Scaffolding in winter: snow loads, ice, frost and clearing roofs
A site in December feels different. Frost covers the steel decks in the morning, the ground under the base plates softens at midday and everything freezes again at night. The scaffold itself does not change, but everything on it and under it does. Snow adds weight, ice removes grip and frost moves the ground. This guide goes through the winter issues one by one and ends with a job that is often underestimated: clearing snow from a roof while a scaffold stands against the house.
Snow as a load
Every working scaffold has a load class under EN 12811-1, which states the uniformly distributed load allowed per square metre of deck: 0.75 kN/m² for class 1, 1.50 kN/m² for class 2, 2.00 kN/m² for class 3, rising to 6.00 kN/m² for class 6. One kN/m² is roughly 100 kg per square metre. Snow counts towards that load, and snow varies a great deal.
| Type of snow | Approx. weight per m² at 10 cm (4 in) | At 20 cm (8 in) |
|---|---|---|
| Fresh powder | 5–10 kg | 10–20 kg |
| Settled snow | 20–30 kg | 40–60 kg |
| Wet or old snow | 30–50 kg | 60–100 kg |
| Ice | about 90 kg | about 180 kg |
Example: a painter's scaffold of class 2 allows 1.50 kN/m², about 150 kg per square metre. Fifteen centimetres of wet snow weigh 45–75 kg per square metre, up to half of the allowance before anyone steps on. Add a worker with tools and a bucket and the margin is thin. On a class 1 scaffold, a heavy fall of wet snow can reach the full permitted load on its own. Details in load classes and width classes.
So snow is cleared from the lifts before work starts or material is put down, without dropping it onto lower lifts or passers-by. A plastic shovel is kind to steel and aluminium decks; sharp metal edges damage the coating.
Snow on fans, sheeting and temporary roofs
More critical than snow on decks is snow on surfaces not designed to be walked on. A protective fan over a footway catches falling objects but is not made to collect unlimited snow. Sheeting that sags between two frames forms a hollow where meltwater collects, freezes and carries the next snowfall. For a temporary roof, the instructions state permitted snow loads and usually a snow depth at which it must be cleared. Keep to those values. Clear sheeted roofs early, before the snow becomes wet and heavy, and from a safe position at the edge, never standing on the sheeting itself.
Ice and slippery decks
Steel decks have perforated or embossed surfaces that grip reasonably when wet. Against hoar frost and ice they help little. The dangerous cases are the ones you cannot see: a thin film after drizzle at sub-zero temperatures, meltwater from the facade freezing on the lower lifts, ice on ladder rungs.
- Grit with sand or chippings, not salt. Salt speeds up corrosion of galvanised steel and attacks aluminium. If salt was used, rinse the parts thoroughly with water after the winter.
- Sweep the grit off again. Left on the decks in spring, it acts like ball bearings.
- Ladders and stairs first. Everyone uses the access, so clear and grit it first.
- Footwear: treaded soles, free of mud and ice; knock off boots when coming from the excavation.
- Handrails: often iced; wear gloves with grippy palms.
Whether work can go ahead on an icy morning is decided by the person in charge on site. If the ice cannot be removed, the work waits.
Frost in the ground
Frozen ground carries loads well. The trouble starts with the thaw: water that froze in the soil has lifted and loosened it, and when it melts the ground turns soft and base plates can sink. With repeated freeze-thaw cycles a base point can first rise and then settle, giving the scaffold uneven support. Particularly vulnerable are clay and loam in gardens, freshly backfilled trenches along new buildings, spots where roof or meltwater runs, and block paving on a loose sub-base.
The cure is load-spreading sole boards of sufficient size, laid on firm ground rather than on ice or a layer of snow. Clear snow from the base points before erection and divert downpipes so water does not run past the base plates. After every longer frost or thaw period, check the base jacks and readjust if needed. A hard thaw counts as an event that may affect stability, which under the UK's Work at Height Regulations 2005 means a new inspection; other countries handle this through their own national rules. See scaffolding inspection.
Tying in cold weather
Ties are fixed with eye bolts and anchors in the facade, and frost changes the conditions. Plastic plugs become brittle. Injection mortar cures much more slowly in the cold and has a minimum application temperature. Damp masonry can freeze inside the drill hole, so the anchor sits on ice instead of stone. The anchor manufacturer's instructions apply in winter too, including temperature limits and curing times. Blow out drill holes and check them for ice. When tying in the cold, pull-out tests are even more worthwhile; see ties, patterns and pull-out tests.
Heated enclosures
To stop render, mortar or adhesive from freezing, scaffolds are often wrapped in sheeting and heated inside. That changes the scaffold fundamentally:
- Wind load: closed sheeting catches the full wind. The tie pattern must be designed for sheeting; otherwise the enclosure is an alteration that needs a new inspection.
- Fire: heaters need the manufacturer's clearance to sheeting and combustible material, and the sheeting should have suitable fire behaviour.
- Fumes: gas or oil heaters inside an enclosure can produce dangerous levels of carbon monoxide. Ventilate well or use electric or indirect-fired heaters.
- Condensation: warm, moist air condenses on cold steel, so decks inside are wet or icy in the morning.
Erection and dismantling in the cold
With numb fingers every coupler is harder to grip and every pin more fiddly; gloves take away feel. Allow more time. A house that is scaffolded in one day in June can take noticeably longer in January, with short days and cold hands. Across northern Europe it is dark by mid-afternoon in December, so scaffolds on the footway must be lit and every access well illuminated.
Couplers and pins freeze solid and decks stick to icy ledgers. Do not hammer frozen parts loose; let them thaw or free them carefully. Keep strictly to the dismantling sequence and close off the area below. Let wet, snowy material dry before storing it: frames and decks stacked damp in a closed container will show white rust in spring. Frames and tubes have small drainage holes; when they are blocked with dirt or concrete, water collects inside, freezes and can bulge or split the tube. Such parts show dents or longitudinal cracks and must be scrapped. See maintaining and storing scaffolding.
Clearing snow from a roof with a scaffold in place
Two hazards have to be separated: the person falling and the snow falling. An ordinary facade scaffold ending below the eaves does not stop anyone sliding off a snowy roof. Only a scaffold built as roof edge protection, with a catch platform near the eaves and a protection screen rising above the gutter, does that; see roofing scaffolding. A slide of wet snow, on the other hand, can hit the screen and platform with a mass they are not designed for. Fans over the footway are not built for it either.
- Check whether clearing is necessary at all. For unusual amounts, flat roofs or halls, ask a structural engineer or specialist firm.
- Close off the footway and the area below the eaves first.
- Work only with suitable fall protection: roof edge protection with screen, or an anchor point with personal fall protection, used by trained people.
- Push off snow in small amounts from top to bottom, over the scaffold into the closed area where possible.
- Clear anything that lands on the lifts immediately, then check screen, platform and fan for deformation.
Roof lights and thin roof coverings are invisible under snow and not walk-on. Leave large flat roofs and hall roofs to specialists. If you need extra ties, sheeting or edge protection for a winter job, see our scaffolding components.