Bendy timber

[booky1]

I'm coming to the end of fitting the first floor joists in a new extension, they are 250x47 spanning 4.15M. I had only intended to put in a single line of struts (full depth timber) down the center but have ended up putting in 2 extra lines of noggins along the ends of the joists in order to pull out all the bends and twists that have formed. This has worked well but I can't do anything about the bends in the vertical plane (about 20mm in the worst case) but I will be able to pack above/below for floor/ceiling so it'll be OK in the end.

The SE's spec asked for C16 stress graded, dry, preservative treated SW timber - which is what I used. I inspected in on the wagon when it arrived, it was nice and straight and dry. I stored it correctly supported and under cover and it's all been installed in the dry ---- so why is it all b****y bent and twisted?

I'm concerned because the next job is the roof which will be constructed from similar C16 timber but 175x47 with a rafter length of 7.2M.

My questions are:----

1).Is there any better grade of timber out there I could use that is guarenteed to be straight?

2).I've had a quick look at engineered timber 'I Beams' but they seem a bit of a faff for the roof which has a few complicated bits in. Has anyone out there used them as rafters and how did it go?

3).If I stick with the same type of timber are there any restrictions on the number of noggins I could use in a roof to make it all straight?

4).If some of the rafters also bend in the vertical plane by 20mm or so will this be noticeable on the final roof finish or will I need to adjust the tile battens to straighten it all up?

Any thoughts would be greatly appreciated.

 

[hotrod]

You didn't get it from Berrys or Page+Taylors did you?

Just noticed your location.

 

[noseall]

why such deep timbers?

is it to acommodate full fill insulation over a garage perhaps?

deep timbers like yours will certainly 'do what they want' when drying out.

the trick is to fit and secure them whilst still wet.

i shouldn't worry too much about the roof timbers though, any twisting won't be noticed. are there any purlins going in to break the span?

 

[Shytalkz]

why such deep timbers?

He pressed the wrong button on his design software .

 

[booky1]

Thanks for your replies.

I didn't get them from the places mentioned. I got them from a local (Lancaster) sawmill with a good reputation.

The floor is actually over a garage but the SE has also specified 250mm deep joists for a second extension on the other side of the house with the same span that isn't over a garage. The SE is newly qualified, he may be playing it safe.

Yes, the rafter span is broken on each side roughly mid way with purlins.

From your comments do I understand that it's not out of the ordinary and that there isn't any 'better' timber I can buy to prevent it? Also, if I do want to straighten out the rafters with noggins are there any restrictions on doing so?

Thanks.

 

[noseall]

Also, if I do want to straighten out the rafters with noggins are there any restrictions on doing so?

Thanks.

not that i am aware of, though it may be a touch overkill as they will be birdsmouthed onto the purlin.

 

[Shytalkz]

The SE is newly qualified, he may be playing it safe.

There's an understatement .

 

[booky1]

Thanks, the point about the birdsmouthing makes a lot of sense so maybe the noggins won't be needed after all. Anyway, from what you've said I'll just carry on with the same timber and deal with the bends if and when they occur.

Even if the SE is playing safe I don't mind too much as I'll be living in the house when it's finished.

Thanks a lot for the advice, it's been helpful as usual.

 

[r896neo]

Get your bridging/ noggins in asap as soon as you get them up to stop the bends. Also the classic 'keep them under a large sheet of dpm' doesn't help. Its a little bit like a small damp oven under there! (not saying you have done this but it is preety common)

 

[joe-90]

and deal with the bends if and when they occur.

You'll have to get yourself to a decompression chamber quick-smart.