Floor Joists: Open Web Engineered VS. I-Joists VS. Traditional Timber

[Patrick]

Hello,

 

was looking into the available options of Floor Joists and was wondering what people in here are using. I read a lot about the advantages of the Open Web Joists , e.g. plumbers/electricians do not have to cut out parts of the Joists, Lightweight, but also seen that they are quite expensive. At least where I seen them. I-Joists seem to be the best of both worlds and I read in another Forum that they do not get the problems of the Open Web Joists of sometimes sagging after a few years , especially on wider spans.

And then there obviously is the traditional 2x10 or 2x12 Timber Joists. Solid and Cheap - I do think they are still cheaper then the other 2, but I'm not 100% sure.

But they have the problem that you have to cut out openings whenever you want to run pipework or ducting through the ceiling, which probbaly is VERY often in a house with MVHR .

So please give me your Ideas and why you chosen your Joists . Obviousy a lot of you will havenot chosen at all but being given what the Kit-manufacturer is delivering, but others might have already looked into the pro's and con's .

 

 

[joe90]

I have i joists and think they are great, no sag, no twists, over engineered, you can cut quite a few holes in them as long as the cuts/holes are in the right places.

[Simplysimon]

going i joists, as well as for walls and roof

[Redoctober]

What you decide to put upstairs for heating may have an impact of which type of joists you choose. Some structural engineers may insist on web joists if UFH with a biscuit screed is being planned for.

[Oz07]

Can a 4"/5" hole go in an I joist if placed correctly?

[ProDave]

We had ordinary timber joists and UFH with a biscuit screed upstairs in our last house.

 

But definitely pleased we used posi joists in the new house.  The vent pipes for the mvhr would have been a real challenge with anything else.

[PeterW]

Never heard of open web joists sagging - they are usually well specified and over engineered. The issue is normally when they aren’t being used as designed and additional loads have been added or the ends have not been restrained correctly. 

 

I prefer open web but they are sharp on the edges so you have to be careful with pipes and wires.

 

The downside with I-joists is that you can get trades putting holes in the wrong place as there are very strict rules that are provided with the products. Sadly, some trades can’t read ....

[ToughButterCup]

34 minutes ago, Patrick said:

[...]

So please give me your Ideas and why you chosen your Joists

[...]

 

MVHR.

[PeterW]

7 minutes ago, Oz07 said:

Can a 4"/5" hole go in an I joist if placed correctly?

 

Yes but only through a 245 beam with a minimum 3m span ... 

 

https://www.jamesjones.co.uk/assets/downloads/subdir/SAL04-20jm Site construction guide Sept 17.pdf

[Patrick]

3 minutes ago, PeterW said:

 

Yes but only through a 245 beam with a minimum 3m span ... 

 

https://www.jamesjones.co.uk/assets/downloads/subdir/SAL04-20jm Site construction guide Sept 17.pdf

Thats very handy. Thanks, I will keep it for later

[Patrick]

How about Price difference? Anybody took that into account or you all just went with the best product for their building route

[Crofter]

I used JJI joists and yes they are a bit more expensive than a solid timber joist. From memory I would have spent around £25 on each joist in solid timber, and £36 for JJI. So the total extra cost over my build was around £165 (it's a small house, only 15 joists were needed!).

The advantages are several. Much much easier to work with- I installed them all singlehanded as they were so light. Every single one was perfectly straight. Thermal bridging greatly reduced. They use less timber overall so are probably a more ecologically sound option.

I don't have any experience of posi-joists, but I imagine they offer similar advantages.

[Thedreamer]

I've just got your standard old fashion joists.

 

I have attic trusses at the gable end and for a centre middle section I order the rafters and joists from the truss fabricator as well.

 

Our plans showed C16 but I went for truss grade for the centre joists/rafters. If it helps this was the cost of this timber.

 

 

Not having MHVR but plan to install a joules aero, so shouldn't have to many large holes.

[dpmiller]

I asked for- and received- quotes for both plain timber *and* and upgrade to posijoists from a number of TF companies. The upcharge varied between 2-3k depending on whether they were re-sizing for screed upstairs as well.

[Patrick]

On 11/11/2018 at 20:38, Thedreamer said:

I've just got your standard old fashion joists.

 

I have attic trusses at the gable end and for a centre middle section I order the rafters and joists from the truss fabricator as well.

 

Our plans showed C16 but I went for truss grade for the centre joists/rafters. If it helps this was the cost of this timber.

 

 

Not having MHVR but plan to install a joules aero, so shouldn't have to many large holes.

 

Seems expensive. For regular beams.

Edited January 28, 2020 by Patrick
Confidential information

[Moonshine]

I am bring this thread up again as its now relevant to me, so have things changed or I-Joists still the preferred choice?

[gavztheouch]

From the little I have heard so far from builders and architects they seem to prefer I-Joists as they are a lot stiffer than posi-joists

Edited February 2, 2020 by gavztheouch

[MJNewton]

Following up on some of the mentions about hole limitations in I-joists, Simpson make an 'I-Joist Hole Support' that enables you to put holes upto 250mm wide (and full height of the webbing) anywhere you like beyond 50mm from the bearing points if need be.

 

Edited February 2, 2020 by MJNewton

[Big Jimbo]

1 hour ago, MJNewton said:

Following up on some of the mentions about hole limitations in I-joists, Simpson make an 'I-Joist Hole Support' that enables you to put holes upto 250mm wide (and full height of the webbing) anywhere you like beyond 50mm from the bearing points if need be.

 

And the above work very well.

[ProDave]

I have also seen a steel gusset plate bolted to the web where multiple large holes were needed.