Help with steel beam size

[e175]

I'm looking to purchase a rectangular hollow section (RHS) steel beam to use as a door lintel for a garden room, similar to the one shown in this video.

The door opening is 3200mm wide. What size RHS beam would be suitable to support a flat roof constructed with 6x2 joists spaced at 400mm centres?
The roof deck is 7200mm x 4200mm and weights about 1050kg (including insulation and finish).

Front wall is constructed from 2 x 5 (45mm x 120mm) C24 Treated Timber, studs placed at 400mm centres.
Back and slid walls are constructed from 2 x 4 (45mm x 95mm) C24 Treated Timber, studs placed at 400mm centres.

The ends of the beam will be supported by a 300mm long jack studs constructed from 2 x 5 (45mm x 120mm) C24 Treated Timber as in the following picture:

 

[freddiemercurystwin]

What's wrong with using a couple of timber joists to work as the lintel?

 

[e175]

What's wrong with using a couple of timber joists to work as the lintel?

which timber joists should be used? 6 x 2? and how many would need to be bolted together?

 

[tony1851]

RHS is unnecessarly expensive for that sort of loading - a channel '[' section would be just as effective and cheaper.
Timber is also perfectly OK, depending on what maximum deflection you can put up with; 2 or possibly 3 piece of C24 screwed together, depending on the load.
It's not just the dead load of the roof structure you need to allow for but also the live load of snow, typically 0.75kN/m2.

 

[e175]

RHS is unnecessarly expensive for that sort of loading - a channel '[' section would be just as effective and cheaper.
Timber is also perfectly OK, depending on what maximum deflection you can put up with; 2 or possibly 3 piece of C24 screwed together, depending on the load.
It's not just the dead load of the roof structure you need to allow for but also the live load of snow, typically 0.75kN/m2.

Thank you for your reply. What channel size would you use?

 

[tony1851]

125 x 65 or 150 x 75.

 

[noseall]

Thank you for your reply. What channel size would you use?

Have a few holes drilled in the centre of the web so that you can fill it out with timber if needs be.

 

[e175]

125 x 65 or 150 x 75.

I checked my local steel supplier, a 150 x 75 x 18mm Channel weighs the same as a 150 x 100 x 5mm Rectangular Box Section (both 18kg/m) and the channel is only £13 cheaper than the RHS. Is RHS structurally better than a Channel?

Product	kg/m	Total weight for 3800mm long	Price inc. VAT
150 x 75 x 18mm Channel	18 kg/m	68.4 kg	£200.3
150 x 100 x 5mm RHS	18.7 kg/m	71.1 kg	£214.6
125 x 65 x 15mm Channel	15 kg/m	57 kg	£158
120 x 80 x 5mm RHS	14.80 kg/m	56.5 kg	£174.5
120 x 60 x 5mm RHS	13.30 kg/m	50.5 kg	£152.2

 

[stevie888]

For this application a Universal Beam would be the best bet if you want steel, but it could easily be done with timber

 

[Scally-Ho]

If you want to build as per that video, then it was a 160mm x 80mm box beam. IMO a good length of straight timber would do just as well and save you some money.

 

[e175]

If you want to build as per that video, then it was a 160mm x 80mm box beam. IMO a good length of straight timber would do just as well and save you some money.

What timber would you use? 6x2 C24? or 8x2?