TJI Joists Garage Extension

[IanNE]

I plan to have a double garage extension made that was 6metre in length with rooms above. I then changed to a 7metre extension as I had the room and I'm told I need to use TJI joists now because of the additional span and this will mean slightly lower ceiling height in garage..

Is this anything to worry about and will it incur more cost.. It was mentioned I could have a pillar, but not rally keen on a pillar stuck in the centre of the garage..

 

[r896neo]

what was specified for joists before hand? A 6m span with any useful room above would have needed engineered joists anyway i think.

Its nothing to worry about, they are easier to move and handle and much faster if cables or pipes need running in them. They will be bit dearer though and need a little bit more time spent bridging/ putting in noggins etc.

 

[freddiemercurystwin]

They would not be dearer given the span as doing that span in conventional timber joists would be silly money anyway.

 

[IanNE]

what was specified for joists before hand? A 6m span with any useful room above would have needed engineered joists anyway i think.

Its nothing to worry about, they are easier to move and handle and much faster if cables or pipes need running in them. They will be bit dearer though and need a little bit more time spent bridging/ putting in noggins etc.

Would I lose much height using TJI's?

Could I not put a rsj through centre and use normal/smaller joists

 

[chickenlips]

Based on a 6mt span, you would have to put in minimum 300mm deep I-joists. Even at that, I wouldnt recomend it, you are going to get spring in the floor once all the furniture is up there.

What is the actual dimensions of your extension ? Can the span not be turned around the other way ?

Otherwise your suggestion of an RSJ to split the span would be a far better option

 

[noseall]

From another thread:

Trussform in Staffs have just quoted me for some 219mm 'Easi-joists' and they are working out at exactly £11 p/m including the dreaded.

This was to supply 76 linear metres of joists, metalwork and strongbacks etc. In other words joists plus all ancillary materials.

We never space our joists (or trusses for that matter) at 600mm c/c as i think the span it too big. We space our Easi-Joists at 450mm c/c and they seem fairly bounce free. I know one or two builders that have complained of bounce when spaced at 600mm.

 

[IanNE]

I was told to use 360mm TJI joists over the 7metre span but would lose some headroom with them..

I prefer normal joists really but don't know any alternatives never being in this position before..

Not too sure I like the idea of bounce in the floor, I know its a large span and I'd prefer the garage full open without a supporting wall in centre..

 

[r896neo]

there will not be any bounce if you use correct sizes at correct spacings.

I have worked on a house which had big spans of I joists, some were close to 7m and there was no 'bounce' That is just scaremongering.

IF you can afford to loose the head height go for them, there is no problem. I see no reason why you should be afraid of them over normal joists.

 

[IanNE]

So I would lose 60mm when compared to conventional joists or would I lose more? Would this cause any problems, I know the more height the better really..

 

[noseall]

I have worked on a house which had big spans of I joists, some were close to 7m and there was no 'bounce' That is just scaremongering.

It is not scaremongering it is a fact and i can give you an address.

None of the easi-joists we have installed have 'bounced' but they do flex more than say a well braced solid joist floor.

 

[chickenlips]

there will not be any bounce if you use correct sizes at correct spacings.

I have worked on a house which had big spans of I joists, some were close to 7m and there was no 'bounce' That is just scaremongering.

IF you can afford to loose the head height go for them, there is no problem. I see no reason why you should be afraid of them over normal joists.

Thats my point, both an engineered I joist or traditional joist is going to suffer bounce or flex with a clear span of 7mts.

And to source a traditional joist to span 7mts is going to be difficult and costly !

Its not scaremongering to offer advice based on ones own professional opinion or experience.

IanNE - What has been specified on the drawings ?
360mm Deep joists would be at 300mm centres, using the steico brand they only just pass on design. 96% stressed.

 

[jeds]

I much prefer timber 'I' joists or metal truss joists over standard timber joists. I specified them in a four storey conversion a couple of years ago with 7m spans and the floors were like concrete. They are also much easier to handle; much, much easier to run services and don't warp like a lot of the crap timber you seem to get these days.

 

[IanNE]

Heres an example of joist layout spanning 7 metre.

Untitled

• IanNE
• 24 Jan 2013
• 1

Also one with engineered column.. not sure if it would be better to change the double garage door to two singles and run the steel beam opposite direction to one shown between doors and split joists, although the beam would cause a low point down to 2 metre, not sure if this would cause me issues, not sure on best solution really... what would others do for the large span..

 

[chickenlips]

The beam could be position within the floor void, so you are not loosing so much headroom. The joists then can be supported in top hung hangers off the steel beam.

 

[noseall]

The beam could be position within the floor void, so you are not loosing so much headroom. The joists then can be supported in top hung hangers off the steel beam.

or....

Get some holes drilled into the web, fit a timber into the web each side, bolt the timber sandwich together trough the web, then use regular jiffys face fixed into the web timbers.

The only niggle within the above solutions is if the steel beam is deeper than the joists. It would not be a great problem but the beam would poke through the ceiling in the garage. You would then fix a batten to the ceiling each side of and parallel with the beam then double board this section of ceiling.