Joining walls of different thicknesses

[bmb4cjt]

We bought our first house a few years ago and are set to self build our extension early next year. I have most of the build right in my head but wondered if anyone could puzzle out one point of the joint on a brickwork.

The thing that's puzzling me a little is that various wall constructions have been used previously and how they are going to join with the new. The original house is built of solid wall construction.

The previous occupants built a first floor extension above the original kitchen and the old drawings suggest this is built with a 250mm cavity wall on top of the solid wall with a cavity tray. The 2 story extension we're building is on the side of the house and the initial drawings are suggesting a newer 300mm cavity wall construction.

The perpendicular joint at the front of the house is easy enough with wall starters off the original brickwork. How am I best joining the 300mm wall up at the rear where the solid wall ground floor and 250mm cavity upstairs will be extended and old butts up with the new 300mm at is going to be out of whack in 2 places as the wall goes up?

Thanks in advance for any advice

Read more: https://www.diynot.com/diy/threads/extension-brick-work-query.560510/#ixzz6iWMIwF1s

 

[^woody^]

Nope. Can't make head nor tail of it. Is there a drawing or something?

 

[bmb4cjt]

Hey @^woody^

I don't have the actual drawing to hand but I've tried to mock something up to give an idea of the dilemma.

Drawing 1 is the SE drawings from the previous occupants 1st floor extension w/ 250mm cavity wall over the original solid ground floor wall.
Drawing 2 is the schematic
Drawing 3 rough sketch to show how the back of the house is proposed to look in this area and the 3 different wall constructions

4 earlier planning permission drawings, essentially to extension is everything to the right hand side down the side of the house from the front door.

Hope this helps

 

[^woody^]

I've had a look and a couple of gins. It's not helped.

Is the problem building a 300 cavity wall on top of a 250 wall?

 

[bmb4cjt]

Haha, I'll try post a clearer drawing tomorrow. It's more continuing a ground floor solid wall/upstairs 250mm cavity to a 300mm cavity end on.

So the new wall will be 300mm from floor to wall plate (on the left of drawing 3) but the walls I'm extending from are thinner and of different sizes on the ground floor and first floor (right of pic 3)

 

[^woody^]

I'll look forward to it!

Perhaps circle the area on the floor plans and show location of existing wall and proposed wall connection.

I can show you 'building on a thinner wall', but it's the location of the "end on" junction I can't seem to find

 

[bmb4cjt]

No problem, will get on it tomorrow. Enjoy the gins!

 

[bmb4cjt]

Hope these are a little better . I've circled on each floor where the wall is to join and annotated the rear elevation where new and old all join to give an idea of where the issue is.

 

[Charlie George]

use a steel beam at floor joist level in bedroom 3 sat on new 300mm wall internal blockwork,and internal wall in corner of bed 3 on padstones,ideally designed by structural engineer,the wall below can be plasterboarded inline with new wall

 

[bmb4cjt]

Thanks @Charlie George

How am I best joining the ends of the brickwork above and below the steels to continue the cavity as is where or am I overthinking it and just wall starter from the end of the wall also and just remove the remainder of the wall where we are knocking through?

 

[bmb4cjt]

Kinda like this?

 

[Charlie George]

I seen this as you building on top of existing, but are your leaving the existing bedroom 3 250mm front wall in ?,if so no steel needed.

 

[bmb4cjt]

Sorry yeah we're building on the side of the house. Essentially everything to the right of the dotted line in the above picture is to be the extension. So we're leaving the front wall of bed 3 in and extending from it to make one large room, demolishing the current wall through the middle (where the dotted line is).

I've tried to show the layout of the rear aspect of the house once the extension is done by drawing over the drawings the previous occupant has had done. So stuff in pen is new extension and the computer generated lines are already there.

 

[^woody^]

It's poor design. You certainly don't want a step in the wall, neither do you want the internal face of the 250mm wall insulated or boarded out and end up with two different wall surfaces and properties.

Build the new cavity wall in 250mm cavity to that elevation to match the existing (block bond new to old), and then line the whole inside of the elevation with suitable insulation to get the required u-value on that elevation only.

In addition, you probably don't want half that elevation to be in old brickwork, and then the other half in a different new brickwork, which will look a bit crap. Potentially three different bricks on that elevation?

 

[bmb4cjt]

Cheers @^woody^

Build the new cavity wall in 250mm cavity to that elevation to match the existing (block bond new to old), and then line the whole inside of the elevation with suitable insulation to get the required u-value on that elevation only.

That makes sense and defo a lot easier! Thanks for the advice. Where the 250mm meets up with the original solid wall would it be easier to start again or is there a way of tieing these in?

In addition, you probably don't want half that elevation to be in old brickwork, and then the other half in a different new brickwork, which will look a bit crap. Potentially three different bricks on that elevation?

Just a bit - original pre-war imperial bricks, 1st extension outer thermalite sheild and the new one. Luckily the whole house is otherwise rendered but as that's knackered too we'll have it all taken off and new placed to covered up the patchwork of brick/block etc.