timber block supports for rafters

[infinity]

Does anyone fit timber block supports to the rafters when fixing brackets with screws?

We have tried a new structual engineer who has sid because of the percentage of wood the fixing takes we have to fix 400mm blocks to the rafters where the brackets will be.

We havent had any trouble with any others we have done previous this seems like overkill, and very time consuming with over 30 brackets!

 

[jason121]

Use Spax screws, can be used on 35mm rafters without noggins

 

[Gavin A]

not on 50mm rafters, but we've been doubling up the rafters for 35/38mm rafters for a long time even prior to napit telling us we needed to use a structural engineer to tell us we had to do what we were already doing.

 

[jason121]

The tests were carried out on the following roof hooks used for installing above roof solar systems:

·
Mount Solar slate hook

·
Mount Solar long arm pantile hook

·
Mount Solar standard pantile hook

The roof hooks were manufactured from bead-blasted stainless steel with a nominal thickness of 5mm.

The Spax screws 6mm by 80mm washer head A2 grade stainless steel. These screws are self-drilling.

Tests were carried out with the screws in the self-drilling mode and with pilot holes drilled to a depth of twothirds

of the screw length.

The hooks and screws were tested with 35mm x 72mm timber rafters. This is generally the smallest

standard rafter size used in roofs of UK houses.

The rafters used were nominally C16 timber grade which is the lowest grade usually specified for timber

rafters in the UK. Truss rafters will generally use grade TR26 which is slightly denser than C16 and will

have fewer knots, however, TR26 timber is only generally available to truss rafter manufacturers. Using

C16 timber will therefore give a conservative test result.

 

[Gavin A]

we use something similar, though 6.3mm x 80mm rather than 6mm for the spax.

never yet seen a 35mm rafter split after driving a self tapping bolt into it, and until I do....

it's the point loading that's the issue with them rafters I think.

 

[Worcester]

And eurocode 5 on the screw size which is what the structural engineer will have been going on about.

 

[jason121]

Spax have been tested to MCS012, I have a 35 page test report.

 

[infinity]

its the eurocode as worcester mentioned.

They are only 35mm rafters. Although personally it does seem over the top adding to the rafters.

Gavin.. do you have a quick method in installing these braces? maybe slid the tiles up where the brackets will be to locate where to place them.

I think doing the first one this way is going to take a while.

 

[Gavin A]

Gavin.. do you have a quick method in installing these braces?

we just do the entire rafter, on the thin trussed roofs, so just place new rafter next to existing rafter, drive bolt in at top, drive bolt in at bottom, fill in every 500mm or so in between, move on to next truss.

Doesn't take long in an open boarded loft, bit longer if there's loads of stuff in the way.

 

[docka]

Apologies for resurrecting an old thread but I'm faced with the same situation on 38mm rafters, the structural engineer hasn't stated the need for noggins and it's difficult to find info on Eurocode 5?
My thinking is that adding a new rafter the entire length of the existing rafter will add a significant amount of weight to the roof structure so I'd be happier using 6mm Spax or Redtip screws.
Anyone shed any further light on this?
Thanks

 

[Worcester]

The weight will be more than compensated for by the added strength, so long as you properly support then at the eaves and ridge and tie it to the existing rafter.

 

[docka]

ok so ideally the new rafter, of the same dimensions as the existing one, would be sitting on the wall plate and purlin and connected in at the ridge board and coach-screwed along it's length?
In that case can anyone suggest a mounting system that is ok @900mm centres at 170m.a.s.l. and not in the roof "edge zone" on a 13* pitch please?
I was planning on using Redtip but that would mean doing every rafter like this as these rafters are @450mm centres and Redtip say maximum roof hook spacing is 600mm. thanks

 

[Worcester]

What are the tiles?

 

[docka]

What are the tiles?

They're green double romans
thanks

 

[infinity]

I think installing an extra rafter and fixing it to the wall plate and bid mouthing it at the ridge is impossible in most the roof spaces i have been in

 

[Gavin A]

I think installing an extra rafter and fixing it to the wall plate and bid mouthing it at the ridge is impossible in most the roof spaces i have been in

doesn't need to be - you're strenghtening the existing rafter to ensure it can cope with the extra point loading in the middle of the spans, not strengthening the actual fixing to to the wall.

if it's got a purlin in the middle you can just cut the extra rafter in the middle and bolt each side separately to the rafter above and below the purlin.

eta - usually, unless you structural engineer says different of course.