Anyone have experience of using this method? What are the pro's and cons?

After spending a few weeks reading up before I got in touch with my energy supplier I came to the conclusion beads are best. As Tony says - there's now the carbon coated grey beads which decrease the u value even more. Probably about 10% more expensive but the energy saving is increased by 10% IIRC. So payback is actually increased much more.

Beads have the advantage of not sagging if they get condensation forming in them. Beads won't wick moisture across the cavity as gravity pulls it downwards, they won't settle over time (or in an earthquake??). They also require less drilling than the fibre insulation - just at eaves, under windows and a few extra points at corners.

Fibre isn't bad but I think the long term practicalities of beads make more sense. When fibre gets wet due to interstitial condensation or prolonged heavy rain causing water to run down the internal face of the outer skin, it can lose some of it's insulation properties.

The basic white beads cost the same as fibre. You may find the wait for beads longer than fibre some times as much as 8 weeks or more - as most companies have a ratio of vans about 4:1 in favour of fibre. So get yourself booked in now rather than waiting till September.

Steer clear of expanding foam. It's not very widely used now for good reasons. Formaldehyde off gassing, capillary action causing damp spots on walls exposed to driven rain, and "over expansion in poor condition walls causing cracking!".

Simon

If you have any elcetricity cables in your cavities then be aware that contact with polstyrene may cause the cable insulation to become brittle and crack.

One reason why they should NOT be in there.

I've had foam beads for over 20 years. Seem to work well. One slight problem is that not enough glue was used so I had a few beads blow about. Also one corner was not filled properly - I think it was due to an old wisteria plant in the cavity which finally rotted and allowed the non-stuck beads to sink. I topped up the cavity myself with a vacuum cleaner on blow, pressurising the bead bag, allowing them only to escape via another vacuum cleaner hose. It all worked OK.
Frank

Hi Mike

I've only used this system on a new build but can't see why there should be a major performance difference with refurb. For the build in question the deciding factor was the wall structure. The house was being built in random stone, drawn to courses on the outer leaf and block inner leaf. We've built in this type of walling before and have seen similar problems with 73mm bricks. The outer leaf coursing does not match in with the inner-leaf blockwork. If using any of the batts either wool or rigid board you tend to get gaps and holes in the insulation. If you build with a clear cavity and inject later you can eliminate the problem. Stone is irregular in the depth (on bed) and the face in the cavity is very rough. Accepted wisdom is that blown fibres do not flow well into cavities on stone masonry. Polystyrene beads do appear to do so. On that house, we had an aggregate cavity width of 135mm. The beads were the graphite impregnated type. The installer was duly approved and certificated. As a new shell it was insulated before internal plastering so all access holes were covered in the finishing. No measurements on performance were taken but I lived in the house and can confirm that I was very impressed. The heat retention was excellent and only marred by the box sash windows forced on me by the planning department (the wind howls through the weight box and out the pulley slots).
The costs of the bead insulation system were effective. The beads were less expensive than using an equivalent insulation in PU batts. The installation was quick and would have been quicker if the installer had turned up with enough material.
I was worried about water ingress because I once rented a new build with fully filled cavities (glass wool) where, every time we got driving rain, we had wet patches on the internal walls. In practice we had ingress problems.
I'd use the bead system again but I'd find a different supplier. I had a hell of a job getting the certification from the installer. That made a dubious building control officer a bit suspicious. The price invoiced was way more than the price quoted too. The supplier also has a roofing division and they supplied some really rubbish roof slates. All in, not an outfit to go back to.
Not too sure about the appearance if you inject from the outside. The holes are 20mm diameter whilst brick beds are around 10mm. You could end up with a house looking like it has had wall tie failure. I do have to wonder about a 1940s to 70s house with galvanised ties. They were not too good in a clear cavity, what happens if the airflow is further restricted?

Thanks for the comments all - I am going to explore this further and will keep you updated