Roof beams different answers in calculation program!

[Ulf1]

Hello
We are going to build an outdoor room of about 3.3x4.3m. 2 supports. Load case 0.6kN/m2

When I calculate the roof beams with Moelven's calculation program, I get a completely different answer in Beijer's dimensioning program.

Moelven gives Glulam 90x270 with a deflection of 10mm whereas Beijer shows LT 90x405.

That's an incredibly big difference! What could be the reason???? :eek:
Which program is correct??

 

[Kallebo]

Is it four meters between the supports or is the room in the other direction? Bejiers seems completely off anyway I think...

I think 42x180 sounds a bit weak, but it's a pretty small conservatory...

 

[Ulf1]

There is 4.2m between the center posts. I agree 4.2x80 sounds a bit, but 90x405 is horribly large. The question is, how can there be such a difference... and it seems like both are wrong...

 

[hempularen]

moved from el

/moderator

 

[Finndjävel]

Use regular 45x195 studs instead of glulam and it will be more than half as cheap. I claim it's a sufficient dimension for a 4.2m span without using any complicated tables and theoretical calculations.

 

[Ulf1]

thanks moderator

 

[Ulf1]

The roof of the sunroom will be metal, felt, tongue and groove wood, insulated, plasterboard, and recessed windows. 45x170 joists. cc60 We live on the coast about 200m from the sea, so it gets very windy here. 45x190 feels a bit risky since the entire long side consists of glass panels. Don't want to take any chances ...

 

[Ulf1]

Correction Moleven gives LT 90 x270mm, I'll go with that

 

[justusandersson]

The requirement for maximum deflection is applied only to floor structures, not roof constructions. If you are not knowledgeable in structural strength, you should probably be cautious with calculation programs; it is better to consult an expert. Using glulam in this case seems excessive. I believe that even 45x195 is overdimensioned, somewhat depending on the roof pitch. Snow load in Bohuslän is only 150 kg per sqm. However, it is important that the construction is stable, which is not the same thing. Post constructions without panels always require some form of diagonals. Proper fastenings are also important.

 

[Ulf1]

Thanks for the input. The calculation programs are easy to fill in, it's hardly possible to make a mistake. But as you write, the best is to ask a carpenter/Ulf.