Spray foam cavity wall insulation questions

[Other-Power]

Hello all,

I have a wall with a small 5cm cavity in the construction.

I would like to insulate it and British Gas wont tuch it as the wall is only small, figures.
I have seen two types of insulation, blown fluff and expanding foam. 
From what I read the foam is better at insulating and dosnt sink over time/if it gets wet.


Has anyone got any practical hands on experience using spray foam?

Whats the best option, any idea on cost per m^2, time scales, things to look for, are there kits, these sorts of things?

Thanks

Jon

[biff]

hi jon,
     i guess you are talking about a cavity of 50mm or 2" imperial, and then bonded beads,
                                         bonded beads are blown into the cavity under pressure and coated with a glue which is supposed to make them impervious to water and damp,if conditions are controlled properly and the glue and beads are mixed and pumped accoring to the instructions then you can be assured of a good result.it really works well
                                                                         biff

[Fionn]

My house is the same - 100mm cavity with 50mm of polystyrene insulation on the inner leaf.
My next door neighbour had the bonded beads that Biff mentions installed a few months back and they didn't seem to have any problem with the small cavity.
I have filled approx 50% of my own with Silvapor perlite. I need to get another pallet of it to finish the job.

[Other-Power]

Thanks,

Is this an expensive job or one a competent DIY er could do?

As the cavity is so small i am looking to get the best insulation I can in there.  Are these bonded beads polystyrene?

Thanks

Jon

[A.L.]

hello

Is this an expensive job

- under CERT subsidy the whole of a typical 3 bed semi can be done for £150-£200 or sometimes less - phone the Energy Saving Trust on 0800 512 012

or one a competent DIY er could do?

- I would not recommend trying to loose fill a 5cm cavity from the top and the materials would cost more than the CERT option

Are these bonded beads polystyrene?

- yes

I have seen two types of insulation, blown fluff and expanding foam

- there used to be a product called urea formaldehyde foam which although still approved I did not think anyone was still using. There is also polyurethane foam, 5cm of this is equivalent to 7.5cm of anything else but you will pay a high price for it

CERT = carbon emissions reduction target

[biff]

for what it is worth,
                 it is better to get the experienced installer to pump the bonded beads,getting the mixture right and ensuring a steady flow at the nozzle takes a few efforts,the nozzle has to be held horizontal or else the glue will pour out seperatly all over the shop,i suppose you could do a few trilal runs with a makeshift wall too see if it is working properly,
     after it is pumped,the difference is immediatly noticable.,, n.b.    it is relativly inexpensive,,,12 course of 100mm cavity blockwork,120ft long = 580.00euros,,drilled,pumped and supplied.
                                                                        biff

[Other-Power]

Spoke to a couple of installers.

My wall has been inject DPC treated, apparently this is a silicone based tanking method, chances are if they insulate the insulation will stop the ventilation and allow moisture to track up and bridge the tanking.

Either way then minimum cost is £200 in VAT for bonded bead and they would ask me to sign away any guarantee.

For the size of the extension I suspect its worth knocking it down and starting again by the time I have insulated the ceilings and re roofed it. 

I have a man coming around within a week to have a look and see first hand what he thinks.

Will keep you up to date.

Jon

[Fionn]

Hi Jon,
          Just on the cost side, you're looking at about £4 / m2 of wall for the SilvaPor / Perlite option if you did it yourself.
Each 100l bag at about £6.40 ex VAT & delivery would cover 2m2 of wall with a 5cm gap.
It's dusty stuff though when it's going in!
From an ecological point of view I would think perlite must be as good as anything else out there. When the house reaches end of life it could be vacuumed out of a cavity and reused elsewhere good as new I should think.
Regards,
Fionn.

[Other-Power]

Hi Jon,
          Just on the cost side, you're looking at about £4 / m2 of wall for the SilvaPor / Perlite option if you did it yourself.
Each 100l bag at about £6.40 ex VAT & delivery would cover 2m2 of wall with a 5cm gap.
It's dusty stuff though when it's going in!
From an ecological point of view I would think perlite must be as good as anything else out there. When the house reaches end of life it could be vacuumed out of a cavity and reused elsewhere good as new I should think.
Regards,
Fionn.

What is the story with fitting this, do you just plop it in from the top and poke it down or is there a tool to blow it in?

Cheers

Jon

[Fionn]

I'm not too sure how it's supposed to be done tbh but it pours very freely.
I had an open vertical section of wall cavity in my attic so just poured most of it in there.
The rest I put through a small hole at the top of one of the other walls also in the attic (was there before I started too serendipitously!)
The plan would be to drill the wall plates in 2 or 3 other locations to top it up fully.
In my case it came out in several places where there were holes (found a good hundred litre pile beside the gas meter at one stage!), it flowed around corners etc no problem, however it may leave gaps under window cills.
Apparently there are lots of plans for simple bead blowers online but I was able to rely on gravity so far (have put in a full pallet - 2.8 cubic metres) so haven't investigated.

[clockmanFR]

For blowing and sucking fine insulation particles.

Try the electric garden hoover, (general called a leaf sucker/blower) attach the sucker bit into your bag, attach your hose, i used 80mm dia flexable plastic land drain, non perforated, roll of gaffer tape for joints and take it where you want.

This is a 2 person job, one for the hose, definitely need face mask, the other for keeping the sucker in the bag and switching the machine on and off.  (added bonus here, you can shout at the wife).

The machine is cheap and the system works well, especially in confined spaces, like roof spaces.

Simples! 

[Other-Power]

Hello all,

Had the guy around, Happy to have the bonded beads put in, 25 year warranty and a water barrier.  Cost was £200 inc VAT for ~ 22m^2 so £9m^2 which is not the cheapest I can do but combination of time and other more pressing things to do on the house (rebuilding chimney in the loft) means I am getting someone in.

quoted R value is 0.033 Wm^-1K^-1 so ok, I could get this down to 0.0031Wm^-1K^-1but this would cost £90 on top.

I will post some pictures and stuff later.

Cheers

Jon