Ventilation of chimney cavity - how?

[SJRSJR]

Hello.

Years ago, to make way for a loft conversion, an internal chimney stack/breast was removed and taken down to the floor level of the loft. There’s no ventilation at the top nor in the bedroom it passes through.

On the ground floor room is an unused fireplace that I’d now like to block off. I’ve swept it but will the cavity still need ventilating and if so, is there anything other than the bog standard vents on the wall?

The opening is flush with the wall and there’s quite a deep void below the floor so could I vent into that?

There are no problems with it currently. Would it also need an outlet somewhere else to create air flow?

Thanks

 

[aveatry]

This came up a while ago and the best way was to vent via the void below.
You could keep the opening but create a false wall inside it with the resulting space attached to the the void.
I have dove similar. If you go straight across the old fireplace with skirting board than make that height the height of its internal floor then hidden underneath you can cut away the hearth that you need to to expose the void underneath, you can do this right at the front of the fireplace just behind the skirt.

 

[^woody^]

If this flue is internal, i.e. surrounded by rooms which would be heated, then there would be no need to ventilate it as the condensation risk is low.

Otherwise, common guidance would be to ventilate it but that may bring specific challenges which may mean it may not be practical - in which case it may be better to either wait and see if there are any adverse effects over time and then deal with them if need be.

You should not vent a flue from the ground floor into a bedroom above, the floor void or anywhere else except direct to external air. Otherwise, you create a risk of fire/hot smoke spread and may create condensation issues elsewhere in the building.

 

[SJRSJR]

Thanks for the replies.

If you go straight across the old fireplace with skirting board than make that height the height of its internal floor then hidden underneath you can cut away the hearth that you need to to expose the void underneath

I can’t quite picture that, does that mean I would keep an alcove? My preference would be a flat plasterboarded wall. Could I just dig down inside and though to the void within the room, then conceal with plasterboard and skirting?

You should not vent a flue from the ground floor into a bedroom above, the floor void or anywhere else except direct to external air.

Venting externally doesn’t seem possible. The top is under the loft floor. Maybe I plasterboard it and see how it goes.

Either way, if ventilation was needed would I need two ´outlets’ to create airflow, or would a decorative plaster vent in the plasterboard be enough?

Thanks

 

[Alastairreid]

You don't need a vent in your case as it would only introduce moisture from the room into the sealed flue. Woody explained above.

 

[aveatry]

Thanks for the replies.

I can’t quite picture that, does that mean I would keep an alcove? My preference would be a flat plasterboarded wall. Could I just dig down inside and though to the void within the room, then conceal with plasterboard and skirting?

Yes my design would keep the alcove, gives some space - stick a wine rack in there or some books. Or uour tv equipment with your TV above and running all the cabling up the chimney
The problem with trying to dig down is that the hearth is probably made up of all kinds of bricks - cement - concrete that gos right down to the bottom of the void but nearer the front it will fall away and much easier to dig out what you need.

 

[aveatry]

I think the preference for vent was
1- from outside
2 - from the void
3- from the room

 

[^woody^]

Either way, if ventilation was needed would I need two ´outlets’ to create airflow, or would a decorative plaster vent in the plasterboard be enough?

Thanks

Ventilation means through-ventilation - via two vents where natural air currents bring air in one vent and out the other.

 

[SJRSJR]

Yes my design would keep the alcove, gives some space - stick a wine rack in there or some books. Or uour tv equipment with your TV above and running all the cabling up the chimney

Hmm, you've got me thinking.. I like the idea of TV and cabling there... Thanks.

Thanks to everyone, very helpful