ETTV applies to the envelope of any air-conditioned non-residential building in Singapore, and the calculated value must meet the maximum permissible figure set out in the Code on Envelope Thermal Performance for Buildings before the Building and Construction Authority approves the submission. Project teams should prepare the ETTV calculation early and engage a qualified Professional Engineer to verify the figures before the formal submission is lodged.
TL;DR:
- Achieving a lower ETTV than the regulatory maximum improves a project’s Green Mark energy efficiency score, especially when combined with optimized façade design.
- Proper calculation requires accurate inputs for window-to-wall ratios, U-values, shading coefficients, and correction factors, with errors often stemming from generic data or orientation mismatches.
- The scope of ETTV applies only to conditioned non-residential building envelopes, requiring careful zoning of cooled areas to avoid unnecessary recalculations or compliance issues.
- Design strategies such as reducing glazing area on exposed facades, using low shading coefficient glass, and adding external shading devices are key to meeting strict ETTV targets.
- Early engagement with a qualified engineer and consultant support significantly eases the process and minimizes delays caused by submission errors or mismatched documentation.
Table of Contents
- What ETTV is and how it differs from OTTV, RTTV and RETV
- ETTV calculation: formula components, variables and common inputs
- Regulatory thresholds and Green Mark linkage
- When ETTV applies: scope, conditioned area thresholds and exemptions
- What to include in a BCA/CoreNet submission
- Design and façade strategies to meet ETTV
- How Aman Engineering Consultancy supports ETTV compliance
- Common mistakes and inspector gotchas that delay approval
- Services for ETTV and submission support
- Sources
- FAQ
What ETTV is and how it differs from OTTV, RTTV and RETV
Envelope Thermal Transfer Value, or ETTV, measures the rate of heat gain through a building’s external walls and glazing, expressed in watts per square meter of façade area. It replaces the older Overall Thermal Transfer Value (OTTV) framework because OTTV understated the contribution of solar radiation passing through windows, a gap that mattered increasingly as glazed façades became common in Singapore’s commercial towers, reflecting improved accuracy in ETTV. Academic analysis of the metric’s development has shown that ETTV correlates more closely with actual cooling energy demand than OTTV did, which is the reason regulators moved to the newer formula.
ETTV is not the only envelope metric in circulation, and building professionals need to know which one applies to their project type. The NEA teaching module on building envelope performance sets out the distinctions clearly:
- ETTV applies to the vertical envelope, walls and windows, of air-conditioned non-residential buildings.
- RTTV, Roof Thermal Transfer Value, applies to the horizontal roof envelope and uses a related but separate formula.
- RETV, Residential Envelope Transfer Value, applies to residential developments and reflects different occupancy and cooling patterns than commercial buildings.
- OTTV is the legacy metric that ETTV superseded in Singapore’s non-residential code, though the term still appears in older documents and in some overseas jurisdictions.
Because ETTV feeds directly into a building’s estimated cooling load, it also carries weight in BCA’s Green Mark scoring. A design that achieves a lower ETTV than the regulatory maximum tends to score better on energy efficiency criteria, which links the metric to certification outcomes well beyond the basic pass or fail check at plan approval stage. Building professionals working on both new developments and major additions and alterations should treat ETTV as a design constraint from the earliest schematic stage rather than a compliance exercise left until the mechanical and electrical drawings are finalized.
ETTV calculation: formula components, variables and common inputs
The ETTV formula combines three heat transfer pathways into a single weighted figure: conduction through opaque walls, conduction through glazing, and solar radiation transmitted through glazing. Each pathway is calculated separately for every façade orientation, then combined and weighted by area to produce the building’s overall ETTV. The Code on Envelope Thermal Performance for Buildings sets out the exact formula, the lookup tables, and the correction factors that every calculation must reference.
Preparing an accurate calculation involves working through a defined sequence of inputs:
- Establish the window-to-wall ratio (WWR) for each façade orientation, calculated as the glazed area divided by the total gross façade area for that orientation.
- Determine the wall U-value (Uw) and frame U-value (Uf) from manufacturer data or the material tables published in the code, since these govern the conduction component of the formula.
- Identify the shading coefficient (SC) of the specified glazing product from the manufacturer’s technical data sheet, which quantifies how much solar heat the glass admits relative to a reference standard.
- Apply the correction factor (CF) for each orientation from the code’s lookup tables, which adjusts the solar component for the sun’s path and the local climate.
- Weight each orientation’s contribution by its façade area and sum the results to arrive at the building’s aggregate ETTV.
The most frequent source of error is not a wrong formula but a wrong input: designers pulling shading coefficients from generic glass catalogs rather than the specific coated or laminated product being specified, or applying a correction factor meant for one orientation to a different one. Both mistakes produce an ETTV figure that looks compliant on paper but does not reflect what will actually be built.
A correlation between ETTV and cooling energy demand has been documented in engineering literature examining the metric’s design intent, which is one reason CoreNet reviewers scrutinize glazing data and correction factors closely rather than accepting rounded or estimated figures.
Regulatory thresholds and Green Mark linkage
BCA’s code sets a maximum permissible ETTV for air-conditioned non-residential buildings, and residential developments are assessed against a separate RETV limit rather than ETTV itself. Readers should verify the exact figure that applies to their specific building typology and gross floor area against the current code and the Green Mark 2021 assessment materials rather than relying on a single remembered number, since thresholds can differ by building class and have been revised across code editions.
BCA’s Green Mark 2021 (GM:2021) framework incorporates updated assessment documents and scoresheets that took effect from June 1, 2024, and these materials link envelope performance directly to certification scoring. A few points matter for teams planning a submission around this framework:
- Lower ETTV or RETV values than the regulatory maximum contribute directly to Green Mark energy efficiency points, not just to a pass or fail outcome at plan check.
- Residential projects are commonly assessed against RETV rather than ETTV, and BCA’s residential Green Mark materials reference the applicable maximum for that building type.
- The GM:2021 second edition documents replaced earlier scoresheets, so any calculation template or reference sheet dated before the update should be checked against the current version before submission.
- Achieving a materially lower envelope figure than the bare minimum often costs little at the design stage but becomes expensive to retrofit once the façade is built, which is the practical argument for tackling ETTV early rather than treating it as a late-stage compliance check.
When ETTV applies: scope, conditioned area thresholds and exemptions
ETTV assessment applies specifically to the air-conditioned portions of a non-residential building envelope, which means the first task in any project is establishing exactly which parts of the building are mechanically cooled and which are naturally ventilated. BCA’s legislation pages on environmental sustainability for new buildings and major additions and alterations set out the current scope and the project categories that trigger a submission requirement, and these should be checked directly rather than assumed from precedent, since thresholds have been adjusted across code revisions.
Practical scoping considerations for design teams include:
- Non-air-conditioned buildings and spaces fall outside ETTV assessment entirely, since the metric exists specifically to estimate cooling-related heat gain.
- Residential developments use RETV instead of ETTV, reflecting different occupancy schedules and cooling strategies than commercial or institutional buildings.
- Mixed-mode buildings, where only part of the floor area is air-conditioned, require careful zoning of the conditioned gross floor area so the ETTV calculation only covers the envelope enclosing the cooled zones.
- Major additions and alterations projects are subject to the same envelope requirements as new buildings where the addition affects the air-conditioned envelope, which is a point that some retrofit teams overlook.
Zoning the conditioned floor area correctly at the outset avoids a common rework scenario where a naturally ventilated void or plant area is mistakenly included in the ETTV envelope calculation, unnecessarily tightening the figure the design has to meet.
What to include in a BCA/CoreNet submission
A complete ETTV submission through BCA’s CoreNet X and ES online portal system draws on a specific set of templates rather than a free-form calculation sheet, and reviewers expect the format to match the current published version. BCA’s legislation and templates page lists the current documents, and the ES online portal is the channel through which submissions are lodged.
The typical submission sequence runs as follows:
- Compile the ETTV/RETV Calculation Format, commonly referenced as BPD_BP04, with every orientation’s WWR, U-values, shading coefficients and correction factors clearly tabulated.
- Prepare the Air Conditioning System Information Template alongside an energy modelling form where the project’s mechanical system interacts with the envelope performance claim.
- Attach daylighting documentation where the project claims daylighting credit under Green Mark, since this interacts with the glazing specification used in the ETTV calculation.
- Obtain sign-off from the relevant Professional Engineer, with the mechanical engineer’s endorsement expected on submissions where HVAC system performance is linked to the envelope claim.
- Lodge the design-stage submission through CoreNet X, expecting reviewer queries focused on orientation weighting, correction factor selection and glazing data sourcing.
- Follow through with an as-built submission once construction is complete, confirming that installed materials match the specifications used in the original calculation, ahead of the Certificate of Statutory Completion (CSC) check.
Reviewers most often query submissions where the as-built glazing or shading device differs from what was calculated at design stage, which is why keeping the ETTV file open and revisable through the construction period, rather than closing it at plan approval, avoids a late scramble before CSC.
Design and façade strategies to meet ETTV
Meeting a demanding ETTV target rarely comes down to one design decision, and the strongest-performing projects usually combine several moderate interventions rather than one aggressive one. Façade-level strategies include:
- Reducing window-to-wall ratio on the most solar-exposed orientations, typically west and east façades in Singapore’s latitude, where full glazing carries the heaviest solar penalty.
- Specifying low shading coefficient glazing, including coated or laminated products, which admits daylight while blocking a larger share of solar heat than clear glass.
- Adding external shading devices, fins or louvers, which physically intercept solar radiation before it reaches the glass and can reduce the effective correction factor applied in the calculation.
- Considering double-skin façade systems on premium or landmark projects where the budget supports the added construction cost and the architectural intent favors a fully glazed appearance.
Opaque wall performance matters as well, even though glazing tends to dominate the ETTV conversation. Increasing wall insulation and reducing the wall U-value lowers the conduction component of the formula, and specifying cladding with lower solar absorptance, generally lighter colors, reduces the heat the wall surface absorbs before it conducts inward. These measures carry their own trade-offs: added insulation thickness affects floor-to-floor heights and cladding weight, and any material change must still satisfy fire safety requirements for external wall systems.
Operational and systems-level levers can also ease the ETTV burden without touching the façade design at all. Zoning the conditioned floor area tightly, so that only genuinely air-conditioned space counts toward the envelope calculation, narrows the area subject to the requirement. Coordinating the energy model with the mechanical engineer early, rather than after the façade is fixed, lets the design team trade off WWR and shading against daylight goals without a late redesign.
Pro Tip: Run a preliminary ETTV check at the concept design stage, before glazing products are locked in, since swapping a shading coefficient later in the process is far cheaper than re-detailing a façade that has already gone to tender.
How Aman Engineering Consultancy supports ETTV compliance
Aman Engineering Consultancy supports project teams through the full ETTV compliance pathway, from early screening to final verification. Typical engagement stages include:
- Preliminary ETTV screening at concept design, flagging façade choices that risk exceeding the regulatory maximum before they are locked into tender drawings.
- Full ETTV calculation and reporting using the current BCA calculation format, coordinated with the project’s mechanical engineering scope.
- CoreNet submission support, preparing the documentation set and responding to reviewer queries during the design-stage approval process.
- As-built verification and façade inspection support, confirming installed materials match the approved calculation ahead of the Certificate of Statutory Completion.
Engaging a consultant at the concept stage, rather than after the façade design is finalized, gives the design team the widest range of options for meeting the target without cost penalty.
Common mistakes and inspector gotchas that delay approval
Recurring issues that stall ETTV approval include using the wrong conditioned gross floor area, averaging WWR incorrectly across orientations, pulling outdated correction factor tables, and submitting without the required Professional Engineer signature. A short pre-submission check helps catch these before a reviewer does:
- Confirm the conditioned GFA matches the mechanical drawings, not an assumed or rounded figure.
- Verify WWR and correction factors are applied per orientation, never averaged across the whole building.
- Check that glazing shading coefficients come from current manufacturer data, not a superseded catalog.
Pro Tip: Have a second engineer not involved in the original calculation review the orientation weighting before submission, since this is the step most often flagged by CoreNet reviewers.
— Aman
Services for ETTV and submission support
Meeting an ETTV target and getting the submission through CoreNet without repeated queries takes more than a spreadsheet, it takes coordination between façade design, mechanical engineering and statutory documentation. Consultancy firms provide this coordination directly for developers and building owners across Singapore.
Services relevant to ETTV compliance include:
- Authority Approvals, covering the statutory submission process end to end.
- Periodic Façade Inspection (PFI), verifying envelope condition and as-built compliance.
- Mechanical Engineering consultancy, coordinating HVAC system data with the envelope calculation.
- Green Mark Professional (GMP) support, linking ETTV performance to certification scoring.
Project teams preparing an ETTV submission can review Aman’s full range of statutory and engineering services on the Aman Engineering Consultancy site or go directly to the Authority Approvals page to request a scope discussion for a specific project.
Sources
FAQ
What is the ETTV calculation?
The ETTV calculation combines wall conduction, glazing conduction and solar radiation through glazing into a single weighted figure expressed in watts per square meter, using inputs like WWR, U-values, shading coefficients and orientation correction factors. The Code on Envelope Thermal Performance for Buildings sets out the exact formula and reference tables. Every orientation is calculated separately, then weighted by façade area to produce the building’s overall result.
How is OTTV calculated?
OTTV, the metric ETTV replaced in Singapore’s non-residential code, followed a similar structure of wall and glazing conduction plus solar gain, but it is understood to have represented solar heat gain through glazing less accurately than the current ETTV formula does. Singapore projects today calculate ETTV rather than OTTV, referencing the Code on Envelope Thermal Performance for Buildings. The term OTTV mainly persists in older documents and in some other jurisdictions’ codes.
What is the code for envelope thermal performance in buildings?
The governing document is the Code on Envelope Thermal Performance for Buildings, published by the Building and Construction Authority. It contains the ETTV and RETV formulas, correction factor tables and the submission requirements that apply to air-conditioned non-residential buildings in Singapore. Project teams should reference the current edition rather than an older cached copy.
What does ETTV stand for?
ETTV stands for Envelope Thermal Transfer Value, a measure of the rate of heat gain through a building’s external walls and windows. It applies to air-conditioned non-residential buildings in Singapore and is regulated under the Code on Envelope Thermal Performance for Buildings. Residential buildings are instead assessed against RETV, a related but distinct metric.