Strengthening roof rafters

[Atelectrical]

Hi
We're currently starting a roof conversion where due to only having 3x2 roof rafters we need to stretches the rafters with 6x2, my question is how can I do this with the current perling in place, I can't remove this perling until the new supporting wall/ perling is in place but I need to strengthen the rafters before I can put the new wall in.

Can I do the new rafters in 2 pieces and join somewhere with a metal plate?

Any help/ advice would be great thank you

 

[pinenot]

Your questions are about as plausible as your English seriously you need to rephrase your questions using terms that are understandable; for instance -

Purlins - not perling

Ceiling joists/ties (presumably) not rafters - the rafters are what form the roof pitch

What is the supporting wall supporting? and how does it interface with the purlins??

View media item 59921

 

[Atelectrical]

Hi sorry

It is the rafters that need increasing, this is what the engineer has specified, the wall will replace the purlin and become the new support for the rafters.
Hope that clears it up abit.

Thanks

 

[pinenot]

OK, so you need to temporarily brace the rafters to allow purlin removal and space to erect the stub walls which will replace them!
Could the stub walls be erected below the purlins, the purlins cut out in smaller sections and the beefed up timbers applied under the rafters progressively?...pinenot

 

[Atelectrical]

Ok so you suggest building new wall, then cut out a section of the purlin them put in the new timbers and carry on abit at a time.
Sounds good to me

Thank you

 

[pinenot]

Yes, but I think I should expand that advice a bit more.

Replacing purlins with a dwarf wall is not the full picture, either the purlins will be built into the gable walls and will be of sufficient girth to support the purlins un-braced, or as is more common, braces between the base of the purlins will transfer the load to a load bearing wall.
To provide sufficient load bearing properties, the stub wall should be fixed to the rafters via gusset plates glued and screwed. These will mimic the developed shape of the crux formed between the pitch of the rafters and the vertical suds of the stub wall.

Untitled

• pinenot
• 13 Apr 2013
• 1

Also ceiling collars, with gussets should be fitted at ceiling height...pinenot

 

[chirpychippy]

This doesn't make sense, you say your having a roof conversion do you mean loft conversion? Are you having dormers and veluxs either or? It is normal to beef up the existing rafters with 6x2 where the dormer walls are going to be formed and like wise either side of Velux roof windows but all of this can be done without removing the entire purlin or building the stub wall first.

Are you sure the existing rafters are 3x2 and not 4x2?

 

[freddiemercurystwin]

Just ask the SE for the sequence.

 

[chirpychippy]

Anyway the 6x2's dont go under the 3x2 they go along side them and pushed up to the felt and then bolted to existing rafter. May I say this is difficult to accomplish on your own because the 6x2 have to intersect with ridge and the rafter plate to become mirror of the existing rafter.

Obviously you can't do a full birdsmouth on the 6x2 because there is insufficient room between the outside of the rafter plate and the underside of the felt, so you can only cut the seat cut.

 

[Atelectrical]

Hi sorry yeh it's a loft conversion,
The original rafters are 3x2 and so the engineer has specified them to be beefed up with 6x2, alongside the original 3x2 bolted together.
We will only be having velux windows.

Thanks again

 

[chirpychippy]

Are you doing this loft conversion yourself and are you comfortable with the process? I say this because they are not straight forward.