Reinforcing rafters - trussed roof too high

[Martcarp]

Hi all,

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just got plans back for converting and adding dormer to trussed roof.

issue I’ve got is plans state existing rafters (which are staying) to be reinforced from ridge to wall plate… simple! Or not.

the existing trusses sit on the wall plate via the collars and the rafters sail down past the wall plate approx 8” higher.

So I’ve got 2 ideas and I’m happy to hear more.

ive attached sketches of what I’m thinking.




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Thanks for your help

 

[RandomGrinch]

Presumably you are having new floor joists?
Would they extend past the wall plate and the rafter reinforcement fix to those?

 

[Martcarp]

Thanks for the reply,

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I am having new joists but not at this end. This will be behind the dwarf wall and doesn’t require new joists or them being reinforced.


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[RandomGrinch]

Ok, I see.
Its usual for the new joists to continue through and tie to the rafters.
It may be worth contacting the designer and asking for further detailing of this junction.
Structural calcs would have been done to this plan.
...and you paid for the plan to be done properly

 

[freddiemercurystwin]

Its usual for the new joists to continue through and tie to the rafters.

Not when the steel is under the dwarf wall, like here, how could they, with a steel in the way?

@Martcap Can't you just use some 4x2's to fill the gap and then run a new continuous wall plate or two over the top of the existing trusses until you hit the bottom of the new rafters?

 

[RandomGrinch]

Not when the steel is under the dwarf wall, like here, how could they, with a steel in the way?

I'm sorry, this is the problem of talking on forums. I saw the steel in the plan.
I may have been clearer by saying that most of the (small) conversions I have seen don't have a transverse steel (mid-span) and the rafters are tied to the new joists.

 

[freddiemercurystwin]

What plan? Has it been deleted?

 

[Martcarp]

Not when the steel is under the dwarf wall, like here, how could they, with a steel in the way?

@Martcap Can't you just use some 4x2's to fill the gap and then run a new continuous wall plate or two over the top of the existing trusses until you hit the bottom of the new rafters?

absolutely could build up existing plates between rafters then run a new whole
Length. Just don’t like the amount of movement there’ll be, although I could also fix to top of joists to solidify it all.

Im going back to architects just wondered if I was overthinking it. Definitely need the remaining roof to be structurally sound while removing the other half and getting it done in the right order. Dwarf wall will take a fair amount of pressure off the wall plate.

you can see they’ve assumed rafters meet on top on wall plate.

Will keep you updated.

 

[Martcarp]

What plan? Has it been deleted?

There should be an image in my second message on this thread. I’d does say advertisements removed but I can still see the image.

let me know if you can’t and I’ll try repost it

 

[RandomGrinch]

There should be an image in my second message on this thread. I’d does say advertisements removed but I can still see the image.

let me know if you can’t and I’ll try repost it

The image is there, I believe he may be criticising my use of the word 'plan' when I should have said 'section drawing'!

 

[Martcarp]

Architects just stated it needs to be built up to catch the rafters. Very none descript! So I’ll build it up flush to top of collars then run full lengths over.
I’ll likely cut some right angled ply and fit them to help brace them against slipping outwards too.