Roof restraints

[akist]

In my 80s house, hip to gable roof, I have seen plenty of these restraints built into the walls and lapping over 3 joists and with nails hammered through, as shown in this link.

Not many builders know what these are for, and the only use they know of these L shape restaint bars are for holding down the wall plate.

Could someone please tell me what they are used for?

https://www.jewson.co.uk/building-m...H10F/simpson-restraint-strap-flat-1000-x-5mm/

 

[Ian H]

It says it on your link:

Heavy restraint straps meet requirements for lateral restraint of roof trusses, rafters and joists tied into masonry walls.

• Designed to provide horizontal restraint

I have them in my loft floor but fixed to the wall rather than built in. I’m not sure they do anything but if they are a requirement I guess they need to be there.

 

[noseall]

They are designed to restrain the masonry and not the other way around.

 

[tony1851]

As per Nose, they tie the wall to the roof - which acts as a rigid plate - to stop the gable from being blown over.

Problem is that the diagrams usually show them being built into the wall. Not only is that difficult but - being near the top -offers little
in the way of restraint. Most builders screw them to the inner face of the wall, so their restraint value depends solely on the fixings.

 

[akist]

Therefore you would not use these on a hip-to-hip roof?

Also, considering a hip-to-gable roof, what is the structural element that stops the roof trusses moving laterally like dominoes? I think it is the gables so then what is securing what?

 

[^woody^]

Not many builders know what these are for

Another gem.

All builders know what these are for. Those that don't are not.

 

[^woody^]

Also, considering a hip-to-gable roof, what is the structural element that stops the roof trusses moving laterally like dominoes?

Normally the fact that they are not trusses but rafters, and as such don't move like that.

 

[stuart45]

Another gem.

All builders know what these are for. Those that don't are not.

Not if they get a big draw from the footings and clear off every time.

 

[^woody^]

Not if they get a big draw from the footings and clear off every time.

Hmmmm, groundworkers you mean?

 

[tony1851]

Therefore you would not use these on a hip-to-hip roof?

Also, considering a hip-to-gable roof, what is the structural element that stops the roof trusses moving laterally like dominoes? I think it is the gables so then what is securing what?

If it's a modern roof built with truusses, there will be diagonal braces fixed across the trusses to triangulate them and prevent them toppling sideways.

For an older (say pre-War) roof with a gable, there are ususally one or two purlins on each slope running on to the gable, which tend to stabilize it.

Hipped roofs don't use restraint straps as there is no wall higher than the eaves to restrain.

 

[Ian H]

I bet I didn’t need them then. Mine are fixed to the party wall and are fixed to the first 3 or 4 floor joists.

 

[tony1851]

I bet I didn’t need them then. Mine are fixed to the party wall and are fixed to the first 3 or 4 floor joists.

The problem here is that, from a structural point of view, any traditional low-rise property should be regarded as a separate structural unit, even if it is part of a terrace, or a semi-detached.

In this case, the party wall is then assumed to be an end gable wall, and should be suitably-restrained at floor- and roof level. If the floor joists
run into the party wall, then that would give sufficient restraint, but more often than not, they run parallel to it, in which case a few straps help.
The roof rafters of course are always parallel, so again, a few straps don't go amiss.

Clearly, it's very rare in practice that the people next door would wake up one morning and decide to demolish their house, leaving yours as a stand-alone house.
When I started out many moons ago, I used this very argument following some major internal rip-outs in a semi, only for the councils' checking engineer
to demand restraints to be added. ...........after all the flooring was done.....

 

[catlad]

Funny you should mention that Stuart the mrs friend
has had a quote for a rear extension and in the stage payment plan they wanted 17k for the ground works!!!

 

[Leofric]

Lateral restraint straps are required at ridge ,rafter, and ceiling node points of trusses and taken over at least 3 trusses to provide lateral restraint to the gable and party walls. Lateral restraint straps are also required at about 1.8m centres and taken over at least 3 floor joists where joists run parallel to external and party walls. Vertical holding down straps are also required to wallplates .These are all shown in bldg. regs approved documents and as others have said any good builder is aware of these requirements.