Flat roof Costs per m2 to estimate before construction

Flat roofs are not as common in residential buildings as pitched roofs, but are in the modern residential architecture but increasingly popular. Which costs can be incurred for a flat roof per square meter, and with what individual costs one must expect, explained in detail this contribution.

prime example

In our example, we want to cover a 50 m² flat roof with the entire structure, which means:

  • separating layer
  • vapor barrier
  • thermal barrier
  • lower and upper roofing layer
  • Loading layer (gravel)
layertotal cost
Vapor barrier layer108 EUR
thermal barrier1,193 EUR
Two roofing layers1,388 EUR
Overlay layer (gravel, 50 mm)231 EUR
total cost2,920 euros

Tips

Detailed information about our flat roof can be found in our service description.

All costs in the article are net.

Note

Our price example is only one way to create a flat roof - there are also other options for flat roof construction. In particular, the substructure (often already intact) may be different in many cases. Flat roofs are also often designed as a green roof, which can cause significantly different costs. Bear in mind that, even with a similar design, significant differences to our example costs may occur due to local conditions and additional work required.

Not considered works

For reasons of clarity, we did not mention the costs for the necessary roofing scaffold or the climbing aids in this case. The costs for the edge sealing and for necessary roof penetrations as well as roof exits we did not consider here. We presuppose the substructure as already given.

General

Flat roofs can be done in many different ways, basically you have the following possibilities in the construction:

  • as a lightweight roof
  • as a classically sealed flat roof with and without thermal insulation
  • as a green roof
  • as a patio roof

In addition, one differentiates by the arrangement of the individual layers in the roof construction also:

  • warm roof
  • Cold roof and
  • inverted roof

Further explanations and the advantages and disadvantages of the individual construction work can be found here. Each type of flat roof construction can cause different costs. Our price example is therefore a classic warm roof with surcharge.

Costs for the individual layers

vapor barrier

Vapor barrier layers on the flat roof can be designed differently. In our example, we used 0.3 mm PE foil, on the underside of which a (necessary) separating layer was attached. The cost of such a film is usually around 2 -3 EUR per m².

Other possibilities

Other possibilities exist in the production of so-called leveling and diffusion-inhibiting layers with different sd values ​​from other materials, for example:

  • Aluminum composite film
  • special bituminous membranes for the layer
  • PE film without separating layer

The costs are correspondingly different and can be up to 12 EUR per m², depending on the design of the roof and the corresponding layer.

thermal barrier

The insulation can be made on a flat roof with very different materials. In our example, we have selected typical 140 mm thick polystyrene foam boards (EPS) with a rated value of 0.035 in fire protection class B1, which were stuck to the vapor barrier. In this case you can expect costs in the range of around 20 - 30 EUR per m². For a reversed roof, however, the costs would be significantly higher, namely around 35 - 50 EUR per m².

Different materials

Depending on the thermal insulation class and the thickness of the panels as well as the panel properties, the prices for the EPS panels can vary considerably, from 15 to 60 EUR per m², depending on the required insulation performance.

Some more price examples:

board materialpropertiesPrice per m² (recommended price)
Polyurethane or polyisocyanurate rigid foam140 cm, rated value 0.023, high pressure loadable35 - 45 EUR per m²
Bloat pearlite plate140 cm, rated value 0, 0.04540 - 60 EUR per m²
Mineral wool board140 cm, rated value 0.03738 - 50 EUR per m²
Foam glass140 cm, rated value 0.04065 - 90 EUR per m²

In addition to the plate formats, materials for fillings or injection methods as well as so-called folding tracks are also possible. More information is also available in our article Flat Roof Insulation: Prices.

Gefälledämmschicht

Not all boards are suitable as prefabricated sloping boards for the formation of a sloping insulation layer, with the available boards you will have to count on approx. 2 EUR per m² additional costs as a sloping insulation board.

Lower and upper roofing layer

As a rule, the roof seal is executed in two layers. In general, you can expect prices between 20 and 45 EUR per m² (for both layers), depending on the sealing materials used in each layer and their property classes:

  • Self-adhesive polymer bitumen membranes (property class E1, E2 or E4), only for 1st layer
  • Bitumen roofing membranes, about G200DD (E2)
  • Bituminous welding track, about G200 S4 (E2)
  • Polymer bitumen welding line, only for 2nd layer, eg PYE-PV200 S5 (E1)
  • Polymer bitumen roof waterproofing membrane, for 2nd layer about PYE-PV200 DD (E1)

There are various design options for the design, depending on the expected mechanical and thermal loads on the roof seal:

classburden
IAmechanical: high - thermal: high
II Amechanical: moderate - thermal: high
IBmechanical: high - thermally moderate
II Bmechanically moderate - thermal: moderate
Price differences in the seal

Differences in price then arise through the use of different materials. What different combinations of materials can cost can be seen in the following table as an example:

1st shift2 layerCost per m² (recommended price)
Kaltselbstkl. Polymer bitumen-BahnPolymer Bitumen Welding Line PYE PV 200 S525 - 34 EUR per m²
Bitumen Welding G 200 S4Polymer Bitumen Welding Line PYE PV 200 S522 - 30 EUR per m²
Bitumen Welding G 200 S4Polymer bitumen roof waterproofing membrane PYE PV 200 DD18 -. 25 EUR per m²
Special versions for green roof

If a green roof is planned above the roof, the roof sealing layers must be selected such that they are root resistant (according to DIN EN 13948 or FLL). You have to estimate around 1.50 EUR per m² in addition.

Overlay layer (gravel or concrete slabs)

In our case, we have chosen a Bekieseung, but you have to choose usually between 4 and 6 EUR per m² (at 50 mm bed). But are also possible:

AuflastmaterialthicknessCost per m² (recommended price)
Concrete pavers8 cm, gravel bedding (possible also pedestal or grit position)21 - 30 EUR per m²
Cast stone slabs 50 x 50 or 60 x 40 or 40 x 404 - 6 cm, gravel bedding (also possible pedestal or grit position)28 - 50 EUR per m²
Concrete slabs 50 x 50 or 60 x 40 or 40 x 404 - 6 cm, gravel bedding (also possible pedestal or grit position)35 - 50 EUR per m²

Of course, a green roof eliminates a protective overburden layer. A green roof, whether extensively or intensively greened, then represents the surcharge itself.

Cost of possibly additional work required

Depending on the roof structure, additional or differently designed layers may be necessary.

Green roofs

Green roofs can be designed in different ways, namely:

  • extensive (only mosses and succulents on substrate)
  • min. intensive (other plants, easy to care for, on substrate)
  • intense (also trees and shrubs, on topsoil)

Depending on the design of the green roofs, you may face quite a variety of costs, even with running costs for the care and irrigation of green roofs you sometimes have to expect. More information can be found under Green Roofing: Costs.

Installation of roof drainage

Flat roofs also require roof drainage. Depending on existing local conditions, such drainage must be planned, installed and sealed. There are additional costs.

roof Hatches

Roof exits can be quite expensive. For an insulating glazed roof exit in the size of 150 x 100 cm made of steel they must already expect between 3,000 and 4,500 EUR. Aluminum exits cost the same size but about half (2,000 - 2,700 EUR in this measure). Also important for the price is the opening height (50 cm in our example).

Conservative factors

  • simple roof construction
  • not ventilated roof
  • existing gradient

Increasing factors

  • no gradient available
  • problematic substructures
  • complicated construction types
  • higher thermal insulation capacity
  • Green roofs desired
  • Roof terrace (walkable) desired (many times more expensive)

Saving opportunities through self-construction or personal contribution

The roofing requires high expertise and a very careful execution. Otherwise, flat seals can otherwise lead to massive damage to the entire building later on. In-house services are therefore not possible with this work.

promotion

Subsidies for the renovation / insulation of a roof waterproofing may be possible. Information can be found in our general overview of subsidies.

Tips & Tricks

Be sure to get detailed advice about different roof types and their advantages and disadvantages. Under certain circumstances, you may also notice a green roof, as this may not only provide you with financial but also air conditioning benefits for your house.

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