A cavity wall insulation system is comprised of two leaves of masonry wall with a cavity filled with glass wool insulation board suitably laminated with aluminum foil facing on one side. The density and thickness of the insulation can be selected based on required U-value for the construction. These self- supportive light weight insulation boards need to be applied on wall with the help of polyamide insulation fasteners. Inside the cavity the aluminum face of the insulation should be exposed to cavity to control any possible vapour transmission. The exposed face of insulation boards need to be sealed with self- adhesive aluminium tapes. The other leaf of the wall should be constructed parallel to the insulated wall to complete the insulated cavity wall system. Insulation material should be non-combustible to comply National Building Code’s fire and life safety requirement.
The detail application methodology may vary site to site and should be as per satisfaction of the Engineer-in-charge.
Example of Cavity wall insulation system and U-value calculation
External sand cement plaster[ ref- ECBC-page C.9 max k-value for 1860 Kg/m3 density of cement plaster, sand aggregate]
Air gap (best value available)
Glass Wool Board 32 Kg/m3 and 30 mm thickness
Concrete [ ref- ECBC-page C.12 max k-value for 2400 Kg/m3 density of Concretes]
Internal gypsup plaster[ ref- ECBC-page C.9 gypsum plaster for 16 mm thickness]
Air Film resistance(inside)
The solid wall made out of 200 mm blocks, should be internally insulated with Glasswool insulation boards having Density of 24-32 Kg/m3, Thickness of 50 mm to 100 (or as required by design). A frame structure made of floor/ceiling channel, intermediate vertical and horizontal studs should be adequately filled in with the insulation and covered with wall boards.
Overall Thermal transmittance or U-value of the above system should be less than 0.40 W/m2.K to conform ECBC-2017’s requirement.
Insulation should conform to non-combustibility or incombustibility (BS 476 part 4, IS 8183), A1 fire rating (EN 13501), with limited/zero spread of flames and fire propagation to meet Class 0/Class 1 ( BS 476 part 6 & 7).
Underdeck Insulation system is made of glass wool boards suitably laminated with aluminum foil or alternatively polypropylene based facings. These light-weight insulation boards need to be applied on the underside of the masonry concrete roof with the help of polyamide fasteners; or metal wires and screws. The exposed face of insulation boards need to be sealed with self-adhesive aluminum tapes. Insulation material should be non-combustible to comply National Building Code’s fire and life safety requirement. The detail application methodology may vary site to site and should be as per satisfaction of the Engineer-in-charge.
Example of underdeck insulation system and U-value calculation
Brick bat coba + heat resistant tiles-[ ref- ECBC-page C.9 max k-value for 1120 Kg/m3 density of brick,fire clay]
RCC [ ref- ECBC-page C.12 max k-value for 2400 Kg/m3 density of Concretes]
Glass Wool Board 24 Kg/m3 and 60 mm thickness
Drywall Partition Insulation
Acoustic performance of a drywall depends on the synergic performance of each of the system components. Drywall working principle is based on ‘Mass-Spring-Mass’ concept. ‘Mass’ is the isolator, helps to reflect most of the incidental sound energy. The remaining vibration that tends to get transmitted is mostly absorbed by resilient ‘Spring’. Thus the whole system works in tandem to cut down the sound- transmission.
In a standard drywall, heavy boards on both-side of the stud acts as ‘Mass’ or Isolator and resilient insulation filled in the cavity acts as ‘Spring’ or Absorber.
Suitable/optimum mix of the laminar (good aspect ratio) insulation fibre along with micro-air-pockets uniformly distributed across the section of the insulation helps to absorbs significant amount of the incidental sound energy. It is because of multiple sound wave refractions/energy dissipation. This helps to achieve required acoustic isolation for whole system.
It is observed that with high density insulations, when the volumes of micro-air pockets are comparatively less and fibres are more compact, higher sound transmission takes place; i.e ‘Spring’ effect reduces.
On the other hand when density of insulation is too low, volumes of convective air pockets are comparatively high through which more sound waves may transmit. Hence optimum balance is required to maintain when there is not too much fibre or too much air volume.
Our recent experiments shows that low to medium density (not too low or too high) insulation materials are more suitable for drywall constructions ensuring better sound isolation results for drywall.
Specification on Drywall insulation :
Insulation material for drywall shall be lightweight blanket of Bonded Fiber Glasswool Insulation complying all quality assurance parameters as per IS 8183 having density of 16-20 Kg/m3, 50 mm thickness.
Noise absorption coefficient (NRC value) of the material should be 0.8 - 0.9 or above and when applied within drywall should achieve minimum STC-45.
Thermal resistance of the Insulation (50 mm) should be R-1.2 to 1.3 m2.K/W and thermal conductivity value should be < 0.040 W/m.K when tested as per IS 3346. Insulation material shall be incombustible in compliance with IS 8183. It should also be non-toxic, low smoke emitting, chemically inert, free from impurities like sulphar, chloride and metal shots in compliance with IS 8183. Moisture content should be less than 2% as per IS 8183. Material made of steel plants slag and added chemical pigmentation like pink or brown shall not be acceptable.
The insulation material should have green product approval like GREEN-PRO from CII-IGBC, and/or GRIHA/SVAGRIHA from TERI.
Application of the insulation should be done with the help of insulation fasteners or metal wires and completed with drywall stud, floor channel, ceiling channels and suitable drywall boards as per direction and satisfaction of Engineer-in-charge.