Lean to Roof, corner (hip rafter)

[MFC_1980]

Hello All.

I am designing a lean to roof for a single storey rear and side extension. The span of the rafters is circa 2.6m. The rafters will be notched over wall plates for the straight sections in a standard way, however, I would like some advice on the corner / hip rafter as the roof wraps around the building.

Any info would be very much appreciated. I am particuarly thinking of the connection with the wall of the main house and the bearing on the inner leaf of the extension. I will try and attach pics to assist in my description.

Thanks.

Untitled

• MFC_1980
• 21 Jul 2008
• 2

 

[noseall]

the hip rafter sits at a completely different angle to the common and jack rafters.

therefore the plumb cut, the back cut and the end cut are at a totally different angle. a shallower angle. i use a builders line to find the lie angles in this instance.

there are conversion tables to find the length of the hip rafter so long as you know the pitch of the roof and the horizontal 'going' or run distance.

you can connect the hip rafter to the pitching plate or bearer plate, as you would the rest of the rafters. the last two commons will but against the hip at the junction. it may mean cutting a 45 degree cut at the high end of the hip.

it ain't going nowhere as the jacks as well as the birdsmouth at the plate will keep it steady.

as for the wall plate cut - you need to trim the wall plate, at the 90 degree intersection, to allow the birdsmouth plumb cut to sit against solid wood as opposed to a pointed corner. it is just a case of trimming the point off with a handsaw thus flattening the point of the wall plate angle.

 

[^woody^]

And remember that the hip is at 45 degrees on plan, and so may not meet the house corner like you have shown unless both sides of the extension are the same distance out from the house

And you may need a dragon (diagonal) tie at the hip/wall plate connection to spread the load - if the hip is at a shallow angle and is a deep section

 

[noseall]

And you may need a dragon (diagonal) tie at the hip/wall plate connection to spread the load - if the hip is at a shallow angle and is a deep section

quite so woodster.

the dragon can be constructed with 18mm ply, profile fitted to either of the last jacks.

 

[MFC_1980]

thanks guys.

That explains a few things. My main confusion was how the bearer plate gives enough support to the hip, but I guess trimming it back would give a much better bearing.

Can you give any more info on a dragon tie? I know what they are in principle and normally just ask the builder to ensure they are included, but this one I am getting into myself. Would a steel tie which goes around the top ofthe wall plate at the corner suffice?

thanks again.

 

[noseall]

a dragon can be a piece of ply or a single piece of timber at 45 degrees across the corner.

 

[MFC_1980]

OK. Thanks again.

I have an idea, but what do you guys think the best way to create a vaulted ceiling (in order to install a velux window) would be? The span as mentioned is only c 2.5m, so is there an easy way to get around using ceiling joists to tie the rafters in and provide lateral restraint?

I dont really want the expense of a structural engineer designing a scissor truss or any steel work.

Any ideas?

 

[noseall]

a lean-to roof does not behave like a dual pitch roof. it does not require the same spread restraints.

you can lose the joists - no problem.

just make sure the wall plate is strapped down adequately.

 

[Chipidean]

And you may need a dragon (diagonal) tie at the hip/wall plate connection to spread the load - if the hip is at a shallow angle and is a deep section

quite so woodster.

the dragon can be constructed with 18mm ply, profile fitted to either of the last jacks.

I prefer to use a section of 4x2 for the dragon tie, it requires a longer seat cut to the hip timber but allows a better fixing upwards from under the tie to the hip.

 

[chappers]

I always used to use a piece of 4x2 at 45degrees with the hip notched over but a ply gusset and a twist strap seems to be pretty much the standard method nowadays