Timber frame on top of cavity wall?

[champy]

So I have an existing stand alone garage of cavity brick construction that needs a new roof and roof joists, currently the brickwork is about 1900mm high and as I'm putting a new roof on, i'd like to raise the overall height to 2500mm (it's on a boundary).

My plan is to build a stud wall about 400mm in height (+ 200mm for roof joists, OSB etc) to bring the finished height to 2500. I'll attach the new joists to the stud frame and the frame to the brick work, I could use advice on the best way to do this.

The brick work is 300mm thick - 2x 110mm brick plus 90mm cavity I guess (it's old).

My rough plan is to just replace the existing wall plate with a new one using resin anchors and attach the stud to this, am I missing anything?

Should I be using wall plate straps too?

Thanks in advance.

 

[tomfe]

Just add an extra course of blocks?

 

[^woody^]

Resin or any anchors do jack for holding a plate down. You need to strap it (ie the roof) down with preferably minimum 1m staps. In this case you would strap every 3rd or 4th joist with twisted straps - 1.5m long to allow for the section of studwork and get 1m fixing to the wall.

 

[champy]

Resin or any anchors do jack for holding a plate down. You need to strap it (ie the roof) down with preferably minimum 1m staps. In this case you would strap every 3rd or 4th joist with twisted straps - 1.5m long to allow for the section of studwork and get 1m fixing to the wall.

Thanks Woody, really appreciate the response. I thought I might need straps too.

So to fix the short stud wall on top of the brick I'm fine just using standard masonry fixings? As the straps will be wrapping over them, from the joists to the bricks

Could you speculate how the current roof is still intact without any straps, it's been in place for 100 years or so, just joists resting on a wall plate?

 

[champy]

Just add an extra course of blocks?

I'm a bad bricky and can't find matching bricks, any other brick would look ridiculous.

A stud wall on top is the best solution both economically and aesthetically.

 

[^woody^]

Could you speculate how the current roof is still intact without any straps, it's been in place for 100 years or so, just joists resting on a wall plate?

Straps are a very recent thing (a few decades) whilst roofs have beed around for much longer. You don't tend to see many roofs flying around and that's got nothing to do with straps.

 

[champy]

Straps are a very recent thing (a few decades) whilst roofs have beed around for much longer. You don't tend to see many roofs flying around and that's got nothing to do with straps.

Okay so in your opinion am I fine to just attach the stud construction on top of the brick with bolts and sleeves?

 

[^woody^]

It all comes down to the size (ie roof weight) and location of the garage. If you are in a relatively sheltered location, then that would be different to to being in hurricane alley.

Straps are no big expense nor difficult to fit so why not?

The problem with bolting a plate down, is that bolts are so small and in a very small section of masonry with limited resistance to sideways movement, that any movement in the roof just cracks the top course of bricks or blocks.

 

[champy]

It all comes down to the size (ie roof weight) and location of the garage. If you are in a relatively sheltered location, then that would be different to to being in hurricane alley.

Straps are no big expense nor difficult to fit so why not?

The problem with bolting a plate down, is that bolts are so small and in a very small section of masonry with limited resistance to sideways movement, that any movement in the roof just cracks the top course of bricks or blocks.

I'm definitely putting straps in (from the joists, over the frame and connecting to the brick), just wasn't sure of the best way to connect the frame to the brick as well.