Boarding and bracing?

[PatsPatter]

Morning all.
My question is:
Do I need the lateral and diagonal/chervon bracing on a roof that is fully boarded with OSB?

The new bits being built are a free-standing garage with attic trusses and a sun lounge with raised ties.
Just coming to the bit where we have the trusses up and we are going to FULLY board the roof with OSB3, before battens/counter battens/tiling, etc.
The trusses are engineered, ridge roof with gables, strapped to everything in sight, but I don't want to use the bracing where I don't have to. It means a lot of battening out and a lot more work fixing the insulation inside, plasterboard, etc.

I'm having a little difficulty getting BC and the truss manufacturer to give a definitive answer as to whether - or not - I still need to lateral/diagonal/chevron brace the roof structures. Each one says ask the other - and I seem to have given the BC dept a headache. The last quote from them was 'you are a trouble to me' - because I'm not quite doing things the traditional way. The last thing I want to do is get the boards on and then start having to poke/manoeuvre braces into the trusses.
BC has been quite good but if I can find an official reference, they will probably be happy.
Anyone got any ideas/references/pointers, please?

 

[ree]

Local Regs (local wind effect) will determine bracing altho Mfr's recom is the usual top installation condition.

By and large, on a sheathed roof, just so long as the trusses are braced thro the ridge point, an internal lateral brace on either underside, then you should be good to go.

The sheathing nailing schedule must be rigorously followed - centres, type and size of fixing.

 

[noseall]

When you fix tile battens to a truss roof, particularly if it is a plain tiled roof, you are adding (some) stiffness to the above part of a roof. I appreciate fixing sheathing is somewhat better in that effect.

However, this does not man that you can ignore any of the node bracing details inside the roof. You will still need your diagonal bracing (fixed all the way to the wall plate), node bracing, and chevron bracing if required.

Why have the truss company not informed you of this? It is deffo their domain and not a BC call. Did they not send you a bracing detail?

 

[PatsPatter]

Local Regs (local wind effect) will determine bracing altho Mfr's recom is the usual top installation condition.

The sheathing nailing schedule must be rigorously followed - centres, type and size of fixing.

Thanks for the response.
Just been on the phone to them again. The sheathing idea seems a bit of a mystery to them and the only info I got was for skew nails to be used but no idea of length, or interval - other than 'board it on the underside'.
I have 65, or 75mm ring shanks and my trusty (takes no prisoners) Bostitch air nailer.

By and large, on a sheathed roof, just so long as the trusses are braced thro the ridge point, an internal lateral brace on either underside, then you should be good to go.

Both sets of trusses have a very conveniently sited horizontal up next the ridge, so again, it will be the Bostitch plus ammo.
(the down side of that thing is that the nails are s"ds to get back out if you make a mistake - but I guess that's all to the good, really)

 

[PatsPatter]

When you fix tile battens to a truss roof, particularly if it is a plain tiled roof, you are adding (some) stiffness to the above part of a roof. I appreciate fixing sheathing is somewhat better in that effect.

However, this does not man that you can ignore any of the node bracing details inside the roof. You will still need your diagonal bracing (fixed all the way to the wall plate), node bracing, and chevron bracing if required.

Why have the truss company not informed you of this? It is deffo their domain and not a BC call. Did they not send you a bracing detail?

The trusses did come with all the bracing detail. That's not the issue, I'm afraid, 'noseall'.
I've built a fully boarded roof before but didn't come up against this level of bracing - 'cos I guess it's my first raised tie, the regs have probably changed (in 15 years) and I was living in Scotland, to boot.
One part is a garden room, with lots of windows and the cost of insulating/sealing it alone is not an insignificant consideration. What I'm trying to do is minimise the need for battening out on the entire inside/underside of a fairly large expanse of raised tie ceiling - but not at the expense of safety/strength.
I want to do it right but I don't believe in open season on my wallet.

 

[ree]

I think that a pic of a truss would help - plus a view of the actual roof. OP, Are you talking about intersecting roofs?

Just a couple of things:

- truss ridges are nailing plate points so they are node points, but agreed that "room in the attic" trusses need more bracing.
- and i dont understand what "both sets of trusses have been sited horizontal up next the ridge" means? Do you mean the two braces are already up near the truss peaks?
Anyway, a pic of the in-situ trusses will probably explain more?

 

[PatsPatter]

I think that a pic of a truss would help - plus a view of the actual roof. OP, Are you talking about intersecting roofs?

Just a couple of things:

- truss ridges are nailing plate points so they are node points, but agreed that "room in the attic" trusses need more bracing.
- and i dont understand what "both sets of trusses have been sited horizontal up next the ridge" means? Do you mean the two braces are already up near the truss peaks?
Anyway, a pic of the in-situ trusses will probably explain more?

Will do................. but it'll be tomorrow.
I'm off to the pub - for the first time in a six weeks. Honest!

 

[PatsPatter]

............... - and i dont understand what "both sets of trusses have been sited horizontal up next the ridge" means? Do you mean the two braces are already up near the truss peaks?

A slight misquote, me old, but also an omission on my part.
'Both sets of trusses have a very conveniently sited horizontal up next the ridge....... was the sentence - but I missed out 'member' after 'horizontal', so:
'Both sets of trusses have a very conveniently sited horizontal member up next the ridge'
or............
There are plenty of places to fix laterals adjacent to the node points and indeed the bracing diagram shows them.
As I said in the original post, all I'm trying to do is remove/minimise the need for lots of battening out behind the ceiling covering.
If I can't - I can't................
Pictures coming up.
[/i]

 

[PatsPatter]

I think that a pic of a truss would help - plus a view of the actual roof. OP, Are you talking about intersecting roofs?

Here goes:
//www.diynot.com/network/PatsPatter/albums/
If I got it right, that should show them.
If not - I'll try again
Alternatively:
Garage

Garage 1

• PatsPatter
• 21 Mar 2015
• 1

Garage 2

• PatsPatter
• 21 Mar 2015
• 1

Garage Trusses 1

• PatsPatter
• 21 Mar 2015
• 1

garage Trusses 2

• PatsPatter
• 21 Mar 2015
• 1

Sun room

Sun room 1

• PatsPatter
• 21 Mar 2015
• 1

Sun room 2

• PatsPatter
• 21 Mar 2015
• 1

Sun room 3

• PatsPatter
• 21 Mar 2015
• 1

Sun room Trusses 1

• PatsPatter
• 21 Mar 2015
• 1

Sun room Trusses 2

• PatsPatter
• 21 Mar 2015
• 1

Note: The Sun room roof will intersect the dormer/roof. We have the trusses for that as well.
Will

 

[ree]

I'll drop out at this point. Its different from what i understood its to be, and there are now two roofs involved neither of which is being braced as i would do it.
Get a carpenter who frames roofs involved and it will be resolved immediately the joiner is on site.

 

[PatsPatter]

I'll drop out at this point. Its different from what i understood its to be, and there are now two roofs involved neither of which is being braced as i would do it.
Get a carpenter who frames roofs involved and it will be resolved immediately the joiner is on site.

OK, ree, I understand. Thanks for the effort, though.
Incidentally, when you say 'neither of which is being braced as I would do it', I assume you are talking about the manufacturer's diagrams - not the way they appear at the moment?

 

[noseall]

The diagonal bracing is wrong and needs to go down to the wall plate. This applies to the raised tie roof also. You will need to overcome the diagonal brace where it passes along the vaulted bit by means of a ply thickening gusset.

The bracing schedule is clear and specific and must be adhered to. BC can not authorise a change to this bracing detail.

You will also need to fix solid bridging where the bent straps pass across the rafters/joists.

 

[PatsPatter]

Thanks, noseall. A fair bit to digest

The diagonal bracing is wrong and needs to go down to the wall plate. This applies to the raised tie roof also.

If you're referring to the bracing as shown in the photos, it's only there to locate things whilst we put the trusses up.

You will need to overcome the diagonal brace where it passes along the vaulted bit by means of a ply thickening gusset.

Apologies but not quite sure on that one. Could you elucidate a little, please.

The bracing schedule is clear and specific and must be adhered to. BC can not authorise a change to this bracing detail.

OK, that I can appreciate but.........

You will also need to fix solid bridging where the bent straps pass across the rafters/joists.

Assuming you mean what the builder called 'gable straps' I had worked that one out from reading various other bits and pieces - including that particular truss manufacturer's manual, published on line - but not supplied! There is nothing to stop the gable straps from folding in compression without them in place.
The manufacturer's manual also states that the garage trusses will also need (solid bridging?/dwangs/noggins/whatever terminology suits) between the floor joists as well, even quotes specific sizes. They aren't shown on the drawings, either. It looks as if they are relying on BC to ensure that happens, as well.

As far as I can tell, the information I've got from the truss manufacturer seems a lot less than complete. You've already pointed at a couple of gaps in it. My questions to them have not produced any useful answers. I want somewhere to look/refer to and a bit of good advice and I very much appreciate all that I'm getting on here.

Perhaps you see my quandry? I don't want a disaster and I know I'm perhaps trying to produce a bit of a hybrid but why not? Nothing improves, or progresses, unless it is questioned by someone with an idea.

 

[tony1851]

Raised tie trusses are particularly susceptible to lateral movement in the direction of the ridge.

This is because the rafter between the tie and the wall plate is acting as a slender beam, which can easily buckle sideways.

However, if the trusses are finished with OSB on the top (as they do in Scotland) then this would be sufficient to give you the horizontal rigidity. Use noggins the same depth as the rafters at unsupported board edges. Also, ensure that the gable walls are firmly strapped back to the roof, straps engaging at least three trusses.

It is surprising that your truss-supplier has not given you more advice on this point.

PS see if you can get a copy of C.N.Mindham 'Roof Construction and Loft conversions' - very good chapters on trusses.

 

[PatsPatter]

Thanks, tony. All noted.
When you say ''buckle' do you mean as in twisting along the rafter length, or the whole set of trusses rolling over in the direction of the ridge, like a stand of dominoes?