Brick fireplace acting as a cold bridge?

[fernicarry]

Morning All,

First post on here. We have an 1860's stone rubble construction house in Argyll which we have occupied for about 3 years now. We're semi-rural with the house facing onto a loch so it gets the brunt of the weather when its coming in the right direction. Mostly its been quite sound although we've had a fair few water ingress problems on the two most exposed elevations -- a combination of chimney flashings, blown pointing, blocked downpipes, cracked drains etc. I think previous owners didn't really have much of a regular maintenance regime in place. Hopefully now we're getting on top of all that.

However purpose of this post, the fireplace in one of the front rooms has been replaced by a huge brick-built monstrosity about 8 feet wide at some point. The wallpaper to either side of it is quite damp with dark shadows and white slimy mould developing. My builder has always muttered about condensation whenever I ask him to look at this and urged us to keep a low fire lit to warm the room and dry out the wall. I've now taken notice of him and we have the radiator on 24x7 in that room (the house is gradually being zoned with a heatmiser system) and we've been lighting a fire most evenings for the last few weeks. The shadows on the wallpaper do seem to be receding but then we also haven't had much rain since Storm Freddy so perhaps too soon to draw conclusions.

It occurs to me however that the fire surround is possibly acting as the mother of all cold bridges. Obviously its in contact with the outside wall around the flue opening, maybe even across its full width, and also with the ground through its plinth so it must have a strong tendency to sit at outside temperature. If this is the case then its going to make it a lot harder to keep the room above dew point. We do intend to remove it and put in something more period-appropriate once we get around to renovating that room but realistically thats a couple of years off yet.

What do members think on this theory? Think its worthwhile bringing this job up the priority list? I have quite a backlog of started but not quite finished jobs so starting another one may not go down well with the household authorities but then its soooo ugly I am absolutely dying to take a sledgehammer to it....

Appreciate thoughts and ideas.

Regards, Alan

 

[Tony.]

I hope the external wall is pointed with lime mortar to allow the wall to breathe?

What is the exterior ground level in relation to the inside floor?

What is the room ventilation like, window trickle vents?

I think heating the room, venting it, not drying clothes in the room and checking the above items, I'm sure the wall will dry out, give it time
Best of luck

 

[MatthewC]

My immediate thought is to wait a bit, as drying out thick walls takes AGES. When did you sort out the "chimney flashings, blown pointing, blocked downpipes, cracked drains etc"? Those are all problems I had, and I reckon it took well over a year, if not two (16" limestone walls). If you did it in summer 2015 then you might now be starting to see the benefits of it on the walls, so you should wait for the full benefit - next autumn at least, if not longer (depending on the thickness and construction).

If you have condensation on the wall, you should think about the wallpaper - what it it made of, and has it been painted? Many wallpapers are impervious (e.g. vinyl), a lot of paints are also impervious (e.g. vinyl again) and sometimes (I believe) the adhesive is impervious; you would be better off getting that off and letting the inside of the wall breathe.

When you have a fire on, does the room warm up well, or do you sometimes wonder where the heat is going? If the latter, then I suggest that it is (still) going to convert the water in the walls into water vapour (google "latent heat of vaporization") - it takes heat energy to do that conversion at constant temperature, which is why the air is hardly warmed.

But even after saying that, you could be right about the cold bridge - you're certainly right about the sledgehammer!!

Matthew

 

[fernicarry]

Thanks for the replies.

The outside work started 2 summers ago with the roof and chimney. Most of the pointing was done last summer with a few more bits done just after Xmas. The drain was also repaired just after Xmas as part of the investigation into a slow running downpipe.

The outside ground level is below floor level all around the building and also falls away from the house on this side. The solum under that wall is now dry, last winter there was water running down the inside of the wall and the fireplace plinth.

The pointing has been done in cement unfortunately. I did ask the builder about using lime but at the time I was willing to put his experience of working on the vernacular above my theoretical knowledge, I would do it differently now. He was also of the opinion that the local stone (known as whinstone) isn't water permeable. I don't know if thats really the case but it is certainly as hard as a very hard thing resulting in hours of entertainment trying to core through it. The whole wall already had a very heavy 'coat' of pointing to the extent that some of the stones are almost completely covered which may well be cement too.

I realise the wall will take a good while to dry out and yes, the heat from the fire doesn't do much to increase the room air temperature. The stat for the radiator is set to 13 or 14' and the temperature doesn't rise above that even with the fire lit. There is at least a dry patch starting to show on the outside on wet days so the fabric temperature must be starting to rise.

I don't think the wallpaper is vinyl, it feels, well, papery. and doesn't have a shiny surface. The plaster behind it though is modern. I believe gypsum plaster is less permeable than lime so that could be causing water to prefer to find its way out at the edges of the fireplace?

I'm coming to the conclusion that its better to get this fireplace rebuilt sooner rather than later. That will give us some time to monitor whats going on without worrying about our own decorative finishes.

Now my next question is going to be can I get the Baxi Burnall that we salvaged from the living room incorporated into a nice traditional fire insert?

-Alan