Loft floor joists

[leeco]

Im doing a loft conversion. I have the steel in but just need to know the minimum joists I can put in. The plans say 9" but is 9" the minimum?

 

[RonnyRaygun]

Im doing a loft conversion. I have the steel in but just need to know the minimum joists I can put in. The plans say 9" but is 9" the minimum?

Depends on the span and spacings of the joists. And whether or not any of the joists carry any extra loads from dormer walls and the roof.

Can't say without that information, but as an idea, you'll get about a 4.7m span from 9"x2" C16 joists carrying domestic loft conversion loadings, at 400mm centres.

If you give us some more info, we can give you a better idea of what you need.

 

[leeco]

Hi cheers.

Heres the plans.

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• leeco
• 3 Nov 2012
• 1

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• leeco
• 3 Nov 2012
• 1

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• leeco
• 3 Nov 2012
• 1

.

I an not putting the mid steel in as I don't think it needs it with the brick walls on the 1st floor

 

[RonnyRaygun]

In that case, without the middle steel, the span is 4.7m so 9"x2" joists are the minimum if using C16 timber.
Although, if you close up the centres to 350mm and use C24 timber, you will get away with 8"x2" joists. Don't know if that is of any help to you?

 

[leeco]

In that case, without the middle steel, the span is 4.7m so 9"x2" joists are the minimum if using C16 timber.
Although, if you close up the centres to 350mm and use C24 timber, you will get away with 8"x2" joists. Don't know if that is of any help to you?

Cheers yes an extra 1" is better than none.

 

[RonnyRaygun]

Hey leeco, for a moment then I thought I was going to get my 100th "thanks"!

Come on, don't be shy

 

[chickenlips]

Or rather than using traditional joists, why not look at engineered joists ?
Open web joists will span that easily @ 400mm centers. And will give you a stiffer feeling floor.

 

[leeco]

Hey leeco, for a moment then I thought I was going to get my 100th "thanks"!

Come on, don't be shy

 

[chickenlips]

Or rather than using traditional joists, why not look at engineered joists ?
Open web joists will span that easily @ 400mm centers. And will give you a stiffer feeling floor.

Forgot to mention they would be 202mm deep too.

 

[leeco]

Or rather than using traditional joists, why not look at engineered joists ?
Open web joists will span that easily @ 400mm centers. And will give you a stiffer feeling floor.

Forgot to mention they would be 202mm deep too.

How much do these type joists cost?

 

[chickenlips]

They are more than a traditional joist, on per metre basis but you need to acess the rest of the cost involved.
They also span further and will give you a stiffer floor.

They are minimum 72mm wide so a better fixing for flooring and plasterboarding.

Also any plumbing or electrical services do not need notching or drilling, they will pass through the holes. Far quicker if your paying a electrician or plumber.

Have a look at this website http://www.mii.com/unitedkingdom/
Look at Posi-Joist..

Then if your interested, I can always PM you with more details.

 

[leeco]

If you look at this again.

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• leeco
• 3 Nov 2012
• 1

Why would the architect want me to keep the old hip and purlin and prop them up? I have ripped most of the old roof totaly off.

 

[RonnyRaygun]

Why would the architect want me to keep the old hip and purlin and prop them up? I have ripped most of the old roof totaly off.

Presumably that section of the roof is not being altered? If so, they may have decided it's simpler to leave the purlin where it is rather than allow the rafters to span onto the dormer wall and then put extra load onto the new beam.
Although obviously some load should have been allowed in the beam design due to the prop to the hip member and purlin.

If the rafters could span to the dormer wall and be supported by it, then there's no reason not to remove the purlin. The beam will however then be loaded differently and would need to be rechecked for capacity.