Roofing joint

[Gassafe83]

Dear all,



Currently building my rear 6 meter extension. Not myself, but managing the build in and around work. Builders have thrown up the question and as such I have a structural engineer working on the plans of the roof but will not get back to me by Wednesday so I was hoping to see if anyone could shed some light on the situation before then.

Ok so, 6 meter extension from the rear of the house. 3 meters to the eaves and 4 meters to adjoin the existing rear wall of the house.

From the existing house, a 3 meter flat roof will be installed. From that point there will be a pitch of 18 degrees down to the 3 meter eaves of the front of the extension.

The situation is this, my builders want to build a wooden support frame which would sit under both sections of the roof to provide additional support. However this would create a false ceiling at the 3 meter mark.

I want to retain this space to make the extension feel more spacious with more ceiling height. I would rather plasterboard onto the underside of the roof structure to maximise the space. My builder has told me that he worries about the strength of the structure, hence why I have instructed a structural engineer to design what will be required and what materials to use.

This image is what my builder wants to build

picture 1

• Gassafe83
• 23 Jan 2015
• 1

This image is more of what i'm after.

picture 2

• Gassafe83
• 23 Jan 2015
• 1

Birds eye view of the extension

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• Gassafe83
• 23 Jan 2015
• 1

Side elevation of the extension

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• Gassafe83
• 23 Jan 2015
• 1

Any ideas or experience in this field guys?


All the best

 

[freddiemercurystwin]

You would get away with a single steel beam running from side to side, where you've shown a physics defying nail plate. Then you can sit your rafters and flat roof joists onto this steel. But it won't phase your SE, that's why you're employing him. It should be possible to hide the beam completely, normally there is a good wadge of insulation beneath the joists/rafters.

 

[tony1851]

As above, a beam spanning full width is the optimum solution.

And no, you cannot join timber members as in your second pic.

 

[noseall]

Like wot we did....

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• noseall
• 17 Jan 2015
• 2

 

[Gassafe83]

Guys thanks for the replys!

Noseall, similar to what you have done, but you have multiple pitches and they seem shorter. The velux windows we are having at 1.6m in length and the pitch length will be circa the 3 meter mark.

But in terms of the design, yes that is what I am after. The roof will be a cold deck roof, with insulation running between the roof joists, then I would like just to plasterboard directly underneath this area.

I was thinking the same thing about an RSJ just running before the pitch line to allow for more strength. But then what about where the pitch meets the eaves, seems as though this will be the 'weak point' so to speak.

 

[freddiemercurystwin]

No it's just standard construction.

 

[catlad]

Insulated plasterboard under the rafters.

 

[DIYedboy]

Excuse my ignorance, but in the photo Noseall supplied, I can't see a steel beam at the junction of the flat roof and the start of the pitch, I assume I am looking for an RSJ or am I just being a wombat?

 

[tony1851]

Possibly it is a 'flitched' beam, which consists of a long, thin steel plate sandwiched between two timber joists?

Hopefully Nose will be along in due course and satisfy our curiosity!

 

[catlad]

I think he mentioned in a previous post it was a flitch beam and if you look there is a gap between the timber.

 

[DIYedboy]

Oh yeah, I can see the plate bolted between the timbers. the thing I can't get is how is the flitch beam held up? the far end wall has a roof slope so the beam hasn't got a wall to sit on.

 

[noseall]

Possibly it is a 'flitched' beam, which consists of a long, thin steel plate sandwiched between two timber joists?

Hopefully Nose will be along in due course and satisfy our curiosity!

Correct. And a bloody heavy arrangement too!

2 x 195mm x 47mm timber beams with steel plate between. All bolted together with (staggared) M14 bolts.

The beam is supported off the wall at t'uther end and is on a timber prop (railway sleeper) and another steel beam shown in the image. I have all my beam webs drilled so that I can bolt timber into them as you can see in the images.

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• noseall
• 17 Jan 2015
• 2

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• noseall
• 17 Jan 2015
• 2

 

[noseall]

Oh yeah, I can see the plate bolted between the timbers. the thing I can't get is how is the flitch beam held up? the far end wall has a roof slope so the beam hasn't got a wall to sit on.

If you look at the image in my first post you will see a patio opening with a steel beam across. Directly above and at right angles to it is another steel beam. There is a timber prop supporting the flitch junction off said beam.

All the beams are filled with timber and are bolted to the web. Makes cladding the beam simpler.

 

[DIYedboy]

Gotcha Noseall..............jeez, that's lots of supports supporting the supports!....the beam over the patiodoors supports the beam sitting above it which supports the flitch plate beam!!!

 

[noseall]

Gotcha Noseall..............jeez, that's lots of supports supporting the supports!....the beam over the patiodoors supports the beam sitting above it which supports the flitch plate beam!!!

I know! Scratched my head a bit on that job. steel beams everywhere and all had critical height position relevance. (see below).

The flitch bolts were actually M16 (not M14 as typed) and bloody hard to get hold of because of the size.

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• noseall
• 26 Jan 2015
• 1

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• noseall
• 26 Jan 2015
• 1

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• noseall
• 26 Jan 2015
• 1