Correctly blocking chimney for BER

I.R.Y.E.D

Hi folks,

Was asked this question by a mate but I don't know enough to answer, google throws up different answers, and their one stop shop project manager won't/can't answer the question directly.

Two story 1950s farm house with single brick walls.

They are finally in the process of getting external wall insulation put in place, top up of the attic insulation and heat pump.

They have triple glazed widows in all rooms with trickle vents and extractor fans in bathrooms and utility.

They have a chimney which the previous owners had ripped the fireplace out of but didn't block up, that is on an external wall. There is only a fireplace on the ground level, and not in the room above.

The external wall is going to be covered by the rap, however they cannot get a straight answer on how to bock the fireplace and chimney.

Their one stop shop project manager just sent them a graphic and by reverse searching I've found that it is from/used by the following

https://berwow.ie/ber-improvement-measures/

Close Up Chimney

Sealing up a chimney that is no longer in use will prevent it from being a major air leakage path.

Sealing of the chimney should be done according to the Code of Practice for Retrofit S.R. 54:2014&A1:2019 – see Image 6.3 below.   

The chimney should be sealed:

• Within the room; and
• At the ceiling level of any insulated roof to ensure that the chimney breast within a heated room doe not contain cold air. This should prevent the potential for both surface and interstitial condensation on or within the chimney.

Above the level of the insulated ceiling the chimney should be:

• Ventilated from within the roof space to the outside of the dwelling
• Capped to prevent ingress of moisture or rain whilst maintaining ventilation

Alternatively, ventilation of the flue should be maintained by a vent in the sealed fireplace. Where the chimney is on an outside wall, the internal face should be insulated.

Given the above would they be ok both in terms of the BER assessment and preventing damp issues if they bricked up the fireplace and included an air brick at that point to seal the fireplace and put a cowl on the chimney pot to prevent rain ingress while allowing air flow or do they need to do more work?

They have a roofer that they have used in the past and he and some other older builders I was talking to in work said just to block the fireplace up entirely and seal the chimney at the top with sand and cement to prevent rain etc entering the chimney, with no vents being put in at the top or at the fireplace.

In both cases they have said that dampness in the chimney shouldn't be an issue with this approach. But this goes against some stuff I've read online which say to just block at one end

e.g.

https://chimneychoice.ie/blog/how-to-block-a-chimney/

In short they need/want to ensure that they will pass the BER inspection as their loan is dependent on reaching a minimum of B3, while making sure that they aren't going to be having issues in the future with damp from the chimney.

sydthebeat

as far as the BER survey is concerned, once the fireplace in the room is sealed properly, thats all that is required to not include it as a ventilation heat loss. if there is a permanently opened ventilator on the chimney, then it must be recorded as an "open flue" and that will affect the BER negatively. Interestingly if that ventilator has open areas larger than a 20omm diameter circle, it is back to be recorded as a chimney.

i would recommend sealing the fireplace in the room, and sealing off the chimney at the chimney cap level. The block chimney is a thermal bridge through your ceiling insulation regardless of what sealing you do within the flue at ceiling level.

I.R.Y.E.D

https://www.boards.ie/discussion/comment/122580940#Comment_122580940

Thanks for the reply.

Am I understanding correctly that you recommend bricking the fireplace up in full without a vent and completely blocking the chimney at the cap level with say sand and cement?

Would doing so not cause damp/condensation issues as mentioned in the second link I posted?

sydthebeat

https://www.boards.ie/discussion/comment/122583746#Comment_122583746

the only way, in my opinion, that you can completely negate the risk of condensation in the chimney is to removed all the blockwork of the chimney to beneath the top floor ceiling (insulation) level. That wall the chimney clockwork becomes warm enough to keep the condensation from happening in the first place.

The SR gives you two options. The option with the flue sealed at the ceiling level, and vented in the attic level, is the best from the BER point of view.

in not suggesting not ventilating the chimney as that is what is recommended in the SR, but im just making you aware of the consequences of the location of this ventilation and the impact on the BER. Also remember that most chimneys are on external walls, and the SR recommends you insulate these chimneys specifically.