Help Wanted - Glulam Beam Load-bearing Wall Above Garage Door

[lorens]

Hello,

I am going to build a double garage with a large door on the side where the wall is load-bearing. I would like to know where I can turn to get someone who can calculate the required dimensions for this.

The door width is 5 meters, and the snow zone is 3 (I think, maybe 2.5?, Piteå in northern Sweden).

The glulam beam can extend up to 6.5 meters to get more support if it helps.

The image shows an illustration of the house.

Grateful for help.

Best regards, Lorens

 

[hackatall]

You can also thread a glulam beam through the rafters, i.e., use 2 pieces.
A slightly shorter one over the gate that the rafters rest on and a longer one through all the rafters that distributes the pressure from the rafters over the gate onto the other rafters.

 

[lorens]

A little shorter over the gate? The gate is 5 meters wide and the total wall length is 6.6 meters.

 

[justusandersson]

With the current measurements, all trusses except those possibly at the gables will rest on the beam (provided c/c 1200 mm). Piteå is snow zone 3. What are the garage's depth and roof pitch?

 

[Mikael_L]

You'll probably get better answers.
But I took a chance and input some data into byggbeskrivningar.se's dimensioning tool, and it seems to suggest a glulam beam around 115x405 or maybe even 115x450.
And support posts at 115x115.

 

[lorens]

With the current measurements, all trusses except for those that might be at the gables will rest on the beam (provided c/c 1200 mm). Piteå is in snow zone 3. What is the garage's depth measurement and roof pitch?

That's correct

The depth is 8 meters and the roof pitch is around 24 degrees

 

[justusandersson]

Assuming you have free-spanning roof trusses, it's about 90x495/115x450/165x405 (comparable alternatives). 115x115 posts are sufficient.

 

[Mikael_L]

You'll probably get better answers.
But I took a chance and entered some data into the design tool on byggbeskrivningar.se, and it seems like it would be a glulam beam around 115x405 or maybe even 115x450.
And support posts at 115x115.

And I guessed that the garage would be about 6.5 meters deep, now it's 8, so even stronger glulam ...
Good justice, then it seems the tool from byggbeskrivningar isn't completely off track.
(However, I trust you more than tools on internet pages, just so you know! )

 

[justusandersson]

No Mikael, I don't think that the tools for construction descriptions are completely off the wall. The problem is partly that it's about inputting the right parameters, and partly that the number of options is limited. You also have a certain sense for the dimensions so you know if what you get out is crazy.

 

[lorens]

Provided that you have free-bearing roof trusses, it's about 90x495/115x450/165x405 (comparable options). 115x115 posts are sufficient.

Thank you so much for the help.

I found a tool on Moelven, where I figured out 115x495 with 82mm posts, so they seem to fit quite well then!

Do you think I can place double 45x145 glued and screwed together as posts on either side of the garage door? It will only be 90 wide as support under the glulam beam but maybe it will suffice?

 

[Mikael_L]

Can I set double 45x145 that I glue and screw together as posts on each side of the garage door, do you think? It will only be 90 wide as support under the laminated beam, but maybe it will do?

That's fine. The fact that it's narrower doesn't matter much; the support pressure on the structure doesn't become greater as the support surface increases, so that's even better. The only thing to watch out for is buckling in the weak direction, but calculation exercises via various tools suggest that an 82x82 or 90x90 post should be sufficient, so two 145x45 should work. Yes, laminated wood does have slightly higher strength, of course. But make sure you find fine specimens of 145x45 in C24, and glue carefully, so I don't see why it wouldn't be okay.

 

[lorens]

It goes well. The fact that it becomes narrower doesn't matter much, the bearing pressure on the construction won't be greater, as the bearing surface increases, so that's just better. The only thing to be wary of is buckling in the weak direction, but since calculations through various tools show that an 82x82 or 90x90 post should suffice, then 2 pcs of 145x45 should work. Yes, and of course, glulam has a slightly higher strength. But make sure to find nice specimens of 145x45 in C24, and glue carefully, then I can't see anything but that it will be good.

I could also take a longer glulam beam so that it lies over an additional upright 145x45 in the wall. So the pressure is distributed more, even though the pressure is of course greatest closest to the opening.

Or will it even result in negative pressure on the outermost if I make it longer?

 

[Mikael_L]

Or will there even be negative pressure on the outermost if I make it longer?

Yes, maybe.
Choosing a longer beam than the one spanning across both supports is not an end in itself; you gain nothing real from it.
If due to the rest of the carpentry and construction there was some advantage with a longer beam, you can choose that. Otherwise, it is likely to be worse, e.g. less thermal insulation and a more expensive beam.

However, I am pondering for a few seconds whether there could be less deflection if the beam extends slightly beyond the supports and has a downward load there.
Otherwise, the deflection in the middle of the garage door could be measured in centimeters.
Be aware that at least one cm the beam may deflect in the middle of the door opening under maximum snow load, so keep that in mind when you're putting everything together.

 

[lorens]

Yes, maybe.
Choosing a longer beam than necessary to cover both supports is not an end in itself; you gain nothing real from it.
If there is some advantage due to the rest of the carpentry and construction with a longer beam, you can choose it. Otherwise, it is mostly worse, e.g., less thermal insulation and more expensive beam.

However, I am pondering for a few seconds if it could lead to less deflection if the beam extends a little beyond the supports and has a downward load there.
Otherwise, the deflection in the middle of the garage door could be measured in centimeters.
Be aware that the beam can bend down at least one centimeter in the middle of the opening during maximum snow load, so keep that in mind when you're assembling everything.

I agree with you; it's difficult to apply a downward force on the beam further out if I take a longer one, so it's probably best to forget about it.

Good that you mention deflection, I am aware that there will be deflection with snow load, but it's good to keep in mind if anything for the garage door needs to be attached in the middle of the inside wall.

 

[Mikael_L]

Arrange a 2 cm gap, which you caulk.