steel beam size and joist size

[jc69817]

hi guys
can anyone help with this I am thinking of doing a loft conversion myself and was wondering what size beams I would need. The length of the beams would be 23ft, also what size joist would you recommend, the span is in the region of 12-14 ft. The room will be used as a bedroom with possibly a shower room.

Many thanks in advance guys

 

[freddiemercurystwin]

You realise you will need a structural engineer to get it through the regs? Steel size wise will probably be around a 305x165x46. Timber joists around 50x225's @ 400 centres. All sizes approx.

 

[jc69817]

bloody hell pal didnt think it would be anywhere near that big. was thinking more like 200x100 (ish) beams and 6x2 joists. I know a few in my area with similar houses and they have just used the ceiling joists (4x2) !!!
didnt want to follow that but sounds like it may be running beyond me cost wise. might not be able to go forward now was trying to do it on the cheap but without cutting corners (with regards to safety anyway )

thanks for your advice

 

[Framer]

there is a reason why your current ceiling joists are 100mm and your floor joists are 225mm

 

[jc69817]

yeah i realise that, my 3 years at college werent completely wasted (time served joiner but out of the trade for about 10 yrs) but thought that 6x2 would be enough. never mind though

 

[Framer]

still its no reason not to go ahead, maybe you could source the correct size but cheaper if you shop around

 

[jc69817]

its really the beam size putting me off. gives me 13" above the current joists

 

[Framer]

you could always go alongside the existing celing joists, bit more work and would mean patching the ceilings but its always a option

 

[jc69817]

getting to the wall plate is the problem with that as it is right in the eaves. could possibly do it with 1 beam in the centre and 2 sets of joists cut on an angle at the eaves I suppose.

 

[freddiemercurystwin]

To be honest its pretty difficult to tell without more information on the layout of your first floor and ceiling spans etc, there may be ways of shortening the spans by using additional steels, or using internal walls, likewise maybe using column section like a 254x254x89 or maybe even a 203x203x60 may be possible. That's what engineers are for and I'm no engineer (although have drawn up plenty of loft conversions) and have based steel sizes on the old 1/20th span is the depth rule of thumb. Timber joist sizes have come straight from the Trada tables. Frankly the size of the steel is only a small part to loftys so don't let this put you off. Come back if you have any more questions.

But if you really want to get somewhere and move the thread forward a crude plan with some dimensions and spans of ceiling joists, a few photos inside the loft etc would be helpful.

 

[jc69817]

if the central beam was 75% + sat on the 4x2 directly above a block wall then i presume it could be reduced in size.

 

[freddiemercurystwin]

I gotta go watch a dvd or the missus will have my balls!

 

[Framer]

its possible, you would likely have to block between the joists under the steel

 

[jc69817]

It's been a while (forgot about the post) but I finally got some pics and a sketch. Could I get away with say 8X2 from wallplate to spine ???

(Red line is a spine wall concrete block through to ground floor)

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• jc69817
• 1 Jan 2012
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• jc69817
• 1 Jan 2012
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• jc69817
• 1 Jan 2012
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• jc69817
• 1 Jan 2012
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