Garage roof flat to pitched conversion - removing old ceiling joists

[MartyH]

Hi,

I recently moved into a house that has had the garage roof converted from flat to pitched. It's a double garage and a quarter of it is integral to the house (therefore there is a large column in the middle of the garage where the corner of the house is). See pictures below. The back of the garage has a straight brick wall, therefore there are three section of roof and two tiled ridges. I also found a drawing from the conversion plan (see below - note that the existing ceiling joists are shown as running the wrong way).

When the roof was converted they left all of the original ceiling joists in place. The quarter of the garage that's integral to the house obviously has the joists for the floor above, and the other three quarters of the garage have much smaller joist which presumably only had the function of supporting the garage's flat roof.

There was asbestos board attached to the joists to create the garage ceiling which I've just had professionally remove. I'm converting the garage and want vaulted ceilings for the non-integral three quarters of the garage. I attach a photo showing the inside of the garage now that the asbestos board is gone.

All of the roof rafters are attached to the house walls. Can I just cut away the old ceiling joists? I can't see that they are needed since there is no risk of the walls spreading (due to the rafters being attached to the house? Would they serve any other structural purpose?

They also added some angle ties when they converted to the pitched roof (see conversion plan drawing). These are just 100x75 timbers attached to the wall plates. Are these needed?

Many thanks

 

[noseall]

Effectively your house is your ridge beam so the joists seem cosmetic in terms of structural restraint.

I would be wary of how well connected to the house the tops of the rafters are, before cutting loose with your axe.

 

[MartyH]

Thanks noseall, that's what I was thinking.

Yes - i'd certainly check how well the rafters are connected before I wield the axe!

I don't think the walls could be pushed out (since the rafters can't grow in length!) but now I'm thinking that the weight of the roof could be acting downwards and inwards (especially around the hip rafters) and possibly cause the brick walls to fold inwards (and that the old joists and the angles ties could be preventing this).

I've just taken this photo from inside the garage (facing towards the front of the garage). You can see the diagonal hip rafter and the jack rafters supporting it. You also see the original joists and the angle tie which has just been laid diagonally across the original joists and attached to the wall plates.

Are there any structural engineers on the thread who can give a view on if the old rafters and angle ties are required to stop inward pressure?

Thanks