Cavity trays or stepped DPC

[Ruggers]

Are cavity trays above door and window openings compulsory to meet building regs or can you still use Stepped CPC over a minimum 150mm step between the inner and outer cavity walls with weep vents?

I've never used cavity trays but heard some bad things about them years ago when i done an extension. Getting blocked or leaking maybe.

Having a quick look i can't see how they work as it just shows an angled length of plastic set into the outer bed of mortar and angled up to the inner wall but not into the inner wall.

 

[acurachris]

It's not compulsory to use manufactured plastic cavity trays over doors and windows, you can use DPC stepped from inner to outer with weep vents as you mentioned.

 

[Leofric]

and cavity trays should have stopped ends

 

[^woody^]

A cavity tray performs a different function to a DPC - stepped or otherwise.

A tray is required over any opening where moisture penetration is possible.

A tray can be proprietary or made up from a suitable material.

There are no bad things about cavity trays. Stop listening to whoever is chatting it.

 

[Ruggers]

A cavity tray performs a different function to a DPC - stepped or otherwise.

A tray is required over any opening where moisture penetration is possible.

A tray can be proprietary or made up from a suitable material.

There are no bad things about cavity trays. Stop listening to whoever is chatting it.

How do cavity trays above a door or window opening prevent any moisture from tracking down the cavity against the inside wall if the tray only leans up against it? They obviously work if people are using them but i can't help wondering how the moisture or anything coming down the caving doesn't slip past the tray & cause damp patches above the window opening between lintels or where a catnik is.

 

[^woody^]

if the tray only leans up against it?

Trays are built in to internal leaf.

 

[acurachris]

How do cavity trays above a door or window opening prevent any moisture from tracking down the cavity against the inside wall if the tray only leans up against it? They obviously work if people are using them but i can't help wondering how the moisture or anything coming down the caving doesn't slip past the tray & cause damp patches above the window opening between lintels or where a catnik is.

With the trays you are talking about, they are just placed under the bricks on the outer leaf and have enough "flap" to catch moisture dripping down the outer wall or from the wall ties. This is where the moisture is going to come from, not the internal wall; why would you have moisture dripping down the internal wall?

Using DPC it is built into the inner course to hold it in place.

Trays are built in to internal leaf.

I think he's talking about these...

 

[Ruggers]

With the trays you are talking about, they are just placed under the bricks on the outer leaf and have enough "flap" to catch moisture dripping down the outer wall or from the wall ties. This is where the moisture is going to come from, not the internal wall; why would you have moisture dripping down the internal wall?

Using DPC it is built into the inner course to hold it in place.



I think he's talking about these...

View attachment 170620

Yes they are the ones i was on about. I didn't realise they were just for catching moisture thats found it's way in through he outer wall and tracked it's way down the cavity or what's dripped off the middle of the wall ties. As I've only used stepped DPC before apart from it fixing to the inner leaf to hold it in place, i thought it may find it's way down behind it but now you've explained this would probably only happen if the top of the cavity wasn't closed off or that cheap insulation blown in allowed it to track across.

So neither does a better job than the other trays or DPC is just personal preference.

 

[acurachris]

So neither does a better job than the other trays or DPC is just personal preference

Nothing wrong with the trays I suppose, it's cheaper and easier to use the DPC method, not to mention you can pickup a roll of DPC from pretty much any building merchant.

 

[Leofric]

don't forget stopped ends to cavity trays

 

[Ruggers]

don't forget stopped ends to cavity trays

Why are these important if dpc has no ends

 

[Leofric]

Why are these important if dpc has no ends

exactly ,I presume you mean a cavity tray formed from dpc , can you form stopped ends

 

[Ruggers]

Just re-visiting this one again to see if we said DPC was still allowed over cavity trays under current building regs.
Are there any benefits to plastic cavity trays for above openings and/or below slip sills over using a roll of DPC?
They just look more fiddly and more expensive but i've never used them so your thoughts who have?