Additional insulation to an insulated cavity wall?

muffler

I had a recent query from a client about providing additional insulation to the cavity walls in her house which has been insulated with aeroboard when it was built.

The house is about 25 years old and while I didn't get a chance to check the actual sizes it seem the original cavity would have been 90mm wide approx. and fitted with 38mm aeroboard. The idea would be to pump whats left of the cavity but Im not so sure if its going to be value for money or not. I suggested she insulate the internal sides of the walls but money is tight apparently.

Any ideas or thoughts?

ircoha

IMO, pumping the cavity would be a waste of money:

http://www.externalwallinsulation.com/

was one of many links I got when I googled for 'external wall insulation'

maybe just do the north/east walls to start.

I have just ordered the book [stg17.50] as it is a topic of interest to me so will be happy to share content with you if of interest.
[ very slick order process if u have a paypal account: two clicks! ]

Mellor

Drylining is prob a better option. A products with a much higher resistance available for dryling. 50mm here is far better than the 50mm available in the cavity

muffler

Mellor wrote:

Drylining is prob a better option. A products with a much higher resistance available for dryling. 50mm here is far better than the 50mm available in the cavity

Yeah, my sentiments too. The other problem she has is a few draughts around the house which I believe are coming from the exit points of waste pipes etc and possibly the cavity may not be closed at eaves level.

Pumping the cavity would solve the draught issue and its bound to give a small increase in heat retention and would obviously be cheaper. Dry lining is by far the better option but is substantially dearer.

If she persists with the idea of pumping the cavity Im just wondering is it going to result in a form of bridging for the transfer of damp/water from the outer leaf to inner leaf. The house is semi detached with the gable facing west so its quite exposed to the elements.

ardara1

I THINK there is a restriction as to the minimum cavity that can be pumped - 50mm?

bbam

Interesting... I have personal experience of 2 ~2000sq feet local houses of 15-20 years that have had cavities pumped. Both houses are noticeably warmer, one had new windows fitted at the same time... both owners report lower heating costs and draughts have been reduced...
I have no buisness interest in this but have decided to pump the cavity of our new house based on these feedbacks... i will be fitting 50mm insulated boards on the inside as well...

One of the problems I found when researching is that those with the stronger opinions have often a financial interest in the background when giving advice... We personally knew the owners of these houses so trusted their experiences..

Thanks..
bam

lfcjfc

Bbam.

I am planning to do the same thing as you with a new build - pump the cavity and then dry line too. Have you any concerns regarding moisture with the full filled cavity and internal leaf drylined?

I guess with drylining like this, its important to have it done before 1st fixings to save problems with sockets, window boards etc later on

10-10-20

But isn't a requirement of cavity wall insulation that you provide ventalation within the cavity space, and by pumping it full, there won't be any air-flow?
Leading to...

If she persists with the idea of pumping the cavity Im just wondering is it going to result in a form of bridging for the transfer of damp/water from the outer leaf to inner leaf. The house is semi detached with the gable facing west so its quite exposed to the elements.

I'm sure this is documented...?

bbam

hi all..
Indeed damp could be a problem if the product is used incorrectly. There are very specific external finishes that are unsuitable and indeed areas that experience severe exposure to "driving rain" are also deemed unsuitable.
We feel that for our application these products are best.

These products have agrement board certs detailing these issues and more importantly certifing their use on this market when appropriately used. For the selfbuilder this is still the failsafe for what is suitable and any potential issues with its use, as I stated earlier I've found those with the more forceful opinions often have a financial/business interest in the background.

Any product if used incorrectly can give problems.. how often have you seen insulation hanging round in cavities looking like it was just a great place for a blocklayer to hide it !!

Regarding the 1st fix, from speaking with my sparks we are chasing the walls first so the insulation on the boards isn't compromised..

Cheers...

Viking House

lfcjfc wrote:

I am planning to do the same thing as you with a new build - pump the cavity and then dry line too. Have you any concerns regarding moisture with the full filled cavity and internal leaf drylined?

Drylining leads to lots problems for the following reasons:

The Cold Bridge areas in 4 inch block partial filled cavity walls are where the inside block sits on the foundations and around the windows and doors and where the walls meet the roof. These are the areas where condensation/fungus/mould occur when you dryline. The correct way to dryline is to leave a ventilated air gap between the drylining and the wall which eliminates the effect of the insulation between the blocks.

The best place for insulation is on the outside of your walls or foundations.
2 inches on the outside has the same effect as four inches on the inside.

sunnysoutheast

Hi Viking House

I think this post is far too definitive of things that may or may not happen - "Drylining leads to lots (of) problems", "These are the areas where condensation/fungus/mould occur....", "....eliminates the effect of the insulation between the blocks", "The best place for insulation is on the outside...." and so on.

Surely one of the key factors is how well or otherwise any building method is implemented - I am sure that it is possible to get any or all of the same problems with any of the technologies in use - we've recently heard of a couple of horror stories with the current flavour of the month ICF due to inexperienced contractors.

Yes internal drylining isn't perfect but neither is any other method, and in any case the OP was referring to a prebuilt house where the aim was to increase energy efficiency.

SSE

Mellor

Viking House wrote:

The Cold Bridge areas in 4 inch block partial filled cavity walls are where the inside block sits on the foundations and around the windows and doors and where the walls meet the roof.

I agree with you that these are the areas were there is cold bridging, or at least reduced insulation. Im not actually fully up to speed on external insulation details and I can't see how it make a large difference to this areas.
Could you link to details or even post a simple explaination on why its much different. I am probably missing something glaringly obvious.

ircoha

ircoha wrote:

IMO, pumping the cavity would be a waste of money:

http://www.externalwallinsulation.com/

was one of many links I got when I googled for 'external wall insulation'

maybe just do the north/east walls to start.

I have just ordered the book [stg17.50] as it is a topic of interest to me so will be happy to share content with you if of interest.
[ very slick order process if u have a paypal account: two clicks! ]

this arrived on Friday so i will post a summary here once I have read it.
The attached is a sample of the detail drawings from the cd that came with it.

Please respect the copyright

muffler

If I can get you all back on topic here please. It is great to get the feedback but I am still trying to get specific details of the advantages or problems associated with pumping insulation into a cavity wall that is already insulated with Aeroboard.

Viking House's input is welcome but as this is a 20 + year old house and finished in dash and is semi -d an external insulation method is not an option in this instance. As has been stated also the dry lining system may be the best bet given the circumstances but I would welcome opinions on the topic or links to articles on same.