6m Span flat roof support beam

[iDIY]

Hi Guys,

OK, so the plan is to put a GRP flat roof on the building shown in the picture. This will be constructed with 47 x 170 timbers at 400mm centres, each 3.4m long.

Obviously one end is supported on the 7.6m long rear wall (cavity blockwork) and the other end will be supported on a 1.9m long front wall (cavity blockwork). The rest of the front face opening will be full height upvc double glazed patio doors and side windows.

So the span of 5.7m above the upvc will need a support structure putting in place so the remaining 3.4m long roof timbers have something other than the UPVC supporting them.

Would this have to be an RSJ or will say a pair of 47 x 170 timbers bolted together be ok as far as building regs are concerned?

 

[Mr Chibs]

Whilst not an answer... might give you a few thoughts

I converted a flat roof to pitched, very similar to your sketch, but around 5m wide.
The original construction has a large concrete lintel where your red arrow is... well infact, it's all the way across, anchoring at both ends in masonry.
The lintel was cast in concrete and reinforced (previous owner) my rough calcs estimated 500Kg + and it's cast in situ, this supported the 200x50 @ 450c - 4m long rafters (now removed) with 18mm OSB and GRP roof.. there was NO insulation!

If I were to do this, from fresh... I would just us suitable steel(s), use a beam calculator or get a SE to do the calcs. My old concrete lintel seemed OTT in my opinion

Just realised your 1.9m bit is a wall, looked visually like a doorway... steel will work, think I used 203x102x23, others will comment

 

[Buck_68]

I would speak to a SE.

This will depend on the roof structure and weight?

Also, with the depth of the room, are you going for a solid roof or some form of roof lights? It may be quite dark at its maximum from the glazed areas (unless the rear is glazed / it is a free standing build?) so worth considering now.

We are mid way on our extension which is c.8.5m x 4m with 6.5m full height glazed frontage and three roof lights.

We have a steel going in next week with steel “wind posts” either side (as specified by our SE)

I’d be nervous about the wooden joists sagging over that span which might impinge on the uPVC doors opening?

 

[tony1851]

You would need a steel beam on that span; timber would deflect too much under live load.

 

[^woody^]

You would need a steel beam on that span; timber would deflect too much under live load.

Several timber sections bolted together?

A box beam?

 

[Notch7]

Timber will be no good.

You will need either a universal steel beam, lintel, if you can get them that long, flitch beam or a glulam beam.

The right hand side has a 1.9m of brickwork which will act as a buttress. The left hand side needs lateral support -it may achieve it by the beam and roof connecting it to the right.

Ideally a structural engineer would confirm with calcs. Dont forget to allow for the weight of the doors if they are top hung bifolds

 

[iDIY]

Timber will be no good.

You will need either a universal steel beam, lintel, if you can get them that long, flitch beam or a glulam beam.

The right hand side has a 1.9m of brickwork which will act as a buttress. The left hand side needs lateral support -it may achieve it by the beam and roof connecting it to the right.

Ideally a structural engineer would confirm with calcs. Dont forget to allow for the weight of the doors if they are top hung bifolds

Completely irrelevant to the thread, but I had bifold doors fitted on the house a few years ago, NEVER AGAIN...

 

[^woody^]

Completely irrelevant to the thread, but I had bifold doors fitted on the house a few years ago, NEVER AGAIN...

Same here. I have no room for another set either.

 

[tony1851]

As a matter of interest, the last two posters are critical of bi-folds; any comments on the downsides? Thanks.