Cold bridge - Anyone know how to cure it?

[dres2004]

Hi Tony,
The site still as good as ever, the new layout seems to work pretty well too, congratulations on keeping the quality as high as ever!!!

So my question while may not be in your particular area of expertise maybe one of your regulars may be able to help out.
I have am having a problem in the house (or bungalow really i guess) with mold appearing where the walls meet the ceilings in some of the rooms on one side of the place, which I have been told is due to a cold bridge in the loft, could you or someone explain to me what a cold bridge is and what can be done to prevent it. I'm assuming it's due to condensation forming on the walls/ceiling and possibly something to do with the insulation in the loft?? Any help would be most gratefully received. Thanks...........

[danensis]

A cold bridge is simply something bridging across from one area to another, and conducting away the heat. It could be caused by a lack of insulation, or by a lump of concrete or mortar. I would have thought whoever knew it was a cold bridge would have known the cause.

[Tony McC]

A common cause for cold bridging is when a lintel has been used, especially where it spans or bridges both inner and outer skins of a wall. Another common culprit are roof joists that project across the wall and allow the cold to be transmitted along the length (or, more accurately, the heat to be 'leached' outwards).

Working out how to cure a cold bridge is pretty site specific. You need to identify the actual cause and then the potential remedies can be considered.

You can sometimes control the mould by using a fungicidal paint, or even a waterproofing coat below the paint on the internal wall. This doesn't address the problem of the cold bridge, but it can improve the overall appearance.

Pionta, le do thoil

[dres2004]

Thanks for the replies guys, we had someone out to look at it and that was what they said was a possible cause......I used to work in the motor trade and know what goes on in some peoples heads when the customer replies "so what is that then??"......minds start wandering to that two week holiday in Florida that the job is going to pay for so I thought I'd better try to find out a bit more about it before I give anyone the go ahead to start working on the problem!! Maybe I just have a suspicious nature!!!

Anyhows, had a quick look around in the loft today and from the replies it would seem the culprit is going to be the roof joists, could see nothing else bridging across the inner to the outer wall anyways. If it is the joists what can be done with them to remedy it??

Think I'll take the advice about the anti-fungal paint too.

The problem is only in the main bedroom of the house too and having looked around the outside there is an airbrick on the outside wall but the vent on the inside (after much searching for it) has been enclosed in a wardrobe built by the previous owners, I'm guessing this wouldn't be helping either.

Thanks again,

Cá bhfuil an teach pobail?

[steve r]

I'll put my bit in.
The condensation and subsequent mildew is caused by the warm air in your room meeting a cold surface and condensing out.
When the temperature of the air is reduced to its dew point it can no longer hold the moisture within it.
You need to somehow increase the insulation between the walls/ceiling and the outside, so that the temperature is the same.
Do you have cavity and loft insulation?
If not you may be able to wrap the joists in a Rockwool blanket.
The air brick may be adding to the problem by cooling the inside of the wall.
You should be able to feel any cold spots with your hand and this may give an indication of where the problem is.

Where's those yellow things?

Is é do bhaile do chaisleán

[dres2004]

Thanks for that Steve,so I either need to get the room down to the outside temp (it's getting bloody cold over here at the minute!!) or else heat County Westmeath to match the house!! Sounds easy :;):

The loft is insulated, though I would like to say how well or how long it's been there so it was on the plans to replace that. How long should the loft insulation reach into the eaves - I've had people tell me it shouldn't over hang the external wall and others say it should reach down to the soffit (is that the right name??) and still others say that I need to make sure there is an air gap between the bottom of the roof tiles and the insulation all around the loft, the soffit incidently is pvc with those vent things fitted approx every 6ft or so (not sure if this makes a difference or not).

Not too sure about the cavity insulation though I would say probably not. I was thinking of dry lining the walls but would this cure the problem or would it still lurk on the walls behind the lining?

Thanks again for all the replies!!

Ní hé lá na gaoithe lá na scolb. (kind of relevant really too!!)

[steve r]

Well sort of.
If the temperature of the wall is the same as that of the air, then no condensation.
The minimum depth of insulation on a new build house in the UK is 200mm.
The blanket should should extend to the outside of the inner leaf of your wall, leaving the space above the soffit open to provide ventilation to the roof space (from the pvc thingys).
Don't forget to insulate the water tank(s), leaving the area under them uninsulated. Any exposed pipes above the blanket should be fitted with foam insulation.
Applying insulation to your walls may improve things, but the best solution would be to have your cavity wall filled.

That's enough insulation for now.

Best stay inside the roof at this time of year.

[dres2004]

Many thanks Steve, I'll take a look and see how the loft insualtion is and get everything else up there well wrapped up....

[danensis]

You also need to look at the source of the water vapour. Stopping the inhabitants from breathing may be unpopular, but is there an extractor fan in the kitchen, and in the bathroom? Usage of dwellings has changed, we no longer have coal fires providing through ventilation, and people tend to replace draughty sash windows with double-sealed units. We bathe more often, and showers are notorious for generating free vapour. If you can remove the water vapour at source there will be less of it to condense on the walls.

I would also recommend you look at Jeff Howells site before you think about wall-cavity insulation.

[dres2004]

I would say there would be a few complaints if I only let the kids breathe out in the garden!! Maybe I could run a breathing tubes through the walls to the outside and they could use them..

As for the source of the vapour, I was only thinking the same thing the other day, as the problem is only apparant in the main bedroom and there is an ensuite with a shower in it I have now fitted an extractor fan in the ensuite one of those jobs that is so much easier in a bungalow!! So hopefully this'll stop the problem from getting much worse at least.

Also while I was up in the loft doing the fan had a bit of a look at the loft insulation, the thickness of it seems to be ok at 200mm but it looks to have been cut a bit short in some areas and is stopping at the inner edge of the inside wall (you can actually see where the ceiling is meeting the inner leaf), most of it seems to be ok, as in reaching right to the outside edge of the inner cavity but in the main bedroom there are a few sections that stop early.

So I'll see how the fan works out for the next few days (working nights now till Wednesday, which is nice!!) the if I get a chance pull up the short sections of loft insulation and lay new right up to the outer edge of the inner leaf as I was informed by Steve R. Oh I also managed to get all the pipework insulated up there too, just need to get the cold water tank and the expansion tank for the central heating done....

Thanks again to all for their help and advice!!

Go raibh míle maith agat!