Compositions of walkable flat roofs and terraces
In some cases, flat roofs can be used as a walking roof. This may be the case when the roof of the building serves as a connecting road for pedestrians, or we want to use this space for leisure, which is usually the case with terraces in family houses.
What are the types of walk-on roof designs and the main advantages and disadvantages of each solution, we will describe in this article.
What are the basic types of roof treatments?
The most common footing treatment on such roofs is:
- paving laid in adhesive sealant (in the past mortar bed),
- paving laid on pads (targets),
- paving laid in sand bed.
1. Tiles in adhesive sealant (mortar bed)
In this case, the tiles (concrete, ceramic, terrazzo, stone, rubber) are laid in a flexible adhesive mastic.
The usual composition of such roofs is (from interior to exterior):
- supporting structure,
- thermal insulation layer (with a slope),
- waterproofing layer,
- drainage layer,
- filtration and separation layer,
- concrete screed,
- tiles in a flexible adhesive mastic.
1.1 Principles of design of walkable roofs with tiles in adhesive mastic
- thermal insulation layer made of sufficiently rigid material
- expanded polystyrene (EPS) for higher loads,
- extruded polystyrene (XPS),
- foam glass,
- the drainage layer is made up of either
- spatial loop polyethylene (PE) mat, or
- profiled foil made of high-density polyethylene (HDPE), known as nub foil,
- The entire walkable layer is separated from the waterproofing by a separation layer , which is usually made of filtration geotextile with a surface weight of 500 g/m2 , and which is placed on the drainage layer. The separation layer enables sliding separation of the walkable layer and at the same time prevents the concrete screed from flowing into the drainage layer.
- It is recommended to reinforce the concrete screed with KARI mesh , and it is necessary to make expansion joints in an area of maximum 2 x 2 m ,
- it is necessary to separate the concrete screed from all penetrations and attics,
- The minimum recommended slope is 2% ,
- It is recommended to extend the waterproofing at least 150 to 200 mm above the level of the pavement,
- The tiles are laid in a special flexible sealant designed for outdoor use, again, expansion joints are made in an area of maximum 2 x 2 m , which overlap with the expansion joints in the underlying concrete screed,
- Expansion joints are filled with flexible sealants.
1.2 Disadvantages of walkable roofs with tiles in adhesive mastic
- Due to the presence of a concrete screed substrate under the tiles, laying can only be carried out at temperatures above +5°C,
- concrete screed adds weight to the building structure, this must be taken into account during the static design of the supporting structures,
- when laying concrete screed, the drainage or waterproofing layer may be damaged,
- concrete screed is usually laid on thermal insulation with a slope, sometimes there may be problems with laying,
- The concrete layer is affected by weather conditions, frost (alternating freezing and thawing cycles), rain, snow, which can lead to gradual degradation of the concrete screed.
- very difficult identification of the exact location of any possible waterproofing failure,
- If it is necessary to remove concrete screed, it is very time-consuming and financially demanding.
2. Paving laid on pads (targets)
In this case, the tiles are laid using pads either directly on the waterproofing layer (in the classic order of roof layers), or in the reverse order of roof layers on thermal insulation made of extruded polystyrene (XPS), or in the case of compact roofs on thermal insulation made of foam glass.
The usual composition of such roofs in the classic order of layers is (from interior to exterior):
- supporting structure,
- thermal insulation layer (with a slope),
- waterproofing layer,
- separation layer,
- tiles on pads.
The usual composition of such roofs in the reverse order of layers is (from interior to exterior):
- supporting structure (in a slope) or a slope layer,
- waterproofing layer,
- thermal insulation layer,
- separation layer,
- tiles on pads.
2.1 Design principles for walkable roofs made of tiles laid on supports
- if the tiles on the pads are laid directly on the waterproofing layer ( classic order of roof layers ), it is recommended to use waterproofing made of plastic waterproofing foils , because the pads could be pressed into the asphalt strips by pressure, or to use higher-quality waterproofing asphalt strips modified with APP,
- the thermal insulation layer must be made of sufficiently load-bearing material ( XPS, foam glass ) to prevent the pads from pushing through into the substrate,
- A separation layer made of geotextile with a weight of 300 g/ m2 is usually placed under the pads(targets) ,
- Tile underlays are most often made of rubber or plastic and can be:
- simple (solid) , the slope of the paving follows the slope of the sloped layer,
- rectifiable , which have the advantage that a horizontal walking surface of the paving can be achieved by adjusting the pads to different heights,
- The minimum recommended slope is 2% ,
- It is recommended to extend the waterproofing at least 150 to 200 mm above the level of the pavement.
2.2 Advantages of walkable roofs made of tiles laid on underlays
- work on the walkable roof layer can be carried out regardless of the weather ,
- This is a dry construction process , there is no wet process in the form of concrete screed or gluing tiles into the mastic, as with tiles into adhesive mastic,
- Laying work is faster,
- when using rectifiable pads, we can achieve a horizontal walking surface,
- no need to perform dilation,
- in the event of a waterproofing failure, the location of the failure can be identified more easily,
- There is no risk of damage to the tiles when dismantling them.
2.3 Disadvantages of walkable roofs made of tiles laid on underlays
- the waterproofing layer is not protected as sufficiently as in the case of concrete screed and laying tiles in adhesive mastic,
- The joints between the tiles are not tight , so dust, sand, leaves and other dirt can get stuck, and over time vegetation can grow, so timely maintenance is necessary.
3. Paving laid in a sand bed
This last method of laying paving is not as widespread or recommended, it is more suitable for temporarily creating a walkable layer.
The usual composition of such roofs is (from interior to exterior):
- supporting structure,
- thermal insulation layer (with a slope),
- waterproofing layer,
- drainage layer,
- filtration and separation layer,
- sand bed,
- pavement.
3.1 Principles of design of walkable roofs with paving in a sand bed
- thermal insulation layer made of sufficiently rigid material
- expanded polystyrene (EPS) for higher loads,
- extruded polystyrene (XPS),
- foam glass,
- the drainage layer is made up of either
- spatial loop polyethylene (PE) mat, or
- profiled foil made of high-density polyethylene (HDPE), known as nub foil,
- The entire walkable layer is separated from the waterproofing by a separation layer , which is usually made of filtration geotextile with a surface weight of 500 g/m2 , and which is placed on the drainage layer. The separation layer enables sliding separation of the walkable layer and at the same time prevents the concrete screed from flowing into the drainage layer.
- The recommended minimum slope is 2%,
- It is recommended to extend the waterproofing at least 150 to 200 mm above the level of the pavement,
- Paving (concrete, stone or terrazzo only) is laid in a gravel-sand bed of fraction 4-8 .
3.2 Advantages of walkable roofs with sand bed paving
- no wet process is involved, it can be carried out even at lower temperatures,
- relatively simple and inexpensive installation,
- no dilatations are necessary,
- We can easily achieve horizontal paving.
3.3 Disadvantages of walkable roofs with sand bed paving
- This is more of a temporary solution.
- The gravel-sand substrate may settle irregularly, causing sand to wash out and the paving to sink.
- a gravel-sand bed is not suitable for laying ceramic tiles,
- Plant seeds can enter the gravel bed through the gaps between the paving stones, and vegetation can grow.
