Cavity tray

[george765]

Hi,
I am soon to install a 3.3m lintel. It's actually 2 lintels bolted together with spacers for a cavity wall.
I have already had excellent advice regarding the installation i.e. props etc.
Something has just occured to me. I have heard of cavity trays fitted in the cavity to catch drips.
Do I need to install one above the steels ?
the steels will be sitting at normal ceiling joist height to allow the ceiling to run at the same height through to an existing extension which is getting a new flat roof.
I realise this is a vague question but any advice would be helpful.
thanks
George

 

[^woody^]

A tray, if needed, should be installed above the roof flashing

 

[george765]

thanks, but how do I know if one is needed ?

 

[r896neo]

Its a judgement call really, if the wall is very exposed and gets driving rain or there is a large expanse then do it. If however there is 3 feet before the soffit then you may get away without it.

With planning and measurement you can use the trays with lead skirts as the cover flashing for the roof wall junction rather than put in seperatly.

 

[freddiemercurystwin]

BC usually insist on them. The forum is awash with threads where people experience problems due to their non-fitment.

 

[george765]

I have found a pic of one fitted and can see how it fits into the mortar bed above the flashing and stretches across the cavity to catch drips.
I can see how ths would be easily fitted when building the wall, but how would you fit into an existing wall ?

 

[^woody^]

thanks, but how do I know if one is needed ?

One is needed when an external cavity wall goes down past a roof and becomes an internal wall or is otherwise inside a roof space.

If the wall gets a lot of driven rain, then potentially, water can run down the wall and drip out in the room.

An alternative would be to coat the wall with a good quality clear water repellent, but its not 100% guaranteed, and the BCO may not agree to it

 

[freddiemercurystwin]

Not fun: 2 bricks at a time http://www.cavitytrays.co.uk/pdf/23-Type-E.pdf

 

[r896neo]

To fit into existing wall is difficult and time consuming, you have to remove a course of brick but can only cut so many bricks out at a time because propping a wall is bloody difficult on a roof.

Its like putting in a normal flashing but rather than chase out the joint you remove the whole brick, insert tray and replace leaving weep holes.

 

[george765]

Thanks guys, I understand now and can discuss with B.C. with at least a little knowledge of what may be required.
thanks again, G

 

[catlad]

What building control want you to do is kick the **** out of a perfectly good wall, weakening it when you have normally just inserted a large steel beam

 

[freddiemercurystwin]

What building control want you to do is kick the **** out of a perfectly good wall, weakening it when you have normally just inserted a large steel beam

Or ensure the wall doesn't leak in the future! You never seen light through a single skin of brickwork or seen a single skinned rendered wall leak?

 

[catlad]

I am not against fitting then to wall that look poor, but for them to be specified every time what ever the condition of the brick work I don't agree with, as the wall will not be as strong afterwards however careful you are, they can be fitted retrospectively anyway so why not wait to see if they are required.

 

[freddiemercurystwin]

Because the cost and impact of putting leaks right after they have occurred can be large compared to the cost of fitting a tray in the first place.

If you can find me a skin of brickwork that is impermeable I'll eat my leotard. Rendered blockwork maybe but brickwork very unlikely.

 

[noseall]

The weather conditions needed for a wall to become saturated are prolonged periods of wind driven rain, particularly to a building elevation that is exposed.

These conditions occur more often at the coast.

My argument (against) retrospectively fitting a CT here in the midlands is i have only seen those conditions once.

The problem with retro fitting is unless the brickwork is replaced sympathetically, you can end up with the masonry being more permeable than when you started.

The difficulty is when you are trying to force mortar into joints and getting them full. Plus the fact that often the actual tray is fitted with little care because of the difficulty of getting the blessed thing in.

The most common offender is when a connie has been fitted to a wall and some saturation occurs at the connection. This is visible because there is no ceiling as a buffer and is more of an annoyance rather than a drip.

None the less, i agree to fitting them as part of a build, but am reluctant to mess up well pointed brickwork for the sake of 50 year freak event. However, things may be different at the coast.....