Why catnic lintels for cavity walls?

[pilsbury]

Why use catnic (type) lintels above your windows and doors if doing rendered blockwork and not just concrete lintels filled with the insulation bats and a cavity closure strip?

Surely they do the same thing but the concrete lintel can be rendered on the window reveal whereas the steel catnic could not....

 

[tony1851]

No reason why not.

 

[pilsbury]

cheaper too!

 

[r896neo]

Your aware though presumably that if doing this method then you need to provided a stepped horizontal dpc above the reveal? The catnic performs this function with the need to build in the seperate dpc.

 

[pilsbury]

The stepped DPC is a piece of DPM that goes from the inner skin (higher up) to the outer skin (lower down) covering the whole window gap + 150mm each side right? So I have to put this in if I use concrete lintels.... I was also under the impression I had to put this in with catnic too or the steel would eventually rot through. Either way, I fail to see where the water is coming from.

 

[stuart45]

Water can penetrate a 4 inch outer skin and run down the inside of the outer wall in driving rain. In theory render stops this, but cracks can develop which allow moisture through.

 

[freddiemercurystwin]

Theoretically down the cavity. It's an ancient debate, a rendered wall in good/new condition is gonna be fairly safe bet though the cost of a bit of dpc is peanuts. But compared to fixing a damp problem a decade down the line and its priceless. Its a no-brainer IMO.

 

[tony1851]

The coating on the black catnic lintels is its own dpc (ie cavity tray not required). The galvanized lintels (eg IG) do need a cavity tray, as of course do concrete lintels.

 

[^woody^]

Any cavity wall needs a cavity tray above any opening. The lintel type doors not matter.

 

[pilsbury]

thanks all