How to read greenhouse dimensions and technical drawings

This guide explains how to assess greenhouse dimension drawings, floor plans, elevations and assembly documents systematically. It helps you verify the external outline, foundation, door area, heights, internal space and connection details before ordering and installation.

A greenhouse drawing is a concise technical description, not a decorative product image. It shows the structure's footprint, where components meet, and the clearances needed for foundations, assembly and later use. Mistakes usually come from confusing nominal, external, foundation and clear internal dimensions rather than from difficult geometry.

Do not rely on one dimension. Treat the floor plan, elevations, details and assembly manual as a single document set. Obtain written confirmation of any unclear measurement before constructing the foundation, especially for large orangeries, T-shaped layouts and models joined to an existing wall.

Identify the drawing type first

The type of drawing determines what you can establish. A floor plan shows the greenhouse from above. It is useful for checking width, length, door position, building shape and foundation outline. A front, side or rear elevation describes heights, roof pitches, eaves, ridges and the layout of wall and roof panels. A section looks conceptually through the building and may reveal clear internal heights or profile connections.

Exploded drawings and assembly steps explain component order, fixing points and orientation. Detail drawings enlarge connections such as the base, door threshold or wall profile. Perspective views aid spatial understanding but are not normally reliable for setting out.

Note the model, version, revision and view on every document. On apparently symmetrical structures, mark north or label the garden side to avoid reversing left and right.

Understanding the main greenhouse dimensions

Overall width and overall length

Width and length may reference a profile's outer edge, a base edge, a structural axis or the foundation edge. Dimension arrows and extension lines identify the points. Lines reaching the outermost profiles usually indicate an external dimension; lines ending at an inset base may show a plinth or bearing dimension.

For rectangular models, multiplying two figures does not complete space planning. Roof overhangs, downpipes, door travel and assembly access may extend beyond the stated footprint. Guidance on choosing designs appears under Greenhouses and conservatories. For more complex design background, see the guide to orangeries, sizes and designs.

Eaves, ridge and overall height

Eaves height is taken where the side wall meets the roof; ridge height is the highest point of a conventional pitched roof. Overall height may include extra components. Always use the lower reference marked on the drawing: finished foundation top, ground, plinth underside or another defined level.

Heights matter for more than headroom. They affect proximity to branches, gutters, projecting walls and site features. Open roof vents can also project beyond the closed building envelope. Do not plan solely from the closed elevation.

Door dimensions

For doors, distinguish the rough or frame opening, clear passage width and outer size of the door unit. For wheelbarrows, benches or equipment, the clear opening matters; the frame's outer measurement does not show the usable passage.

Check the opening method and operating space. A hinged door needs swing room; a sliding door needs lateral space along the façade. Threshold height and the finished path may also matter. Assess the door with the external route, internal path and foundation, not alone.

Panel grid and glazing divisions

Many aluminium greenhouses use repeated bays. Dimension chains may show a structural grid, panel widths or overall length. Add partial dimensions only when they share the same reference points. Profile widths or end bays can prevent assumed panel widths from adding up exactly to the external dimension.

These divisions help plan accessories, vents, shelving and planting, but are not a freely selectable building grid. For the material effects of multiwall sheets, read polycarbonate in greenhouses. The technical documents for the specific model remain definitive.

Reading the language of dimension lines

Technical dimensioning normally includes a figure, line, arrows or end marks, and extension lines leading to the measured points. An overall dimension covers the full distance; a dimension chain divides it into sections. Bracketed or specially marked figures may be informational only. Follow the drawing's legend rather than relying on assumptions.

Symbols for diameter, radius, angle, gradient and level have distinct meanings. Do not mistake centre lines or hidden edges for actual outer edges. If no legend is provided, clarify every interpretation that affects construction.

Never measure a screen or printout

Do not put a ruler against a PDF on screen: zoom, display size and page fitting alter its appearance. Printing may also reduce, enlarge or distort it. Even when a scale is stated, the written dimension takes priority unless the document specifies otherwise.

Where “not to scale” or an equivalent abbreviation appears, rely only on stated dimensions. Never infer a missing figure by measuring the graphic.

Check units on every document

Check whether dimensions use millimetres, centimetres or metres. Product drawings often use millimetres, whereas site plans often use metres. Mixed documents increase error risk. Include units in every calculation and convert only at the end.

Watch decimal separators too. Check software or spreadsheet language settings before transferring values because commas and points may be interpreted differently.

Nominal size, footprint and usable interior

A size label often classifies the model and need not match its external footprint exactly. The nominal size is not necessarily a foundation dimension. The actual footprint defines the outline required for the base. The usable interior is reduced by profiles, bracing, doors and fittings.

Dimension type	Typical use	Check before construction
Nominal size	Model comparison and sorting	Do not use directly for foundation construction
Maximum external dimension	Space requirement and clearances	Add overhangs and open components
Plinth or bearing dimension	Planning the load-bearing base	Check reference edges and squareness
Clear internal dimension	Paths, tables and use	Allow for bracing and door areas

Similar terms occur with other outdoor structures too. The pergola size guide, the guide to pergola foundations and the product page for the Elma S outdoor sauna show why product size, external outline and installation footprint should always be considered separately.

Break complex floor plans into individual zones

Assess T-shaped layouts, orangeries and structures with projections by dividing the plan into rectangles and connection zones. Mark the main body first, then every cross wing, entrance and recess. Record each zone's width, length and position relative to the shared axis.

1. Mark the outermost overall outline.
2. Add main axes and lines of symmetry.
3. Dimension each partial area separately.
4. Count and identify internal and external corners.
5. Check dimension chains against the overall measurement.
6. Add the door and access zone.

A plan can contain mathematically plausible partial dimensions yet still be orientated incorrectly on the site. Set one unambiguous reference side, for example “house side” or “garden gate”. Historically inspired ideas from the article on Victorian greenhouses should only be considered after this technical groundwork.

Transfer the drawing to the installation site

Start with a fixed reference line rather than four separately placed points, using a building line, string axis or accurately surveyed baseline. Set out the remaining points at right angles from it, marking the external and foundation outlines in different colours.

Before work starts, ask a perit to classify the proposal under Planning Authority rules, recording its footprint, height, enclosure, land designation and existing permit conditions. Development Notification Order permission is conditional and does not replace other required consents. Planning permission for a greenhouse or pergola offers initial guidance; the currently applicable Planning Authority requirements remain decisive.

Check more than the four corners

Four corner points are insufficient for long sides or articulated plans. Check intermediate axes, door openings, recesses and connections. Measure both diagonals and the side lengths. Equal diagonals indicate a rectangle only under appropriate geometric conditions and do not replace level or height checks.

Also check gradients, high points and level differences. A correct horizontal outline can still cause assembly problems on uneven ground.

Set out a full-size model where space is tight

Strings, marking spray or flat battens reveal the required space. Place a ladder or box at ridge or eaves height, open garden gates and test the route with a wheelbarrow. This exposes conflicts that may be inconspicuous on a small plan.

Drawings for lean-to and wall-mounted greenhouses

For a lean-to greenhouse, the existing wall has an important geometric and structural role. You need more than width and depth: check connection height, roof pitch, wall-profile positions and clearances from windows, pipes, roof overhangs and drainage.

Inspect the full wall connection. Projecting plinths, uneven render or sloping surfaces may stop a profile sitting flat. Assess the wall's suitability and load-bearing capacity for the project. A comparable distinction appears in wall-mounted or freestanding pergola. Further design differences are covered under bioclimatic or classic pergola.

Plan internal space using clear dimensions

Clear widths are decisive for use. Do not simply subtract an assumed profile thickness from the external measurement. Use stated internal dimensions or have critical clearances confirmed. Plan the main path, side paths, work surfaces, planters and door area separately.

Tall crops do not need ridge height everywhere. Beneath a pitched roof, available height decreases towards the side wall. Shelving must not block vents, bracing or gutters. For use-focused planning, see the articles on growing lettuce in a greenhouse and temperature and humidity. The structure must nevertheless remain accessible in accordance with assembly and maintenance instructions.

Use documents in the right order

Check the locally displayed library of assembly manuals early. A sensible sequence is:

1. Identify the exact product version and order scope.
2. Read the technical overview drawing for external outline and heights.
3. Identify the foundation or base drawing.
4. Check the assembly manual for plinth, door orientation and connection details.
5. Compare the current document revision with the supplied documents.
6. Clarify open dimensions before making irreversible components.

Where two documents differ, do not choose the value that merely looks more plausible. Record the model, document title, revision status and affected dimension position, then contact us. General guidance is available under Useful information.

Checks on delivery and before assembly

Before assembly, compare the model name, package count in the delivery documents and visible component labels. Open and store packages only as instructed. A correctly prepared plan may still accompany a different delivered or selected version or door configuration.

• Do the model and version match the order?
• Does the door position match the approved plan?
• Is the foundation complete, level and dimensionally checked?
• Are all required access areas available?
• Have connection details and drainage routes been resolved?
• Is the correct assembly manual available?

Organisational guidance is available under Purchasing and delivery and How to order. For delivery throughout Malta, including all islands, see greenhouse delivery to Malta .

Common mistakes when reading drawings

• Using the model name as a foundation dimension: A rounded size description is not a construction dimension.
• Reading only one view: Floor plans and side elevations answer different questions.
• Confusing external and internal dimensions: This makes paths or work areas too narrow.
• Ignoring door movement: The opening later clashes with a bed, fence or step.
• Planning a mirror image: Perspective images are wrongly read as a binding door orientation.
• Measuring a PDF: Zoom and print scaling produce incorrect values.
• Mixing units: Millimetre figures are interpreted as centimetres or metres.
• Checking diagonals only: Height level, side lengths and intermediate points remain unchecked.
• Forgetting maintenance space: External surfaces and drainage later become inaccessible.

Long-term accessibility guidance is available on the care of an aluminium greenhouse page. Experiences from other buyers in greenhouse reviews may add practical perspectives, but they do not replace a model-specific drawing.

Questions before approving the greenhouse layout

• Has the exact model and equipment version been specified?
• Which line represents the maximum external dimension and which the plinth?
• From which height level are eaves and ridge measured?
• Where is the clear door opening and how does the door move?
• Is the structure correctly orientated on the site plan?
• Are external clearances available for assembly, cleaning and drainage?
• Have wall projections, trees, services and site gradients been recorded?
• Do partial dimensions, overall dimensions and diagonals agree?
• Has the foundation solution been confirmed for the model and site?
• Have local requirements been checked before construction?

Frequently asked questions

Are stated greenhouse dimensions internal or external?

Do not assume either without an explicit label. Product overviews often state nominal or external dimensions, while technical drawings may also include plinth and internal dimensions. Dimension arrows, reference lines and the legend of the specific document are decisive.

Can I build the foundation using dimensions on the product page?

Not without checking the model-specific foundation, plinth or assembly drawing. A product page primarily supports selection. Have critical dimensions confirmed before building concrete, masonry or other components that are difficult to alter.

Why does the nominal size differ from the technical drawing?

Nominal sizes make a model range easier to classify and may be rounded. A technical drawing, by contrast, describes specific reference points. Profiles, plinths and structural divisions can produce different actual dimensions.

What does “not to scale” mean?

The drawn length must not be determined with a ruler or screen tool. Use only stated dimension figures. If a required measurement is missing, ask for it.

How can I tell which side the door is on?

Use the floor plan and look for a door symbol, opening direction or component marking. At the same time, define from which side the building is viewed. If the version can be mirrored or the illustration is unclear, confirmation is needed.

Which dimensions matter for a lean-to greenhouse?

Besides width and depth, consider wall connection height, eaves position, highest roof edge, roof pitch, profile position and distances from existing components. Wall flatness and the structural suitability of the supporting construction must also be checked.

How much additional space should I leave around it?

There is no universal figure for every model and site. The required space depends on assembly sequence, cleaning, open windows, drainage, access routes and local clearance rules. Plan a genuinely usable working and maintenance area, and check local requirements.

Do equal diagonals prove that the foundation is correct?

Not completely. Equal diagonals are an important check for a rectangular floor plan, but must be assessed alongside side lengths, intermediate dimensions, levelness and height. With complex shapes, check every individual zone separately.

Which document applies if two dimensions differ?

This cannot be decided generally by document type. Check the model allocation and revision status, and ask the supplier to confirm the governing figure. Do not alter the foundation until this is resolved.

Where can I find warranty and care information?

The terms are available in the Warranty section. Care guidance must be followed separately, because dimensioned drawings, assembly instructions and maintenance information have different purposes.

Final drawing check

Complete the final check at the set-out site, not only at a desk. Compare model, document revision, external outline, base dimension, heights, door, diagonals and connections. Then test use: can the door open fully, paths remain clear, and roof vents, gutters and outer surfaces be reached?

A reliable plan results only when the same reference points are used in product documents, foundation drawings, assembly instructions and site setting-out.

Record approved dimensions in a simple checklist and photograph the set-out site. This keeps the planned version traceable. For additional ideas on using your greenhouse, visit the Bloomcabin Blog; technical decisions should always be based on the documents for the selected model.