Designing the Right Single Ply Roofing System

Monarplan G Loose Laid & Inverted Ballasted Warm Roof System

Inverted ballasted single ply roofing systems offer an excellent solution for situations where access or recreation are a priority. Ballasted systems also provide maximum resistance against roof membrane damage and UV degradation, protection against thermal shock, fire or noise and maintain the lowest surface tem-perature of all system types.

A ballasted system relies on the weight of a ballast material, such as pebbles or paving slabs to secure the membrane and system in place.

Monarplan_Ballested_Inverted_350 jpg
  1. Concrete Paving Slabs.
  2. River washed pebbles.
  3. Water reducing/Filter layer
  4. Thermazone IVR Insulation.
  5. Separation Layer
  6. Monarplan G membrane.
  7. Protection/Separation Layer.
  8. Structural deck.

Design and Installation Advice

Monarplan G single ply roof membranes incorporate a fungicide additive that prevents organic growth within the ballast layer attacking the plasticiser in the PVC membrane ensuring the membranes performance is not compromised.

The single ply membrane is rolled out loose laid with adjacent sheets of membrane positioned to allow an overlap which is then hot-air welded together with a hot-air welder to provide a continuous waterproof covering.

For inverted roofs the single ply roofing membrane is applied directly to the deck and so the suitability of this method will be dependent upon the condition of the substrate. A protection layer should be placed beneath the waterproofing membrane.

In an inverted ballasted roof, the insulation boards are then placed over the waterproofing. A separation layer may be required to prevent polymer migration between membrane and incompatible insulation boards.

A filtration layer is then installed over the insulation to prevent fines from entering the drainage zones and the whole system is then ballasted using paving slabs on support pads, or 20-40 mm diameter river washed pebbles. The ballast should be sufficient to provide resistance to wind uplift and prevent floatation of the insulation boards.

Perimeter Fastening

Regardless of the type of membrane attachment, mechanical fasteners are always required at the roofs perimeter, angle changes and any details. This ensures that any tensions generated in the field membrane are not transferred to other areas.

Further information regarding the detailing to roof perimeters can be found by clicking here


Positioning the insulation above the waterproofing requires additional performance criteria to the type of insulation used. As it is placed in the wet zone, the board should have a low water absorption and a higher compressive strength to accommodate the weight of the ballast above.

Icopal offers a range of thermal insulation boards.

Typical insulation board used: Thermazone Hydroshield IVR board

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