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.

[Mubbashshir]

On 22/04/2025 at 00:02, saveasteading said:

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.

What I am saying can we do the conversion by not disturbing the raft tie that will give more space....only questions is will it cause problems with building regulation

Edited Friday at 17:24 by Mubbashshir

[Redbeard]

I suspect we won't get anywhere nearer answering your question till you explain more clearly what you wish to achieve by carrying out the work. Obviously without any dimensions, or details as requested by @saveasteading I can only guess what you hope to achieve. The tie-beam cuts across the space, but how big is the space overall? What proportion of the available space is on either side of the tie? 

 

What is the height at various points? What size are the joists? Often loft joists are 75mm deep while (depending on the span) joists for a room could need to be 200, 225 or more (but none of us can know without more detail). Where would the stairs be? The only way I could see of it being acceptable to BC is if you converted the largest space on one side of the beam with the rest left as void or subject to approval) storage. If the use of the room involved wriggling under the beam what would be the effects on emergency egress, in case of fire, say?

 

You said

On 21/04/2025 at 01:32, Mubbashshir said:

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. 

 

How will you 'remove later when we can construct supporting structure' and why can't you do that in the first place? And have you asked this question directly of your local Building Control dept.?

 

Lots more details, please, and then we may be able to help.

[Gus Potter]

29 minutes ago, Redbeard said:

Lots more details, please, and then we may be able to help.

From experience you can go into an attic and think ok.. here is how I might get it to work. You are creating another floor that requires more onerous loading.

 

Now I also know that we are all prone to looking at things with rose tinted glasses. I have learnt that when assessing the potential for attic convertion you need to make sure that when you change the loading and paths that all that can get transferred down to the foundations.. and at that point you find that you don't have wall continuity on the ground floor for example. The cost and potential disruption can rocket.

 

Unless this property has a high value my gut feeling is that when the final design and costs come in it won't be worth it..

 

@Mubbashshir I think you will, at the end of the day get more bang for your buck by extending out the back if you can?

 

 

[Mubbashshir]

I was thinking, can I not do that project in phases like do all this

 

1. Do the Domer and structural bits by taking of the roof and secure everthing back like close off the roof etc. 

2. Remaiing floor joist etc at later point when I get some funding.

 

Any other suggestion if the above approach or steps nees some correction

Edited Tuesday at 16:17 by Mubbashshir

[Redbeard]

If you are really 'taking off the roof' why not try to get a structural design which includes removing that cross-timber and providing alternative strengthening? Have you got a structural engineer? Have you been through Building Control? Is Planning Permission required?

[Temp]

Can you add a tie(s) at floor level?