Rafter to ridge detail

[willbish]

I have a steel ridge specified with two sizes. 203x102x23 joined to 356x171x57

 

 

The pitch of the roof to the front is 45°, and to the rear 16.2°, although there is a section to the rear that is 45° highlighted above

 

The rafters are 195mm x 45mm @ 600c.

 

 

 

I'm having difficulty finding a suitable position for the steel that allows an acceptable birds mouth on all rafters. I've found that if I offset the steel by ~100mm to the rear I get a good seat for both rafters on both sizes of steel. Like this:

 

 

 

 

 

Having an offset doesn't work for the section where the rear rafters are also 45°. So I'm now thinking the steel has to be on center line. But to get a decent bearing for the rear rafters I would need extra timber, a lot of extra timber which is not acceptable, is it?

 

 

Any thoughts greatly appreciated.

 

[Mr Punter]

It is a very odd configuration.  I assume there is some compelling aesthetic reason not to have all the rear rafters at 16.2 deg?  As is, there are some horrible junctions and we are only looking at 4 rafters.

 

Bear in mind that the timber may shrink by 15%, so if you have 50mm one side and 150 the other, the shallow pitch may end up 15mm lower. Can you modify the steel?

[willbish]

  On 26/06/2019 at 09:31, Mr Punter said:

It is a very odd configuration.  I assume there is some compelling aesthetic reason not to have all the rear rafters at 16.2 deg?  As is, there are some horrible junctions and we are only looking at 4 rafters.

 

Bear in mind that the timber may shrink by 15%, so if you have 50mm one side and 150 the other, the shallow pitch may end up 15mm lower. Can you modify the steel?

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It certainly is an odd configuration.

 

The rear rafters at 45 is to achieve symmetrical gable end which mimics the characteristics of the previous property that stood on this footprint.

 

Modifying the steel is an option.

I've considered adding some Rectangular Hollow Section on top of the flange (to the rear half only) so the depth of timber plate used is the same throughout. 

I could also increase the smaller section of the steel to match rest of the ridge which would simplify the RHS modification.

 

Getting the feeling architect and SE have happily created something that's frustratingly fiddly to build..

[Oz07]

Wouldn't a wider steel help eliminate the problem?

[the_r_sole]

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Edited September 26, 2019 by the_r_sole

[Declan52]

Could you put in a ridge board at the top then 2 separate steel beams approx 500mm further down  so each will suit that particular side. 

[Mr Punter]

  On 26/06/2019 at 11:09, willbish said:

It certainly is an odd configuration.

 

The rear rafters at 45 is to achieve symmetrical gable end which mimics the characteristics of the previous property that stood on this footprint.

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Can you post an elevation or even better a Sketch Up showing the gable, just for my own interest?

 

Also, how are the 100 x 100 posts supported? With one it looks like the stairs are in the way.  Lots of stairs btw.

[Russell griffiths]

Can you not raise the steel up so the timbers are plumb cut to the face of the steel, so hiding the steel in the roof. 

[willbish]

  On 26/06/2019 at 11:12, Oz07 said:

Wouldn't a wider steel help eliminate the problem?

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Not that I can see

 

 

  On 26/06/2019 at 11:37, the_r_sole said:

what does the engineers detail of the birdsmouth for the roof timbers look like?

Are you having a full ceiling and boxing in the steel?

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No such level of detail here.

Having an attic space/bat loft

 

  On 26/06/2019 at 11:44, Declan52 said:

Could you put in a ridge board at the top then 2 separate steel beams approx 500mm further down  so each will suit that particular side. 

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I think 2 steels could work, but £££ ?

 

  On 26/06/2019 at 12:08, Mr Punter said:

 

Can you post an elevation or even better a Sketch Up showing the gable, just for my own interest?

 

Also, how are the 100 x 100 posts supported? With one it looks like the stairs are in the way.  Lots of stairs btw.

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Sure, previously

 

Under construction:

 

 

  On 26/06/2019 at 12:23, Russell griffiths said:

Can you not raise the steel up so the timbers are plumb cut to the face of the steel, so hiding the steel in the roof. 

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Now that seems a good idea. Excuse my crappy hangers, but something like this?

 

 

 

Edited June 26, 2019 by willbish

[PeterW]

Two steels is the answer - sorry ..!

 

Engineer who designed that wants a slap, and has completely ignored the lateral forces of the two different pitches. Also, the 356 has been chosen for the deflection over the span, as the intermediate is the same size. 

 

What is the total span of the open space as there looks to be intermediate walls in that design..??  

 

Ridge board, steels around 7-800mm down from the ridge apex and stick decent ceiling binders in as that is one very odd roof design ..!

 

Have you got the engineers sections to show what they think it will look like on the posts too..??  

[Russell griffiths]

if You do my version, you use a specific hanger that is multi angle adjustable, it does not have a birds mouth, it fits plumb to a timber you have fitted into the web of the steel, you then plumb cut your timber and offer it up fixing it with the appropriate nails. 

Loads less cutting, but I think the hangers where £3 each. 

[willbish]

  On 26/06/2019 at 22:02, PeterW said:

Two steels is the answer - sorry ..!

 

Engineer who designed that wants a slap, and has completely ignored the lateral forces of the two different pitches. Also, the 356 has been chosen for the deflection over the span, as the intermediate is the same size. 

 

What is the total span of the open space as there looks to be intermediate walls in that design..??  

 

Ridge board, steels around 7-800mm down from the ridge apex and stick decent ceiling binders in as that is one very odd roof design ..!

 

Have you got the engineers sections to show what they think it will look like on the posts too..??  

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Yes the SE has seeming ignored the different pitches. Looking at the reams of calcs he sent me, he has assumed the roof pitch to be 30° on both sides... coincidence that 30° is the average between 16.2° & 45°

 

Total ridge length is just under 12.00m. The 358 is 8.0m then 203 is 4.0m with the SHS supporting on blockwork wall

 

[willbish]

  On 27/06/2019 at 06:35, Russell griffiths said:

if You do my version, you use a specific hanger that is multi angle adjustable, it does not have a birds mouth, it fits plumb to a timber you have fitted into the web of the steel, you then plumb cut your timber and offer it up fixing it with the appropriate nails. 

Loads less cutting, but I think the hangers where £3 each. 

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Yep still liking this idea after sleeping on it.

Using these hangers, may need to add an extra timber on top of the steel for adequate face fixing

 

[PeterW]

So that 357 weighs nearly half a tonne... and the post detail is odd as the whole of the 203 is hanging on 4 bolts. The other odd bit is the post also only has 2 bolts..?? Should be 4, 2 each flange. 

[willbish]

  On 27/06/2019 at 07:18, PeterW said:

The other odd bit is the post also only has 2 bolts..?? Should be 4, 2 each flange. 

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One each side is what i had assumed, but cant see any reason why it shouldn't be 4

[Oz07]

never liked those hangers prefer a saw slit and sit normal ones in, don't have to do the whole birds mouth

[Mr Punter]

Just a thought I wonder if this would work with engineered timber like LVL or Glulam instead of steel.  You could leave it exposed.

[willbish]

  On 27/06/2019 at 07:31, Oz07 said:

never liked those hangers prefer a saw slit and sit normal ones in, don't have to do the whole birds mouth

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Thanks for that suggestion.

Slope adjustable hangers are £13 a pop so  will use regular.

 

Only (slight) concern is missing out vertical nail fixing up from bottom of the hanger. But out of sight out of mind?!

[Oz07]

Side fixing in normal hangers doing same job

[Russell griffiths]

We used these nothing like the price you mention. 

Made by CULLEN bend to match angle and fit any width timber, I think they where about a couple of quid each. 

I fitted over 70 and didn’t find any problems. 

[Temp]

With a structural ridge don't you normally need strapping to connect one side to the other over the top of the beam? Eg rafters "hang" from the beam.

[willbish]

  On 31/08/2019 at 06:33, Russell griffiths said:

We used these nothing like the price you mention. 

Made by CULLEN bend to match angle and fit any width timber, I think they where about a couple of quid each. 

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What supplier did you get from?

Best price online before picking up the phone seems to be £7.38

[Russell griffiths]

  On 31/08/2019 at 09:29, willbish said:

 

What supplier did you get from?

Best price online before picking up the phone seems to be £7.38

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They came as a package from the i joist company 

webbs timber in Gloucester

it May have been they where cheaper as I had £7000 of timber from them. 

Never priced them separately 

[Oz07]

Isn't it crazy that those angles hangers can take all the thrust out of the rafters. I don't believe what I'm seeing ha

[Russell griffiths]

  On 31/08/2019 at 19:06, Oz07 said:

Isn't it crazy that those angles hangers can take all the thrust out of the rafters. I don't believe what I'm seeing ha

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They don’t really carry a lot of load, if the plumb cut is correct the load pushing down tightens the plumb cut against the ridge, they just keep it all in place, if you think back 10 years all that was used would have been a couple of 4inch nails.