Lets DESIGN the "cheapest" passive,ish house self build

SRV

Hello to everyone, im new to the boards and this is my first post.
I want to say this is a brilliant forum and the level of knowledge from the main contributers is astounding. Ive followed most threads and have learned SO much...thanks.

I have planning to build a 201m2 floor area .bungalow. I want to build it to to passive standards or low energy.......but as cheaply as is possible.
I would prefer to build with some type of block as opposed to timberframe, but lets see, there may be other methods.

I noticed a member `SAS` posted about the "mosart" house. 4" concrete blocks on the flat and external insulation and i thought it sounded like it might be an economical method. Maybe "perinsul" blocks at ground level to lower the cold bridge with the foundation.

Possibly use paroc as the external insulation?
I know about the poroton block but they would likely be quite expensive.

And depending on the level of envelope seal, the use of some type of mvhr unit ( genvex look interesting ) ,. I think they have various ways of raising the temp of the incoming air, when it would be needed. Rarely hopefully, with the right build.

The windows/ doors would obviously need to be good quality.

Regarding the insulation at ceiling level....how would you ensure there are no cold bridges in the area of the wallplate?

If the mosart house is certified passive then surely it cant be such a bad idea. Can it?


my own knowledge is quite limited and any guidence on what ive suggested above will be very much appreciated.:)

I attached my plans which shows the orientation of the house.


SRV

SRV

Hi, just to clarify what i meant by my post..............what would your ideas be on an economical house build to very low energy or passive standards?
I realise that i can acheive these standards by spending lots of money.....but i "feel" i would just be paying upfront for my energy bills.

thanks again

SRV

Mellor

Welcome to the forum SRV.
Heat recovery ventilation is a good area to look at. There are number of good products available, there are many posters who have install various types and i am sure thry will provide suggestions.
One are that is of paramount importantance when it comes to passive designs is solar gains. In your design to appear to have alot of glazing to the north east side. You should concentration the glazing to the south side, and reduce it to the north. What kind of site do you have? Would it be possible to reorientate the house in the site.

SRV

Hi Mellor, thanks.

I realised the full importance of facing the glazing south too late unfortunately. The planners have absolutely tortured me for 2 years to get to this stage and i fear changing the house position would be very problematic....maybe i could make the windows smaller on the N/E side and this might help.

If the windows on the N/E were triple glazed and e-coated to prevent heat loss, and the Soutish facing windows were double glazed in order to avail of the better solar gain that a triple might prevent. Would this be of some help...or am i going overboard on that?

Also i would opt for just a `highly efficient` house as opposed to passive, if it posed too difficult to acheive. But i think a mvhr system would be unsuitable in a house that wasnt passive??

What i mean is......does the house need to be really well sealed to be able to use heat recovery ventilation.?

So would i need to consider types of heating systems other than MVHR?

SRV

Mellor

SRV wrote: »

I realised the full importance of facing the glazing south too late unfortunately. The planners have absolutely tortured me for 2 years to get to this stage and i fear changing the house position would be very problematic....maybe i could make the windows smaller on the N/E side and this might help.

If the windows on the N/E were triple glazed and e-coated to prevent heat loss, and the Soutish facing windows were double glazed in order to avail of the better solar gain that a triple might prevent. Would this be of some help...or am i going overboard on that?

Also i would opt for just a `highly efficient` house as opposed to passive, if it posed too difficult to acheive. But i think a mvhr system would be unsuitable in a house that wasnt passive??

What i mean is......does the house need to be really well sealed to be able to use heat recovery ventilation.?

So would i need to consider types of heating systems other than MVHR?

SRV

Make the north windows as small as possible.

As for triple glazing to north and double glazing to south. This is probably a bad idea. It is true that the double allows for a higher solar gain, but is lets out much more through heat loss than it takes in to solar gain. The extra energy gained is much much less than the extra energy kept in by triple.

HRV is alwys a plus. A house need to be ventilated. Traditional methods of ventilation just let air circulate in and out of the house using wall vents. This air is often heated, this means that energy is freely escaping the house and needs to be replaced.
A HRV unit exchanges the energy from the escaping air to the incoming air, this saves energy as less energy is required to replace what is lost.
In a passive house (or a house approaching this level) a HRV unit can be used with a small heating system to control the temp of the incoming air.
But it doesn'y have to be part of the heating. It has many benefits as the ventilation system alone.

ircoha

En passant, here are some questions for you to ponder: they dont need to be answered here:

think about length of HW pipe run for ensuite shower if applicable

think about inner or outer porch doors front and back

Read up on thermal bridging:

important as u have I believe 18 opes [door/windows] I have 10 for a 4 bed

u have 13 internal external wall junctions: I have 8

but i "feel" i would just be paying upfront for my energy bills

yes that is one way of looking at it but your biils will be much reduced and you can put the capital cost on the mtg.

Is your mind set on the bay windows?

Have you considered external insulation?

SRV

IM happy to learn a mvhr unit is ok in a hse thats nearly passive envelope.
Thanks ircoha, some points i didnt think about. I could make some windows at the back of the hse smaller. I could lose one of the large kitchen windows plus the ensuite window at the end of hall.

The bay windows...why do you ask? I could also have the front flush.....ie..no bay windows.
I want to use external insulation.....as i was saying earlier, maybe like the mosart hse.


SRV

ircoha

SRV wrote: »

IM happy to learn a mvhr unit is ok in a hse thats nearly passive envelope.
Thanks ircoha, some points i didnt think about. I could make some windows at the back of the hse smallersmaller is not really the point as the cold bridging is my concern unless the work is detailed and done correctly. I could lose one of the large kitchen windows plus the ensuite window at the end of hall.nat light in head is nice I believ, would keep that one

The bay windows...why do you ask? more work more expense more detailing, this applies for any non-rht angles;) KISS Keep it straight stupid;) I could also have the front flush.....ie..no bay windows.
I want to use external insulation.....as i was saying earlier, maybe like the mosart hse.


SRV

Am not familair with mosart house so cannot comment, [wagner is the only man:) ]

The other point is to get comfortable with how you reduce/eliminate cold bridging from the foundations/ floor.

My final point on an unrelated topic is to consider rainwater recycling.

u can google for it : the essential point is that u have the heads/washing machines/ hot water all fed from ur rainwater capture tank. the cold water in the kitchen will be from the rising main/ or ur well if u are in the sticks/ and the cold in the wash hand basins will be fresh also for brushing teeth etc.

The plumbing is done such that if u run out of rain water, , the rising main clicks in..

My comment about the HW to shower was 2 fold: 1 the waste of cold water while the hot water arrives, the second is the waste of heat from the water in the pipe once u are finished.
I always try put the HWC as close to where the hw is required

SRV

Obvious when i think about it...the bay windows will now be flush!

I was "thinking" the perinsul block might be an option to reduce the cold bridge at the foundation / wall area.... But they might be very expensive...i dont know.

I will google rainwater recycling.


SRV

ircoha

U might find this link useful, someone posted it yday elsewhere: give them the credit
http://www.planningportal.gov.uk/england/professionals/en/1115314255826.html

anon1

See what you would have to do to achieve an A rating in the new house energy assessments and go for that, the heating source will have an impact there.

Look into insulated cavity closers for around the windows and possibly at top of cavity wall if building with blocks.
Look at whole window U-values, maybe conside wooden windows.

build tight, ventilate right!

Mellor

I imagine the answers to passive solar being in mind is no, basing this on previous comments from the OP. I imagine the house is past PP, but not yet at construction stage.

SRV

The house is past planning and still a green field. I have permission for a cavity build......but ive since realised that with a traditional cavity build, it is very difficult to acheive low energy / passive standards.

I am looking for the most economical method of building this house....and i also believe it should be possible to acheive great standards using simple methods. I just dont have the wealth of knowledge many on this forum have.

I had to laugh tonight watching Duncans about the house show.....they did a blow test on a timber frame build......and the many leaks they found were corrected using small narrow pieces of sticky tape in areas where you just knew they would lift and quickly.



I would love to hear any thoughts on this idea, """ 4" Concrete blocks on their flat, insulated on the outside using paroc ( lesser thickness of paroc required than polystyrene ) Excellent quality windows.
Type of floor and ceiling insulation to be queried. Using a mvhr unit. IT would seem to be a cheap method enough.

I thought this might have been a popular post for people such as myself searching for ideas on overall construction methods.

The posts that are the most informative to me and many others i imagine , are the ones where the well educated contributers have slight differances of opinion.

thanks............SRV:)

sas

SRV wrote: »

I had to laugh tonight watching Duncans about the house show.....they did a blow test on a timber frame build......and the many leaks they found were corrected using small narrow pieces of sticky tape in areas where you just knew they would lift and quickly.

Those exact same tapes and membranes were used in the Mosart passive house to achieve\ensure airtightness. I'm fairly sure I'm going to get contradicted on this one but a regular block wall (on the flat or otherwise) is not particularly airtight according to what I've read. Hence the membrane requirement for the mosart house. Those tapes are invaluable around any opening e.g. door, window etc. when aiming for an airtight house.

davidoco

Would 4" blocks on the flat not be equal in the number of blocks used as 4" block cavity wall? Same number of blocks so lay they on their side and have a cavity at least.

Also in relation to the design, I have a similar entrance hallway (although porch to front) and have found fitting an internal door (two 32" doors that slide out of the way) inside to be a real benefit. No matter what sort of front door you have the cold seems to come through.

If you had the time, a self build timber frame (not prefabricabed in factory) might be the cheapest option, although they can churn them out pretty cheap. Oversize your external wall timbers and use Ibeams or SIP http://www.ttfc.ie/kingspan_building/insulated_timber_panels.htm (self made if your mad enough) vertically to minimise thermal bridging. Counter batten externally and using suitable board and expanded metal to receive plaster.

anon1

Where are you going to source the paroc?

You could use Quinnlite blocks on the flat.

Sparky78

SRV wrote: »

The house is past planning and still a green field. I have permission for a cavity build......but ive since realised that with a traditional cavity build, it is very difficult to acheive low energy / passive standards.

I am looking for the most economical method of building this house....and i also believe it should be possible to acheive great standards using simple methods. I just dont have the wealth of knowledge many on this forum have.

I had to laugh tonight watching Duncans about the house show.....they did a blow test on a timber frame build......and the many leaks they found were corrected using small narrow pieces of sticky tape in areas where you just knew they would lift and quickly.



I would love to hear any thoughts on this idea, """ 4" Concrete blocks on their flat, insulated on the outside using paroc ( lesser thickness of paroc required than polystyrene ) Excellent quality windows.
Type of floor and ceiling insulation to be queried. Using a mvhr unit. IT would seem to be a cheap method enough.

I thought this might have been a popular post for people such as myself searching for ideas on overall construction methods.

The posts that are the most informative to me and many others i imagine , are the ones where the well educated contributers have slight differances of opinion.

thanks............SRV:)

http://www.nsai.ie/modules/certificates/uploads/pdf/IAB060260.pdf
Heres another external insulation product that looks very good and IAB certified which is very important.
The Phenolic insulation would require the least thickness of all insulation materials I think. The Window detail looks very good.
I didn't get a quote for it but i hear this system is very expensive.

Viking House

Hi SRV

Your cheapest option could be to build the house in Timber Frame without the external block wall and plaster directly onto Cement board. Build on a 300mm bed of Polystyrene and put a small heating element in the HRV unit.
A Passive foundation for a bungalow costs about €20/ft2 and TF factory insulated Passive wall and roof frames would cost about €50/€60/ft2. That's about €160k for a 2000ft2 house but you would have a degree of finishing to do yourself. It would be cheaper and more efficient to build a square 2 storey house as you would have a smaller foundation and roof.
You may need to lose the chimney and Dormer/Velux windows are a no-no. A standard Irish Dormer window looses as much energy as a complete Passive house and Velux windows loose up to 6-7 times more energy than a regular window.
Dormer houses are very difficult to get to Passive levels as you need at least 14-16 inches of insulation in the roof and this reduces the head room considerably.
If you follow the guidelines it is not that difficult to get below €200/year in heating costs.
I would also recommenend you to get the (PHPP) Passive House Planning Package as it is way ahead of DEAP or SAP.
You need to forget about cavity wall construction as it is impossible to get that to work for a Passive House. There have been plenty of Timber Frame/Poroton/Ytong Passive houses built but there have been none built using Cavity blocks to my knowledge.

ircoha

Viking House wrote: »

Hi SRV

Your cheapest option could be to build the house in Timber Frame without the external block wall and plaster directly onto Cement board. Build on a 300mm bed of Polystyrene and put a small heating element in the HRV unit.
A Passive foundation for a bungalow costs about €20/ft2 and TF factory insulated Passive wall and roof frames would cost about €50/€60/ft2. That's about €160k for a 2000ft2 house but you would have a degree of finishing to do yourself. It would be cheaper and more efficient to build a square 2 storey house as you would have a smaller foundation and roof.
You may need to lose the chimney and Dormer/Velux windows are a no-no. A standard Irish Dormer window looses as much energy as a complete Passive house and Velux windows loose up to 6-7 times more energy than a regular window. [VH have you some details on how this is arrived at please? Does it relate to the fact that they are generally on a slope in the roof or are there other considerations?
Dormer houses are very difficult to get to Passive levels as you need at least 14-16 inches of insulation in the roof and this reduces the head room considerably.
If you follow the guidelines it is not that difficult to get below €200/year in heating costs.
I would also recommenend you to get the (PHPP) Passive House Planning Package as it is way ahead of DEAP or SAP.
You need to forget about cavity wall construction as it is impossible to get that to work for a Passive House. There have been plenty of Timber Frame/Poroton/Ytong Passive houses built but there have been none built using Cavity blocks to my knowledge.

VH: just wondering are u referring to both Cavity wall and cavity block construction interchangeably here? Thanks

ps thanks for PHPP link: here for others
http://www.passive-on.org/en/index.php

Mellor

Viking House wrote: »

There have been plenty of Timber Frame/Poroton/Ytong Passive houses built but there have been none built using Cavity blocks to my knowledge.

BedZED was built using cavity construction (cavity wall, not blocks).

This is one of the fore runners of low energy development. Construction is only one side, lifrstyle is the other. BedZED is low energy in both, a passive house on its own up the mountains uses lots of energy in terms of lifestyle,

Mellor

Mellor wrote: »

BedZED is low energy in both, a passive house on its own up the mountains uses lots of energy in terms of lifestyle,

That, unfortunately is a major problem with the majority of housing in Ireland, I have built a "low energy" house, but then commute to Tallaght!

Need a local job!!! - problem reduced!

Viking House

Mellor wrote: »

BedZED was built using cavity construction (cavity wall, not blocks).
This is one of the fore runners of low energy development. Construction is only one side, lifrstyle is the other. BedZED is low energy in both, a passive house on its own up the mountains uses lots of energy in terms of lifestyle,

BedZED I agree is a very impressive development but it is not certified as a Passive House, maybe it could reach Passive standards but has it any energy calculations which show 15kw/m2 for heating.

Viking House

ircoha wrote: »

VH: just wondering are u referring to both Cavity wall and cavity block construction interchangeably here? Thanks

I meant the Cavity wall Irocho, my mistake. The 9 inch cavity block wall should be possible with 20cm wrap around insulation system and a Passive foundation.
As regards the cavity wall come to think of it, the Dutch build quite good houses and regularly use Ytong 20cm as an internal wall with heavy 10cm Rockwool batts in the cavity and Brick on the outside. I am told that there are a few Passive Houses built in Holland. I would like to see how they are built.
The walls in a Passive house are going to be thick enough though without adding extra cavities and cold outer walls. The outer wall is doing the same Rain-stopping job that a good plastering system on external insulation will do and it takes up 2 cm compared with 15 cm in a cavity wall.

SRV

Hi again, thanks for the help.

Viking House...... the idea of the 9" cavity block sounds to be an option then. IM very much leaning towards the idea of a low energy build now..for cost reasons.
When you say about 8 inches of external insulation, which type are you talking about....paroc, is it?
Would i get away with 6 inches and still have good values?

Is the external insulation very expensive?

Does the 9" cavity block with external wrap around need to have a membrane anywhere?

SRV

Sparky78

SRV wrote: »

Hi again, thanks for the help.

Viking House...... the idea of the 9" cavity block sounds to be an option then. IM very much leaning towards the idea of a low energy build now..for cost reasons.
When you say about 8 inches of external insulation, which type are you talking about....paroc, is it?
Would i get away with 6 inches and still have good values?

Is the external insulation very expensive?

Does the 9" cavity block with external wrap around need to have a membrane anywhere?

SRV

6 inches of this would do the trick.

http://www.uvalue.ie/html/pdfs/kingspan/Kooltherm%20K5%20EWB%20-%20Mar%202003.pdf

Viking House

SRV wrote: »

Viking House...... the idea of the 9" cavity block sounds to be an option then. IM very much leaning towards the idea of a low energy build now..for cost reasons.
When you say about 8 inches of external insulation, which type are you talking about....paroc, is it?
Would i get away with 6 inches and still have good values?
Is the external insulation very expensive?
Does the 9" cavity block with external wrap around need to have a membrane anywhere?

Hi SRV

The Rockwool insulation costs about €20/m2 for 10cms batts but we have to buy a truckload at the time from Germany and store it until we need it. The plaster, glue and mesh comes to about €30/m2 to buy and the labour is about €30/m2 and we charge €20/m2 for the company. So we charge €100/m2 which compares well with Greenspan and Weber who are €140/m2.
We found substantial differences (30-35%) in the heating costs of two similar houses. One was externally insulated with 150mm Polysterene and the other was externally insulated with 150mm Paroc of a similar U-value.
But Paroc is very hard to get at the moment and the nearest factory is in Poland and they have a 5 month lead time.
We now use Knauf Krimpact and Rockwool dense external waterproof insulation from Germany as they are not available here.

Most decent Polish builders are aware that you can use 125mm of Paroc which is more expensive than 150mm of Polysterene and get a better result (lower heating costs) even though the U-value of the Paroc is similar to Polysterene.
Mellor will probably pick me up again on this one but I have spoken to enough guys from the Cold Scandinavian countries to believe it. If U-value was the only factor at play here then there would be no market for the more expensive market leader. They would all use the cheaper Polysterene.

There is plenty of German/Scandinavian research to show that non breathable insulation (Polysterene, Polyeurethene) fixed externally onto a block wall increases the moisture content of the block. A damp wall looses heat quicker and this reduces the overall effect of the external insulation by 20%.

The plaster will act as an Airtightness membrane on a concrete or Poroton block wall.
Make sure they plaster down as far as the floor behind the skirting and use special tape where the wall meets the roof and where the wall meets the window frames, Foam is not enough!

Why not import a few truckloads of 175mm T16 blocks for your external walls for a better result and insulate them externally. These are relatively compact and you would fit a lot on a truck.

Mellor

Viking House wrote: »

Mellor will probably pick me up again on this one but I have spoken to enough guys from the Cold Scandinavian countries to believe it. If U-value was the only factor at play here then there would be no market for the more expensive market leader. They would all use the cheaper Polysterene.

I don't think anyone ever said that U-Values are all one should go on. I certainly didn't. I am well aware that there are much more factors to consider. Infact I could show you an example of a large building were improving the u-value (regardless of the insulation used) would actually cause the energy usage to increase.
Viking it is well know on this forum that you dislike cavity construction and block building in general. This is fine in its self, but you allow this dislike to create a bias in the info you post. You post info that could be misleading to a layperson, and have even posted info that you knew to me untrue.
I have no problem with any of the building materails you use and/or post about. And I would even consider some of them if I was in a position to build right now. But the misinformation that goes with them has no place on the forum.
You really put alot of thought and research into the low energy building field, and its a credit to you. In promoting the products you use in the way you do I feel it does more harm than good.

Just a quick note on cold bridging, there is one area that I forgot about in my build and that is where the floor meets rising walls at external doors .

I now have a cold spot at the foot of each external door where the floor concrete is resting on the concrete of the rising wall, I should have lowered this rising wall and placed another piece of insulation here, the doors are mounted outside of the concrete walls, therefore the concrete in the main walls is "inside" the insulation envelope.

But the rising walls are also attached to the foundations, I was unaware of the scandinavian "insulated foundation" system as mentioned by Viking house when I started.

mudz

hi, wondering if anyone can give me some advice. We are planning to build a 320msq house and are planning to use cavity block with 60mil of external kingspan cooltherm insulation. Our design is a mono pitch roof and we are now thinking how to do the roof. My husband likes the idea of a pre fabricated insulated sipts roof, (not sure if that is the correct spelling) and then a zinc finish. I am more leaning towards a normal roof using a good thickness of a natural insulation. I am looking at Homeatherm wood fibre insulation, as I feel to get a bit of natural product abouve us. Has anyone any adivce on this or other natural products, have also read about the soya bean spray stuff. Am I being silly to not want to be totally surrounded in a sealed phenolic box? We plan a Kacheloven tile stove heat for our main living area backed up with a boiler for the other areas and are aiming to get a pretty good energy efficient house. Any advice or links would be much appreciated. Thanks

galwaytt

don't want to pick on Viking, but Greenspan did a quote for me a couple of months ago for a building I was quoting on, and it was Eur95/m2, not 140.........this is supply & fit.

As always, one should always get their own quotes, as things are constantly changing.......

s2_ireland

Hi SRV,
A few pointers if I may...

passiv haus standard building is primarily about comfort while you are in the building.

Therefore it is worth considering the triple glazed windows as you would NEVER feel a chill when standing inside them on the coldest day. Even though the double glazed window will allow more solar gain inwards it will also lose more heat through it. Over the lifetime of the mosart house it was calculated that the triple glazed windows would provide more energy to the house than they would lose.

Window & door installation quality is crucial and can be done relatively cheaply. Expanded foam is not good enough, don't let anybody tell you it is. Having sorted the windows & doors for thermal performance & airtightness the remaining is actually simple to achieve.

With the mosart house all of the walls were plastered inside to make them airtight. No mystery there.

The 1st floor ceiling had a membrane attached before the plasterboards were added giving 2 layers of airtight sealing. One point for you to consider is the number & nature of the penetrations to the ceiling. Downlighters are probably not possible as they usually need free space above them to ventilate.

If you have a lot going on in the ceiling you could consider making the house airtight from the top of the insulation in the attic, rather than the traditional solution of airtightness materials installed below the insulation.

Consider using a raft foundation & plan for a significant depth of insulation. In the end the type of structure you use will not matter, the issue will be quality. Specifications are great but jo bloggs builder needs to be minded.
Contact Paul at SEI in Cork & buy a copy of the PHPP 2007 software. The best €140 you'll ever spend.

If you try to build near-passive it will cost you more than a passive house as you will need to install a conventional heating system. If you install a wood pellet stove with water heating & connect it to the HRV it will provide your space heating requirement.

Hope this is helpful...enjoy the project.

S

metalscrubber

Sorry bout double post,

S2, what is PHPP 2007 software?

Metal.

sas

metalscrubber wrote: »

Sorry bout double post,

S2, what is PHPP 2007 software?

Metal.

Passive House Planning Package

http://www.passiv.de/

sinnerboy

Viking House wrote: »

Most decent Polish builders are aware that you can use 125mm of Paroc which is more expensive than 150mm of Polysterene and get a better result (lower heating costs) even though the U-value of the Paroc is similar to Polysterene.

There is plenty of German/Scandinavian research to show that non breathable insulation (Polysterene, Polyeurethene) fixed externally onto a block wall increases the moisture content of the block. A damp wall looses heat quicker and this reduces the overall effect of the external insulation by 20%.

.

Not "picking you up" on anything here Viking House , but does this German and Scandinavian experience you describe ( trapped moisture in blocks) arise when buildings are installed with HRV units ? I might expect a problem with external non breathable insualtion on blockwork , where ventilation was not properly designed . In other words wouldn't the HRV tend to reduce the internal air moisture content too ( as well as recover heat ) ?

Leading on from this , I think the OP should take a good look at ICF - insulated concrete formwork - ( with HRV naturally ) . There are AFAIK now 2 companies with IAB certs , one carrying the Homebond logo .

Also to OP

No open fire - use glass front gas type or norwegian solid fuel type

Avoid recessed light unless fire safe and ait tight housing is used http://www.kaiser-elektro.de/Pressetexte/Bauen%20im%20Bestand_formular.htm- Credit to 1not24get

Silicone seal window frames intrnally and externally

Caulk to recesses in platered wall and ceiling surfaces anywhere they are pentarted by pipes or electrical services
The last few pages of this download show by photos http://www.planningportal.gov.uk/uploads/br/accredconbk.pdf

Fit front and rear entrance porches ( < 2m2 - exempt from planning in case of front <40m2 exempt from planning in case of rear)

Fit solar panels for DHW - ( exempt from planning )

No matter what construction method is chosen - buy the Homebond Manual

SRV

Thanks to everyone who helped with suggestions. S2 IRELAND...your post was very helpful!

looking into timberframe now

srv

ollie30

how about a cavity wall with 100mm insulation and 25mm insulated plasterboard to get a theoretical u-value of 0.15,but you'll have an instant heat response from your internal insulation but it's stiil not thick enough to lose the thermal mass of the block and also have the gains of the cavity board.i know thermal looping is an issue but again keep standards up and looping should be kept to a minnimum.use cavity closers or rubberoid's insulated dpc at openings,wrap an airtight membrane around 1st floor joists or concrete slabs where they rest on the inner leaf.you can put the 25mm insulation onto the internal wall first,tape the joints and seal the floor and roof junctions then apply the plasterboard seperatly,a lot more work but should get good airthightness.i'm not sure if you can wet plaster over plasterboard ,it would be easier if possible.seal all pipework,electrical points etc.i know i'll be told that the cavity system doesnt really meet the u-value stated but i think if your going to live in the house the proof will be in heating it and over a year it shoudnt be that big of a diffrence between some of the other more proven methods,but it can be a lot lot cheaper.not much point in spending 40 or 50k+interest more just to tell anyone who'll listen what u-value your walls,floor and roof are!just my say and i'm no expert but done quit a bit of research

250882

Any system you intend on using, make sure there are lots of examples of their work and they have an Irish IAB cert. I specified a certain External Insulation system on an apartment block and when it rained 3 days later all the plaster washed off.