How to assess wind and snow loads for greenhouses

Wind and snow load figures are meaningful only when the reference basis, test method, greenhouse configuration, foundation and site are compatible. This guide explains how to compare technical data reliably and what to clarify before ordering and installation.

Wind and snow load data are intended to show which climatic effects a greenhouse in a defined specification can withstand. Yet one figure rarely answers the whole question. The calculation method, reference basis, installed accessories, anchoring and actual plot location all matter.

This guide helps you read technical documents methodically. It does not replace a local assessment or structural review where needed. Find an initial overview of designs in greenhouses and conservatories. Other buyers’ experiences in greenhouse reviews can be useful, but they do not replace documented load values.

What a load-capacity figure really tells you

A structural load rating describes the behaviour of a specified construction under stated assumptions. It is not a general promise that every model will deliver identical performance at every site, with every installation method and in every weather condition.

For a reliable interpretation, at least the following must be known:

• Load type: wind pressure, wind suction, snow or another action.
• Reference basis: for example speed, area load or weight per area.
• Design condition: The figure may relate to serviceability, calculated capacity or a test condition.
• Tested configuration: dimensions, glazing, number of doors and windows, braces and other components.
• Boundary conditions: foundation, fixings, closed openings and defined ground conditions.

If any of these points is missing, do not use the figure alone to make a purchase decision. Request the supporting explanation and confirm that the documented version matches your order.

Wind data: clarify the meaning before comparing

Wind can press against a greenhouse, create suction on the sheltered side and cause uplift at the roof. Forces are uneven. Corners, roof edges, ridges, doors and vents can experience higher local loads.

A stated wind speed cannot therefore be judged by its size alone. Establish whether it refers to a gust or averaged wind, the height at which it was applied and the terrain profile used. Open ground, a coastal site, a slope and dense development produce different airflow.

The building envelope also matters. A closed door produces a different pressure distribution from an open or incompletely locked door. The same applies to roof vents. When choosing lean-to or freestanding structures, consider their different load paths; the guide wall-mounted or freestanding pergola explains this principle for pergolas.

Terms that can change a wind rating

Term	Why it matters
Gust speed	A short peak cannot be directly compared with a longer averaged value.
Reference height	Wind speed changes with height and the surface roughness of the terrain.
Terrain category	Open land and dense development result in different wind profiles.
Basic or design wind	Terms can represent different calculation stages, depending on the documentation system.
Wind pressure	A pressure value already includes assumptions that need checking for a simple speed figure.
Closed building envelope	Open doors or windows can alter internal pressure and component loading.

Do not simply compare two speed values. Compare the complete definitions. The same applies to other outdoor structures. For winter weather effects on a pergola, see Pergola in winter: snow, ice and wind.

Snow loads: ground snow is not roof snow

Snow load on the ground describes a climatic action at a site. It is not automatically the load a particular greenhouse roof may carry. Roof shape, pitch, drifting, adjoining taller structures and local snow accumulation all affect roof loading.

Snow can slide from a pitched glass or panel roof, but this must not be assumed without limit. Wet snow can stick, ice can obstruct drainage, and uneven load patterns can form at eaves, ridges or junctions. As well as evenly distributed snow, asymmetric loading matters.

Ask specifically whether a manufacturer figure means an allowable roof load, an assumed ground snow load or only a test load. If documents merely state “snow load” without the reference area and underlying configuration, the statement remains incomplete.

Why snow depth alone is unreliable

Ten centimetres of loose fresh snow weighs considerably less than the same depth of wet, compacted snow. An ice layer can be heavier again. Ageing, temperature changes and rain increase density without a matching visible rise in depth.

A blanket conversion from centimetres of snow to an area load is therefore unsuitable for safety decisions. Mass per area, rather than depth alone, is decisive. Also observe whether snow gathers on one roof side, behind an obstruction or at a connection.

Compare greenhouse specifications correctly

Create the same comparison matrix for every model considered. Product size and construction must match, because a figure for a smaller version cannot be transferred to a longer or wider version without confirmation. The pergola size guide shows why dimensions and intended use must be considered together in a related product group.

1. Record the model, external dimensions and roof shape.
2. Record the type and thickness of glazing or panels.
3. Check the precise definition of wind and snow load.
4. List all required braces, reinforcements and anchors.
5. Check whether doors, windows and accessories form part of the assessed specification.
6. Compare identical units and the same design reference.
7. Keep exclusions and installation conditions in writing.

Roof-covering material is also part of the system. Background information on multiwall sheets is available in polycarbonate for greenhouses. Material thickness alone does not prove overall capacity; profiles, connections and fixings must transfer forces together.

The site can determine the decision

A structure suitable for a sheltered urban location is not automatically suitable for an exposed plot. Relevant factors include local wind and snow conditions, topographical features, terrain elevation and nearby obstructions. The criteria applicable at the actual site must be checked locally.

Pay particular attention to escarpments, changes in ground level, open fields, valleys with channelled airflow and spaces between buildings. Taller neighbouring buildings can redirect wind and drift snow onto a lower roof. Trees may partly break wind, but can also cause turbulence, falling branches or falling snow.

The desired garden design must not be confused with structural suitability. Inspiration such as Victorian greenhouses or an orangery greenhouse helps with design choices, but load requirements must still be confirmed separately.

Record site exposure systematically

• Is the plot densely built-up, loosely developed or largely open?
• Is the installation location on a crest, slope or near a terrain edge?
• Are there taller buildings, walls or roofs from which snow can slide or drift?
• Could trees, loose objects or roof tiles strike the greenhouse in a storm?
• Is there sufficient clearance to inspect the roof and fixings safely?
• Can water drain away from the foundation?
• Will doors remain reliably shut and locked during storms?

Document the site with dimensions and photographs from several directions. If a sauna is also planned, assess its location separately. This applies whether you choose an outdoor sauna Elma S or a barrel sauna HC150 ; documents for different construction types must not be mixed.

Permission, local criteria and professional assessment

Whether permission, notification or another approval step is needed in Malta depends on the Planning Authority classification, planning policies, sanitary rules, site restrictions, size, use and location. The Development Notification Order is conditional and does not remove other consents. Ask a perit to assess the specific proposal before ordering.

For an introduction, see planning permission for a greenhouse or pergola. Only the competent authority or appropriately qualified professionals can give binding advice for a specific plot.

Professional assessment is particularly worthwhile where local requirements approach the documented limit, the site is exposed, a special foundation is planned or the intended configuration differs from the documents. For unresolved technical questions, you can also contact Bloomcabin.

Foundation and anchors are part of the load path

Wind and snow forces do not end at the aluminium frame. They pass through profiles, corner connections and base points into anchors, foundations and the ground. Any break in this load path can limit overall performance.

A level foundation supports plumb, aligned installation. It must also suit the specified fixings and subsoil. Existing paving, a thin slab or kerbstone cannot automatically be assumed to provide a load-bearing anchor base. Consider drainage and potential settlement too.

Do not transfer foundation requirements from one product group to another. The pergola foundation guide explains general planning principles, but does not replace greenhouse installation requirements. The requirements of an outdoor sauna Elma L also differ from those of a light glazed structure.

Basic rule: High frame strength does not compensate for inadequate anchoring. Use every specified fixing point and do not change the load path without technical approval.

Before ordering: technical-document checklist

• Is wind data available with definition, unit and boundary conditions?
• Is it clear whether snow load concerns ground or roof?
• Does the figure apply exactly to the required size and glazing?
• Are required reinforcements and anchors included or obtained separately?
• Is the required foundation design described?
• Are restrictions for doors, vents and accessories stated?
• Have local permission and load criteria been checked?
• Is access suitable for delivery and safe temporary storage?
• Are current installation documents available before work begins?

Guidance on the ordering process is available under how to order. Information about logistics and goods receipt is in purchasing and delivery. For information on cross-border greenhouse deliveries, see greenhouse delivery to Austria and Switzerland .

Goods receipt and installation

On arrival, check the number and external condition of all packages. Compare labels and parts lists before disposing of packaging. Profiles, panels and fittings should be stored dry and safely in line with product-specific instructions. A complete check before installation reduces the risk of a missing part during a critical step.

Use only the documents supplied for the delivered version. Instructions for a similar size or visually related model may specify different drillings, connectors or braces. This principle also applies to kits such as the barrel sauna HC 180. Do not mix parts or instructions from different models.

Quality checks during installation

1. Check foundation dimensions, level and diagonals before assembly.
2. First align the frame as instructed and secure connections in the specified sequence.
3. Install every brace in the stated position.
4. Fit panels or panes without stress and in the correct orientation.
5. Check doors and windows for free movement, full closure and secure locking.
6. Install every specified anchor; do not omit fixing points.
7. After completion, inspect frame geometry, connectors and drainage routes.

Improvised drilling, omitted braces or independently substituted screws can alter the assessed configuration. If anything is unclear, stop installation and clarify the technical question before continuing.

Maintenance preserves the installed condition

A load rating normally assumes correct installation and proper maintenance. Regularly inspect anchors, screw connections, seals, glazing retainers, doors and roof vents. An additional visual inspection is sensible after a severe storm or unusual snow loading.

Remove leaves and debris from drainage routes. Rectify loose parts promptly and use suitable replacements. More detailed advice is available in caring for your aluminium greenhouse. Information on possible guarantee terms is available separately under guarantee.

The internal climate affects use, but must not be planned as snow-load protection. See temperature and humidity in the greenhouse for control guidance.

Common mistakes when reading load ratings

• A gust speed is directly compared with an averaged wind speed.
• A ground snow load is interpreted as an allowable roof load.
• A value for a small model is transferred to a larger version.
• Material thickness is equated with whole-system capacity.
• A sheltered garden is considered wind-free without a site assessment.
• Anchoring is regarded as an accessory rather than part of the load-bearing structure.
• Open roof vents are ignored in wind assessment.
• Photographs, reviews or many years of use are treated as structural proof.
• A visually similar structure is assumed technically equivalent.
• Later-installed accessories are not checked for structural effects.

The distinction between a bioclimatic and classic pergola also shows that outwardly similar garden structures can work differently in technical terms. Always read load values for the specific product and configuration.

Frequently asked questions

Is a higher wind speed always better?

Only if both figures use the same wind definition, reference height, averaging period, terrain category, safety basis and product configuration. Otherwise, the higher number may simply result from a different presentation method.

Can I convert wind pressure into wind speed?

A rough physical conversion is possible, but normally inadequate for product comparison. Pressure coefficients, gust assumptions, height, terrain, roof shape and internal pressure influence actual component loading. Do not use a conversion instead of the complete specification.

Is ground snow load the weight my greenhouse roof can carry?

No. Ground snow load is a site value. Roof load is derived from it while considering roof and site conditions. Ask for the specific design basis of the greenhouse you want.

How many centimetres of snow equal a stated snow load?

This cannot be answered reliably without knowing snow density. Dry fresh snow, compacted old snow, wet snow and ice have very different weights. Mass per area, not visible depth alone, is decisive.

Does an aluminium frame remove wind and snow risks?

No. Aluminium allows lightweight, corrosion-resistant construction, but does not remove the need for correct design. Profile geometry, connections, glazing, braces, anchors and foundations determine performance together.

Does a greenhouse attached to a house automatically become stronger?

Not automatically. The connection can transfer forces, but must be suitably designed and installed. A house wall, roof edge and airflow also alter loading. Fixing to façade layers without a proven load path is not a reliable reinforcement.

Do trees or fences provide sufficient wind protection?

They can influence airflow but cannot guarantee adequate protection. Turbulence forms behind obstacles; trees change with the seasons and can lose branches. The structure must suit the governing local action.

Should roof vents remain open during a storm?

Openings should generally be closed and locked securely in line with product and operating instructions. An open window can increase internal pressure and be damaged itself. Check automatic openers for correct function and closing behaviour.

Will heating melt enough snow to protect the roof?

Safety should not depend on this. Heat distribution, outdoor temperature, power failures, insulation and snow type are not reliably constant. Partial melting can also create heavier wet snow or ice.

Can I add braces or anchors to increase the load rating?

A modification can improve or impair force transfer, or shift loads into unsuitable components. Adding material alone does not create a higher load rating. Changes need a technically sound assessment and should be agreed with the manufacturer or suitable professionals.

What if the local requirement exceeds the product rating?

Do not assume the product is sufficient in that documented configuration. Choose a demonstrably suitable specification or have a professional solution assessed. A lower manufacturer value cannot be replaced by experience or assumptions.

Do customer photos prove load capacity?

No. Photos can illustrate design, installation surroundings and use. They do not show hidden anchors, actual wind and snow loads or possible later damage. Technical documents and site criteria are needed for assessment.

Final decision rule

Order a greenhouse only when three levels align: the locally governing wind and snow criteria, the clearly documented product configuration, and the foundation and anchoring at the specific site. If any of these levels is unresolved, check it before ordering or installation.

Further planning and product information is available in useful information. Never assess figures in isolation: a sound decision comes from definitions, the site, the complete load path and careful execution.