INSUL
The building acoustics software used by acoustic consultants to predict the sound insulation performance of walls, floors, glazing, and composite building elements against regulatory standards.
What it is
About INSUL
INSUL, developed by Marshall Day Acoustics (New Zealand), is the leading software tool for predicting the airborne sound insulation (Rw, Dw, DnTw) and impact sound insulation (Lw, LnTw) performance of building elements. The software uses a combination of theoretical mass-spring-mass modelling and an extensive database of measured element constructions to predict the weighted sound reduction index (Rw) of single-leaf and double-leaf walls, composite floors, glazing systems, and roof constructions across the one-third octave frequency spectrum. These predictions are compared against regulatory requirements — Part E of the Building Regulations in England and Wales, BB93 for schools, BS 8233 for residential buildings, and ISO 16283 for post-construction measurement — to determine whether a proposed construction achieves the required acoustic performance before the building is built. INSUL is the first tool in the acoustic consultant's building design workflow. When an architect proposes a party wall construction, the acoustic consultant models it in INSUL, checks whether the predicted Rw meets the required Dw,50 dB standard for a party wall between dwellings under Part E, and identifies whether additional elements (resilient bars, acoustic quilt, floating floor) are needed to close the performance gap. The tool's ability to model composite constructions — a wall with a window, a floor with a ceiling void — makes it practical for real design scenarios rather than isolated elements. Contractors and developers also use INSUL to verify that specified constructions will pass pre-completion testing under the Robust Details scheme. INSUL is available for Windows and macOS, and is one of the few acoustic software tools that runs natively on both platforms.
What you can do with it
Capabilities
Model a proposed separating wall construction in INSUL — selecting the base leaf material (medium-weight blockwork, metal stud, CLT), adding the finish layers (plasterboard, resilient bar, acoustic quilt), and reading the predicted weighted sound reduction index (Rw) to check whether the construction achieves the required 45 dB Rw for compliance with Part E Table 1a (new build dwelling party wall)
Compare two competing floor constructions in INSUL — a 150mm concrete slab with a floating screed against a timber joist floor with an acoustic mat and suspended ceiling — by running both models and reviewing the one-third octave frequency performance curves, identifying which construction has better low-frequency performance (where mass-spring resonance effects cause most dips) for a mixed-use residential development above retail
Model a glazing system in INSUL — entering the glass thickness, cavity width, and secondary pane for a proposed double-glazed unit — and predict the Rw of the glazed element to check whether it meets the minimum Dw,50 dB standard for a bedroom façade on a site where the road traffic noise level requires enhanced glazing
Use INSUL to check a composite wall construction — combining a primary blockwork leaf (modelled separately) with an attached window area — and calculate the composite Dw for the whole façade element, then compare against the BS 8233 target indoor noise level to determine whether the proposed glazing upgrade is sufficient
Investigate the effect of increasing cavity width in a double-leaf wall construction in INSUL — modelling cavity widths of 75mm, 100mm, 150mm, and 200mm with the same leaf masses — and identify the point of diminishing returns where additional cavity width produces less than 1 dB of additional Rw to optimise construction cost and acoustic performance
How to learn it
Learning Resources
INSUL user manual (insul.co.nz) — free with licence; comprehensive documentation covering all element types, input parameters, and the theoretical basis of each calculation method; essential reading before using the tool professionally
Marshall Day Acoustics INSUL tutorials (insul.co.nz/tutorials) — free video tutorials covering the core workflow: creating a new element, selecting materials, adding layers, reading results, and modelling composite constructions
Institute of Acoustics (IOA) Diploma — the Building Acoustics module covers the theoretical basis of sound insulation prediction (mass law, mass-spring-mass theory, critical frequency) that underpins correct INSUL use; essential context for interpreting predictions
NHBC Technical Guidance and Robust Details (robustdetails.com) — free; the Robust Details scheme documents tested constructions and their pre-completion test performance; cross-referencing INSUL predictions against known-passing Robust Details constructions is a good validation method for new users
Pro Tip
The Rw number INSUL gives you is for the element in isolation — not the installed Dw or field DnTw you'll see in a real building. The difference (typically 5–8 dB) is due to flanking transmission through junctions, structure-borne sound paths, and installation quality. Always design to a predicted Rw 5–8 dB above the regulatory Dw target to leave flanking margin, and cross-check your critical junctions against the robust details guidance before specifying.
Skills that use this tool
Roles that use this tool
Alternatives