Rainscreen cladding works by creating a rear ventilated cavity between the back of the facade panel ( or plank ) and the outer face of the building . This structure enables air to circulate , forcing out any moisture that penetrates the joints of the cladding , before it reaches the building structure .
INLET / OUTLET PRINCIPLE
One of the basic tenants of good cladding ventilation is the inlet / outlet principle . To provide an effective ventilation cavity behind the façade this space must be provided with adequate inlets and outlets . For most structures , Cedral recommend a minimum 30mm continuous gap between the cladding and the building fabric and a minimum 10mm continuous gap at openings .
The use of perforated closures can also have a surprisingly significant impact on the level of ventilation . In cases where airflow is restricted , we recommend a minimum equivalent of 10,000mm2 equivalent to 10mm per 1000mm of façade length . It ’ s also important not to overlook the importance of proper ventilation around soffits , sills and parapets . Your cladding manufacturer should be able to advise you on this .
CAVITIES TO ENABLE VENTILATION
While different manufacturers may specify slightly different recommended cavity depths , Cedral advises a minimum of 30mm . The aim of the façade design should be to enable natural ventilation of the building wherever possible .
Cedral facades are installed using the ventilated rainscreen system . A cavity is created between the wall insulation or substructure and the cladding , allowing air to flow in at the base and out at the top . This ‘ chimney effect ’ helps to maintain an ambient air temperature year-round , effectively protecting against moisture .
" The advantages of installing a ventilated wall include increased energy efficiency , reduced structural movement of the building and extended lifetime of the facade ."
TIPS TO REMEMBER
When installing a ventilated rainscreen cladding system , here are a few key tips to consider .
Closure calculations - Perforated closures should be installed at the top and bottom of the facade boards and around each door , window head and sill to protect against entry by birds , rodents and some insects . However , be careful when specifying the closer , making sure you calculate how this will affect the effective airflow behind the façade to ensure it stays within the manufacturer ’ s recommendations .
Mind the air gap – We all understand the importance of an appropriate air gap at the base and other openings within the cladded areas . As well as protecting the insulation or substructure against moisture , the ventilation gap enables rapid drying of external walls to reduce condensation and humidity , and also offers fire , sound , heat and weather protection .
In hot weather , air can rise to the top leaving space below for cool air to enter and keep the building cool . In wet weather , the air flow allows the cladding to dry quickly , preventing a build-up of condensation . We sometimes see this vital space being reduced once sand , shingle and vegetation are laid down around the footings , effectively blocking the ventilation . At higher levels , take care with the use of sealants to close off air gaps under windows and soffits . When using membranes , ensure they are installed in way that will not restrict airflow to the cavity .
HEATING , VENTILATION & INSULATION
Don ’ t forget about ventilation around all windows and doors , to reduce condensation and humidity coming from inside and outside the building . The same principle also applies to any fittings on the facade , such as gas or services boxes .
There are grilles and other products that can improve poor ventilation , but they often spoil the look of the cladding . In our experience , it pays to read up carefully before you start a facade project and don ’ t be worried about calling the manufacturer for guidance . At Cedral we have a dedicated technical support team on hand and ready to help with topics such as ventilation .
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