T90 - Support Structures

T90 Cladding System: Wide Cavity


The PRIME.design T90 system consists of an aluminium ventilated rainscreen support structure for cladding products.  The main difference with the T50 system is that the cavity is much wider, allowing for external grade thermal insulation to be placed.  This is of particular interest in systems where the rigid wall underlay has a poor vapour permeability, with high potential for internal condensation as a consequence.

To get an indication if internal condensation will occur, the saturated vapour pressure (max vapour content for air at certain temperature - RED LINE) and the actual vapour pressure through the wall section are compared (GREEN LINE).  When the saturated vapour pressure runs below the actual vapour pressure line, this means there is more moisture present than what the air can absorb, and as a consequence internal condensation may be expected (Dewpoint method).  The Dewpoint method is a simplified method, and does not account for vapour movement within the wall or hygroscopic activity (limited in light weight construction).  It gives a good comparison of different construction options and choice of materials. 

Images below compare the Dewpoint method for 1) an insulated timber stud wall covered with building paper and a T50 cavity cladding 2) same as 1, yet with plywood as rigid wall underlay instead of building paper and 3) the insulation to the exterior of the plywood inside the T90 cavity system.  When plywood is used as rigid wall underlay, it is recommended to install the thermal insulation to the exterior of the underlay (within the cavity), shifting the dewpoint away from the framing.  An exterior-grade mineral wool is an excellent solution for this application.  The equivalent air layer thickness of plywood is considered to be around 5.00m against 0.09m for instance Ferrari wrap

1) Standard building paper with T50 cavity system

Glaser1 (1)


2) Add a layer of plywood as Rigid Wall Underlay: the condensation get trapped behind the layer of plywood and can only dry towards the interior

Glaser2 (1)


3) Use exterior grade mineral wool in the cavity and use thermally insulating PE or PVC pads under the T50 brackets to avoid condensation at the base of the brackets.