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I've just had my house re-roofed and as part of the work had the chimney stack taken away - myself and a couple of neighbours all had the roofs done at the same time by the same company and got a pretty keen price from as a result - and we all had the chimney stacks removed as part of the work. All hunky dory.
One of the neighbours recently had another contractor in and they took issue with the fact that the remaining part of the chimney inside the loft hadn't been capped. I'm assuming that ours will be the same, although we'd had the fireplaces removed long ago up until the removal we had kept an air flow through the chimney to prevent damp in the chimney itself and give some ventilation in general to the house.
Personally I'd have presumed having some ventilation through the chimney, even just into the loft space, would still be beneficial (I was evening thinking it would be worth fitting some positive pressure ventilation) Â - but is it not? Should I be getting it capped before paying the final installment?
leave it open imo. needs airflow as its only single skin.
IANAB
I suppose it depends by what is meant by "capping"
If the chimney is now within the house, i.e. not substantially into a colder loft space, then the only capping might be insulation attached to a sheet of OSB to prevent heat loss, water ingress and falls.
If you feel that the spread of smoke and flame is an issue then Building Regulations 2010 Approved Document B Volume 1, 2019 edition talks about,
Cavities
5.16 Cavities in the construction of a building provide a ready route for the spread of smoke and flame,
which can present a greater danger as any spread is concealed. For the purpose of this document, a cavity is considered to be any concealed space.
which may be the new contractor's POV of the de-commissioned chimney. The regs may not be applicable to your works and chimneys run uninterrupted through floors in any case.
Here's the properties and materials list:
Construction and fixings for cavity barriers
5.20 Cavity barriers, tested from each side separately, should provide a minimum of both of the following:
a. 30 minutes’ integrity (E 30)
b. 15 minutes’ insulation (I 15).
They may be formed by a construction provided for another purpose if it achieves the same performance.
5.21 Cavity barriers in a stud wall or partition, or provided around openings, may be formed of any of the following.
a. Steel, a minimum of 0.5mm thick.
b. Timber, a minimum of 38mm thick.
c. Polythene-sleeved mineral wool, or mineral wool slab, under compression when installed in the cavity.
d. Calcium silicate, cement-based or gypsum-based boards, a minimum of 12mm thick.These do not necessarily achieve the performance specified in paragraph 5.20.
If the loft is ventilated to the outside I'd say leave it uncapped. If not, I'd cap it otherwise warm, relatively moist air from the house may cause condensation in the loft. But if you cap the chimney there is a risk of dampness in the old flue. Best solution would be to cap it, vent the flue with an airbrck to the outside (assuming it's on an external wall), and another vent in the blocked up fireplace so there's some airflow.
It's an interesting question.Â
Timba raises good points above re fire and smoke.
My initial concern would also be the possibility of warm air entering your loft space if it is above the insulation layer. There's a possibility of condensation forming. Conversely cold air dropping down the chimney in certain weather situations.Â
None of these things might happen in reality though, and it depends what arrangements you have at the old fireplace eg is there a vent there?
Id probably cap with something removable - if you are concerned about airflow you could at least then check all is well. It also removes the possibility of anything falling down the flue, however unlikelyÂ