Max truss centers width for a slate roof.

[epsilonGreedy]

My roof trusses arrived last week and are ready to be fitted. Now a potential slater for the natural slate roof cover has commented that slates are a pain to fit when the gap between trusses is more than 450mm. The slater says the extra flex in the "lats" at 600mm centers causes bounce when nailing the slates into position and this bounce causes extra breakage.

 

Is the slater making a valid point?

 

I am no looking at four remedies:

1. Buy an extra 10% of slates to cover the additional wastage. Not a preferred solution because apparently some cracked slates won't become apparent for a few months.
2. Fit stronger lats, 50mm x 50mm has been suggested to reduce bounce across the 600mm centres.
3. Buy a few extra trusses to get say 70% of the truss spacing down to 450mm. However because I have a hipped roof there is no simple way to reduce the centres where the prefab intermediate hip end trusses are sized to fit at 600mm centres.
4. Go back to Plan A and fit Nulok to sidestep this whole issue with Nulok's its nailless design.

 

Hmm! This good weather won't last much longer.

 

[nod]

I can’t remember ever  seeing roof trusses at anything other than 600 centers 

I would go ahead and put them in at 600 As per manufactures drawing 

[joe90]

4 minutes ago, epsilonGreedy said:

Is the slater making a valid point?

Yes, my builder wanted 400mm centres and mentioned bounce (or break when stood on ?). My slates are fitted on hooks, not nails, looks great and no breakages (also easier to replace broken slates). Perhaps hooks and 50x50 batts.

Edited September 17, 2020 by joe90

[Oz07]

25mm lath for 600 centres.

19mm lath for 400 centres.

 

Perhaps he's been on jobs with wrong thickness lath

[Mr Punter]

25 x 50 with trusses at 600 ctrs is standard here.

[Oz07]

think 50mm is to do with hanging weight ie tiles. 25x38 should be okay for slate but double check

[PeterW]

25 x 50 lath and should be fine. Issue normally is the laths aren’t down tight so bounce, so double nail them 

[dnb]

I have a 600 centres and 50x25 battens. Yes it can be a little bouncy but so far it isn't being a problem in the slightest.  But I am only an amateur with roofing!  

Edited September 17, 2020 by dnb

[Russell griffiths]

How about using a sarking board. 

[epsilonGreedy]

18 hours ago, nod said:

I can’t remember ever  seeing roof trusses at anything other than 600 centers 

 

 

The truss manufacturer knew I was having a slate roof cover and did not raise the option of 450mm centres. The boss visited onsite to confirm measurements and we had a long chat about self building hence there was time to discuss the 600mm / 450mm option, hence it must be a specialized choice.

[epsilonGreedy]

18 hours ago, joe90 said:

Yes, my builder wanted 400mm centres and mentioned bounce (or break when stood on ?). My slates are fitted on hooks, not nails, looks great and no breakages (also easier to replace broken slates). Perhaps hooks and 50x50 batts.

 

My building moto is "when in doubt copy Joe90's build".

 

Do you remember the name of your slate hook system? While chatting about Nulok with my guy he conceded hook slate fixing is the norm in Brittany, it should be a robust option given the wild weather in Finistère and their > 45 degree roof pitches.

[joe90]

8 minutes ago, epsilonGreedy said:

My building moto is "when in doubt copy Joe90's build".

 

You ol chammer you!!!, I found this on u tube, may be helpfull. One of my hates about slates is the difficulty replacing broken ones where tile are easy but not with hooks!!!!

 

 

[epsilonGreedy]

19 hours ago, Oz07 said:

25mm lath for 600 centres.

19mm lath for 400 centres.

 

Perhaps he's been on jobs with wrong thickness lath

 

 

My slater has clocked up 30 years in the building trade. I think he just wanted me to adopt some of the standards he has applied to his on recent self build with its slate roof. He is circumspect about most modern building techniques e.g. he is not happy about being persuaded to accept 50mm of flow screed thickness for his UFH ground floor slab. He reckons many dry ridges will fail before the life expectancy of the rest of the roof and he does not think breathable membranes are as breathable as claimed "the nice thing about old tar based felts is that the nail holes self sealed compared to these flimsy modern underlays where the nail holes open up as the wind tugs the membrane". 

 

He went on to state that he encounters many newish modern attic spaces with mould on the timbers because of insufficient ventilation. He recommended eave vents that reach up 600mm i.e. well over the insulation.  

Edited September 18, 2020 by epsilonGreedy

[Gav_P]

11 minutes ago, joe90 said:

 

You ol chammer you!!!, I found this on u tube, may be helpfull. One of my hates about slates is the difficulty replacing broken ones where tile are easy but not with hooks!!!!

 

 

 

Interesting, but possibly the most boring voice over guy ever employed! 

Edited September 18, 2020 by Gav_P

[Mr Punter]

8 minutes ago, joe90 said:

You ol chammer you!!!, I found this on u tube, may be helpfull. One of my hates about slates is the difficulty replacing broken ones where tile are easy but not with hooks!!!!

 

I am also keen on hook fixing.  It stops any rattle and makes sense to have the tail of the slate held down.  Even if the slate were to crack (which is less likely than with nails) it will not slide down off the roof on onto who or whatever is below.

[epsilonGreedy]

5 hours ago, Russell griffiths said:

How about using a sarking board. 

 

 

Hmm now there is a radical thought for England. Something to consider if there is likely to be a long delay before the slates can be fitted. A sarked roof with felt over is good for a few months I assume?

 

Trouble is I guess extra measures are required to make up for the loss of moisture egress via a breathable membrane?

 

My roof has a cold attic space BTW.

Edited September 18, 2020 by epsilonGreedy

[joe90]

16 minutes ago, epsilonGreedy said:

He reckons many dry ridges will fail before the life expectancy of the rest of the roof

I wonder which part of the dry ridge he expects to fail?, stainless screws?, perhaps the plastic inserts!. I still think Mortor (stiff) on a timber (flexible) roof structure is asking fir failure.

[epsilonGreedy]

21 minutes ago, Mr Punter said:

 

I am also keen on hook fixing.  It stops any rattle and makes sense to have the tail of the slate held down.

 

 

I am nearly convinced the only problem I have is with the final aesthetics. I remember observing, while touring around Brittany, that the exposed hooks are noticeable. I wonder if hooks would upset my local conservation area officer.

 

I think NUlok's hooks protrude less because the main fixing for each tile is groove in each of the special metal inserts.

 

21 minutes ago, Mr Punter said:

 

Even if the slate were to crack (which is less likely than with nails) it will not slide down off the roof on onto who or whatever is below.

 

 

Or in the case of @ToughButterCup's roof, a scaffolding board is scooped up by the wind and thrown onto the freshly laid slate roof.

Edited September 18, 2020 by epsilonGreedy

[joe90]

19 minutes ago, epsilonGreedy said:

He recommended eave vents that reach up 600mm i.e. well over the insulation. 

definitely with cold lofts and lots of ceiling insulation.

[nod]

1 hour ago, epsilonGreedy said:

 

The truss manufacturer knew I was having a slate roof cover and did not raise the option of 450mm centres. The boss visited onsite to confirm measurements and we had a long chat about self building hence there was time to discuss the 600mm / 450mm option, hence it must be a specialized choice.

I can see where he’s coming from

Nailing skates onto 450 centers would be much easier 

But if he was working for a building contractor he would just arrive and the roof would be ready for him with 600 centers 

[PeterW]

6 hours ago, epsilonGreedy said:

 

Hmm now there is a radical thought for England. Something to consider if there is likely to be a long delay before the slates can be fitted. A sarked roof with felt over is good for a few months I assume?

 

Trouble is I guess extra measures are required to make up for the loss of moisture egress via a breathable membrane?

 

My roof has a cold attic space BTW.

yep it’s fine. 
 

just done a small sarked roof today - boards are 95x20mm rough sawn tanalised and laid with a 3mm gap between the boards. You need counter battens though unless he’s nailing onto the boards at which point I think they need to be 25mm ..?

[epsilonGreedy]

11 minutes ago, PeterW said:

yep it’s fine. 
 

just done a small sarked roof today - boards are 95x20mm rough sawn tanalised and laid with a 3mm gap between the boards. You need counter battens though unless he’s nailing onto the boards at which point I think they need to be 25mm ..?

 

 

Thanks, does the 3mm gap allow moisture to pass the sarking and then up through a breathable underlay?

[PeterW]

Yep that’s the point of leaving the gaps and also allows it to swell and not bend 

[Cpd]

If the sarking is wet I lay it without gaps as when the roofing membrane goes on the boards Start to dry out and  shrink And you then have your gaps. 
My local builders merchants keep the sarking outside and as it’s the west coast of Scotland the sarking is always wet ! 
it’s quite alarming how much shrinking you can get.