loft conversion (in Singapore)

[bananapunk]

Hey guys, I'm converting an attic to a loft. I think the construction is a bit unusual, like a combination of king post and queen post. Is the beam marked in red a collar tie or a stranding beam? Do you think I can safely remove it or shift it higher or lower/flush with the base?

PS. right below, marked in blue is the RC beam, supported by columns.
PS2. disregard the diagonal plank, not sure what it's doing there but its lose and non structural.

 

[noseall]

That horizontal racking brace is there presumably to prevent any wind thrust. It is positioned just below mid-span as this is the most advantageous position in terms of vulnerability. not sure how you would counter this by putting the brace higher up...?

Great loft, by the way.

 

[catlad]

Unusual roof! is it a commercial property? You could build some ashlar walls out of ply at either side which would help brace it if you wanted to move it up .

 

[freddiemercurystwin]

Normally you'd just sling a steel beam under (parallel with) each of the lower purlins and then build a structural timber wall up to support the purlin, then lose the tie. Just employ a decent structural engineer (as you'll need to no matter what) and you'll see what's what.

 

[bananapunk]

thanks for replies everyone!
@noseall - So if it's positioned in the lower 1/3, it would make it a rafter tie rather than collar tie correct? The thing is there already is a horizontal rafter tie on the bottom marked in blue, sitting on the rc beam.
@catlad - it's a residential property, in Singapore. About 50 year old. The purlins are supported by the vertical posts, I assume the horizontal brace is to keep these steady or as @noseall suggested prevent the uplift?
@freddiemercurystwin Makes sense, but I'm not even planning on removing any of the vertical supports. In fact this structure is half way through my loft, and I wanna keep it all as is, build a partition there and split it in 2 small rooms. The only exception is the issue marked in red, I need a doorway and the beam is in my way . Do you think cutting it as I drew here in red and adding an extra frame (green) would still tie it all together? I will consult an engineer, however here in Singapore, to say it lightly, they're lacking imagination. I need to make suggestions otherwise they'll just say, hey why want you just pay 30k and change the whole roof

 

[bananapunk]

forgot to add an image

 

[bananapunk]

any feedback guys?

 

[catlad]

You could build a sheer wall down the middle with a doorway if you want to split the loft in half,
That should allow you to move the beam higher. You need to take the weight off the roof to make these changes.

 

[bananapunk]

@catlad we’re going to be replacing all tiles, so sounds like that would be a good moment for that change. But if we first build the supporting wall and only then take the beam off, shouldn’t matter right?

 

[catlad]

I wouldn't make those sort of structural alterations without taking the weight off first. Consider thinking about what you will replace the old clay tiles with as that would be an opportunity to decrease the overall loading on the structure.
As a matter of interest what is the silver ish material on the top few rolls of tiles?

 

[bananapunk]

Im replacing old tiles with new ones, so same weight in the end. Good question regarding the silver stuff, the roof currently is complete crap, patched up all over, it seems to be some temporary waterproofing sheet.

 

[Deleted member 174758]

Yes, I think it is a collar tie. In some ways similar to the roofs we had on one of the mills we finished earlier this year. In the case of our roofs new ties had to be installed further up with paired "boiler plate" truss extensions fixed one each side of the original trusses, through bolted to a bolted and plated apex with new collar ties installed further up nearer the ridge, before the old collar ties were cut. I think you could do something similar, possibly with the new (doubled-up) collar tie directly supporting the king post providing the queen posts and the primary beam below them are big enough to carry the redistributed load. In our roof the trusses terminated in timber blocks fixed at either end of primary beams which spanned the building. Not sure why yours really needs the king post - is there anything on the floor below that to take the load from it, or is it just transferring load into the primary beam?

The first photo just about shows the boiler plating and replacement collar ties at a higher level

You can make out where we trimmed back the old collar ties to make it look neater together with a couple of the new collar ties in the background

The second photo shows the knee brace, truss and queen post arrangement which is similar to your roof

As you can see, the timbers and bolts are fairly substantial.

As catlad says, though, don't attempt this without stripping the roof first

Sorry the photos aren't the best (I have trimmed them to take out a lot of extraneous detail), but I wasn't trying to capture the collar ties at the time - it's just luck that I did