Browse Forums Building Standards; Getting It Right! 1 May 22, 2013 11:37 am I've done some research regarding roof tile installation and timber in general, but so far I've been unable to find any specification for how far a timber roof batten may bow or spring from plumb and still be within spec, or how much deviation from plumb the edge itself may have (ie: how not-flat is the edge). I can see specs for distances between battens, tolerance for alignment of battens to other battens, spans that they may cover, etc, and that roof tile courses must be aligned, which arguably implies that the batten surface must be flat, but nothing referring to the aforementioned aspects of the battens themselves. Do such standards exist, as Australian Standards, or some other set of general building practices? Re: Standard for bow/spring, flatness of timber roof battens 2May 22, 2013 1:58 pm I'm sure there would be some sort of Australian Standard or BCA rule for any kind of deflection although I don't know what it is.
I seem to recall when I was building one of the engineers telling us to allow for L/50 where L is the length of the span. This was for most horizontal beams - floor joists, ceiling joists, roof battens etc Say you have your rafters set at a 600mm spacing that requires a 75 x 50 batten laid on its flat according to the span tables. L/50 would be 600/50 which is 12. So a span of 600mm between the rafters using a 75 x 50mm batten shouldn't have any more than 12mm deflection on it when under full roof load ( doesn't matter whether it is a Colorbond roof or tiles ) I don't know whether this was just a general rule of thumb that they used to tell us uneducated chippies or whether it was based on something more substantial. I also looked in my copies of "NSW Timber Framing Manual" and "Acceptable Standards of Domestic Construction" and the "BCA" but didn't find anything in there either. I think they rely on the span tables minimum sizes for the span. Someone more learned than me may know. Stewie Re: Standard for bow/spring, flatness of timber roof battens 3May 22, 2013 3:39 pm Thanks for that Stewie, Would batten deflection under normal full load (which I would tend to think would be bowing) tend to cause roof tiles to appear to kick up at the side lap? Or should the joins still hold the tile course in alignment, if the battens were flat and not bowed or sprung when the tiles were being laid? Re: Standard for bow/spring, flatness of timber roof battens 4May 22, 2013 6:22 pm I think a lot depends on the tile profile. The ones we have on our old roof here are Marseille style terracotta and are quite forgiving for any discrepancies in either the roof battens or who laid them. I think that is one of the reasons this shape is so popular. Whereas at the other end of the spectrum flat slate tiles show any little bump in the roof timbers. YMMV as they say. What sort are yours ? Stewie Re: Standard for bow/spring, flatness of timber roof battens 5May 23, 2013 11:19 am We have flat concrete tiles, and if I had heard before our selection studio appointment what I have since heard since about the use of rough cut timber for battens and the tendency to rush or just not care about presenting a level surface for laying tiles, and similar tendencies for some roofers themselves, I probably would either have picked different tiles or not suppressed as much my natural tendency to nitpick while the frame and roof was going up. I don't know exactly what's happened to our roof so I'm not going to point fingers at anyone in particular yet - just saying there are more risks than I knew about before. It's a bit of a shame, because I really like the look of those tiles. Maybe if we build again years from now, but not with a volume builder, and use what I've learned from this build, they'd do it right the first time. Re: Standard for bow/spring, flatness of timber roof battens 6May 29, 2013 8:33 am It appears that the standard for "alignment" of battens specified in the AS document refers to alignment to the flat plane across the hypothetical ideal roof line, ie: how much it is permitted to bow or spring. 20mm over 4000mm is permitted. My question then is, that given that the specification in the Standard for the alignment of the tiles themselves only says that they must be "aligned", does the specification for battens imply that this degree of tolerance also applies to the alignment of tiles given that tiles must be laid on battens, or is the builder obliged to ensure that the battens are level enough that when the tiles are laid that a reasonable person would say that they are aligned no matter how much flatter that requires the batten to be than what the standard permits? Re: Standard for bow/spring, flatness of timber roof battens 7May 30, 2013 10:01 am I think in any roof you'd be able to find some discrepancy in the tiles. Some profiles when they are made have an inherent bow in them or other small fault just like ceramic tiles which means you will not be able to lay a perfect roof. With volume builders the roof tilers aren't going to point out to the roof carpenter that there are a couple of roof trusses that are out of alignment with the others. They're there to just lay the tiles so that is what they'll do. Point out to them that the roof looks a bit wavy and 99% of them will just shrug their shoulders and say talk to the builder. He'll just say it is within normal tolerances etc etc. Stewie Re: Standard for bow/spring, flatness of timber roof battens 8May 30, 2013 11:19 am Oh well. Maybe I can nudge some of the more annoying ones near the gutters myself, and/or just learn to live with it. I suspect it's not worth going to the BC over. Hopefully I won't have to get it re-roofed in order to sell if I ever want to sell. I've had friends over who didn't notice anything "off" about the roof. I'm a bit annoyed that the builder were happy to take plenty of our money for the roof tile upgrade and never mentioned any potential difficulties aligning flat tiles, and are now essentially telling me "Oh well, you get that with flat tiles". Thanks for all your help and advice, Stewie. DIY, Home Maintenance & Repair We purchased a 1960s property that is on timber stumps mostly, and a newer section is on concrete stumps. We had a building inspection initially and they reported some… 0 12739 |