Lintel type for 3m span

[L.Lam]

Hello,

I want to put in 3m bifold doors in a garden room. The construction is block and render with flat roof. Currently trying to work out what type of lintel is best for the bifold doors. I guess there are 3 options:
1) RSJ (is 127x 76 x13 sufficient?)
2) Flitch beam (8x2 joists with 8/10mm plate?)
3) 2 or 3 8x2 joists joined together

Can anyone advise on which is the best option? A diagram of the proposed roof is attached.

 

[^woody^]

You'll need to work out the loads from the roof and doors before you can select a suitable support.

Whether there is external masonry is also a factor.

 

[L.Lam]

Thanks for replying Woody. No load from door as it’s ground supported. Just load from near flat roof. Can I assume dead load of 0.75kN? Do I need to add in additional load if the joists are sitting on the lintel? Hoping to avoid paying for SE to do calculations since building control is not required.

 

[^woody^]

You can assume 0.75 or more conservative 1.0 kN/m2, plus snow loading (another 0.75 kN/m2) and plus the limit state factors of 1.4 and 1.5 for live and dead loads.

Work out the area of roof being supported - half the span plus any soffit projection.

You'll then need to be able to work out a suitable steel or timber section to support those loads.

Standard steel lintels are designed to have some masonry above before the joists. Check with the manufacturer.

The choice then is mainly cost, and ease of installation.