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    • CommentAuthorRadioman
    • CommentTimeOct 25th 2008
    Hi i am new here so hello:bigsmile:

    I am currently improving all aspect of the insulation on my 1930s semi and i am in the process of getting grant assisted cavity wall insulation. I have done much research on the subject and will probably opt for Polystyrene balls (bonded) however during my research i have discovered all U values for cavity wall insulation are similar 0.040 apart from Polyurethane foam which is quoted as 0.020, my problem is nobody seems to offer this as an option for cavity wall insulation, i am assuming there is a good reason for this like damp, cost possibly?

    Cavity fill installation is somthing which can't be reversed so i want to get it right first time and achieve the best U value for the wall for the 65mm cavity i have available. I don't want to just go with the normal materials only to find out i could have doubled the performance of the insulation for a little extra cost.

    Has anybody had any experience with Polyurethane Foam in cavity wall insulation, or done some deeper research, any advice or tips would be greatly appreciated.

    Thanks Radioman
    • CommentAuthorCWatters
    • CommentTimeOct 25th 2008
    Polyeurathane has indeed got a better U-Value than polystyrene but I think there must be a technical reason why loose Polueurathane beads can't be used.

    Celotex (a widely used insulation) is a polyisocyanurate which is a modified Polyeurathane foam but as far as I know they only make it in sheet form.
    • CommentAuthorMike George
    • CommentTimeOct 25th 2008 edited
    Some confusion with u-values and k-values guys. The u-value is not better for either -it is the thermal conductivity of PUR [k-value or lambda value] which is better than that for polystyrene. The u-value will be dependent upon the thickness of a given material at a particular k-value.

    Eg. If insulation A has a k-value 0f 0.02W/mK and insulation B an k-value OF 0.04W/mK. Then you would need half the thickness of insulation A over B to achieve an equal u-value

    k values measured in W/mK
    u- values measured in W/m2K
    • CommentAuthorEd Davies
    • CommentTimeOct 25th 2008
    Still some confusion, I'm afraid. R-value is simply the inverse of the U-value.

    R-values are measured in m²K/W. http://en.wikipedia.org/wiki/R-value_(insulation)
    U-values are measured in W/m²K.

    It's the k or λ value which is the conductivity of the material, independent of the thickness of a particular installation and is measured in W/mK.

    • CommentAuthorMike George
    • CommentTimeOct 25th 2008 edited
    Yes sorry Ed - I must be losing it completely. Of course I meant k-value not R-value [I did say thermal conductivity though and I did get the units right ] I'll amend that last post before I die of embarrassment:shamed:
    • CommentAuthortony
    • CommentTimeOct 25th 2008
    Re pu foam as cavity fill -- it is not used for many reasons, not formulated foe injection as beads, more dense than polystyrene, as foam it is not good as it tends to expand on curing so blows the walls apart and the house falls down!

    Your choice of polystyrene beads is a good one. I think that they may be available "platinum" coated for an even better U value
    • CommentAuthorCWatters
    • CommentTimeOct 25th 2008 edited
    Mike - I meant the U-value is better for a given thickness but I'll let you off :-)

    I have a far more embarassing story. Yesterday I did half the brick plinth for my shed and then as I was finishing I discovered a little bag of cement at the bottom of what I thought was a bag of ready mixed mortar. Had to redo it all today. :-(
    • CommentAuthorCWatters
    • CommentTimeOct 25th 2008
    Tony - so the reason is that PUR beads would have to be made in a factory whereas polystyrene beeds can be foamed on site?

    PS I've blown a wall with expanding foam. It was a stud wall in a gerage that the previous owner had driven into. I decided to foam the hole and plaster rather than cut back the plasterboard to the studs and fit a new bit. Big mistake. The wall looked fine from the garage side but when I went into the workshop on the other side the wall in that area was bowing outwards due to pressure from the expanding foam. I hardly used any foam but it keeps on expanding for a long time after you stop.
    • CommentAuthorRadioman
    • CommentTimeOct 25th 2008

    Great forum this, i have learnt loads thanks for the comments, still getting my head around the R an U values thing, i think the figures i had seen where comparisons per inch of insulation material which i didn't make clear, oops.

    I think I will forget about the expanding PU foam for my cavities, the exploding walls thing seems to make sense as it seems PU foam is mainly applied under floors or roofs where it has room to expand but not for cavities.

    I will look in to the platinum coated polystyrene balls, thanks for the tip, are there any other similar materials with higher performance i should consider?

    Thanks Paul.
    Of course an American R-value is different to a European R-value....

    • CommentAuthorRadioman
    • CommentTimeOct 29th 2008
    Found this on the National Insulation Association web site and thought it might be useful for somebody else looking in to cavity wall insulation, i think i will opt for the Carbon coated (grey) beads as the performance looks better than anything else i have seen, thanks for the help and advice and the tip about coated beads

    1 Thermal Conductivity: The k value of White expanded polystyrene bead should be taken as 0.038 W/m C - 0.040 W/m C (ref. individual BBA Certs)

    The k value of Carbon (Grey) expanded polystyrene bead should be taken as 0.032 W/m C - 0.034 W/m C (ref. individual BBA Certs)

    2 Density: A typical installed density is 12kgm3 +/- 2kgm3 (ref. individual BBA Certs)

    3 Fire: The use of polystyrene bead for cavity wall insulation does not prejudice the fire resistance properties of the wall.

    4 Water: The material is resistant to water penetration and will not transmit water across the cavity by capillary action or from below dpc level. Any rainwater penetrating the outer leaf will drain harmlessly to the footings. The product is not designed to be a water vapour barrier.:thumbup:
    Hi Radioman. Can you post a link to that web page by any chance? Very useful info and would like to see the BBA for the Carbon beads.


    • CommentAuthorCWatters
    • CommentTimeOct 30th 2008
    I had my cavities done with the platinum/silver/grey beads last year, the U value is just a tiny bit better than the white beads, but as the OP said its something that you can only do once so I looked for the best I could reasonably get.

    Product was Springvale Platinum Ecobead


    Got it done via a grant so was no more expensive than usual cavity fill, just a little bit more difficult to get the right grant that used a particular installer that used the ecobeads, thats all.

    • CommentAuthorGREGORIAN
    • CommentTimeFeb 5th 2009
    Richard, could you please advise me how you got the grant - contact details etc? I have found 2 local installers (south Wiltshire) who offer polystyrene beads but one of them has already said that I would have to pay approx 500 more than for rockwool! That was on the phone - they've yet to do the survey. Thanks, Ian
    Hi Ian,

    I contacted Springvale the manufacturer, who informed me (bear in mind this was a year ago) that Miller Patterson could install Ecobead. I contacted them, at that time only a few of the branches were using the ecobead (I think it was Salisbury one that was nearest to me), I contacted them and specifically mentioned that I wanted Ecobead. They dealt with the grant thing and then came and did the survey and install a bit later. I think it was around 200 for detatched house which is fairly typical.

    T: 01722 417132

    • CommentAuthorSimonH
    • CommentTimeFeb 5th 2009 edited
    Some other points to put you off foam and steer you towards [grey/carbon/eco] beads.

    There have been cases of properties with foam cavity fill where damp has been introduced. I believe its do to the fact it is water proof - so water wont drip down internally, but becuase it's injected from different holes you end up with hairline cracks where the separate injections meet. I.e. the crack acts as a capillary point to wick water across the join. This is olny on properties that are regularaly exposed to driven rain, so most BBA certifiactes include an assesment of whether this is likely. Even so - its still a very marginal failure rate - like a few dozen houses in the million plus that had it installed. Beads won't have this problem as there are gaps - and gravity will do it's job and make the water run down still.

    Formaldehyde! Some people after having the installation get reactions - coughing fits, skin reactions. Don't know whether this is common or substantioated, and depends on if the cavities can vent into the house - but sounds feasible.
    • CommentAuthorIanD
    • CommentTimeFeb 7th 2009
    Assuming a house is suitable for polyurethane foam, would it not improve air tightness to a much greater extent than polystyrene beads and blown mineral wool, especially where the upper floor joists penetrate the inner cavity wall? If so, does the combination of better insulation performance and air tightness mean that the performance of polyurethane foam is significantly better than those other insulations? (More so than is indicated by its lower U value alone.)

    Put another way, would polyurethane foam - in combination with other improvements in insulation and air tightness - make it possible to upgrade an existing cavity walled house to a significantly higher overall standard than could be achieved if polystyrene beads were used?
    Yes it definitely would. A current project in London is planning to use PU foam on an entire terrace of RSL houses.

    Since you only insulate a cavity wall once, and it's very expensive to further upgrade a wall with a U value of 0.4-0.65, I rather question the wisdom of giving grant aid for the inferior methods. The improved wall will permanently have a U value of 0.65 or more instead of around 0.4.
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