Cavity trays

[Oz07]

Is there really a need for cavity trays? When talking cavities 150 or 200mm how likely is it that moisture bridges the cavity. I'm thinking about stepped cavity trays where single storey garage abuts a house. Such a pain to do and if using cavity batts the insulation is never going to be as good around the tray detail. How likely is it any significant amount of water is making its way past the brickwork let alone getting to the inner skin. 

[Mike]

30 minutes ago, Oz07 said:

How likely is it any significant amount of water is making its way past the brickwork

Very likely, unless the brickwork is rendered. In an exposed elevation it can run down the inside of the external leaf pretty freely, especially if the joints aren't well filled.

[Mr Punter]

If the brickwork faces south west and is a large wall, a fair amount of water will get in.  If a stepped tray is difficult, do it horizontal and a coat of Stormdry on the remaining triangle of brickwork for belt and braces.

[Oz07]

I just can't envisage that much water getting in. How many weep vents do you ever see dripping water. How do you know its running down the wall inside?

[Oz07]

Found this on YouTube demonstrating the problem i suppose blown insulation avoids the problem IF it gets in around the trays ok. Probably best to avoid this type of abutment if the insulation can't be don't well and water really does stream down inside of cavity. 

 

[ADLIan]

3 hours ago, Oz07 said:

I just can't envisage that much water getting in. How many weep vents do you ever see dripping water. How do you know its running down the wall inside?

I've worked on the testing of cavity walls and cavity insulation to resist wind driven rain. Once the outer leaf brick is saturated the rain will drain down the inner face - add the effect of increasing wind speed and the water can actually 'spray' across empty cavities (or attempt to through the insulation and any joints).