# best options for cavity wall insulation?



## bb12

i'm sure this topic has been done to the death in the past, but the more i read up about it, the more confused i become. 
i'm looking for advice on how to achieve the best insulation i can in a new build while keeping it at a low cost.

its for a 300mm cavity wall ie 100mm outer leaf, 100mm cavity, 100mm inner leaf.
my initial quote from builder had 60mm kingspan thermawall (don't even know much about that) insulation.
when i asked about increasing insulation, the second quote came back with 80mm kingspan thermawall insulation to fit into the 100mm cavity.

however i've just read today that there should be a minimum of 40mm in the cavity between the insulation and the outer leaf. is this correct? i also read that you should not increase the cavity beyond 100mm because things can then get tricky when the 2 other leafs remain at 100mm.

if so is my best option to go back to the 60mm insulation and then maybe put some plasterboard with insulation up on the inside to help increase the u-value? to be honest i don't even know much about this type of plasterboard. 

any advice appreciated but bear in mind i'm not a building expert, i just want to be armed with more information for when i go back to the builder to haggle.

btw i know enough to know i don't want to go with full-fill cavity insulation with beads etc...because of cold bridging and possible future dampness etc...i'm set on sticking to the cavity wall construction.


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## Sconhome

bb12,
if you stick with the 60mm insulation in the cavity you will need to use a 25mm laminated insulation + 12,5mm plasterboard (warmboard) to just about achieve the Part L compliance of U value 0.27.

I would be very inclined to use a minimum of 50mm PIR and even up to 100mm PIR with the plasterboard laminate. The comfort levels and heat retention will be very good.

HOWEVER, it will all be a waste of time and money if the floor and the roof are not up to scratch on the specification. Or if the airtightness is not correctly installed.

If you are happy to stick with the minimum requirements so be it, for comfort in the long term you will be better off with a thermal design for the insulation of your house as a complete system. It also depends where you are in the stage of building and how flexible you budget / builder is in relation to this.

Regards,

Sean
[broken link removed][broken link removed]


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## Seanba

Before you decide on what way to construct your wall you should be aware that regulations will change in 2010 requiring a U Value of 0.21 in walls.  You would be well advised to try and achieve this.  One way is to use the QUinnlite block as the inner leaf with the 60mm kingspan board (or a similar quinn board).  The joints where the boards butt together should be taped to avoid air movement behind the boards.  Irish Agrement Board have certified the QUinnlite blocks for this type of construction so they are safe to use.  www.nsai.ie


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## RKQ

IMO 80mm kingspan in the cavity is a minimum requirement with an insulated plasterboard to the face of all external walls is a minimum requirement to meet current regulations. I'd recomment a 40mm cavity which ives an overall cavity of 120mm.

Aeroboarb Platinium can achieve similar u-value with a 95mm cavity board. Their Engineer can specify wall-ties for a larger cavity / board if required.

The general feeling is that blow-in cavity fill requires 150mm cavity to achieve current regulations. It is always a good idea to try to surpass current requirements as the regulation are changing regularly. Passive house standards will be required in afew years time.

It is easier to insulate the walls and floor during construction, to try and meet future requirements. It may be possible to retro-fit attic insulation to meet future requirements but it will be expensive to try to retro-fit wall insulation.

It really should have been specified at the design stage, as its extremly important to design the house with floor, wall & roof insulation together. I'd suggest that you get a prelimenary BER rating for your design, as this with take account of solar gain, orientation etc. I'd also suggest you do your homework and costings to compare Kingspan, Quinlite, Aeroboard etc.

Talk to your Certifier to get advice on your particular project. IMO the better you insulate your home now the more you will save in the long term.


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## joer

Just wondering if it would make a differance to pump insulation into the walls of a ,cold,bungalow which already has the aeroboard type already.
Has anyone any experience of getting it done,if it is a good job and was it very expensive.
Thanks


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## tommysmith

I got a crowd to pump insulation into a newish house , aeroboard was in the cavity but there was a good gap.  It made a big difference, as the house is warmer in the morning. I cant rember the cost but it was possibly about 1700. It was a foam that I got pumped in. The job took about half a day.  I have no regrets. 

Also top up your attic insulation.


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## joer

i did re-insulate the attic but i have not noticed any differance,that is why i was asking about getting the walls done.
Thanks for the info.


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## LouisCribben

joer said:


> i did re-insulate the attic but i have not noticed any differance,that is why i was asking about getting the walls done.
> Thanks for the info.


 
Doing the attic is good, it reduces heat losses through the ceiling.

However, most houses are a cube with 6 surfaces where heat can escape, i.e. 4 external walls, the floor and the upstairs ceiling.

So basically, insulating the ceiling is only tackling 1/6th of the problem.

A lot of heat gets out through the walls facing to the outside ........mostly through the windows. The walls are are two thirds of the surface area through which heat can escape ! 

It's definitely worth getting the walls done (and double or triple glazed windows), but even more important to eliminate all draughts.
Nothing lowers the temperature as much as draughts which is basically cold air from the outside coming into your room.

Keeping heat from escaping is a lot about common sense, the more insulation the better (up to a point where economics and the law of diminishing return comes into it).

On the subject of bungalows, my parents bungalow was built in 1980, they got the insulation redone with pump insulation recently and they doubled up the attic insulation..........the house is still quite cold, mainly because they have a lot of draughts (3 fireplaces) and lot of recessed lights, which are a terrible idea.


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## sfag

"plasterboard with insulation up on the inside to help increase the u-value" 

Double insulation generaly offers no increase in the insulating benefits. 

60mm in the cavity and 25mm on the internal wall equates to 60mm worth of heat retention and not 85. Counter intuitive I know. The heat will merely stop at the thickest piece of insualtion and pass thru the thinest. 

In 2005 the regulation was 60mm HD insualtion in the cavity.


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## eggerb

sfag said:


> Double insulation generaly offers no increase in the insulating benefits.
> 
> 60mm in the cavity and 25mm on the internal wall equates to 60mm worth of heat retention and not 85. Counter intuitive I know. The heat will merely stop at the thickest piece of insualtion and pass thru the thinest.
> 
> In 2005 the regulation was 60mm HD insualtion in the cavity.


 
Are you positive about this sfag? [broken link removed] would seem to suggest otherwise.


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## onq

sfag said:


> "plasterboard with insulation up on the inside to help increase the u-value"
> 
> Double insulation generaly offers no increase in the insulating benefits.
> 
> 60mm in the cavity and 25mm on the internal wall equates to 60mm worth of heat retention and not 85. Counter intuitive I know. The heat will merely stop at the thickest piece of insualtion and pass thru the thinest.
> 
> In 2005 the regulation was 60mm HD insualtion in the cavity.



sfag,

I'm afraid that's not only counter-intuitive - its not correct.

For the same kind of insulation, greater thickness of material reduces heat transfer.
Your comment about heat passing through the thinnest doesn't reflect the above fact - both will retard transfer.
Admittedly more efficient heat-retardent materials use less "thickness" to achieve the same level of insulation but that's like comparing apples and oranges.

However, and I want to make this perfectly clear, placing insulation on the far side of a ventilated cavity will have less of an effect due to convection, although it will still have some effect.
Ventilation of cavities is required in some forms of construction, such  as timber frame construction, to carry away moisture that has condensed on the face of the building paper.
The wider and more "open" the cavity, the more ventilated it is and the more like the external ambient environment conditions inside of the cavity become.

I fail to see the reason to keep a cavity in block construction if you're also using fully weathered external insulation - the cavity becomes redundant.
Cavities were introduced as a lightweight and materials-efficient way to prevent water penetrating to the inside of a building from outside.
If you insulate externally the insulation is protected from the effects of weather by the render coat.
This assumes you have also upgraded the ope returns, thresholds, steps and window sills.

ONQ.

[broken link removed]


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## eggerb

bb12 said:


> ... its for a 300mm cavity wall with 100mm outer leaf, 100mm cavity, 100mm inner leaf...
> 
> ... go back to the 60mm insulation and then maybe put some plasterboard with insulation up on the inside to help increase the u-value?


 
So, getting back to the OP's original question....

With a 100mm cavity, a good solution is a 60mm insulation (Kingspan seem to have two different types: Therma & Kooltherm) in the cavity and an insulated dry-lining board on the inside?


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## boots

eggerb said:


> So, getting back to the OP's original question....
> 
> With a 100mm cavity, a good solution is a 60mm insulation (Kingspan seem to have two different types: Therma & Kooltherm) in the cavity and an insulated dry-lining board on the inside?


 

This is what I think I am going to use, after going to tender on using blown bead in a 100mm cavity. 
I can always pump beads into the remaining 40mm in the future


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## RKQ

Insulation is relatively cheap especially when compared to the overall cost of a house. There are many options. Do your homework & make your own decision after advice.

I think all readers should investigate, with there Designer, Certifier & BER Assessor the correct thickness of cavity insulation required to comply with current Building Regulations.
I would not advise retro pumping a 40mm cavity, when the correct thickness can be installed now!


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## onq

RKQ said:


> Insulation is relatively cheap especially when compared to the overall cost of a house. There are many options. Do your homework & make your own decision after advice.
> 
> I think all readers should investigate, with there Designer, Certifier & BER Assessor the correct thickness of cavity insulation required to comply with current Building Regulations.
> I would not advise retro pumping a 40mm cavity, when the correct thickness can be installed now!



+1

Your BER Assessor should be able to give you advice on this and the manufacturers are more than willing to advise.

ONQ.


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## Paddycol

I read your comment with a bit of alarm : The general feeling is that blow-in cavity fill requires 150mm cavity to achieve current regulations. I am due to begin a new house build in a couple of weeeks and I have specified 150mm cavity, I had originaly specified 100mm rigid insulation and 50mm pumped but am being advised to pump-fill the entire 150mm cavity due to budgeting constraints thus saving arouind 3.5k. In addition I have specified drylining with 38mm HPDE and 12mm plasterboard. 

I had hoped that the above specification with the 150mm pumped insulation would exceed the current regulations comfortably so I would be interersted in your opinion on the above specification and would welcome your feedback.


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## onq

Paddycol,

I presume you're talking about RKQ's comment.
I think you need to find out a bit about blown fill insualtion and not from a salesman trying to sell it to you.
Then whatever specification you decide on, you need to make sure your building meets the current Part L for dwellings.
So, before you go anywhere near building you need to speak to a BER assessor confirming the type and location of your insulation.

Check here regularly for updates on Part L:

http://www.environ.ie/en/TGD/

This appears to be the current one

http://www.environ.ie/en/Publicatio...g/BuildingStandards/FileDownLoad,19069,en.pdf

The specification of a house is not something you can do in detail on AAM.
Building physics has become more and more important  since the Green Minister started cranking Part L requirements up over the past few  years.

There is a more widespread awareness of the effects of infiltration in both the house proper and unsealed interstitial cavities.
You don't just seal the internal spaces to prevent infiltration, you  seal the insulation proper to prevent a reduction in its effect to due  wind action in inclement weather.

Blow-in cavity insulation can give good results if it is correctly installed, but the difficulty is checking it afterwards to ensure there are no voids. Short of a full infra red survey of the property, how can you check without opening up averywhere?

While I have seen it used to good effect, personally I would employ it in addition to either internal of external insulation, with say a 100mm cavity.

I understand that a house with just such a hybrid approach achieved an A3 rating two years ago.

Can I direct you to the http://constructireland.ie website where you will find cutting edge reviews and discussions on all matters to do with Part L.

The latest article, with comments by Joe Little architect seems to prefer external insulation as opposed to other types, but its your choice.

[broken link removed]


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon           as a defence or support - in and of itself - should legal   action    be      taken.
Competent legal and building professionals should be asked to advise in           Real Life with rights to inspect and issue reports on the   matters    at      hand.


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## RKQ

ONQ +100%

Paddycol,TGD L is a complicated document. To comply there are many factors to consider & IMO it is not possible just to compare wall specs. One must use the combined spec for the house - floor, walls and roof.

On a personal note, at a conference last year, a Speaker believed that 150mm blow in insulation was required just to meet current standards. 

The point I was making above is insulation is very important, so get the spec right before you start to build. Surpass the current Build Reg. requirement if you can. Seek the advise of a BER Assessor.


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## Lemlin

I'm planning to go with:

100ml cavity beadding.
scratch coat on external walls for airitightness.
50ml insulated slab.
Spray foam in attic and roof areas. 
Air tightness membrane and draught taping. 

Have I enough here to go above regulations. I'm going with MHRV so want to have good insulation. Walls are block.


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## onq

You know, the whole cavity beading thing had me concerned for a long time.
Back in the day when I was learning detailing, the whole point of a cavity wall was that the outer leaf was wet and the inner leaf was dry and an air cavity plus dpms kept it that way.

Now we have a continuous link between the two leaves in the form of interstitional/cavity fill insulation.
I know there are measures taken in the matrix to resist water transfer, but still...

Sneaking suspicions linger.
The use of cavity fill in the house mentioned above was per client instruction and the cavity fill had an agrement certificate.
Workmanship generally was good, and there was no convincing or overwhelming reason for not certifying.
So the architect dodn't have a huge choice in the matter,

(drums fingers...)

ONQ.


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## Birds

I am just about to build a new house and it is with interest I read all the various options, like an earlier post I am lost as to the best foot forward. I was planning to go with Xatherm or Kingspan 60mm cavity with the joints taped and have a 62mm internal/external wall, so I was quite happy until i was then told all of these options....

150mm bead filled cavity
150mm cavity 60mm hard and the remainder bead filled.

I seem to agree with ONQ that for years we have talked about this cavity and stopping damp and thermal bridging and now it is all ok. i find it impossible to great real advice as most BER assessors ( I stress most and not all) only got into this game a few years ago and have some basic knowledge but no more. My real question is despite all the posts here I am still confused as to what is the best option I want to achieve as high a rating as is practicable...


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## threebedsemi

The point made by Birds is an interesting one, and I would like to provide some historical context to the situation which we now find ourselves in. 
Before WW2 in the UK, the function of an external wall was twofold, these being:
1. to provide structural support and 
2. to offer resistance to moisture penetration. 
Such walls were generally constructed in solid concrete or masonry, and were typically quite think. Their thickness was dictated mainly by the depth required to avoid moisture penetration through the wall to the interior of the dwelling. 
During the rebuilding effort which was required after the war, a drive to reduce the amount of material required in the walls of dwellings led to the development of the cavity wall, with the cavity taking the place of material in the role of stopping moisture ingress. These early cavities were quite narrow (40-50mm being typical) but fulfilled their stated role.
In the late 1940s and early 50s, the introduction of insulation in external walls was phased-in in order to reduce the costs of heating for working class families. The obvious location for the insulation at this stage was in the cavity, where it would be protected from both the weather and from the occupants’ use of the house internally.
The oil crises in the 1970s resulted in further insulation being incorporated into the cavity, thus resulting in ever widening cavities.  
With current and proposed levels of insulation getting ever higher (with ‘passive’ and ‘carbon neutral’ standards around the corner), the width of cavity currently which will be required in the near future (150-225mm) is in my opinion becoming impracticable.


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## onq

Looks like someone's been on the RIAI Conservation Course threebedsemi - most impressive 

Birds,

Its sounds like you've been talking to a beads salesman.
One way to have your cake and eat it is to externally insulate.

One concern will be security and structural sound deadening as well as the cold bridges at threshold/ground floor and at eaves.
Structurally the house might be built using; -


 225mm solids and hollow blocks with
 precast or cast in situ floors if required
 resting on a ring beam
 
- all to your structural engineers sepification.

External insulation, with open cill and threshold details from an approved supplier can be considered.
All of this method needs careful detailing, but it seems to be gaining popularity, even if it does seems to rest on the render for its water tightness.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon                              as a defence or support - in and of itself -         should       legal        action    be      taken.
Competent legal and building professionals should be asked to advise in                              Real Life with rights to inspect and issue       reports    on     the         matters    at      hand.


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## threebedsemi

Onq
haven't done the course, but I do seem to have more time on my hands to read lately for some reason...

In relation to your suggestion, I have recently used exactly this wall build up on a dwelling house, and I was very impressed with it. It deals with cold bridges at most junctions a good deal better than traditional cavity wall construction, allows you basically unlimited depth of insulation, and has in my opinion a clear advantage that all the insulation is in the same location. I have some concerns about the 'cavity insulation and drylining' systems currently being used, as they can have surprising results with regard to interstitial condensation within the structure.

Any external insulation system should have at least BBA certification (British Board of Agrement) if not the more expensive Irish Agrement certification, and that the fitter be approved and trained by the system supplier. Ideally meet with both the fitter and the technical advice guy from the suppliers company on site at the start of the project.

My only other reservation would be that you wouldn't want your aspiring Henry Shefflin practicing penalties up against the wall.


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## Birds

Onq, yeah a beads man as well as kingspan, builders, geothermal: everyone has a different view point, finally decided that i am going with 150mm blown cavity and then as the house is a dormer I am going to use the spray insulation for the upstairs as I can get the best result for airtightness with this method. Have investigated using other methods to and this appears to be the easiest and most straight forward. 

Has anyone done this up stairs???


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