Rafter Joist- can we construct supporting structure without re-installing roof. If we cannot do it can we just leave it in between and complete loft conversion, will it pass Building Regs

[Mubbashshir]

There is rafter tie joist in the middle of the loft and structural engineer has recommended not to disturb it and build the loft room on other side. As constructing alternative support for this and later removing this Rafter tie Joist safely can be expensive as we have to remove all the roof joists and roof to construct alternative supporting structure. Also for your information there are some joist which are cracking due to age however it is not causing any structural integrity issues as told by the structural engineer and he will be recommeding to contact some timber treatment company which can inspect and provide further feedback. 

Note: My structural engineer is charted sturctural engineer so he is quite competent however since he owns the company he may not want to design anything which can put this insurance at risk unless, I suggest him or push him.

 

My Questions: 

 

1. Any possible way of building alternative supporting structure in place of Rafter tie joist(without reonsturcting the roof). If you have any idea, I can ask the structural engineer to design in that direction. 

 

2. Can we keep this Rafter tie joist  as it is and  finish loft coversion. Will it be approved by BC?. It may look odd  because to go on other side of the tie joist, we have to bend below it or go over it. However we can remove later when we can construct supporting structure as this may require re-constructing whole roof by removing existing room. 

Edited April 21 by Mubbashshir

[ProDave]

You roof has been extended when the garage and extension was added.

 

The "joist" you talk about is the original end purlin from the original roof structure.  It is not functioning as a purlin any more, there is nothing attached to it.

 

As to whether it could be removed?  That is a question for a Structural Engineer. Yours appears to say no.  I would be interested to know why.  Perhaps it is performing the task of a tie bar to prevent the purlins front and back that are still under load from spreading apart?  If so providing alternative means to prevent spreading is what should be considered?

[saveasteading]

All the sloping timbers are under loads trying to make them level, thrusting out at the walls. The cross ties resist that thrust, triangulating the forces.

If anything it seems low on such ties. Yous SE is maybe even being pragmatic in not saying to add more...I.e. it's working, so leave it be.

 

The roof space has not been designed as a room, and sometimes you have to accept the limitations. Better than it falling down.

8 hours ago, Mubbashshir said:

he may not want to design anything which can put this insurance at risk unless, I suggest him or push him.

No. He is is giving best , expert advice, simple as that.

[Mubbashshir]

If you could answer my send question, i.e. can I do loft conversion by keeping rafter tie as it is. However it(Rafter tie) will come in at about 1/3 length of the room. May look odd in the room after conversion. However will building regulations accept it or will have any objections 

Edited April 21 by Mubbashshir

[saveasteading]

We don't know the geometry. That tie seems to preclude movement.

Maybe your SE can propose alternative bracing, esp if you can have a division wall there.