I'm having a hard time convincing the misses that the above will cause rain water to transfer across the cavity from outer to innner skin into the house.

Or does this new stuff avoid that somehow?

Do those that have it notice a benefit / drawbacks?

It's pretty cheap but the quotes never state a spec or the U-value co-efficient of the product. It could just be camel sh1t.

What puts me off is the number of holes drilled in the external wall.

No don't do it , the wall cavity is there for a reason
Without it you're home won't breath properly and you
Risk damp and moisture building up inside the house,

You need to be very sure your bricks aren't too porous. All bricks absorb water to some extent. Mine are terrible, they're like a sponge. If you live in a windy or wet area or your house is in an exposed position this will exacerbate the water ingress to.

The insulation companies will tell you the glass fibre, polystyrene beads or expanding foam are water proof. They are, unfortunately the whole point is they trap air between them. This allows the water to seep between the individual insulation components. Worse still it can lead to capillary action.

Even if you don't get penetrating damp it is very difficult to make sure the cavity is completely full. If you get voids you'll get cold spots which will lead to condensation on the internal wall which in itself can become a damp problem.

Cavity walls were originally conceived on the west coast of the UK to combat penetrating damp in the wetter parks of the country.

You already have insulation in the cavity air. As long as it is not moving around too much it will insulate to some extent anyway. If it is moving around chances are you have air bricks in which case you want the air to move which cavity insulation will stop.

Lots of people have a had it done with no problems and will claim the house 'feels' warmer. There are lots of others who have had to have walls pulled down to remove faulty insulation.

Personally I'm not entirely convinced cavity insulation saves that much extra heat, there are better ways to save energy, makes sure the loft is prperly insulated, makesure you've got properly fitted functioning quality double glazing. I looked at it and decided I wasn't having it fitted and put another layer of insulation in the attic.

Last point, new homes have insulation installed in the cavity when they are built. This is very diffferent from after build insulation. It should be fitted so there is still at least a 20mm cavity (the panels are held against the inside leaf of the wall) and they have a reflective and waterproof face which faces outwards. Finally you don't get voids.

If you want any more info just Google 'cavity wall insulation diasters'. The photos of walls being ripped down should convince her.

its not the best solution.
if you dont mind losing a couple of inch of room space, stick insulated plasterboard on all external walls. i've done this on quite a few properties and it works a treat.

^^ thats sounds like a much more sensible suggestion.

Forgot to ask, how old is the house? Mine is 9 years old but has no cavity insulation. Instead due to the brick choice and exposure the builders had to use much better insulating blocks on the inner leaf. So in theory my house should already have the same U value as a simlar house with traditional breeze blocks and cavity wall insulation.

My house was built in 1893. And yes it does have a cavity of about 50mm. Bricks are quite crumbly (as is the lime mortar).

Just to redress the balance, got a 1920s semi with DG and good loft insulation, and we had cavity wall insulation done 12 months ago.
It's noticeably warmer, especially overnight, and has reduced condensation problems in the bathroom by a large amount.
Worked very well for us…

Some very valid points there Stumpyjon.

Personally i stay in a mid terrace 480ft ASL. The properties either side of me had blown bead insulation installed in the Autumn, just in time for the coldest winter in 50 odd years.

Obviously they cant give an accurate comparison to previous years due to the radically colder winter we had but i am hanging off from having it installed till i see if they have any condensation problems.

Certainly i did upgrade my loft insulation (rockwool type) from the 3 inches (pathetic) installed by the builders (in 1976) to a minimum of a foot deep with a thin fleece membrane above (cuts airflow). This made a huge difference to the temprature upstairs. Oh and don't forget to insulate the access hatch too.

Another major benefit is obtained by getting some proper draughtproofing installed. I have quality double glazing, doors included, but it is surprising how many other places leak air. Pipe runs into rooms being a prime culprit in kitchens and bathrooms.

It is important though to remember you do need ventilation to prevent condensation issues.

Fair bit of info in this article…

http://www.askjeff.co.uk/cavity.html

I was thinking of getting this done as I live in an area with no mains gas so we can get grants for insulation.

The house is a 1950's semi, clay block internal skin, normal redbrick exterior with a white painted pebble/render external finish. There's double glazing throughout inc the front and back doors.

Loft is well insualted, might get that done too as we can again get it cheap due to the lack of mains gas.

Waddya reckon folks?

http://www.bricksandbrass.co.uk

this guy has the answer to all you questions, he knows his stuff,
😉