--- title: "Acoustic underlay for timber: a complete floor specification" description: "Choose acoustic underlay for floating or bonded timber by checking the full system, moisture, fixing details, floor height and apartment test evidence." canonical: "https://monkeyfloors.com/acoustic-underlay/timber" language: "en-AU" published: "2026-09-25" updated: "2026-09-27" --- [Part of: Acoustic underlay: the layer that deserves a closer look](https://monkeyfloors.com/acoustic-underlay) # Acoustic underlay for timber: a complete floor specification Quick answer Choose acoustic underlay for timber after settling whether the boards will float, bond to the underlay or sit on a supporting sheet layer. The fixing method, moisture provisions and complete tested construction matter together, so obtain written acceptance of the proposed system and check it against your apartment requirements before installation. By [Monkey Floors editorial team](https://monkeyfloors.com/about) · Published 25 September 2026 · Updated 27 September 2026 · 4 min read ## At a glance Start with Floating, bonded or a supported timber system Evidence needed Board, underlay, fixing method, structure and ceiling Check before ordering Moisture, preparation, finished height and approval Timber’s character is visible in the grain. How the floor feels and sounds also depends on its support and fixing. Decide how the boards will be installed before selecting an acoustic layer. A floating engineered floor, a bonded parquetry floor and solid boards on a supporting sheet do not share one interchangeable underlay detail. ## Which timber construction are you planning? The [ATFA information sheet](https://www.atfa.com.au/uncategorized/installation-over-acoustic-underlays-consumer/) describes floating, adhesive-fixed and plywood-supported systems. Its central point is that the flooring and underlay suppliers need to accept the installation together. Questions for different timber floor constructions | Construction | Detail to confirm | Evidence to request | | --- | --- | --- | | Floating engineered timber or bamboo | Support, joints, underlay and movement allowance | A report for the proposed floating assembly | | Bonded engineered timber or parquetry | Underlay adhesion and flooring adhesion | The accepted adhesive system and a relevant bonded-floor report | | Solid timber on a supporting sheet | Sheet layer, board fixing and isolation from the slab | The complete structural and acoustic specification | These are starting points for a specification, not instructions to assemble a floor from separately selected parts. If an installer proposes another method, ask them to explain its support, fixing and evidence. Floor build-up and impact path. An impact meets the floor covering and underlay. Energy can travel through the supporting structure and radiate sound into the room below. This is a schematic, not a tested construction. Floor build-up shown schematically. The whole construction matters. ## Is floating or bonded timber quieter? Separate the sound you hear while walking in the room from the sound transmitted to the room below. A description such as “solid underfoot” does not establish a field acoustic result. For transmission, compare the proposed assemblies rather than the installation labels. The board, underlay, fixing, slab and ceiling should all be identified. [ISO 10140-3](https://www.iso.org/standard/79483.html) explains that laboratory results need allowance for conditions outside the laboratory before being applied to a building. Ask for the actual report, not a table assembled from different tests. If the proposed floor differs, have the acoustic consultant identify which differences matter and whether a site test is appropriate. The [floating versus glue-down guide](https://monkeyfloors.com/guides/floating-vs-glue-down-flooring) covers the wider installation decision. ## What should be checked when timber is bonded to underlay? Obtain written details for both bonds: underlay to substrate and timber to underlay. Identify the primer, moisture treatment and adhesive where these form part of the specification. ATFA highlights the need to consider warranty and installation practice when flooring is fixed directly to acoustic underlay. Before work, ask who accepts the complete arrangement and which instructions govern it. An underlay recommendation on its own does not answer the flooring supplier’s compatibility question. Include preparation in the quote. The installer should record the surface condition and the work required before bonding. Resolve conflicting instructions before covering the slab. ## How should solid timber fixings be detailed? Where the design includes a supporting sheet, identify its material, thickness and attachment. Ask for a section showing how the boards are fixed without creating an unintended connection through the resilient layer. The [ABCB handbook](https://www.abcb.gov.au/sites/default/files/resources/2022/Handbook-sound-transmission-insulation-in-buildings.pdf) warns that nails or screws connecting an isolated floor to the slab can reduce its acoustic performance. Use the specified fixing detail rather than choosing fastener lengths on site by guesswork. The same review should cover thresholds, skirtings and adjoining tiled areas. Read [floating-floor expansion gaps](https://monkeyfloors.com/guides/floating-floor-expansion-gaps) if the proposed timber system floats. ## Will the finished floor fit at doors and thresholds? List every layer, including supporting sheets, preparation and adhesive. Measure from the existing substrate and also compare the new finish with the floor being removed. Ask the installer to check doors, kitchen clearances, bathroom transitions and any stair junctions. A proposed reduction in underlay thickness to solve a height problem needs another compatibility and acoustic review. It is a change to the specification, not merely a dimensional adjustment. The [floor-height calculator](https://monkeyfloors.com/tools/floor-height-calculator) helps total measured layers. It does not establish clearance requirements or approve changes to a door. ## What moisture information does a timber floor need? Request the subfloor moisture assessment, the chosen system’s limits and any required treatment. ATFA explains that excessive moisture beneath timber can lead to expansion-related problems and distinguishes a vapour barrier from waterproofing. Have the flooring, adhesive and underlay requirements reconciled in one installation detail. Keep test records and preparation photographs before the surface is covered. If moisture remains unresolved, settle the cause and the specified remedy before proceeding. ## What should go into the apartment application? Start with the building’s actual by-laws or rules and any written approval requirements. The [AAAC explanatory note](https://aaac.org.au/resources/Documents/Public/AAAC%20Guideline%20for%20Apartment%20and%20Townhouse%20Acoustic%20Rating%20-%20Explanatory%20Note%20V2.0.pdf) cautions that an underlay alone cannot guarantee a rating in the completed building. - The exact timber, underlay and installation method - Any supporting sheet and the complete fixing detail - Relevant acoustic report with the full structure and ceiling described - Written compatibility of adhesives and moisture provisions - Finished height and perimeter details - Approval conditions, any test requirement and records of accepted changes Use the [flooring application reviewer](https://monkeyfloors.com/tools/flooring-application-review) to check what is missing from the document pack. For the full range of floor finishes, return to the [acoustic underlay hub](https://monkeyfloors.com/acoustic-underlay). ## Questions, answered ### What is the best acoustic underlay for engineered timber? Choose a compatible system with evidence relevant to your construction and fixing method. Neither the material name nor the thickness establishes a universal winner. Have an acoustic consultant assess differences between the test assembly and your building. ### Can engineered timber be glued to acoustic underlay? Some systems use bonded flooring over bonded underlay. Obtain a detail accepted by the flooring and underlay suppliers, including adhesives and moisture provisions. ATFA warns that direct fixing to underlay can fall outside published flooring installation practice. ### Is floating timber always quieter than glued timber? No general winner is established here. Compare reports for the proposed board, underlay and fixing method, with the same metric and relevant floor and ceiling construction. Sound heard in the room is also different from impact transmission below. ### Do solid boards need a supporting sheet over the underlay? ATFA describes systems that use plywood between solid timber and acoustic underlay. Ask for a design for the specific boards and fixing method rather than treating that as a universal detail for all solid floors. ### Is acoustic underlay also a moisture barrier? Do not assume so. Obtain the specified moisture assessment and treatment for the timber system. ATFA distinguishes moisture vapour barriers from waterproofing membranes. ## Sources 1. [Installation over acoustic underlays (consumer information)](https://www.atfa.com.au/uncategorized/installation-over-acoustic-underlays-consumer/) · Australasian Timber Flooring Association · Accessed 2026-09-27 2. [Sound transmission and insulation in buildings handbook, Version 4.0 (March 2021)](https://www.abcb.gov.au/sites/default/files/resources/2022/Handbook-sound-transmission-insulation-in-buildings.pdf) · Australian Building Codes Board · Accessed 2026-09-27 3. [ISO 10140-3:2021, laboratory impact sound insulation, published scope](https://www.iso.org/standard/79483.html) · International Organization for Standardization · Accessed 2026-09-27 4. [AAAC Apartment and Townhouse Acoustic Rating, Explanatory Note V2.0 (May 2023)](https://aaac.org.au/resources/Documents/Public/AAAC%20Guideline%20for%20Apartment%20and%20Townhouse%20Acoustic%20Rating%20-%20Explanatory%20Note%20V2.0.pdf) · Association of Australasian Acoustical Consultants · Accessed 2026-09-25 ## Goes well with Underlay ### [Acoustic underlay: the layer that deserves a closer look](https://monkeyfloors.com/acoustic-underlay) Choose acoustic underlay by floor type, installation method and test evidence. Check thickness, moisture, star claims and strata approval before work. 4 min read Acoustic flooring ### [Acoustic flooring: choosing a quieter floor](https://monkeyfloors.com/acoustic-flooring) Understand acoustic flooring as a complete system, compare test evidence and choose useful next questions about the floor, underlay and building. 15 min read Apartments ### [Best flooring for apartments: quiet, finish and fit](https://monkeyfloors.com/guides/best-flooring-for-apartments) Choose apartment flooring around sound, appearance, installation and scheme approval, with evidence to compare carpet, timber, laminate and hybrid. 25 min read