What are these straps for in my design

[marsaday]

The engineer has specified some straps in my loft conversion. I assume they are to hold the roof down to the gable and party walls.

"provide 30x5th gal ms straps fixed over no3 rafter with timber noggins between rafters and packed tight to gable and party walls"

there are 6 straps on each side.

Any ideas ? I have tried to email the engineer, but no good as away.

 

[noseall]

They are lateral restraint straps, designed to add stability to the gable via the roof timbers.

 

[marsaday]

ok, so they are L shaped and tie into the wall then ?

Are they really needed ?

the roof structure is not changing at all. just adding in new floor and velux windows.

i will happily put them in, just cannot figure out why they are required.

 

[noseall]

Lateral restraint straps are crucial.

Usually set at 2m (max) centres.

They are usually 1.2m long with part of that 1.2m being bent at 90 degrees. these must be fixed to 3 rafters with solid bridging or noggings between rafters.

Fix them to the underside of the rafters.

 

[marsaday]

Right thanks, but could you tell me why i need them now ? The house has been here 100 yrs and is doing very well.

I assume it is something to do with the conversion process placing a new load somewhere, but i cannot work out where/how.

 

[masona]

It's to do with wind loading, a bit more windy now than 100 yrs ago

 

[marsaday]

ok, thats interesting. ta

 

[JoeMar]

if you look carefully on the left handside you'll see 2 of those straps...granted those are on floor joist but they do the same job as those on roof rafters. they basically 'tie' everything together.

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