# best cavity wall insulation method



## ollie30 (20 Feb 2007)

myself and a friend went to the self build show in belfast at wend,we spoke to the main insulation companys present i myself am intersted in external insulation he is going to use cavity insulation,to exceed way beyong regs. kingspan said they have a 100mm cavity board but couldnt say what u value he'd get,it's not in brochure or web site,xtratherm say to use 80mm cavity board,insulated dry line to reach .015,when asked about dew point at party wall meet outer wall they say its insulated anyway by cavity insulation and any differnce wont affect it finally aerobord say to use their 140mm cavity board in a 150mm cavity to reach u value 0.019.is this the best method ,and is dry lining that bad when cavity is insulated.some pople say kingspan is best but as far as i can see aerobord wins for being the most straight forward ,any thoughts?


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## NOAH (20 Feb 2007)

The practice these days is to blow fill the cavities with beads as that fills the lot. I am looking at various methods and to be honest its all a sales pitch. The bigger the cavity, the bigger the amount of inuslation used , = better u value.  My builder used 60mm aerobord, wrong thickness should have used 75mm but at least I have some insulation. I am going to fill gap with polybeads. I think  the new cavity is 6 ins.  Started at 2, then 4 and now 6.  My advice use the best possible at the time, do floors as well, use underfloor heating, double glazing and thats it.

noah


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## ollie30 (20 Feb 2007)

thanks noah,thats my worry,what is and what isnt a sales pitch i thought a lot of people werent confident of bead fill but i suppose each person has their own prefernce,i like the sound of the aerobord 140mm it comes with wall ties and at 0.019 u value (if thats true)it's pretty good.does any one have an oppinion on the cavity insulation and interior insulated slabs would mould and damp occour at party wall junctions in time????


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## nutty nut (21 Feb 2007)

ollie30 said:


> i like the sound of the aerobord 140mm it comes with wall ties and at 0.019 u value (if thats true)it's pretty good


With partial fill insulation it would be necessary to leave a 40mm air cavity so the overall width of your cavity is going to be 180mm or just over 7 inches. I would be concerned about this in a standard cavity wall with 2 conc. block leafs.


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## Carpenter (21 Feb 2007)

Whatever product you go for ensure it has a current IAB cert ensuring it is suitable for use in our climate.  Extra large cavities will require special care and attention with regarding to wall ties, lintols, cills and DPC treatment!


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## tufty1 (21 Feb 2007)

Is not the whole point of a cavity to provide insulation (using a board) and prevent moisture passing from the outer leaf into the innner leaf? Cavity ties have a little knot or dip in them so any water passing along the tie will drip off. By filling the cavity with these beads you are now providing a perfect route for water to pass to the inner wall! 
I have always been told to stay well away from these cavity filling companies as its basically a con! Much better to dry line your walls internally.


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## PaddyH (21 Feb 2007)

My builder filled the cavity and both the builder and I regret he did it - we've had alot of problem with damp - builder filled the cavity in 2 other houses and said he had same problem - also spoke to another builder last week who said that cavity filling was not a good method - he also said that it was important to keep the cavity air tight - as whatever inches of air were left after the insulation board would help the insulate the house - if the air was moving - it would not help.


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## Carpenter (21 Feb 2007)

There are some conflicting views on full vs. partial cavity insulation.  Most full cavity fill products (including blown bead etc) are only suitable for buildings of limited height in certain exposure conditions (generally best avoided in coastal regions or in buildings more than 3 storeys in height).  Using full fill is not a good idea where the external wall is brickwork- brick is (relatively) porous by nature and this coupled with the many mortar joints provide a ready path for wind driven moisture to penetrate a building cavity like the cavity in cavity wall construction.  For this reason alone it is wise to have some residual cavity as opposed to full fill insulation.  Rendered blockwork (particularly dry dashed finishes) will resist wind driven moisture (except for the occassional hair line crack) and are at less risk from moisture migrasting across a cavity.  As PaddyH says air movement in the cavity should be minimised where possible- this can cause "thermal looping" which will dramatically affect the performance of your insulation.  This also applies to dry lining- air gaps at board edges must be sealed to prevent "looping".  There are a number of considerations when deciding on the best way to insulate a dwelling (or any other building)- response time, thermal mass, likely use patterns of the dwelling and pay back.  Dry lining is great, it delivers a rapid response time but the thermal mass of the concrete blockwork behind is lost, somewhat....


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## sas (21 Feb 2007)

PaddyH said:


> My builder filled the cavity and both the builder and I regret he did it - we've had alot of problem with damp - builder filled the cavity in 2 other houses and said he had same problem - also spoke to another builder last week who said that cavity filling was not a good method - he also said that it was important to keep the cavity air tight - as whatever inches of air were left after the insulation board would help the insulate the house - if the air was moving - it would not help.


 
Would you care to mention what full fill product was used in your home? Something I'm interested in. 

If its one of the products with an IAB cert then I presume you intend making a complaint to the relevant body?


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## PaddyH (21 Feb 2007)

I'm currently waiting for the builder to get back to me with this information


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## Johnny Boy (21 Feb 2007)

Although I have put insulation in the cavity cost around €2000 I am kinda of suspicious that it does give value for money. However good that the blocklayer tries mortar will fall down between it and the wall creating a space. What purpose does it have or what good does it do in the cavity? Would one be better to have insulated boards or the same insulation on the inside of the house? This is buggin me


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## ninsaga (21 Feb 2007)

Johnny Boy said:


> Although I have put insulation in the cavity cost around €2000 I am kinda of suspicious that it does give value for money. However good that the blocklayer tries mortar will fall down between it and the wall creating a space. What purpose does it have or what good does it do in the cavity? Would one be better to have insulated boards or the same insulation on the inside of the house? This is buggin me



I can picture the scene a few years from now....people visiting their psycho analysts ..... driven demented trying to find out what is really happening inside their walls!


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## ollie30 (21 Feb 2007)

nutty nut said:


> With partial fill insulation it would be necessary to leave a 40mm air cavity so the overall width of your cavity is going to be 180mm or just over 7 inches. I would be concerned about this in a standard cavity wall with 2 conc. block leafs.


guy from aerobord reckons a 150mm cavity(ties come with the insulation)the boards have little 10mm ridges that form a way to channel any moisture down,cant remember are the ridges inward or outward touching the outer leaf (i think inward)                                                     i would have a fear of the fulfill beads for the damp reasons.can anyone say if an insulated cavity(lets say 60mm kingspan)with interior insulated slabs would get mould or condensation in future years at a party/outer wall junction as some suggest in forums??would slabbing all interior walls be the answer if that is true or is that just too expensive in the real world.thanks ollie


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## masonchat (22 Feb 2007)

as a blocklayer myself i can say that the cavity is one of the most important things to watch out for  when building a house, a good block layer will have a clean cavity with no mortar behind the insulation or on the wall ties, would run a hundred miles from filling a cavity, any anyone who has done so and is having trouble with damp, best option is to dry line but the key is to run dpc behind the 2by1s  b4 you secure them to the wall


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