Condensation can occur in places of thermal bridging.
The temperature difference between cold spots and the internal air temperature coupled with the high internal humidity.
This condensation can lead to mould growth.
Breathability
Breathability can be engineered into an EIFS system by proper choice of finish/insulation.
Extruded Polystyrene (EPS) based systems have good breathability which can be further enhanced using a vented base profile and a sub-insulation cavity.
Mineral wool (MW) is a breathable insulation which when used with silicone/mineral based finishes produces an EIFS system with excellent breathability suitable for old structures without a DPC.
Interior insulation seals the inner wall and does not allow internally generated humidity to escape through the wall thereby leading to high levels of humidity and hence condensation.
Space Saving
Buildings are in general valued according to their interior floor space.
Interior insulation systems typically reduce internal floor space by approx 6%.
Exterior Insulation systems have no effect on the interior space thereby increasing the property valuation by an equivalent amount.
Thermal Efficiency
External Wall Insulation (EWI) has the design flexibility to fit any u-value requirements and is commonly used for Passive Construction with u-values down to <0.1. U-value range 0.1 – 0.35
Interior insulation is normally limited to 70-80mm as reducing floor space is a serious consideration. U-value range 0.35 – 0.45
Cavity wall insulation is limited to the dimensions of the cavity which is normally 50-70mm. U-value range 0.45 – 0.6
Neighbouring properties with and without EIFS
Interior Insulation
Cavity Wall Insulation
Thermal Mass Utilisation
With an exterior insulation system all energy used to heat or cool the inner space is used and stored in the wall mass of the structure.
It uses the mass of the structure as a storage heater/cooler.
The stored energy radiates back into the structure to help maintain the desired temperature.
Interior insulation does not have this effect leading to more temperature swings in the building.
3-in-1 System
Exterior insulation is a 3-in-1 construction system:
Insulation
Plastering/levelling
Decoration
Interior insulation and Cavity Insulation only insulates.
Exterior Insulation therefore does more for your money.
Convenience in Use
Exterior Insulation renovation projects can be done while the building is in use.
With interior insulation there is substantial disruption to interiors. In most cases the property needs to be vacated when such works are in progress.
