Replacing W trusses in flat loft.

I want to remove the W trusses in the loft of my flat. Not for a full conversion but just for extra useable space.

I realise that i may need a structural engineer or architect. But in the terms on my lease i am covered and i have got permission from the management company. I am the head leaseholder so they couldn't really argue. Below my picture of how it looks.

the ceiling joists from the flat below are 35mm x145mm at 430mm centers.



I want to do something like this below. I am wondering whether people think this is possible, and if it could be done by a DIYer or if i would need a professional or if it's a bad idea altogether. I have a basic grasp of the physics involved and can't really see any major issues. Anyone have experience or concerns with what i am planning?


Thanks in advance!

There's a good chance the existing truss sizes are insufficient to do as you propose, would have thought you would need to replace the roof.. there are more complex ways to do it with steels but may end up more expensive..

Not something more DIY'ers can do..

As far as i am aware steels are only used when the trusses have no loadbearing partitions below them.

And this type of truss is capable of holding the load of an average roof with 80 x 40mm timbers and a span of 12 meters at 600mm centers. As the maximum span from one load baring wall to the next is less than 4 meters at 430 mm centers i can't see why steels will be needed or where major load change will take place.

However thanks for your thoughts i will certainly get a structural engineer to take a look.

Its mainly because you are changing the form of the truss, it will rely more on the ceiling tie which would probably need to be larger.. you are increasing the load on this as well by about a factor of 3..
Course you never know.. whoever designed the truss in the first instance may have over egged it and there may be some redundancy for change..

If it is actually a premanufactured truss, with metal plates at the joints then its doubtful that would work.

Now Im looking at your drawing and I'm seeing a hip end on the right and are the trusses stubbed at the back (going onto the concrete blockwork) or bob-tail ? IE does the roof continue down past the blockwork to form a triangle ?

Its not just about whats supporting below, its how the roof is supported, cutting all of the internal webs out will lose any triangulation the truss has in that formation. Not to mention any of the structural bracing you will need to remove to achieve your plan.
Also dont forget about the girder truss thats holding up your hip end (if it is a hip end), which will be in the way.