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Cavity Trays and Cavity Insulation

Cold spots and thermal bridges, caused by lack of insulation around the area of stepped cavity trays, has been highlighted as a possible cause of defects in new dwellings, with specific attention to roof abutment areas.
 

Insulated - Cavity tray built into a locally adapted partially filled area

For a cavity tray to be most effective in its function and to reduce any impact on the thermal performance of the cavity wall construction, it would be ideal to always have a minimum of a 50mm clear cavity void to maintain a clear drainage and ventilated channel along with a constant insulation layer against the inner wall to a depth required to achieve required U-values.  

The function of an abutment cavity tray is to collect and discharge water that enters the cavity from the outer wall of a cavity wall at the junction between an abutting roof and gable wall.  
To integrate abutment cavity trays around insulation we advise that the integrity of the insulation is not broken and to achieve this the preformed ‘proprietary’ cavity tray up-stand is rigid in its design to rest up against cavity insulation (such as Timloc’s Everdry cavity tray range).

We understand that clear cavities are not always possible with the need to minimise the width of a cavity wall construction, while maintaining the required thermal values, but we can assist in detailing work around full fill applications.

For full fill rigid batt insulations, we advise that a localised clear cavity is incorporated around the area of the cavity trays.  To achieve this detail the full fill cavity insulation is reduced in thickness to form a localised partial fill cavity area around the cavity tray run.  This localised detail will support SAP calculation data based on an area weighted U-value and will allow for the effected gable wall and show a marked improvement to having cold spots across the gable wall.

Cold spots are caused when the cavity tray breaks the integrity of the insulation and the exposed and uninsulated areas are left without making good, particularly around the up-stand of any cavity tray.

For fully blown fibre insulations we recommend the cavity tray is suspended within the cavity beyond any wall tie drips (as for a clear cavity) and allow the fibres to layer around the abutment area to minimise cold spots.  The information issued from manufacturers of full fill insulation reassures that the material is not hygroscopic and will repel water and hold it to the outer wall which should reduce the amount of overall water entering the cavity wall. 

Timloc have a wealth of cavity tray experience, spanning nearly 40 years.  Please don’t hesitate to contact our Technical Team for further information regarding Timloc’s cavity tray product, support and service solutions on 01405 765567 or email technical@timloc.co.uk.  We love cavity trays!



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