Why thresholds matter — and why they are often wrong
Ask ten different site managers what wind speed stops a crane lift, and you will get ten different answers. Some will say 40 km/h. Some will say 50 km/h. Some will give a number in knots. A few will say it depends on the crane and the load. That last group is correct.
The problem with weather thresholds in construction is that they are often held as informal knowledge — passed from one supervisor to the next, remembered from a previous project, or picked from a weather app without any connection to a published standard or manufacturer requirement. When a project reaches a weather EOT claim or a safety investigation, those informal thresholds fall apart.
The thresholds in this guide are drawn from published standards, manufacturer guidance frameworks, coating specification bodies, and industry safety publications. Where a single number is given, it represents a widely-cited reference point rather than an absolute across all conditions. Actual thresholds for any specific operation depend on the equipment, the product, the site conditions, and the applicable local standard.
Why thresholds differ by trade
Weather affects construction operations in fundamentally different ways depending on the physical mechanism at work:
- Wind creates dynamic loads on lifted objects, increases the risk of equipment overload, affects precision, and creates surface conditions (turbulence, sway) that make certain operations unsafe regardless of the measured wind speed at ground level.
- Rain affects surface preparation and adhesion for coatings, causes material degradation for certain products, creates slipping hazards on elevated work surfaces, and can directly affect concrete placement, curing and chemical mixes.
- Temperature controls curing rates for concrete and adhesives, changes the viscosity of coatings, and triggers cold-weather protection requirements for masonry, concrete, and structural steel connections.
- Humidity governs whether coating products will cure correctly or blush, whether steel surfaces will flash-rust after abrasive blasting, and whether solvent-borne coatings can be applied without film defects.
Each trade operation has a specific set of physical constraints — and a specific body of published guidance or standards that defines what those constraints are. Understanding which standard governs the operation on your project is the first step in using weather thresholds correctly.
Craneage and lifting operations
Wind is the primary weather constraint for crane operations — but the correct threshold depends on the crane type, the load geometry, the load weight and the configuration of the lift plan. "The wind speed" is not a single number for any given crane.
How crane wind limits work
All mobile cranes, tower cranes and crawler cranes are rated by the manufacturer with a maximum in-service wind speed and an out-of-service wind speed. The in-service limit governs the maximum wind at which lifts may proceed. The out-of-service limit governs when the crane must be secured or slewed to weather.
The in-service wind limit is typically specified in the crane's load chart and may vary by:
- Crane configuration (boom length, jib attachment, luffing jib, fixed jib)
- Load size and shape — large surface-area loads (formwork panels, steel decking, pre-cast façade panels) catch significantly more wind than compact loads of equivalent mass
- Load weight as a percentage of rated capacity — some load charts reduce the allowable wind speed as the lift approaches rated capacity
- Radius and operating sector — longer radius lifts have different wind sensitivity than short-radius high-lifts
| Wind Condition | Indicative Threshold | Notes / Reference Basis |
|---|---|---|
| In-service wind limit (typical mobile crane, compact load) | 48–72 km/h (13–20 m/s) | Varies significantly by manufacturer and load chart. Always defer to the specific crane's documentation. Liebherr, Tadano, Manitowoc manufacturer guidance frameworks. |
| In-service wind limit (large surface-area loads) | Reduced — often 30–50 km/h (8–14 m/s) | The Rigger / Dogman must assess sail area effects. Formwork panels, pre-cast façade elements, and steel decking carry much higher wind loads per unit mass. AS 2550 series (Cranes, hoists and winches — safe use). |
| In-service wind limit (tower cranes) | Typically 45–72 km/h; some manufacturers rate specific configurations lower | Tower crane in-service limits vary by mast height and jib configuration. Out-of-service (free-slewing) limits are separately specified. EN 13000 (European), AS 2550 (Australian/NZ), manufacturer-specific load charts. |
| Gusts vs. sustained wind | Gust peaks, not 10-minute averages, govern | Load charts reference gust speed. A 10-minute average of 30 km/h with gusts to 55 km/h may breach the in-service threshold even if the average seems low. |
The practical implication for weather thresholds is that a standard weather forecast showing "wind 30 km/h" does not tell the site team what they need to know. The gust forecast, the load characteristics, and the specific crane's load chart together determine whether the lift can proceed.
Roofing and cladding
Roofing and cladding work is exposed, elevated, and wind-sensitive. Wind is the dominant safety constraint, but rain, temperature and surface moisture also create quality and adhesion risks.
| Condition | Indicative Threshold | Notes / Reference Basis |
|---|---|---|
| Wind (metal roofing / cladding installation) | Generally ≤ 45 km/h sustained; review with gusts > 50–55 km/h | Large metal sheets act as sails; installation becomes hazardous. Safe Work Australia Code of Practice — Working at Heights; manufacturer installation guides. |
| Wind (membrane and torch-on roofing) | ≤ 32–40 km/h | Membrane control and adhesion affected above this range. Fire risk from naked-flame application equipment increases with wind. NRCA (National Roofing Contractors Association) guidelines; AS 4654.2 (Waterproofing membranes for external above-ground use). |
| Rain / surface moisture (any roofing type) | Dry surface required | Wet surfaces compromise adhesive bonding, create slip hazards on pitched surfaces, and affect asphalt-based product application. Dew and residual moisture count — not just active rainfall. |
| Temperature (membrane application) | Typically ≥ 5°C substrate; ≥ 10°C for some cold-applied systems | Below threshold, adhesives and cold-applied membranes will not achieve design bond. Product technical data sheets — always the primary reference. |
| Humidity (torch-on, self-adhesive systems) | Surface dewpoint clearance required | High relative humidity with falling temperature causes condensation on the substrate. Apply when substrate temperature is ≥ 3°C above the dew point. |
Concrete placement and curing
Concrete is affected by temperature, rain, humidity, and wind across two distinct phases: placement (fresh) and curing (early age). Each phase has different weather constraints, and both matter contractually.
Hot weather concreting
Hot weather increases the rate of hydration, shortens the workable period, increases the risk of plastic shrinkage cracking, and can cause difficulties in achieving the specified compressive strength if the water-cement ratio is adjusted upward to maintain workability.
| Condition | Threshold / Action Level | Reference |
|---|---|---|
| Ambient temperature at placement (hot weather) | ≥ 32°C: precautions required. ≥ 38°C: exceptional measures | AS 1379 (Specification and supply of concrete) — hot weather provisions; ACI 305R (Guide to Hot Weather Concreting). |
| Concrete temperature at point of discharge | Typically ≤ 35°C (project-specific maximum in specification) | Chilled water, ice substitution, and shade for aggregate storage are common mitigation measures. AS 1379; project specification. |
| Evaporation rate | Precautions when ≥ 0.5 kg/m²/h; active protection when ≥ 1.0 kg/m²/h | Evaporation rate is a function of ambient temperature, concrete temperature, relative humidity and wind speed combined. Not wind speed alone. ACI 305R nomograph; AS 3600 curing provisions. |
Cold weather concreting
Cold weather slows hydration — extending setting times, extending the period of vulnerability to frost damage, and potentially leaving concrete unable to achieve design strength if exposed to freezing before it has reached a protective level of maturity.
| Condition | Threshold / Action Level | Reference |
|---|---|---|
| Ambient temperature at placement (cold weather) | Precautions required at ≤ 5°C; do not place when ≤ 2°C without approved cold weather plan | AS 1379 cold weather provisions; ACI 306R (Guide to Cold Weather Concreting). |
| Frost during early curing | Protect concrete until compressive strength ≥ 5 MPa (minimum) before exposure to freezing | Unprotected concrete that freezes before reaching 5 MPa will suffer irreversible damage. AS 3600; ACI 306R. |
| Rain during placement | Avoid direct rainfall onto fresh concrete surface | Rainfall alters the water-cement ratio at the surface and can cause surface defects. Covers and pour sequencing are standard mitigations. |
| Relative humidity during curing | Maintain curing conditions; low RH accelerates moisture loss | Wet hessian, curing compound or plastic sheeting required per specification. AS 3600 clause 19. |
Painting and protective coatings
Protective coatings are among the most weather-sensitive construction operations — and the technical data sheet (TDS) for the specific product is the primary threshold document. The thresholds below represent common parameters found across industrial, marine, and structural coating systems.
| Condition | Indicative Threshold | Notes / Reference |
|---|---|---|
| Substrate / ambient temperature | Typically ≥ 5°C; many epoxy systems require ≥ 10°C | Below minimum temperature, curing reactions slow or stop. Products applied in cold conditions may never achieve design DFT, adhesion or chemical resistance. Product TDS; AS/NZS 4506 (Thermosetting powder coatings for architectural applications). |
| Dew point clearance | Substrate temperature must be ≥ 3°C above the dew point | The single most commonly violated threshold in protective coating work. Condensation on a substrate that appears dry causes adhesion failure and early delamination. Measured with a dew point meter — not estimated. AS/NZS 1580.108.1; ISO 8502-4. |
| Relative humidity | Typically ≤ 85% RH; some moisture-tolerant systems rated to 95% | High humidity prolongs drying/recoating windows and can cause amine-cured epoxies to blush (surface whitening). Always check TDS. Product TDS; ISO 12944-7 (Execution and supervision of paint work). |
| Wind (application) | Typically ≤ 32 km/h for spray application; brush/roller less wind-sensitive | Wind causes overspray, increases solvent flash-off rate (affecting wet-film build), and contaminates adjacent surfaces. Enclosure or wind-break required above threshold. Manufacturer application guide. |
| Rain / imminent rain | Do not apply if rain within 4 hours (or per TDS); no application on wet substrate | Rain during or shortly after application can wash uncured coating, cause sagging, blushing, or catastrophic adhesion failure. |
| Maximum substrate temperature | Typically ≤ 50°C; varies by system | Hot steel in direct sun can exceed 60–70°C. Application to overheated substrate causes immediate solvent flash, pin-holing and reduced adhesion. Product TDS. |
Abrasive blasting and surface preparation
Abrasive blasting prepares steel surfaces for protective coatings. The quality of surface preparation is the single biggest determinant of coating life — and it is entirely weather-dependent.
| Condition | Threshold / Requirement | Reference |
|---|---|---|
| Relative humidity during blasting | Typically ≤ 85% RH; some specifications ≤ 80% | High humidity causes flash rusting of freshly blasted steel before coating application. Once flash-rusted, the surface must be re-blasted or treated. AS 1627.4 (Metal finishing — Preparation and pretreatment of surfaces — Abrasive blast cleaning); ISO 8501-1. |
| Dew point clearance | Steel temperature ≥ 3°C above dew point at time of blasting and coating | The coating must be applied before the freshly blasted surface flash-rusts. Both conditions must be satisfied simultaneously. ISO 8502-4; AS/NZS 1580.108.1. |
| Time window between blasting and coating application | Often ≤ 4 hours in high-humidity conditions; ≤ 8 hours in controlled environments | Flash rusting begins within minutes to hours on a freshly blasted surface in humid conditions. The specification defines the maximum permitted interval. AS 1627.4; project specification. |
| Rain / surface moisture | Dry, moisture-free surface required | Any surface moisture ruins the profile and triggers immediate rusting. Blasting in rain or on wet steel is ineffective and creates a safety hazard with abrasive-laden water. |
| Wind | Dust and abrasive containment required; wind affects blast pattern | HEPA-filtered vacuum blasting or containment shrouding is used in wind-exposed areas. Loose abrasive becomes an eye and skin hazard with sustained wind. Safe Work Australia — abrasive blasting guidance; state WHS regulations. |
Earthworks and compaction
Earthworks are among the most rain-sensitive construction operations. Rainfall saturates fill material, prevents compaction from achieving specified density, and can cause established fills to fail or move. Recovery from over-wet fill is time-consuming and expensive.
| Condition | Threshold / Requirement | Reference |
|---|---|---|
| Moisture content of fill at compaction | Within ± 2–3% of optimum moisture content (OMC) per Proctor test | The OMC is determined by laboratory testing of the specific fill material. Compaction outside this range will not achieve the specified density ratio. AS 1289 (Methods of testing soils for engineering purposes); project geotechnical specification. |
| Rainfall threshold for earthworks operations | Project-specific, but typically operations cease during active rainfall ≥ 1–2 mm/day for clay fills | Clay fill absorbs rainfall quickly and can become over-wet within a single rain event. Sandy and gravelly fills are more tolerant but not immune. The geotechnical engineer's recommendation governs. Project geotechnical specification. |
| Drying period after rainfall | Material-specific; may require 24–72 hours of dry weather and turning | Over-wet clay fill must be spread and allowed to dry — sometimes with mechanical mixing — before compaction can restart. There is no shortcut for this process. |
| Trafficability | Plant should not operate when working platform becomes unstable or rutting ≥ 75 mm | Large earthmoving plant on soft ground can destroy the compaction of previously placed layers, compounding delays. AS/NZS 4024.1 series (Safety of machinery); project supervision plan. |
Masonry and blockwork
Masonry is affected by temperature, rain and frost — particularly during mortar setting. Both very cold and very hot conditions create problems that require active management.
| Condition | Threshold / Requirement | Reference |
|---|---|---|
| Frost / freezing during setting | Do not lay mortar when ambient temperature is at or below 2°C or when freezing conditions are forecast within 24 hours | Frozen mortar loses strength permanently and may never achieve design bond. AS 3700 (Masonry structures); NZS 4210 (Masonry construction — Materials and workmanship). |
| Ambient temperature (cold) | Protective measures required when ambient temperature is ≤ 5°C | Mortar setting is significantly slowed at low temperatures. Enclosure, heated shelter or admixtures may be required. AS 3700; site-specific work method statement. |
| Ambient temperature (hot) | Precautions when ≥ 32°C | Hot conditions dry mortar too rapidly, preventing adequate workability and hydration. Dampen units, reduce batch sizes, and work in cooler parts of the day. |
| Rain during construction | Protect freshly laid work from direct rainfall | Rain washing into fresh mortar joints leaches cement and reduces bond. Cover completed work and fresh joints with sheeting. |
| Wind | Monitor when sustained ≥ 40 km/h on exposed elevated work | Wind accelerates mortar drying and presents working-at-heights hazards for scaffolded masonry. Safe Work Australia — working at heights guidance. |
Scaffolding and work at heights
Wind is the dominant weather constraint for scaffolding — both during erection and dismantling, and for the ongoing safety of workers on scaffold platforms.
| Condition | Threshold | Reference |
|---|---|---|
| Wind during scaffold erection and dismantling | Operations typically cease at sustained wind ≥ 45 km/h (12.5 m/s); site-specific safe work method statement governs | Safe Work Australia — Code of Practice: Managing the risks of falls at workplaces; AS/NZS 4576 (Guidelines for scaffolding safety). |
| Wind during ongoing scaffold use (workers on platform) | Assess at sustained ≥ 40 km/h; halt and evacuate at ≥ 55–65 km/h unless enclosed scaffold provides wind protection | Workers on open scaffold platforms face increased fall risk and dropped object risk in high winds. The scaffold supervisor must hold a current inspection card and enforce wind limits. AS/NZS 4576; site SWMS. |
| Rain and wet surfaces | Standing water and wet platform boards increase slip risk; assess before mobilising | Non-slip boards and drainage are standard. In persistent rain, assess each shift. |
| Lightning | Evacuate exposed scaffold before electrical storm; metal scaffold is a conductor | A lightning protection policy should be part of the project's emergency response plan. No formal wind or distance threshold — the risk is binary. Site-specific emergency response plan. |
Structural steel erection
Structural steel erection is governed by wind limits for crane operations (covered above), but also has specific weather constraints for welding, grouting, and bolted connections.
| Condition | Threshold / Requirement | Reference |
|---|---|---|
| Welding in rain or on wet steel | Not permitted without approved shelter enclosure | Moisture in or near the weld pool causes hydrogen pickup, porosity, and cracking. This is a quality defect, not just a safety concern. AS/NZS 1554.1 (Structural steel welding); AWS D1.1. |
| Preheat requirements (cold weather welding) | Material and heat input-dependent; preheat required for higher-carbon steels when ambient ≤ 5°C | Cold base metal accelerates hydrogen cracking in high-constraint welds. The Welding Procedure Specification (WPS) governs preheat requirements for the specific steel grade and joint configuration. AS/NZS 1554.1; project WPS. |
| Wind (welding) | Shielded metal arc (stick): assess above 25 km/h; gas-shielded (MIG/MAG, TIG): typically cease above 15–20 km/h unless sheltered | Wind disrupts the shielding gas envelope in gas-shielded processes, causing porosity. Enclosure or windshield required. AS/NZS 1554.1; AWS D1.1. |
| Epoxy grout for base plates | Temperature requirements as per epoxy grout TDS — typically ≥ 10°C substrate and ambient | Epoxy grout set time is highly temperature-dependent. Cold conditions require heated enclosures; hot conditions may require chilled water and rapid placement to avoid premature setting. Product TDS. |
Using thresholds contractually — what this means for EOT claims
The thresholds in this guide do more than help site teams make better daily decisions. They are the evidentiary bridge between a weather event and a contractual claim for extension of time.
An adverse weather EOT claim must demonstrate that the measured weather conditions exceeded the threshold applicable to the operation planned for those days. That requires two things:
- The applicable threshold — drawn from the standard, manufacturer's guidance, or specification that governs the operation. Not an estimate. Not site convention. The published reference.
- The measured conditions — ideally from a verifiable weather data source at or near the site, covering the relevant metric (wind, gust, rainfall, temperature, humidity) for the relevant period.
When both are documented — the threshold that applies and the conditions that exceeded it — the claim has a defensible, testable basis. The contract administrator cannot simply disagree with the weather data or dispute that the threshold exists. The evidence speaks for itself.
Standards and guidance references
The thresholds in this guide are drawn from or informed by the following published references. This list is not exhaustive — individual projects may specify additional or alternative standards.
- AS 1379 — Specification and supply of concrete (Standards Australia)
- AS 1627.4 — Metal finishing — Preparation and pretreatment of surfaces — Abrasive blast cleaning of steel
- AS 2550 series — Cranes, hoists and winches — Safe use
- AS 3600 — Concrete structures (Standards Australia)
- AS 3700 — Masonry structures (Standards Australia)
- AS/NZS 1554.1 — Structural steel welding — Welding of steel structures
- AS/NZS 1580.108.1 — Methods of test for paints and related materials — Determination of water condensation resistance
- AS/NZS 4576 — Guidelines for scaffolding safety
- NZS 4210 — Masonry construction — Materials and workmanship
- ISO 8501-1 — Preparation of steel substrates before application of paints — Visual assessment of surface cleanliness
- ISO 8502-4 — Preparation of steel substrates — Guidance on the estimation of the probability of condensation
- ISO 12944-7 — Paints and varnishes — Corrosion protection of steel structures by protective paint systems — Execution and supervision of paint work
- ACI 305R — Guide to Hot Weather Concreting (American Concrete Institute)
- ACI 306R — Guide to Cold Weather Concreting (American Concrete Institute)
- Safe Work Australia — Code of Practice: Managing the risks of falls at workplaces
- Crane manufacturer load charts — Liebherr, Tadano, Manitowoc, Kato and others publish specific in-service and out-of-service wind limits by configuration
How Construction Weather uses these thresholds
Construction Weather's trade advisory system applies weather thresholds by operation type — mapping the forecast conditions against the published limits for each trade to produce Green, Amber and Red advisories.
The 14-day advisory forecast lets site teams see, days in advance, whether forecast wind, rain, temperature or humidity conditions are likely to breach the applicable threshold for the operation they have planned. This moves the decision away from the morning weather app and towards a standards-based, advance assessment.
When the forecast moves to Amber or Red:
- The site team can make informed mobilisation and planning decisions — before labour and plant are committed.
- A formal early warning notice can be issued to the Employer while the risk is still a forecast — not after the weather has already occurred.
- The advisory record becomes part of the project's weather management history, supporting the claim narrative if an EOT is needed later.
When the weather occurs, the EOT evidence tool benchmarks the actual measured conditions at the project location against the same threshold framework, and against the historical baseline for the location and month. The result is a formatted claim document that shows the qualifying days, the threshold exceeded, and the historical context that the contract administrator needs.
Conclusion — from site knowledge to contractual evidence
Weather thresholds for construction operations are not guesswork. They are published in crane load charts, coating data sheets, concrete standards, and safety guidance. The contractors who use them systematically — to make daily decisions, to notify when thresholds are forecast to be exceeded, and to evidence when they were actually exceeded — are the ones who can demonstrate a defensible, standards-based case when a weather delay becomes a contractual claim.
The thresholds in this guide are a starting point. The primary sources — manufacturer documentation, project specifications, and the applicable standards on the specific contract — are the governing documents for any real project or claim.