# Why can't you inject cavity block walls



## White cloud (9 Jul 2009)

I know it's not covered by SEI grants but could someone tell me WHY cavity block injection insulation isn't included exactly? Is it ineffective? 

There seems to be a lot of complications with external insulation and exisiting building features to accomodate...

Has anyone had external insulation done and are they happy with the results? Does it change the look of a house significantly?


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## mathepac (9 Jul 2009)

Cavity-block wall injected insulation doesn't work.


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## sydthebeat (9 Jul 2009)

reasons here...

http://www.josephlittlearchitects.com/documents/hollow%20block%20wall%20assessment_BLC_260609.pdf

http://www.josephlittlearchitects.c...he Mould_Construct Ireland_Issue_6, Vol_4.pdf


to basically summerise...

there are cold bridges all over the place with hollow blocks (the webs of the block extend from outside to inside...)
these have a perverse action that allows a certain amount of air ventilation around teh walls that actually drys out the wall, making it warmer than if it was saturated with water... this aids its insulative properties...
if you pump the hollows you aid in the transference of moisture from the external to teh external, which actually reduces its insulative properties and serious increases risk of condensation and mould growth on internal surfaces... which is very bad for the health of the occupants...

and furthermore there is NO certification for any product out there for this use, and if anyone tries to tell you differently they are to be considered cowboys..!!


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## david ross (12 Jul 2009)

White cloud said:


> I know it's not covered by SEI grants but could someone tell me WHY cavity block injection insulation isn't included exactly? Is it ineffective?
> 
> There seems to be a lot of complications with external insulation and exisiting building features to accomodate...
> 
> Has anyone had external insulation done and are they happy with the results? Does it change the look of a house significantly?


I did external insulation and i m really happy with the results. Technologically, outsulation puts  forward a new way of using materials, methods and standards in  construction. 
Lightweight and speedy application has made it cost effective and convenient for all structures built in the modern day. 
Outsulation is also resistant to sun, wind, moisture, heat, cold and fire, a feature that has made it top choice in construction.


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## onq (12 Jul 2009)

sydthebeat said:


> and furthermore there is NO certification for any product out there for this use, and if anyone tries to tell you differently they are to be considered cowboys..!!



sydthebeat am I correct in saying you are talking here only about cavity block/hollow block single leafe walls and not cavity wall construction using two leafs of blockwork separated by a cavity.

I don't want to veer off topic, but I think there is insulation you can use within the continuous cavity of a cavity wall construction and I just wanted to confirm what the positon is.

ONQ.


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## Sconhome (12 Jul 2009)

This is all about 9" hollow block walls that became the vogue for Dublin builders. As sydthebeat has said it is not feasible to be done. There have been methods mooted with expanding foam to fill the voids, this does not work and serves no purpose.

The only way to insulate this ridiculous construction method is by external insulation methods. Internal drylining is far too ineffective to give you a return on the cost.

As sydthebeat pointed out Joseph Little's paper and publications in Construct Ireland explain the pros and cons of hollow block insulation methods.

People often confuse hollow block construction, which has a cavity void, with cavity wall construction which is twin wall or double leaf construction with an insulated air cavity. You can pump the remainder of this void with insulation.

If in doubt you can remove internal vent covers to see what the construction type is. A hollow block wall will be 225mm thick and most likely drylined (plasterboard on timber battens with insulation- hollow sound when tapped) giving you approx 300mm overall.
A cavity wall construction will give you plasterboard fixed to the internal block skin by spot and dab bonding (most likely) or plaster skim on render scratch coat directly on the block. You will most likely see the cavity when removing the vent cover.


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## onq (16 Jul 2009)

Thanks Sconhome, and I note I've used Kingspan products to good effect relatively recently with Hollow Block rendered construction.

It was a new extension and we used the mushroom fixings.

Most of the built up insulation was in the ventilate flat roof.

 Its warm as toast



ONQ>


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