dehumidifier are obvious other but clunky solutions. 

 

The house is not airtight and doesn't have MHRV, although I have read about single room units, if that could be another option?

 

 

Can you explain this better?

 

Are you saying the 4" pipe from the cooker hood is venting INTO the cold loft space?  It should not do that, it should be routed either to a 4" soffit vent ot a roof tile vent.

The pipe comes thru' the kitchen wall, into the cavity wall of the extension and then outside, just below the soffit vents (under an overhang).

 

Does that make sense?

Edited April 9, 20233 yr by Jilly

And what is the issue exactly? 

 

Are you worried about steam getting into the attic? 

2 minutes ago, Iceverge said:

And what is the issue exactly? 

 

Are you worried about steam getting into the attic? 

Yes, this particularly. Steam could get into the 50mm void of the cold roof of the vaulted ceiling and a flat roof, so I want to get the vapour to condense in a controlled manner.

Ah. 

 

The expelled gasses including water vapour will dissipate pretty quickly once outside and any slight breeze should prevent almost all of the steam from getting into the vents. 

 

Cooking is a pretty sporadic event with a fan running maybe 15mins per day, that's only 1% of the time. 

 

For decades gas boilers have been expelling steam under soffits, many hours per day and I've never heard of any issues. 

 

I can't see your situation being a problem. 

There is another I'm fussing about this... I have an external wooden shutter that is located right next to the vent and can't be moved, so again, I would love it to be away from the steam. 

What you doing to generate so much steam you are even thinking about it?

 

Our kitchen fan is just a recirculating one and we don't have any steam buildup inside the kitchen

Stick a directional cowl on it and simply point it away from the bits you don't want the extract getting to.

1 hour ago, Conor said:

Stick a directional cowl on it and simply point it away from the bits you don't want the extract getting to.

Or block off that bit of the eve vent.

I can’t block it off as the joist ‘bays’ need top and bottom air flow. It’s not a loft per se.