I-Joist quality. Expectations.

[flanagaj]

I had a load of i-joists delivered 10 days ago and the chippie and I put the joists up today and the quality of them is far from ideal.   As I've never had any experience of i-joists before, I was sorting of expecting sections that didn't resemble traditional timber in terms of straightness or curvature.   Was I naive in thinking that i-joists should be spot on straight and level along their length.   The delta across one 5.5m is around 15mm and the timber used doesn't look like it's been sorted.   When I ask the manufacturer about it today, he told me that the timber is pressed straight as part of the joist manufacturing process.

[SteamyTea]

Composites, which I-Joists are, can suffer from differences stresses which only becomes apparent after they have 'settled'.

There may also have been a manufacturing problem. Hard to tell.

They tend be quite wobbly along their length, but should be dimensionally accurate across the width, and especially the depth, which is where they get their strength from.

Ask the manufacturer for the design tolerances, then get measuring.

[saveasteading]

6 minutes ago, SteamyTea said:

wobbly along their length

That needs to be named after a scientist.

True though. The point of I beams is a reduction in timber used, so the stiffness is lost as a result. Noggins sort it.

It's from a factory so the timber will not have been exposed to the weather. 

Should be fine.

[SteamyTea]

2 minutes ago, saveasteading said:

That needs to be named after a scientist

But what would the derived unit initial be, can't use W.

 

[Gone West]

9 hours ago, flanagaj said:

Was I naive in thinking that i-joists should be spot on straight and level along their length.

I wouldn't have thought so, based on my experience. At my last house, the whole frame was built from timber I-beams and I never saw any beams out of 'true'. They were Steico beams and IIRC the flanges were made from LVL.

[-rick-]

1 hour ago, Gone West said:

They were Steico beams and IIRC the flanges were made from LVL.

 

That was I thought the common construction method. Not normal timber on the flanges. If @flanagaj has found a cheaper make than doesn't use LVL then that might explain things.

[Russell griffiths]

Mine all came very wobbly. 
they won’t be straight down the length until you install them as they bend way more than you would expect. 
most of mine had a crown in them that you mark and put the crown facing up. 
but I would not expect them to be up and down, just a slight crown up is fine. 
once the ends are secured you need some fairly substantial blocking to take the wobble out. 
 

I hope you don’t have much mvhr to run through them. 

[sgt_woulds]

Steico is one of only 5 major international companies that use LVL flanges that I'm aware of.   They are also the only I-Joist company to make their own web material (incredibly dense fibreboard) - the rest rely on OSB from 3rd party manufacturers.  

 

Most other joist manufacturers, including the majority that import into the UK, use finger jointed softwood - and there is nothing wrong with either method!  I’ve used JJI finger jointed I-Joists for my extension and never had any issues with the build quality or dimensional accuracy. 

The only issues I’ve had have come from bad storage, with joists that have been allowed to soak up water and then not been stacked flat to dry. 

 

An OSB web is more prone to issues with dampness and swelling and structural weakening than hardboard, but LVL flanges also more prone to mould than softwood.  It’s all horses for courses, - whatever type you use, they should be properly stored -flat - and protected from the damp.

 

However, it is also true to say that it is much harder to obtain softwood of the right quality and strength to make flanges; LVL manufacturing always makes for consistent and controllable structural properties whereas softwood is limited by what nature produces.  Hence a lot of softwood is steam treated and pressed for straightness, and there is considerably more wastage of raw timber to produce something suitable. 

 

Unfortunately, there is also now a lot of engineered timber products available from 'dubious' sources.  I was at a TDUK meeting recently where the OPSS basically admitted that 100% of timber imported into the UK from Turkey was 'not compliant' with UK Timber regulations.  If you don't know where the timber comes from, you also cannot guarantee the quality.

 

That’s not to say that all engineered timber using sanctioned Russian Timber produced by Chinese mills and imported into the UK via a Turkish trading company will be poor quality.  But there is usually a reason why it is much cheaper…

[sgt_woulds]

17 minutes ago, Russell griffiths said:

Mine all came very wobbly. 
they won’t be straight down the length until you install them as they bend way more than you would expect. 
most of mine had a crown in them that you mark and put the crown facing up. 
but I would not expect them to be up and down, just a slight crown up is fine. 
once the ends are secured you need some fairly substantial blocking to take the wobble out. 
 

I hope you don’t have much mvhr to run through them. 

 

 

So these were not Trus Joist, Steico, or James Jones then?  These manufacturers don't need to grade for curve as they only produce straight joists.

 

Crown marking is a workaround for grading bent softwood timber (C16/24) and it would be surprising to find it on a proper engineered timber product. 

 

As far as I know, only certain glue-lam companies deliberately 'pre-crown' their products; they make custom glulam headers and long-span beams with a built-in upward camber. These are engineered to flatten out perfectly only after the full weight of the roof or upper floors is added.

 

[Nickfromwales]

Just whack some noggins in and get on with the next bit of the project   
 

Wood ain’t straight, but it gets pulled straight during the install. 
 

As above, have the cup of the beam facing upwards, and when you load them they'll lat flat.

 

Just another day in the office, and nothing to worry about 🤝

[saveasteading]

3 hours ago, SteamyTea said:

what would the derived unit initial be

It is measured as number of wobbles exceeding 3mm/m per 6m length. 

Or disturbing wobbles per length. 

Called a Steamy or ST. 

 

 

1 hour ago, sgt_woulds said:

sanctioned Russian Timber produced by Chinese mills and imported into the UK via a Turkish trading company will be poor quality.  

That's convincing.

I must say I've never heard of such sources so that's worth knowing, and avoiding.

There's a video of the production of James Jones joists. It's an endless joist which is then cut to the lengths ordered. Zero waste.

The timber will be delivered daily, totally wrapped, from Scandinavia so high quality and dry.

[SteamyTea]

26 minutes ago, saveasteading said:

disturbing wobbles

Sounds like a wave function, ψ.

Could do a Fourier Transformation on it.

[IanR]

14 hours ago, flanagaj said:

 Was I naive in thinking that i-joists should be spot on straight and level along their length. 

I was happy with the Quality of I-Joists from JJI. But laterally, they do flex, so to some extent will take the shape of what you have them stacked on, especially the 13m blanks.

 

[sgt_woulds]

I-joist packs should always be stored covered (original wrappings, and on edge (flanges) until use.   They should never be laid on flat as shown above. 

 

It doesn't matter which manufacturer, their handling and storage instructions will always say the same and incorrect storage may void any warranty claims

 

This is especially important for finger jointed softwood flanges as lateral deflection under pressure can cause the joints to open and reduce the structural integrity; since these are likely to have been forklifted into place the risk is greater.

 

Setting on edge not only helps to prevents physical damage to the flanges and web glues, but it also reduces the risk of structural compromise of the web from water sitting inside.    (More of an issue for OSB than Fibreboard, but frowned on for both)

 

 

https://www.jamesjones.co.uk/assets/uploads/files/technical-info/jji-joist-and-glulam-site-storage.pdf

 

https://www.steico.com/uk/products/construction/i-joists/steicojoist

 

https://forestproductsgroup.com/wp-content/uploads/Nordic-Installation-Guide.pdf

 

 

Ditto for metal web joists.