cavity wall insulation - good idea ?

bobula

just bought a 1950s Brick built - 2 layers with an air gap between. - no wood work in the cavity to sweat. its been suggested i cavity wall insulate with blown insulation

im sceptical due to the gap being there to stop damp bridging and to let the house walls breathe - sticking the insulation in there will create a bridge ....

So would you wouldnt you ? once its in there it ait gonna come out......

other option is to kingspan 38mm the external walls before taping and skimming and then up the loft glass wool by 3 for the roof spaces.

the blown cavity insulation is easier - cheaper but logically has issues if my basic understanding is correct.

or am i barking up the wrong tree ?

Ectophile

You'll find opinions either way. Personally, I don't want it - even if somebody is giving it away free with a grant.

My house has a very exposed South-Westerly facing wall, which gets lashed by gales and rain in the Autumn. I don't want to risk the damp problems that might be caused.

Casati

We are also 1950s double skin brick, had blown cavity insulation a few years ago and no problems . Actually it's been a bit of a lifesaver in the bedroom at the North-East corner of the house, that was always like an icebox but it's greatly improved now. The loft is also insulated but that has been up there for 20+ years and to be honest could probably do with something much thicker. Even so, when it snows the snow sticks around on our roof for days on end whereas some of the houses on this street it melts almost instantly, so it must be helping to some extent.

Can't comment on the kingspan stuff as I've never even heard of it!

Koicarp

bobula wrote: »

no wood work in the cavity to sweat.

How do you know what is in the cavity?

Usually the cavity below damp proof course, has lots of mortar deposits in it, sometimes so high they bridge the DPC. Because there are plenty of air bricks there you have a good breeze blowing around your cavity keeping everything dry, they vent under the groundfloor too. Floor joists were built into the internal skin, usually cut to tolerances of a couple of inches, meaning that often they protrude into the cavity. This is a great system, and does exactly what it was designed to do.
50+ years on, some berk comes trotting along with his foam gun, and stops the air movement, condensation builds on the joist ends and the wall ties and moisture appears in the groundfloor carpets, having travelled along the joist. There will be damp in the walls just above DPC, and when you call the berk back, he will tell you he missed a bit with his gun, squirt a bit more in and leave quickly. Unfortunately the cause is as stated above, the only cure is to remove his foam.

LisaW123

Sounds like we live in a similar house to yours. It is on the cool side and we've debated whether or not to have cavity wall insulation for years and have come to the conclusion it is not a good idea. Koicarp has given a very good explanation of the reasons why. It is especially not a good idea if you live in the areas of the country most prone to suffer from wind driven rain, that is in the west. Almost every week some "surveyor" turns up on our doorstep extolling the virtues of this type of insulation but apparently it is a nightmare if things go belly up and it has to be removed, and what if your wall ties need replacing? I would think very carefully before having this done. Cavity walls are there for a reason.

wellused

The thing that has put me off is the fact that some years ago my son had it done and a few months later he needed to put a hole through the wall to install a tumble dryer duct, when he knocked the hole through there wasn't any insulation in that area. The company came back to pump some more insulation in but the question remains how do you know if the company have filled all the cavity up or not?

LisaW123

You don't.

wdbamber

just bought a 1950's house and thinking about getting cavity wall insulation done, anyone had it done? does it work? any problems?

TB

Sprigs

My house was built in 1954. Took up the free BG Cavity Wall insulation offer last year. I'd say much warmer over winter than before and only had CH on for 3 months (couple of hours in the evenings).

27col

I cannot believe that people are still querying the efficacy of cavity wall insulation after all these years. We have very exposed south west facing walls. The insulation was inserted from the inside when I built the house and there has never been the slightest problem whatsoever in over 35 years. Personally, I would never live in a house that did not have wall insulation. Still, if you want to go on paying for heat to flow out through your walls, then feel free to do so.

tony6403

27col wrote: »

I cannot believe that people are still querying the efficacy of cavity wall insulation after all these years. We have very exposed south west facing walls. The insulation was inserted from the inside when I built the house and there has never been the slightest problem whatsoever in over 35 years. Personally, I would never live in a house that did not have wall insulation. Still, if you want to go on paying for heat to flow out through your walls, then feel free to do so.

Agree entirely. Have got polybead insulation which was installed more than 25 years ago - no problems (property in an extremely exposed location).
I don't know where Koicarp gets the idea that cavities are generally vented by way of air bricks. Cavities are not normally vented .The air bricks are there to ventilate the space below suspended wooden floors and , in order to ensure that air flow is NOT lost into the cavity ,make a small enclosure between the outer and inner walls - more recently with plastic sleeves or telescopic units.