Roof Spread

[Cocopop17]

Hi All,

We have a 1970s bungalow with a traditional cut roof. The rafters are supported mid-span via a structural stud wall in 8x2. This consists of a top and bottom plate with uprights under each rafter, all in 8x2. The stud walls are sat on steel beams.

Now we had some ceiling joists that were removed following advice from the structural engineer so we could achieve a vaulted ceiling.

To our surprise, the engineer later said these may have been stopping roof spread and he hadn’t realised they were tied in to the rafters. Following this, he stated he had advice from a second engineer that stated we shouldn’t need a form of tie as the structural stud wall is acting as a purlin and the roof span is theoretically split in half.

So, our question is do we actually need to tie the rafters in? Pictures for reference. Thanks in advance!

 

[blup]

If your engineer is properly qualified and carries insurance I would rely on his advice, but get it in writing. Ridge beams and ridge boards have different functions, sounds like when he saw rafters were tied in he thought this was as part of the design loadings, but had second thoughts after taking a second opinion. Presumably building control signed off the plans back in the day, the Council may still have the records.

Blup

 

[Notch7]

I wonder if the roof can still spread because whilst there is a structural stud wall supported by a steel, that may not in itself stop the rafters spreading - because the structural stud wall could twist.

later said these may have been stopping roof spread and he hadn’t realised they were tied in to the rafters

This seems very surprising - surely that would be the most basic of checks

 

[DAZB]

Assuming the rafters are actually fixed to the structural stud wall and not just sat on it then i would say it is supporting the roof adequately. The very essence of a "structural" stud wall rather than a standard stud wall is that it is designed to support floors, roofs, walls etc and i always build them and clad in either OSB or ply, glued and screwed to resist warping, twisting and deflection etc. The SE is correct in saying it has reduced the span and would be worth looking at the TRADA span tables using the rafter size vs the span just to be sure it is correct.

 

[catlad]

Copa
Its not looking good from the photo you have provided.

 

[robinbanks]

What's bothering you about it, @catlad?

the structural stud wall could twist

Where are you thinking the torque that would do this will come from?

 

[Cocopop17]

Thanks for all the responses so far!

@blup good point on the bc docs. I’ll speak to them.

@DAZB the top plate is screwed with two 5x80 screws into each rafter. The stud uprights are in tight and screwed to both the top and bottom plate. The bottom plate is coach bolted to the rsj. The studs are going to be covered in 10mm ply and 12.5mm plasterboard on both sides. Hopefully this should help to stiffen it up. It’s adequate for stopping the rafters sagging, it’s just whether it can prevent the spread or not.

I’m imagining that if the rafters are sat on the stud wall, this should stop the ridge dropping thus preventing spread?

When the joists were removed they weren’t under tension.

 

[robinbanks]

It’s adequate for stopping the rafters sagging, it’s just whether it can prevent the spread or not.

Rafters sagging don't result in spread, btw, but the opposite

What supports the ridge?

What fire protection is being applied to the steel beam?

 

[Cocopop17]

@robinbanks its a ridge board. The steel will be double boarded in 12.5mm fire board.

 

[^woody^]

If a rafter is fixed at the top point, and the thing it is fixed to is rigid and can not move downwards, then the rafter, or roof, can't spread.

The crucial thing is that the rafter is suitably fixed at the top.

Alternatively, if the top point is not rigid, but there is a suitable intermediate support, such as a purlin or beam, the rafter or roof can't spread.

 

[Cocopop17]

If a rafter is fixed at the top point, and the thing it is fixed to is rigid and can not move downwards, then the rafter, or roof, can't spread.

The crucial thing is that the rafter is suitably fixed at the top.

Alternatively, if the top point is not rigid, but there is a suitable intermediate support, such as a purlin or beam, the rafter or roof can't spread.

Thanks, this is the way I was thinking of it too. Maybe some twist straps to hold the rafters and the stud uprights tighter together would be useful?

 

[^woody^]

Thanks, this is the way I was thinking of it too. Maybe some twist straps to hold the rafters and the stud uprights tighter together would be useful?

If fitted perpendicular to the movement they are intended to restrain ie not vertical.

 

[Cocopop17]

If fitted perpendicular to the movement they are intended to restrain ie not vertical.

I‘ll get some fitted, may help a little.

 

[Cocopop17]

Any other input please?

 

[freddiemercurystwin]

WTF, this is basic roof stuff, get your SE to confirm it in writing one way or tother, that's what he's no doubt charged handsomely for!