Roof strength.

[richard1600]

thanks for the advice so far guys.

well i have single skin block garage/workshop. 7m x 4m

just doing the roof now, gonna be felt over board.

pitch is 2.5m high wall plates are 2.2m,, so its a very slight pitch.

i have cut all wood (50mmx97mm) and placed it all in postion,. 400mm apart. "butting up against the beam" my question is,,, am using galvanised screws to join the 2 angles to the middle, then through the birdsmouth into the wallplates,,,,,,,, then the crossbeams are sat ontop of wallplate across 4m width... to stop the spread is it ok to screw down into the wallplate and into the angled beams (is this substantial enough)?

i know in house roof structures, the cross struts are not on the wall plate but higher up and dog bolts are used.

thx again.

 

[noseall]

I use galv nails and screws. Not a problem.

It is just as important, in fact more important to have tight joints and precise saw cuts, this is where the real strength is.

A pair of 4" galv nails will hold tonnes.

We would typically use say 3 fixings per connection. You should always have a minimum of two fixings working in opposing directions so as to make pulling apart difficult.

Anyone who has tried to release a rafter from a ridge-board with three 4" nails in will now exactly what i mean. By the time you have finished with the sledgehammer the rafter is ruined.

 

[noseall]

i know in house roof structures, the cross struts are not on the wall plate but higher up and dog bolts are used.

Not so. You are referring to raised ties or collars.

The most common scenario is the one you are doing with the joists sitting directly across the wall plates and will afford you optimum restraint.

 

[richard1600]

brilliant,, thx,,

am using 4inch galv screws,,, 1 in at top going diagnoly down,, 2 at bottom going diagnoly up..

then on plates, one straight down,. 1 eacxh from both side diag down,,

so if its crossbeam to rafter, rafter is already 3 screws,, annother 3 screws ??

so 6 in total for both peices joined together and into wall plate ??

my diag cuts are perfect to centre main apex beam... the birds mouths 50% are seated niceley,, a would say a few of them are not seated 100% perfect to wallplate, but the cut in (birdsmouth depth) is tiny, like 3/4 inch due to very slight angle,, so i have over 3 inches of wood above.

hope this is ok.

thx again mate

 

[noseall]

We scew nail the rafters on to the wall plate by hammering in a 4" nail each side of the b/m. 2 nails in total. These nails have to be hammered in flush (at least one side) to allow the joist to sit tight against the rafter.

We then fix the joist down onto the wall plate with a pair of nails and one through the joist into the rafter.

 

[richard1600]

perfect,,

seriously, mate you have helped alot... the garage is looking great,, the roof is getting looking good also,, just good to get some advice on best ways to do some things,..,,

not got any decent nails so doing all you said with screws should be ok also??

 

[richard1600]

the main thing i am worried about is the spread...

i have beams (temp) supporting the middle at the moment, and until i screw the x-beams into the rafters they will stay there,,,,

was just worried that only screwing x-beams into the rafters it wouldnt be enough to stop the roof spreadign....

 

[noseall]

Like i said we use screws as much as we use nails. Screws will be belt and braces.

We tend to use screws a lot when fixing jacks onto a hip board whereby the joint has nothing to lock into and just floats until you can get a fixing.

In this instance screws are priceless.

However, i like the feeling of hammering 4" nails into a b/m joint as i get the impression i'm tightening the joint with every blow. Screws can be prohibitive if you are using solid threads and do not completely locate the joint prior to staring the screw through the join. The thread can actually keep the joint apart.

Hope this makes sense.

 

[richard1600]

perfect sense yes... i see..

prob a good idea too seeing as not all my birdsmouths are 100 flat and nice against the plate...

the main thing i am worried about is the spread...

i have beams (temp) supporting the middle at the moment, and until i screw the x-beams into the rafters they will stay there,,,,

was just worried that only screwing x-beams into the rafters it wouldnt be enough to stop the roof spreadign....

 

[noseall]

We lay a pair of slave joists across the wall plates and pop a fixing in each end to prevent spread. If you have no restraint then the plates WILL spread.

Remember to accurately parallel the wall plates prior to fixing.

Alternatively you can fix galvanized bent holding down straps to steady the plates but this isn't 100% reliable.

If the ridge is not to high you could always fix a vertical prop up to the ridge board to prevent spread. The risk with this method is you need to pitch 2 pair before adding the props.

 

[richard1600]

plates are pretty damm good level,, i spent a while getting it right,, they are ontop of a bed of mortar,, i have 6 large wallplate screws in each side that go 1/3 of way into block below plate. and 4x straps screwed in, facing inwards, so happy with wallplate..

but guy who helped me with this,. just said,, coz the xbeam is just sitting ontop of plates on both sides,,, then butted up against rafters ... screwing down into the plate and then across into rafter it wont spread..

just not sure,, doesnt seem hugely strong, i have visions of wallplate being ok but the rafters spreading and bending the screws or something, lol...


i cant prop from middle with beams as i have door one end and window other,,,

but could on the centre cross beam,, double it up and build upto the pitch stop it dropping from centre?

sorry, if not making sense am not a builde,r hope your kinda getting it,,

thx again.