Smoke Hatches (II) – Types of Roofs
The types of roofs on which smoke hatches are installed fall into one of the following three categories: concrete roofs, sandwich panel roofs, corrugated sheet roofs, or wooden roofs.
1) Concrete Roofs
This situation is predominant, with many projects involving the rehabilitation of an old structure. In this case, the existence of the concrete curb must be checked. If the concrete curb exists, in most cases the beneficiary must restore the flatness, which generally deteriorates due to existing wear, and subsequently communicate its dimensions.
If there is no concrete curb, the smoke hatch includes a base made of sheet metal (for economic reasons and due to waterproofing) with a height between 300 and 500 mm; these values provide safety in case of snow deposits. We recommend purchasing the base even in cases where there is a concrete curb, but its height is not within the above values. The thickness of the sheet metal used for making the base is 1 mm up to a height of 500 mm; above this value, the supplier must be consulted.
We also recommend using a thermally insulated base with expanded polystyrene, 50 mm thick, with the exterior prepared with a bituminous membrane, as this eliminates the risk of condensation and facilitates the waterproofing with a hot-applied membrane.
Special attention must be paid to waterproofing, which is done with a hot-applied bituminous membrane (the flame can burn the dome).
Considering these extremely important details for the reliability and lifespan of smoke hatches, the installation is done in 2 steps: first, the base is installed and waterproofing is done, then the frame and dome are installed.
2) Sandwich Panel Roofs
This structure is constantly used in new constructions, with a wide range of thicknesses and dimensions of the outer surface. To be as precise as possible, the distance between the roof purlins must be known (generally between 1 and 3 meters).
ATTENTION! The base of the hatch must be placed in line with the purlin, otherwise, there is a risk of the roof collapsing due to snow loads or if the point is repeatedly stepped on!
The existence of bracing or other metal structures that can obstruct the rotation movement of the piston and thus prevent the normal opening of the hatch must be checked. Since installation involves cutting the panel, the hatch must also include interior masking skirts; thus, the total thickness of the sandwich panel (panel + corrugation) must be known.
In the case of this type of covering, the position of the smoke hatches is essential in relation to the roof ridge because there are 2 completely distinct situations:
a) Positioning near the roof ridge, which has a set of advantages:
- The area where the largest amount of smoke and hot gases resulting from combustion accumulates
- The risk of infiltration is the lowest
The base made of polyester resin reinforced with fiberglass WITH UNIVERSAL SOLE is used.
We recommend using the THERMALLY INSULATED base with polyurethane, 30 mm thick, to avoid condensation.
The advantage of this type of base is the ease and speed of installation, as the upper part of the sole is inserted under the roof ridge skirt (provided by the client), and the lower part is cut according to the profile of the sandwich panel used. Waterproofing is done with mastic introduced between the base sole and the sandwich panel around the entire perimeter of the base.
Although all resin bases are protected against UV radiation with a gelcoat that also acts as a waterproofing agent, increased attention must be paid to the possibility of small cracks appearing upon completion of the installation.
If the hatches need to be installed at a distance between 0.5 and 1.5 m from the roof ridge, a simple solution for waterproofing is the sheet metal skirt that connects the roof ridge to the upper part of the hatch base.
b) Positioning in the roof field is the solution that ensures a uniform distribution of smoke vents across the entire roof surface.
In this situation, a base made of polyester resin reinforced with fiberglass WITH CORRUGATED FLANGE is used, which mimics the profile of the roof panel. Therefore, it is VERY IMPORTANT to know the model of the sandwich panel. The advantage of using this type of base is that the profile of the base perfectly follows the contour of the panel, thus reducing the risk of leaks at the junction between the two elements.
Another advantage is the constructive solution of the base, which, being made from a single piece, prevents the occurrence of leaks at the joints between the flange and the base of the vent. Again, at the end of the installation, we must pay special attention to the possibility of small cracks appearing. Waterproofing is also done with mastic.
Since the junction between the base flange and the sandwich panel must be perfect, samples must be sent to the supplier if they do not have a mold with the respective sandwich panel. Additionally, all bases must be THERMALLY INSULATED with polyurethane, 30 mm thick, to prevent condensation.
VERY IMPORTANT! The model of the sandwich panel must be communicated in writing to avoid such problems!
3) Corrugated Sheet Roof
This type of construction is used due to the very high load-bearing capacity of the corrugated sheet compared to the sandwich panel (span of 13 m versus 4 m). Due to the structure of such a roof – corrugated sheet, basalt wool, PVC membrane – we must consider a greater base height, between 650 mm and 800 mm.
Thus, the sheet base will be made from two overlapping segments that must reach the desired height. For this type of covering, it is very important to install the corrugated sheet in such a way as to maintain the dimensions of the installation opening for the vents.
For fixing the base, a metal structure mounted under the sheet is needed, which follows the profile of the opening, as the base is mounted on this structure.
In this case as well, the installation is done in 2 steps: first, the base is installed and waterproofing is done, and then the frame and dome are installed.
4) Wooden Roof
An application used in environments with high humidity (pools, swimming pools, polo pools) or in environments with a high degree of corrosion (salt mines, salt warehouses). Given these conditions, we recommend smoke vents with a thermally insulated base made of sheet metal, which is treated against corrosion.
In this case as well, special attention must be paid to the waterproofing process, which involves applying the membrane hot (with a flame).
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