Cavity tray - tempted not to bother

[pilsbury]

On my single story extension I'm using concrete lintels (as opposed to catnic) on both skins of the wall as the whole lot will be rendered. This will obviously leave the cavity open (but filled with insulation) above where the windows and french doors will be. I was thinking of just using regular cavity closures just as I will around the rest of the opening.

I've searched the forum and have found a mixed bag of responses. As a novice, my thoughts are this - Above the concrete lintel will be 1.5 blocks rendered. Overhanging these will be the exposed rafter roof (no soffits or fasia) by about 30cm.

I've no idea how water could penetrate the cavity above the window, unless there is a monsoon with rain being blown upwards. Not an exposed location either, hence me thinking about leaving the cavity tray out.

Interested on others thoughts - am I mad not to put one in? If you think it's a must, I would simply cut some DPM and mortar it in to the blockwork joints sloping to the outer skin with some weep joints at 450mm (which would look crap on my rendered wall)

 

[23vc]

Well I wasn't planning to put weep vents on my upstairs windows by the same logic, only a couple of courses to soffit ?

 

[Alastairreid]

The Bco may be looking for them.

 

[pilsbury]

THe BCO is next coming once roof is going on. Apart from weep vents, how will he know they are there? Don't mind blagging him that I forgot to put weep vents in then just drilling out a perp or two before skimming the over when signed off.....

But I'm just after someone confirming or rubbishing my initial thoughts. Want to do it right but can't see in this case the cavity tray doing anything at all.

 

[23vc]

I agree, ultimately it's the bco's call. I will check with mine.

 

[John D v2.0]

Nhbc state that when there's no exposed brickwork ie rendered completely, no weep vents are needed due to the render helping prevent water penetration. For your case you wouldn't need weep vents.
My comment would be better to put the trays in, you don't want to find out after wards that you need them. But if not it's probably not going to be a problem if it's under cover.

 

[^woody^]

A tray is intended to stop water getting in. If the area above the frame is sheltered, then the tray could be left out.

 

[pilsbury]

sheltered, rendered and painted.