Building design - waterproofing, structural loading and climate forces

Root resistant waterproofing

It is vital that the waterproofing is robust and proven to deliver long-term root resistance, preventing plant roots and rhizomes from growing in to or through it.  Consideration must be given to the appropriate form of waterproofing so that it can meet the demands placed on it by the green roof, as such performance characteristics for durability and thickness of membrane (density), tensile strength (EN 12311-1) and elongation at break (EN 12311-1) need evaluation before appropriate selection can be made.

Bauder waterproofing membrane systems and liquid systems are manufactured in accordance with FLL guidelines for root resistance and carry BBA certification for green roof applications.

When designing  the detailing (e.g. upstands, pipe penetrations, rooflight upstands etc)  it is important that you take into account the increased build-up of the green roof construction. Building Regulations typically require the waterproofing detailing to finish 150mm above the finished roof surface i.e. the green roof surface not the surface of the waterproofing.  Our technical team can work with you to produce the correct detail drawings for your green roof project.

Structural loading

Most roof deck constructions are suitable for some form of green roof provided that they can support the dead and imposed load, though intensive green roofs should only be constructed on concrete decks.

Dead and imposed loads - should be calculated in accordance with BS EN 1991-1-1, BE EN 1991-1-3 and BS EN 1991-1-4 and should include the weight of the waterproofing system, saturated weight of the green roof components and substrate, vegetation, snow loads, and imposed loads such as access by people and vehicles as well as point loads for items such as water features and trees.

Shear forces - need to be combated generally on roof pitches in excess of 10 degrees, though this depends on the levels of substrate being installed and the vegetation used.  Anti-shear measures should suit the individual system and on a Bauder sedum blanket system this comprises a simple mechanical retention strip with spikes that hold the blanket onto the waterproofing.

Our Technical Team can provide information and advice so relevant data can be passed to the structural engineer.

Wind uplift and erosion

The need for stability of the system is increased because the negative pressure forces that can develop during high wind conditions are counteracted by the weight of the green roof system. Wind can also lead to erosion problems on exposed sites, especially if plant establishment is in the early stages.