We've instructed a local cavity wall installer to inject our 1960s detached property with graphite EPS beads.

We aren't looking to make any structural alterations to the property other than a single storey extension at a later date.

Any tips or questions I should ask prior to the fill? Or anything we should be doing to ensure it's done to a high standard?

2/3 of the property has never been filled before, 1/3 is an extension and has cavity batts. Can I ensure that they 'top this up' ?

Thanks

They can only blow the beads into reasonably sized air gaps. If the extension is full fill cavity batts there shouldn't be any gaps so no where to blow beads to top up what's there. If it's partial fill then the air gap is likely too small to get any significant quantity of beads in.

We had blown fibre installed decades ago and trusted that they'd done a good job. When extending the loft insulation to the top of the cavity fill a few years ago we found large areas that hadn't been filled which a warranty claim sorted out. If I was having blown cavity insulation now I'd make it clear that every part of the cavity needs to be filled and happily pay more for additional holes to be drilled to make sure they could reach every part of the cavity

''Would it be worth asking them to install beads in the original external walls (that are now internal walls) also?''

Yes, if you think there is any chance whatsoever that cold air could get in there and cool the house - from open joints in the wall below a suspended timber floor, perhaps?

Very positive! Flexibility is good, and something I have struggled to get from some CWI installers.

Tony, not sure if your '?' relates to my comment 'Flexibility is good, and something I have struggled to get from some CWI installers.' but if it does, what I mean is that I and colleagues have had CWI installers refuse to fill residual vented cavities left after partial fill - something that one would not do normally, but which you want to do - to prevent air movement and thermal by-pass, in addition to closing the vents - if you are EWI-ing over that cavity wall. No-one I have found in my part of the world has been keen to do it. I believe it is not considered a 'normal' installation in CIGA terms.

Well they turned up today and advised they can't top up batts even if I were to sign a disclaimer.

They want £3300 for ~180m2 using graphite beads. 80mm cavity. I think I'll do a calc. without the windows as that seemed a bit high in cost or so I thought I'd they haven't made deductions.

How cost effective would it be to buy in beads and DIY? ?

Bear in mind they will/should blow in PVA so that the beads 'clump' whereas if you fill the cavity 'dry' any holes you chop could drain some or (worst case) all of the beads out. If you are satisfied that you can get them in right and you won't be making any holes in future then you may want to go for it, though technically I am not sure where you stand with Bldg Regs. Probably OK if you can prove the beads you use are used in CIGA-approved installations. (All of that is a guess). In terms of the insulation value, if you EWI you will be (I hope) less than the 0.3W/m2K target with the EWI and the CWI is effectively mainly performing an air-stilling role.

I have used a garden vac successfully and it is fast, also useful for cleaning up beads

I have an eps bead blower gun but someone is borrowing it, slower but can use 22 or 28mm holes

A friend made his own simple Venturi and that worked well - last two options need a compressor

Transporting the beads is another issue/cost.

Have you got a quote.
I bought small volume from Ebay for recent works but only 4 big bin bags full. Checked samples to make sure fire resistant.