Fitting rafters and wall plate when outer leaf is bowed?

[Digmixfill]

I have new inner leaf with cavity against an external 9 inch solid wall. When I fit the new roof the ridge will be level and the new wall plate on the inner leaf will also be level.

With the rafters sitting on the new ridge to wall plate line the gutter line on the bowed wall will be quite a way off on some places - up to 100mm bow.

 

The building has suffered roof spread in its past and some parts of the spread have been repaired. Structural engineer didn't seem too bothered by it so it is how it is.

 

When re-roofing a building where the eaves, wall plate and ridge don't line up how does one tweak the eaves end of things? I'm making the assumption that I can't just make the wall plate cock-eyed and call it done.

[Dave Jones]

is this trusses or a cut roof ?

[Digmixfill]

Cut roof.

 

Currently with purlins and ridge board, but will probably become ridge beam with purlins removed.

[Dave Jones]

put the roof on square of course, sort the gutter detailing after. leave long tails for example, if they become too low bump height a little by counterbattening. post a picture.

[Digmixfill]

If everything was true the rafter position would be like this

 

 

Hopefully the pictures show enough detail.

 

This is the short side. The gap between the inner leaf and the old wall plate is 240mm.

 

This is the longer side. The gap between the inner leaf and old wall plate is 305mm.

 

The bits of new timber aren't in the correct positions, but are relative so will hopefully be a decent visual representation that the larger gap will cause the rafters to terminate much lower in the void behind the corbelling.

 

[Dave Jones]

change the pitch to lift the feet ?

[Digmixfill]

That would fix the bowed section and raise the other section accordingly. Would I just plane down the rafters that would become too high?

Edited July 6, 2023 by Digmixfill

[Dave Jones]

8 minutes ago, Digmixfill said:

That would fix the bowed section and raise the other section accordingly. Would I just plane down the rafters that would become to high?

 

you cant it would change the plane of the roof if parts of it were higher than others, it has to stay the same. It's all going to be a compromise, lower the pitch a little slot the outside wall for some of the feet to travel through it ?

[Digmixfill]

The rafters terminate in the wall cavity. Nothing protrudes through to the outside.

 

[Digmixfill]

A plan view crudely indicating where the bows are.

Black = solid 9 inch wall. Red = rough line of bows.

End to end is approximately 14m. Top to bottom approximately 4.5m.