Insulation is specified by performance and installed by people. Comparing the common options on both.
Insulation is the material with the largest effect on running cost and the least visibility after construction. Selection should consider not only the stated performance but how reliably that performance survives installation.
Rigid board insulation at a glance
Pre-formed boards fixed in position, offering consistent thickness and predictable performance where installed carefully.
Sprayed or injected insulation at a glance
Applied in place, filling irregular spaces and conforming to the geometry it is applied into.
Thickness consistency
Rigid board insulation: Consistent by manufacture, so performance depends mainly on continuity of coverage.
Sprayed or injected insulation: Depends on application, and variation is not visible once complete.
Handling of irregular geometry
Rigid board insulation: Requires cutting, and every cut introduces a potential gap.
Sprayed or injected insulation: Conforms naturally, which is its main advantage.
Inspectability
Rigid board insulation: Visible until covered, so gaps can be identified and corrected.
Sprayed or injected insulation: Harder to verify, making applicator competence more important.
Continuity around fixings
Rigid board insulation: Interrupted at every fixing and junction unless detailed carefully.
Sprayed or injected insulation: Better, since the material flows around obstructions.
Retrofit capability
Rigid board insulation: Requires access to the space, which usually means opening construction.
Sprayed or injected insulation: Can sometimes be injected into existing cavities without major disruption.
When rigid board insulation wins
- Cavity or external applications where boards can be fixed continuously.
- Consistent thickness matters for predictable performance.
- The installation can be inspected before concealment.
- The substrate is regular enough for boards to sit flat.
When sprayed or injected insulation wins
- The space is irregular or difficult to access with boards.
- Continuity around obstructions matters.
- Retrofitting into an existing cavity.
- An experienced applicator is available with the right equipment.
How to decide
Use boards where geometry is regular and installation can be inspected, and applied systems where geometry is irregular or access is limited. In both cases the decisive factor is continuity, since gaps degrade performance far more than the choice of material.
Whichever system is used, require photographs of the installed insulation before it is concealed, floor by floor. Insulation is invisible after construction, and this record is the only evidence that what was specified was actually installed.
If you are procuring materials for a project, Domira can specify, source and verify them against the standards your drawings actually require.
Frequently Asked Questions
How much insulation is appropriate?
It should follow the performance target set by the design and any applicable requirements, rather than being chosen by thickness alone. What matters most is that the specified performance is achieved continuously, since gaps undermine the whole assembly.
Does insulation matter in a climate without cold winters?
It matters more, not less. Insulation reduces heat gain during long hot periods, which is where the cooling cost accumulates. A poorly insulated building in this climate pays for the omission every month.
Can insulation be added to an existing building?
External insulation can be retrofitted, and some cavity systems can be injected. Both are more expensive and more disruptive than installing during construction, which is why it is a decision that should be made before building rather than after occupancy.
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