Screws for roof joist straps

[paulweller84]

Hi all,

I am looking for advice on the best choice/size of screws to attach roof joist straps to thermalite blocks. Another post on here suggested 3"/75mm but only about half of this would actually be embedded into the rawlplug. Is there any benefit of having such a long screw when only the end of it is physically in contact with the inside of the hole? Also, how many screws per strap would be ideal?

Thanks

 

[^woody^]

You could screw a course or twin thread 75mm screw directly into the block. Do it slowly.

 

[rougharsedbrickie]

Personally I’d go for a wallplate bat strapped every 1.2m and the joists fixed to that with truss clips

 

[paulweller84]

You could screw a course or twin thread 75mm screw directly into the block. Do it slowly.

Something like this?

https://www.screwfix.com/p/goldscre...k-multipurpose-screws-5-x-80mm-100-pack/17131

 

[23vc]

Yeah they’d do it although the slightly more expensive twin thread ones may be even better. I’ve always fixed straps to thermalites by screwing direct with no plug, always works

 

[cdbe]

I fixed mine in with 75mm self drilling concrete screws. No pilot holes and you need to stop the second your impact driver (mine does anyway) makes that noise to let you know it's starting to hammer them tight - carry on and they'll spin. My blocks were 2.9Nm and even more like weatabix than normal thermalites. In any case the pull on them is upwards not outwards so a dollop of mortar or board adhesive will keep them in place as well.

 

[^woody^]

I fixed mine in with 75mm self drilling concrete screws. No pilot holes and you need to stop the second your impact driver (mine does anyway) makes that noise to let you know it's starting to hammer them tight - carry on and they'll spin. My blocks were 2.9Nm and even more like weatabix than normal thermalites. In any case the pull on them is upwards not outwards so a dollop of mortar or board adhesive will keep them in place as well.

Were your blocks aerated or normal concrete?

 

[catlad]

I've used concrete screws into thermalite before with 4mm pilot first. They fix solid because they have a large thread, be careful not to over tighten.