fibre or beads for cavity wall insulation?

thekooman · 03-07-2007 02:44PM #1

ok, this has been done to death. currently coming near the stage for pumping the cavities in a new house. we have a normal 4 inch cavity for a blocked house.

i have lived in houses previously which had bead (polypearl) filled in the cavities.they weren't the warmest. the house never retained the heat. in my parents house, they have fibre pumped in. this was a house previous to this where mould was on the walls and i remember as young fella going to bed with my hot water bottle. no need for hot water bottles now!draughts are all gone and the house is roasting within no length of time. they also have the attic pumped with fibre (looks like rockwool, something i will be going for in the attic).

anyways, everyone i talk to has a different idea on this. one crowd i got a quote off for fibre say they wouldn't touch bead; but of course they would say that.

i've also heard that you will need to top up the fibre as it can settle.
we aren't drywalling the house. just pumping the walls with fibre... or bead, if i can be convinced!

any advice would be great.

Viking House · 03-07-2007 10:23PM

Hi Kooman

Here are my thoughts on your dilemma!!

The fibre insulation is probably Cellulose and made from waste paper. As far as I know there are 2 grades of Cellulose available, the dense one is much better and less prone to slumping. Because of its density it holds onto heat a lot longer than lighter insulation.
Dense Cellulose is about 10 times heavier than Polysterene so balences out Summer overheating a lot better than Polysterene. By the same action it also slows down heatloss in the Winter. This is the perfect insulation for your roof and is one of the main reasons Lars Petterson from Scan homes gets the lowest heatloss in the country when he puts 500mm of the stuff in his roofs reaching a U-value of 0.6.

Cellulose can get wet if there is a crack in the plaster but it is also highly Hydroscopic and has a great ability to dry out as it naturally moves moisture and water vapour from damp places to drier places, displacing moisture and allowing it a greater surface area to dry. With Fibreglass for example the moisture stay in the same spot!!

Polysterene is made from closed bubbles with air inside and doesn't loose its U-value even after 10 years floating on the sea. So if it gets wet the U-value is maintained but it is too light-weight for walls in my opinion. When you get wind blowing on walls with lightweight insulation the cold is pushed through a lot quicker. Dense insulation is much more resistant to windchill.

It seems that you know from experience that denser insulations work better. So if I was in your situation I would insulate the walls with Dense Cellulose and plaster the outside of the house with one of the fibreglass mesh supported breathable mineral plasters like Drywit, Stow or Weber that are designed for single leaf applications.

I read some research recently that showed non breathable insulation in concrete block walls kept the walls damp because they were not able to dry out, making the U-values worse by 20% which could be the case with Polysterene glued together in the walls.

eoghan.geraghty · 05-07-2007 10:57AM

There is gaps of air between the beads in the bonded bead type insulation, which allows the house to breathe.
If you are going all out then render the outside wall as VH suggests, and have cellulose in the cavity.
Otherwise I would recommend the polypearl type insulation.
Ask whichever company you choose for a thermal image of your house after the work is done, pref on a cold day with heating on to ensure theres no spaces missed.
Look forward to hearing how you get on with this.

thekooman · 05-07-2007 11:14AM

thanks for the feedback guys. have decided to go with the fibre based on what has been said here, from my parents experience and from the bad experience of beads in a house previously owned by my partner.

thing is; scratch coat is nearly complete on the house so it is too late for the breathable membrane.

i have 2 quotes got for the fibre; i must investigate further with them about the thermal imaging and also the correct technical term for the fibre. will keep this post updated.

Viking House · 05-07-2007 10:37PM

Linseed oil paint could be painted onto the external cement plaster making it waterproof and breathable. Its more expensive but you dont have to paint as often.

Noviceman · 06-07-2007 02:50PM

kooman, who you got the fibre based insulation from, is it polypearl or do they just do the beads? i'm about to pump my cavbities also and was just going to go with the beads until i seen this thread...

as for the outside, starting the plastering next week, is it much more expensive to use those mineral plaster like Drywit, Stow or Weber ?

thekooman · 06-07-2007 03:10PM

got quotes from Connaght insulation in Kilkelly and Walter Moran in Castlebar for the fibre pumped insulation. they both have british standards but not irish. i haven't had time to ring them back yet to get the "technical details".

my plasterer has started outside; most of it is scratch coated. i didn't know about the membrane on the outside but vikingHouse's idea of the linseed oil paint sounds like a good idea also.

Waters10 · 04-01-2012 12:04AM

thekooman wrote: »

got quotes from Connaght insulation in Kilkelly and Walter Moran in Castlebar for the fibre pumped insulation. they both have british standards but not irish. i haven't had time to ring them back yet to get the "technical details".

my plasterer has started outside; most of it is scratch coated. i didn't know about the membrane on the outside but vikingHouse's idea of the linseed oil paint sounds like a good idea also.

Hi Kooman - At the same stage as you were above, would apppreciate if you let me know which way you went fibre pumped insulation or beed? also which of the above providers?

thekooman · 04-01-2012 12:42AM

Waters10 wrote: »

Hi Kooman - At the same stage as you were above, would apppreciate if you let me know which way you went fibre pumped insulation or beed? also which of the above providers?

Hi waters10,
I went with the fibre in the end which was done by Walter Moran in Castlebar.
I end up putting in 12 inches of Rockwool in the attic.
I think it's all a great job but the main thing is to try asnd get as much draught proofing done around doors and windows before plastering... One mistake we made but our house isn't bad.
I would love to get the thermal imagining done at some stage to see where the issues are.... An open fire chimney is one of them! :rolleyes:
Hope that's of some help

stretchaq · 04-01-2012 05:51PM

Kooman,

the blown rockwoll is a top job in my opion provided eaves ventelation is maintained etc. would you not be worried about fibre( or wool) insulation in walls sagging over time at the under neath windows and at wall plate level evectivly leaving you with a ''cold spot'' have seen this happen with wool in my existing house i am leaning towards bead in my new house?

fibre or beads for cavity wall insulation?

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