What provides the best bearing capacity?

[dannelu]

Hello!

I'm in the process of expanding my garage. The existing part is very cobbled together on my own, so I'm thinking of reinforcing it a bit. One consideration I have is what provides the best load-bearing capacity of the following:

Increase the size and replace the roof beams

OR

Add more roof beams of the same size and thus reduce the cc distance from about 100-110 cm to 50-60 cm

 

[Oldboy]

In general, increased dimension, especially in height, is best, but it is often also the most work and expensive.
Everything depends on how under-dimensioned it is, you don't do more than what is necessary.
Then there are different ways to reinforce a floor structure. Which one you choose depends on the specific conditions in that particular building.

So if you want more concrete advice, much more info is needed, and it is best in combination with pictures.
If it's about the outer roof, the snow zone is also needed.

 

[dannelu]

Generally, increased dimension, especially in height, is best, but it's usually also the most work and expensive.
Everything depends on how under-dimensioned it is; you don't do more than what is necessary.
There are also different ways to reinforce a joist. Which one you choose depends on the specific conditions in that particular building.

So if you want more concrete advice, much more info is needed, and it would be best in combination with pictures.
If it's about the outer roof, the snow zone is needed.

Thanks!

I live in snow zone 2.5. According to today's standards when talking about dimensions and the wood guide's dimensioning program, my current garage wouldn't even support its own weight, but it is built like this from top to bottom:

3-4cm layer of gravel, rubber membrane, board, 45x145 joists cc 100-110cm, 100x300 homemade beam (2 different joists and 3 layers of 12mm plywood), 45x145 joists hanging from the upper 45x145 joist with the help of mixed boards, 22mm batten boards and then ceiling plasterboard.

The roof has a slope of about 2 degrees. This has held since the garage was built in 1979.

I have already started to extend and have replaced the old beam with 2 glulam beams at 140x270 resting on 3 (2 in the outer walls and 1 in the middle) 140x140 glulam posts. The idea is to remove the lower 45x145 that only hang from the upper joists (what function can these serve?) and place new 45x145 joists between the old ones over the beam to increase the number. Remove the gravel on the roof and only have roofing felt as external cladding.

I understand this is barely sufficient, but since it has held before, this is what I ordered to continue building with, but of course, I want to do what I can to make it as sustainable as possible. One thought I have is to reinforce the joists by gluing and screwing plywood to them.

The garage currently measures 7x9m but will become 8.5x12.5m after the extension.

Unfortunately, I don't have any pictures right now.

 

[bossespecial]

Unfortunately, it is difficult to understand what it looks like without sketches and images. Spontaneously, I would probably consider redoing it properly according to today's standards rather than continuing on the previously chosen path.

 

[Oldboy]

Some pictures and sketches/drawings are also needed, because just like bossespecial, I don't quite understand how it is constructed.

If it is constructed as I interpret/guess based on the description, it seems to be under-dimensioned, yes. However, it seems doubtful to use suspended 45x145 mm beams only as nail beams for the ceiling. They feel unnecessarily thick. Therefore, one (I) wonder if it might be some form of truss construction. Then the beam dimensions become more reasonable, as does the load-bearing capacity. If the garage is 7 m wide, the span for the beams is 3.5 m, which with cc 110 - 120 cm on a flat roof with gravel/chippings in snow zone 2.5, is clearly under-dimensioned. Further in my interpretation, the central carrying beam is 9 m long, which makes a wooden beam of 100x300 mm also appear clearly under-dimensioned. Maybe it's placed crosswise? Then the span becomes a bit more acceptable, albeit still a bit too much. At the same time, it gives a span of 4.5 m for the 45x145 mm beams, making them even more under-dimensioned...

Continuing with the same construction, and especially the timber dimensions, while increasing the span to 8.5 m instinctively feels very bad, even if the existing construction is sufficiently load-bearing for the original garage.

 

[dannelu]

Then some pictures and sketches/drawings are needed, because just like bossespecial, I don't really understand how it is constructed.

If it is constructed as I interpret/guess from the description, it appears to be underdimensioned, yes. However, it seems doubtful to use suspended 45x145 mm studs only as nailing pieces for the ceiling. They feel unnecessarily thick. Therefore, one might wonder (I) if it is some form of truss construction. Then the stud dimension becomes more reasonable, as well as the load-bearing capacity. If the garage is 7 m wide, then the span for the studs is 3.5 m, which with 110 - 120 cm spacing on a flat roof, with gravel/shingle on it in snow zone 2.5, would probably be clearly underdimensioned. Furthermore, in my interpretation, the middle support beam is 9 m long, which makes a wooden beam of 100x300 mm also appear clearly underdimensioned. Perhaps it is placed transversely? Then the span becomes a little more acceptable, although still a bit much. At the same time, it gives a span of 4.5 m for the 45x145 mm studs, which makes them even more underdimensioned...

To continue with the same construction, and especially timber dimensions, while the span increases to 8.5 m feels instinctively very wrong, even if the existing construction is sufficiently load-bearing for the original garage.

Here is a simple sketch of what it looks like in the current garage. The beam of 100x300 doesn't go the entire 9m through the garage but stands on a "post" made of mixed boards 3-4 pieces that stand about 1.5m from the back wall and there the beam ends. There was a small partition wall the last bit previously that supported the last 2 roof studs.

 

[Oldboy]

Is the span from left to right in image 7 m?

And does the longitudinal central beam (100x300 mm) also have a free span of 7 m?

 

[dannelu]

Is the span from left to right in the picture 7 m?

And does the longitudinal center beam (100x300 mm) also have a free span of 7 m?

Exactly!