Could cavity wall insulation be a bad idea if...

[karl666]

...you possibly have interstitial condensation within the cavity ?

I have a 1930's semi and I’m thinking about getting cavity wall insulation. Because of its age, I’m worried that the cavity might have some condensation.

If the insulation in the cavity gets wet then you will basically have a cold bridge across the gap and onto the inside all.

I've seen many houses having the cavity filled but i'm wondering if anyone ever bothers to check the state of the cavity before attempting these jobs. Its probably better to have no insulation that wet insualtion.

Am I being over cautious ?

Regards
Karl.

 

[JohnD]

...If the insulation in the cavity gets wet then you will basically have a cold bridge across the gap and onto the inside all.

what makes you think that happens? the mineral wool has a water-repellent coating.

It is much more common for cavities to be wet when the brickwork or renderin is cracked and gappy and rainwater gets inside. So cavity wall installers (should) avoid them until the defects are corrected.

A normal cavity wall will get wet on the outside bricks during rain, and dry off when the sun comes out.

 

[tony1851]

Not all houses with cavity walls are suitable for insulating. For one thing, you do not know the state of the wall (eg have the ties got mortar on them? - insulation can exacerbate any problems with them).
Also, some external brick skins are built of bricks which are not of good quality. Insulating them from the heat of the house will cause them to be permanently wet in winter and subject to frost damage
My 1920s house is cavity construction, and I would never contemplate injecting it.

 

[karl666]

Hi,

Thanks for your replies.

Tony1851, seems like you are thinking along the same lines as me. My fear is that once the cavity is filled there is no way to reverse it should there be any problems. Think ill try and seek some further advice before taking any action.

Regards,
Karl.

 

[^woody^]

A cavity would be unlikely to experience interstitial condensation, as that is a phenomenon for a different situation. Any moisture in a cavity would be getting in via the external leaf.

 

[JohnD]

I have seen records of cases where cavity fill was done to an unsuitable wall, and having failed to rectify it in any other way, the installers were forced to remove it. I believe it can be done by removing a brick at each end and pushing a powerful vacuum cleaner pipe inside. The installers are supposed to inspect the wall for various potential problems before they carry out the work, so would be liable if they failed to do so.

I have actually used a similar method to remove builders rubble and fallen mortar snots from the bottom of a cavity, leading to damp. I found it quite tedious.

 

[karl666]

Was looking to make the house a little warmer this winter. Its these sorts of horror stories that puts me off getting it done. Think ill buy some wooly socks and a jumper instead.

Thanks for your suggestions/advice.

Regards
Karl.

 

[JohnD]

I've had my cavities filled and am very pleased with it. So are almost all the other people.

The only oners you ever hear about are the ones with a problem, and there aren't many of them.

What are you expecting to go wrong, and why?

 

[karl666]

I've had my cavities filled and am very pleased with it. So are almost all the other people.

The only oners you ever hear about are the ones with a problem, and there aren't many of them.

What are you expecting to go wrong, and why?

To be honest, the outside walls are not in tip top condition. There are some rendering issues and cracks in mortar in places. Also, there has been an open air brick to vent the cavity wall in place for many years. All of this leads me to think that there could well be water or condensation in the cavity. I’ve touched a damp meter inside the property at skirting board level and there are raised levels on most walls until about 12 inches up.

My fears are as I’ve pointed out in previous posts. It seems to be (in my mind anyway) that you roll the dice and take a chance. It could be fine and there would be no adverse effects. The downside is that it could cause raised moisture levels inside the house.

 

[tony1851]

Was looking to make the house a little warmer this winter.

Could you install more/better loft insulation? That is probably the most cost-effective way to reduce heat loss.

 

[^woody^]

As heat rises, a cooler bit of wall near the floor will have little impact.

 

[karl666]

I had a new roof about 2 months ago and ive just re-done the loft insulation. Hopefully that will make a bit of difference when the cold weather arrives.