Plan Your Own Carport – Size, Structure, Roof Type and Cost

A carport protects your car from rain, hail and UV, and as a timber structure it is well suited to building yourself. For the project to succeed, you need realistic dimensions, adequate cross-sections and a plan that accounts for snow load and wind bracing.

Size and parking space: how much room does a carport need?

The most common planning mistake is a parking space that is too tight. Allow at least 2.7 × 5.0 m per car – it becomes comfortable from 3.0 × 5.5 m upwards, because you can then get in and out easily even with the doors open and shopping in hand. For an SUV, estate or van, it is better to reckon on 3.5 × 6.0 m. For a double carport, 5.5 to 6.0 m of width has proven its worth; anything less makes getting out between two vehicles cramped.

• Single carport (compact/mid-size car): 3.0 × 5.5 m as a practical, everyday standard
• Single carport (SUV, estate, van): 3.5 × 6.0 m
• Double carport: 5.5–6.0 m wide and 5.5–6.0 m deep
• Clearance height: at least 2.2 m clear height, or nearer 2.5 m with a roof box or camper van

Do not forget ancillary space: a store at the rear costs only 1.5–2.0 m of extra depth and creates room for bikes and tools. Around 5 m of manoeuvring space should stay clear in front of the carport.

Distance to the property boundary

In many areas a carport may be built close to the boundary, usually with restrictions on wall height and the length running along the boundary. The rules vary considerably from place to place – so clarify the boundary distance and whether planning permission is required with your local building authority before you start detailed planning.

Carport roof types compared

Flat roof with a fall (3–5°)

The classic choice: clean looks, little material, easy to build. A minimum fall of 3–5° – roughly 5 to 9 cm per metre – ensures the water runs off. Suitable coverings include EPDM membrane, bitumen felt or trapezoidal steel sheet. The downside: snow lingers on flat roofs, so the full snow load has to be factored in.

Mono-pitch roof (5–15°)

A mono-pitch (lean-to) roof directs rain to one side and looks modern. It works well with trapezoidal sheet or sandwich panels. Put the high side towards the driveway and you get a generous clearance, while the lower rear side keeps out wind and weather.

Gable (dual-pitch) roof (18–30°)

A gable roof visually suits many houses, can be covered with roof tiles and creates storage space under the ridge. In return you need considerably more timber and labour – as a rule of thumb, the cost is 20–40 % higher than a comparable flat-roof carport.

Sizing posts and purlins

For a single carport in areas with moderate snow load, the following cross-sections have become established as guide values. The structural calculation for your specific site is always the binding reference: in high snow-load areas, for spans over 5 m or a green (planted) roof, there is no way around a structural engineer or a certified kit.

As a rough guide, the purlin depth is about one fifteenth to one twentieth of the span. A purlin with a 4.5 m clear span therefore works out at 22–30 cm deep – or you add an extra post and get away with 20 cm.

Snow load: the underestimated factor

Snow is usually more decisive for the sizing than the dead weight of the roof itself. Characteristic snow loads typically range from around 0.65 kN/m² in lowland areas to more than 3 kN/m² in upland and Alpine regions. A worked example: on a 30 m² flat roof in an area with 1.0 kN/m², the design case comes out at roughly 2.4 tonnes of snow – on top of the dead weight of the roof covering and the structure.

The higher the snow load, the larger the cross-sections or the closer the spacing. You can get the values that apply to your plot from your local building authority or a structural engineer; together with the wind load, they are the basis of any sound design.

Bracing: keeping the carport standing in a storm

A carport has no bracing walls. Without diagonals, the structure behaves like a parallelogram and racks sideways under wind load. Three proven solutions, which can also be combined:

1. Knee braces: diagonal timbers (e.g. 10 × 10 cm) at 45° between post and purlin – in both the longitudinal and transverse directions and at as many posts as possible.
2. Fixed (moment-resisting) posts: columns rigidly fixed into heavy pad foundations carry horizontal loads through bending. This only works with sufficiently stiff post anchors and must be verified by calculation.
3. Shear panel or bracing: a sheathed rear wall, a store or diagonal wind-bracing straps in the roof plane brace the structure over a large area – sensible in wind-exposed locations.

Foundations and post anchoring

Pad foundations of 30 × 30 cm or 25–30 cm in diameter are usual, dug at least 80 cm deep so they sit below the frost line. Into the fresh concrete you set H-shaped post anchors, or bolt-on post feet added afterwards. Key to durability: the timber ends 5–10 cm above the ground and is never cast directly into the concrete – standing moisture on the end grain is the most common cause of rotting posts. Structural timber protection – keeping clear of splashing water, capping end-grain surfaces and using back-ventilated joints – works better in the long run than any wood stain.

Materials and costs

The standard for the structure is engineered solid structural timber (KVH) in spruce or fir: kiln-dried, dimensionally stable and planed. For long purlins from about 5 m of span upwards, glued laminated timber (glulam) pays off, as it is more dimensionally stable and allows larger cross-sections. For heavily weather-exposed components, Douglas fir or larch are a good choice thanks to their higher natural durability.

For comparison: ready-made kits cost around €2,000–5,000 depending on quality, while a carport erected by a professional firm including foundations usually runs to €5,000–9,000. Self-building therefore saves you noticeable money – provided you plan carefully and order to the right dimensions. All prices are guide values and vary by region.

Permits, planning and next steps

Whether your carport is exempt from approval or needs planning permission is governed by your local building regulations and development plan – the limits on floor area, height and boundary building vary widely. Clarify this with your local building authority before you order any timber. After that, planning follows a few clear steps:

• Set the parking-space size, roof type and clearance height
• Find out the snow load and size (or have someone size) the cross-sections
• Plan the bracing and the foundations
• Draw up a cutting list and get quotes for timber and roofing

Tip: in a 3D planner such as HolzBau 3D you position posts, purlins and rafters to scale, check the clearance height and roof overhang directly on the model, and export the cutting list with all lengths ready to order.