I cannot comment in detail on the build up Jack Dunne - you'd have to be paying me to do thermal resistance calculations
but I will offer the following comments.
I don't use foam - I am very wary of insulation applied in a foam, very concerned about heat build up in and around services and potential fire hazard from foam components.
Normally all my alarms go off when I see this kind of specification.
I have very little time for importing solutions from other climates to work in Ireland.
We have a climate that is high in humidity and that varies from -16 to + 31 degrees C.
American foam solutions that claim to reduce moisture build up are hard to directly relate to Ireland.
Similarly wood pellet heating systems developed in freezing winter climates with low humidity are unlikely not work well in milder, more humid Ireland.
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To answer your question
1. I remain unconvinced by the effectiveness of applying cavity bead insulation in such a small space both in terms of its "cover" in getting into all the nooks and crannies, and in terms of its effectiveness should it start "bunching" and leaving cavities.
2. Mechanical Ventilation and Heat Reclamation Systems (MVHR systems) are in their infancy as far a I can see. In terms of permitting noise to travel from room to room they are a nightmare and in terms of allowing the penetration of adjoining spaces by cold smoke and fumes in a fire emergency they are a fatal accident waiting to happen. Finally in terms of the known issues in commercial aircon systems regarding quality of air and risk of infection (Legionnaires Disease) for example, I remain unconvinced that they are an appropriate means of addressing this matter of energy conservation in a home.
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Now for some additional comments to flesh this out a little.
These are my personal observations and opinions and I am a bit of a traditionalist when it comes to detailing.
Studies on the use of external insulation by Joe Little Architect as reported on
Construct Ireland suggest this may benefit the structure more than internal insulation. There is a trade-off in that it may take longer to heat up the space than using internal insulation. However there are a lot of one-off items to take account of when specifying external insulation like positioning of services, services penetrations, insulation below floor level, one-off insulated sills and the damage that can so easily be done by impacts.
Internal insulation requires to be not to be so super-insulating that it allows a build up of moisture on the inner face of the outer walls and so minimization of any cavity between the warm board and the walling is required. This may limit the amount of insulation you can put on before problems arise.
Both forms of insulation need to carefully consider threshold and roof details and the spread of fire through opes.
Measures to resist ropagation of flame though cavities also applies to timber frame with blockwork outer leaf construction and cavity insulation.
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Be very wary of "solutions" that suggest lite-weight, low density solutions as insulation, such as building off "solid insulation" or that rely on Autoclaved Aerated Concrete [eg Quinn-Lite]. These are useful in some situations but require careful detailing. AAC blocks are 20% the density of concrete and sometimes only 10% the compressive strength. Quinnlite need special restraints to fit heavy door frames or they may pull out of the wall in use.
Some detail suggests insulating materials at rising wall level.
Point loading of insulation is a disaster waiting to happen.
So far I have resisted the use of MVHR.
I tend to use traditional loadbearing construction and I use Rockwool when specifying timbers for roofs or walls as it resists moisture and is inherently fire retardant.
I am speccing up an extension at the moment and I am looking at both internal and external insulation solutions with a view to offering a robust, cost-effective and warm solution.
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One other thing - be careful of self-coloured render. I have had a recent report that it is softer than ordinary sand and cement render and that it can erode in high wear or severe exposure conditions. After that you have to paint it anyway, which defeats the purpose. Anyone else able to offer feedback should post to AAM to advise others.
I trust this is of some use.
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.