Binders in cut roof

[garyo]

Is there a point where your ceiling joists are so over spec'd that you don't require roof binders? Is it a problem if, because of the design of the roof, the binders can be fixed to all joists but not to a wall at either end?

Thanks!

Gary

 

[^woody^]

If the joists are deep enough for the span, then you don't need a binder.

If a binder is required, then it needs to be supported at each end. I can't picture a situation where a binder can't be supported at the ends

 

[garyo]

Ah okay - in that case I think I'll be able to do away with them - I'm using 50x200mm over a 4 metre span, at 600mm centres.

Out of interest, how would you have fixed the binders in this scenario:

At one end there's just a loft cavity and rafters for the existing roof, at the other end, due to the hip, it's not possible to get the binder over the wall.

While I have your ear, do you have any view on my proposal to support the old rafters off joist hangars off a doubled up beam (the existing rear wall us being completely removed so the ghosted out middle wall in the diagram can't be used)

Untitled

• garyo
• 9 Feb 2012
• 2

(edited to improve detail on diagram)

 

[^woody^]

The binders would go on some sort of post or timber over the existing wall, and bolted to a rafter at the other end which would have a doubled up section taking the load down to the wall plate

The timber beam idea is OK as long as it has been designed to take the load from the rafters, but it will also need some sort of restraint/stiffening to stop it being pushed sideways by the rafters

 

[garyo]

Cheers woody. The ceiling joists comply with the floor joist span tables so I think I'll remove the binders.

I'll add some restraint to the doubled beam. I was hoping that lateral push from the rafters would be limited by the triangular shape of the existing roofs construction.

Thanks

Gary

 

[Sledge]

garyo,

just to add that the binders you were thinking of fitting do many tasks:

- prevent joist twisting / bending
- tie the rafters and stop them pushing out your inner leaf
- reduce the effective span.

Only the last of these is obviated by selecting larger joists.

I have asked hip questions here in the past, in particular concerning bringing binders down onto supporting walls, so I have a good deal of sympathy. I have also seen what lack of binders can do. I was invited to look at a neighbour's house whose inner leaf had pushed out so much it was distorting the outter leaf. They've since had it patched up: lots of metal straps and such that tie the rafters across 3 or 4 joists (at right angles). Personally I don't rate that methos much. Better safe than sorry imho.

People will doubtless accuse me of over-caution. After all these methods have been used for ages etc. Okay, but I was struck yesterday by a note entitled "IMPORTANT INFORMATION" that accompanied my house insurance renewal quote:

"4. Weight of snow damage
You will need to have purchased additional accidental damage to your buildings cover in order to be protected from this type of damage, which will be considered under 'damage caused by external means'"

This clause makes no apperance in the policy summary, not even under "exclusions", but it has been issued nonetheless.

Doubtless the actuaries have noticed an increase in snow damage claims which the names are not happy shouldering. I'm thinking the absence of the clause in the policy document is an attempt to make you feel reassured and allow them to charge the sam epremiums for diminished cover. Either way, the message is clear: the heavier snowfall of recent years has taken its toll on what we assumed to be 'solid' structures. Don't get caught.