There is a requirement for cavity barriers / stops within timber frame construction and the minimum period of fire resistance is commonly 30 minutes, even where the internal fire resistance of the structure is greater. TRADA has drawn attention for barriers to be sleeved in polythene dpc to ensure moisture is deflected away from the timber frame structure and to the outside.

However, cavity stops are usually rectangular and have a flat/horizontal upper surface, therefore even if sleeved penetrating water can still use the upper surface as a bridge to track across the cavity unless prevented from so doing. Thus it prompts a question of how water will be deflected in the right direction by such sleeving, unless the actual shape of the stop or an accompanying protective medium promotes such direction?

Currently stops are being incorporated within cavities of buildings without deflection or protection provision. Whilst the timber inner skin is surfaced with a membrane, to what extent will that membrane remain serviceable in the long term if water collects and pools against it?
Is the timber frame and its membrane designed to have water pooling against it during the intended life of the structure? In decades to come, could such pooling against the inner leaf act as a catalyst and promote deterioration?
Such a construction detail is not best practice.

The cavity barrier / stop must deflect the water forward, and there is now a ready to use product that automatically offers this + fire stopping + acoustic suppression.

Cavi 60 SAF Stop

Cavi 60 SAF Stop is designed to provide acoustic, fire barrier and water-deflecting qualities within a cavity wall.

The Cavi 60 prefix denotes 60 minutes fire integrity rating for this multi-purpose cavity stop, whereas SAF is the acronym for sloping – acoustic – fire, the most important qualities advanced by this product.

Non-combustible rock wool is profiled and encapsulated within a polythene sleeve. The unique sloping upper surface of the encapsulation deflects penetrating water forward towards the outer leaf. The lower sloping surface permits lengths to be lapped whilst maintaining deflecting, sound and fire integrity status.

The Cavi 60 Type SAF Stop is compressible and may be friction fitted within the cavity, taking advantage of placement upon naturally occurring ties to aid stability. Thus it is incorporated without attachment to the inside or outside skin. Unlike conventional stops that are rectangular and thus level between skins, the new Cavi 60 Type SAF is sloping. It naturally deflects penetrating water forward, thus promoting best practice at all times. A hard finish protective upper surface cap is also available.
This new design offering twice the minimum fire protection period plus acoustic suppression plus a water deflecting shape is a product of Cavity Trays Ltd, the only cavity tray manufacturer awarded European Technical Approval.