Ventilation in chimney stacks (where over 50% removed)

[David WE Roberts]

Hi,

one of our chimneys has been (before our time here) removed down to first floor level to make more space in the bathroom.

Having just brutalised the old shower tray and taken it out in pieces, then brutalised the underlying (non-waterproof over time) chip board which was installed over the remains of the chimney (and also taken it out in pieces - spot the trend) I find myself with the remains of a brick chimney stack just under floor level with two chimneys open at the top.

However when the wood was down it effectively sealed off both stacks apart from the small space directly under the wood. No access to the surrounding under floor to allow ventilation between floors. [It would have been nice if whoever did this had swept the chimney before hand instead of leaving it full of soot.]

I cannot see any provision for ventilation at the top of the stack in the bathroom, nor any provision in the dining room and kitchen (where the fireplaces used to be) for ventilation there either.

Is this normal practise, or should the chimney area be ventilated even though it is not open to the outside?

We have noted a strong smell of soot in the cupboard built into the chimney breast in the kitchen which makes us think that it might be a bit damp.

Should I consider installing ventilation top and bottom during the re-install of the new shower tray, or is it O.K. to leave sealed?

TIA

Dave R

[This is not a long term problem (not more than two years we hope) as we intend to rip out the rest of the chimney and merge the kitchen and dining room into one large south facing living area.]

[R]

Why would it need ventilating if not used?

Given that there is a perfectly good outside vent from above the shower not being used (Assumed as not mentioned) could it not be used to assist removal of steam etc from the bathroom using a small fan?

Is the dampness/sooty smell on a wall that is exposed to the elements? If so have you checked that the outside is watertight or render (if there) intact? If not exposed I suspect perhaps leakage from the old shower has dampened the inside of the chimney, hence the smell.

If the lower part of the stack (With the cupboard in) has an outside wall and it needs ventilation perhaps a soffit vent might suffice. Enough to allow fresh air in without too much draught.

[David WE Roberts]

This is the question that I asked!

Not sure I understand this bit at all - the remaining part of the chimney is all below the shower. There is no outside vent above the shower - it is in a bathroom alongside the bath, and the bathroom has a wall mounted extractor fan (and opening windows).

The chimney is in the centre of the house. No signs that the leakage from the shower has got further than the chipboard below the shower - certainly not all the way down the chimney to the kitchen. It is more likely that the base of the chimney (where the fire was) is not as well damp proofed as elsewhere.

Unfortunately as stated above the chimney is in the centre of the house. I was assuming I would have to use the usual (possibly hit-and-miss) vents by removing a brick or two at the bottom of the chimney where the fireplace was, and putting some kind of vent at the top under the shower.

[Andrew Gabriel]

It needs to be ventilated if there's any chance of moisture ingress. If the chimney is on an outside wall, or has an exposed stack (not your case), the normal route for moisture ingress over time is through the wall/stack. Once the moisture is in there, it is effectively trapped unless there's ventilation as the rate of egress is slower than the rate of ingress, so it slowly gets worse. Moisture eventually comes through the inner side, damaging plaster and decorations. Because soot dust is so fine, that can also be carried through the brick by moisture in bad cases, leading to soot stains on decorations.

Soot has a strong smell decades later (or rather the tar products do, pure soot itself has no smell at all and is used to absorb smells).

If it's on an outside wall, I would ventilate the stacks top and bottom to the outside (you need a through draft). OTOH, ...

... if it's been like this for some time without any problems, and it's only going to be there another 2 years, I wouldn't worry about it.

Whilst you have the bathroom floor up, you should investigate how the floor is supported. If you find it's supported by the chimney breast in any way, now is probably the time to remove that dependency so you can later remove the stack from below without having to rebuild the bathroom floor again.

[David WE Roberts]

Thanks - a good thought but we are going to rip the shower (entire bathroom) out when we redo the house anyway, so changing that bit of the bathroom floor then is likely to be less hassle than lowering the stack further so that we can get a joist or two in now.