Tony trays - what to make them from?

[G and J]

On 25/07/2025 at 09:41, Nickfromwales said:

Do you have a section drawing of that junction? 

Here’s a section.  Happy to share more if interested.  Ground floor will be clad in 100mm block then k-rend, upstairs vertical wood cladding.

 

[G and J]

OK, assuming I use my VCL for my Tony trays that means I need to choose my VCL product earlier than I had expected.  Lots of anoraky reading needed!  But on first glance I’m surprised at the prices of VCL, as I’m obviously missing something.   
 

Why isn’t it just simple 1200 gauge plastic sheet?

[SteamyTea]

1 hour ago, G and J said:

Why isn’t it just simple 1200 gauge plastic sheet

Probably is.

 

https://en.wikipedia.org/wiki/Vapor_barrier

 

You need to get the gm.m^-2.day^-1 from the makers.  Moisture Vapour Transmission Rate, MVTR and this.

 

[Nickfromwales]

2 hours ago, G and J said:

Here’s a section.  Happy to share more if interested.  Ground floor will be clad in 100mm block then k-rend, upstairs vertical wood cladding.

 

OK, stupid question maybe, but why block when it could be insulation and thin coat?

 

What's the spec for cold bridge mitigation at the cavity, where it meets the posi's, if you go block?

[G and J]

45 minutes ago, Nickfromwales said:

OK, stupid question maybe, but why block when it could be insulation and thin coat?

Mortgage-ability.  We switched to block skin downstairs from render board and more timber cladding so that we significantly increase the number of lenders, especially lifetime mortgage lenders, that we could have access to under current criteria.  Not a guarantee but hopefully helpful if and when we do want to pull money out of the house for whatever reason.

 

49 minutes ago, Nickfromwales said:

What's the spec for cold bridge mitigation at the cavity, where it meets the posi's, if you go block?

The block stops just short of the joists/rimboard.  

[G and J]

1 hour ago, SteamyTea said:

Probably is.

 

https://en.wikipedia.org/wiki/Vapor_barrier

 

You need to get the gm.m^-2.day^-1 from the makers.  Moisture Vapour Transmission Rate, MVTR and this.

 

Crumbs.  Ta for this though my head is too full of toolstation order details to take all that in.

 

I really want to do a good job at a sensible cost as I want the house to be really nice to live in without depleting our coffers completely.  But it’s not straightforward with all the choices one must make. 

[G and J]

On 26/07/2025 at 18:42, G and J said:

Here’s a section.  Happy to share more if interested.  Ground floor will be clad in 100mm block then k-rend, upstairs vertical wood cladding.

 

Well, I guess it’s good that (so far) no one has laughed or pointed out a major flaw…

[Nickfromwales]

1 hour ago, G and J said:

Well, I guess it’s good that (so far) no one has laughed or pointed out a major flaw…

Oh, I do apologise, I've been making a list for disaster management, but it's huge and I've not finished it yet.

 

I'll double my efforts and get it to you by 08:00 lol.

 

Just wondering if the posi's should be clad in a high-performance insulation where they protrude, as the cavity will be cold and the posi's are sticking their bare arses out into it?

 

On 26/07/2025 at 21:54, G and J said:

The block stops just short of the joists/rimboard.  

Who's done the interstitial risk on this? The posi end and it's internal void are part of the heated and airtight envelope, but the end timber will be cold as feck as it's in the cavity?

 

[G and J]

My word that is a bloody good point - thank you @Nickfromwales
 

Perhaps that’s why the articles that J found [citation needed J!] stated breathable Tony trays. 

[G and J]

@Nickfromwales we are wrapping the ends of the joist in a water vapour permeable membrane as mentioned in articles found on the net.  We had already planned to fill the ends of the joists with insulation. The ends of the joists are closed with a rim board and the gap between the joists and the header plate will be filled with mineral wool.