Timber internal cavity leaf

[Malc]

Hi,

Anyone know what the regs are on a timber internal leaf for a cavity wall?

The problem I have is where 2 doors join at a corner. Over these doors is a corner lintel, L shaped. At the corner this has a support post 80x80mm. Cavity is only 50mm. In plan view this is a 250x250mm pier. Outside is a 100mm wide L of brickwork, inside a reverse L of 100 of blockwork. Vertical DPC between inside and outside leaf. This leaves a 50x50mm cavity in the middle. Opps, 80x80 post doesn't fit 50x50 hole. And 70mm blocks don't exist.

What I need is something other than blocks. I was wondering about vertical DPC on post and outside wall, then then timber, OSB3 and 47mm timber maybe. What is normally done with pillars with posts?

 

[^woody^]

I know the regs, but I'll be dammed if I can understand the question.

 

[AronSearle]

Also can't understand the question, got a drawing?

 

[freddiemercurystwin]

There won't be a detail will there but if ever there was a need for getting some decent drawings done it's for a timber frame jobby with awkward details. A bit of brick cladding here sounds like it'll never work and there either needs to be a meaty bit of brickwork to build or clad it another way. This is how I've detailed a mildly similar situation though obviously this isn't a corner but the principal is the same,

 

[Malc]

OK, it could have been clearer if I had attached a drawing . Here is a rough drawing. Windows are just something I've found, not the real windows, but they show where the windows go. Outside is brickwork to match house. For a old style wall, 100+50+100, then pier is 250x250, with 50mm square hole in the middle. Vertical DPC is marked in green BTW. But I need to get an 80x80 post in the 50x50 hole so my rear blockwork (??? on diagram) would need to be 70mm blocks in that case which doesn't work.



Freddymercurystwin, if I understand you right then your suggestion would be a big metal post. I assume the post would need to be about the centre of the wall. Windows are usually with back to outside edge of cavity so +25 to +95 from centre line so a 125 or 140mm square post then? I guess that could be pulled back about 15mm, windows would be 70mm deep with screw line in the centre, i.e. 35mm from front edge, or 20mm if post is moved back. Is your DPM a breathable membrane? Or are relying on the insulation at the front and the rear VP to prevent condensation?

 

[^woody^]

If a post is required then why not a timber post?

 

[Malc]

Over the top is a corner lintel (L shape). This comes with a metal post. Standard size is 80x80mm, 100mm in from outside edges (so allows for a 100mm brick front). The post does all the work I'm told.

 

[freddiemercurystwin]

You can't build a 250x250 brick pier like that, you need some insulation between the brick and the column at least and besides as mentioned it's impracticable to build a brick pier in this situation and that size it's not even a brick dim. Better to insulate the column and clad it. In something other than bricks. If a brick pier was essential here then it needs to be bigger and you shouldn't of skimped on paying for some decent drawings.

 

[Malc]

First off, I am paying for drawings but I like to be in advance of the drawings so I know my options. Current drawings, simple for planning, building regs to follow, show a brick face as that's what I said. I'm now wondering how that's going to work out. I don't see what's wrong with having a brick front face. The corner lintel is clearly designed for that otherwise why have the default position of the supporting column 100mm back from the outside edge?

However, I'd agree that it might be tricky to make a neat job of the brickwork on the front face since it is so small and cladding might be simpler. That was a concern and fallback was to render to match 1st floor render (ground is bradstone outer).

If front was brick then insulation would all have to be to the rear, such as celcon's, if we had 100mm of course.

 

[Malc]

I have a think about this and is there any reason I couldn't do the rear leaf as a stud wall but with a vertical DPM (Blue plastic stuff like used for floors maybe?). I'd use treated timbers as well I reckon. So something like this:


Top left is brickwork, middle is 80x80 steel post, then rockwool (cavity fill type), DPM (blue line), studwork, and bottom right, plasterboard. I won't fill behind the plasterboard as that risks damp at the DPM. Better to keep same temperature as room so same relative humidity.

Any problems with this approach?