I would appreciate if someone could give some interesting input on my problem.
I have a local extension (workshop addition) with a severely undersized roof.
Width inner dimension between the long sides = about 5.60 m. No inner walls.
Length inside = 10.2 m, but that doesn't matter in this context.
Roof slope about 7°, so quite flat. Roof slope and type cannot be changed as this is a small part of a larger building, and I want everything to have a uniform appearance...
Snow zone NW Skåne, so no large snow loads...
The existing roof is built with 145x45x6000 beams with 850-900 centers (varies quite a bit).
On top of that, there's raw boards and then felt...
As everyone quickly understands, this is neither a good nor a stable roof, and it both flexes/sways significantly when you walk on it, and it has sagged significantly in the middle (I have placed props to minimize the risk of collapse)...
So, I'm going to replace this roof with a new one, and the question is how to build the new one the cheapest, simplest, and best way.
One option is a shed truss, but with only a 40 cm height difference in roof height today, it might not be the absolute best option.
So I'm looking at glulam. Available long enough as stock items, so good price and quick delivery. Sloped roof indoors is completely okay.
I have looked at glulam beam GL24h 56x225x6000mm, and glulam beam GL24h 42x180x6000mm.
I thought of placing them 600 centers, on top of this raw boards and then felt again.
I know nothing about how to calculate the correct dimensioning, but played with the idea that it has 100 kg/m² self-weight on the roof, as well as 200 kg/m² for snow/leaves/rain/similar and a hefty homeowner running on the roof which I believe gives a load of up to 950 kg per beam. Those of you who know about this are welcome to correct me...
Can I go with 42x180, or should I go up to 56x225?
Advice, tips, and reflections are welcome...
I have a local extension (workshop addition) with a severely undersized roof.
Width inner dimension between the long sides = about 5.60 m. No inner walls.
Length inside = 10.2 m, but that doesn't matter in this context.
Roof slope about 7°, so quite flat. Roof slope and type cannot be changed as this is a small part of a larger building, and I want everything to have a uniform appearance...
Snow zone NW Skåne, so no large snow loads...
The existing roof is built with 145x45x6000 beams with 850-900 centers (varies quite a bit).
On top of that, there's raw boards and then felt...
As everyone quickly understands, this is neither a good nor a stable roof, and it both flexes/sways significantly when you walk on it, and it has sagged significantly in the middle (I have placed props to minimize the risk of collapse)...
So, I'm going to replace this roof with a new one, and the question is how to build the new one the cheapest, simplest, and best way.
One option is a shed truss, but with only a 40 cm height difference in roof height today, it might not be the absolute best option.
So I'm looking at glulam. Available long enough as stock items, so good price and quick delivery. Sloped roof indoors is completely okay.
I have looked at glulam beam GL24h 56x225x6000mm, and glulam beam GL24h 42x180x6000mm.
I thought of placing them 600 centers, on top of this raw boards and then felt again.
I know nothing about how to calculate the correct dimensioning, but played with the idea that it has 100 kg/m² self-weight on the roof, as well as 200 kg/m² for snow/leaves/rain/similar and a hefty homeowner running on the roof which I believe gives a load of up to 950 kg per beam. Those of you who know about this are welcome to correct me...
Can I go with 42x180, or should I go up to 56x225?
Advice, tips, and reflections are welcome...
Both beam options are too weak according to my calculation. The question is what you want to prioritize, the lowest beam height or the lowest possible price. If you want to keep the beam height down, I would go for 90x225; if you want to keep the price down, choose 42x315. 100 kg/m2 for self-weight sounds reasonable. You probably don't need to consider a snow load as high as 200 kg/m2. Nor do you need to worry about heavy homeowners, as they constitute temporary point loads.
Just out of curiosity. In what way are they too weak?J justusandersson said:
Does it sag too much in the middle of the roof?
Will it move too much, or???
I mean:
The existing roof is built with 45x145x5800 and about 900 cc, and it did sag a little (maybe 5 cm in the middle), but it held up for almost 50 years before some sheet metal work broke, allowing rainwater to leak in and the entire roof structure became wet and started to rot/mold (and lost its strength)...
With 225x56 I am still increasing the beam height by over 50%, the width by 20%, and the amount of beams in the roof by 60% as well (from 10 to 16)...
You cannot build like that. An acceptable deflection of 1/300 of the span means 19 mm. You are too close to the breaking point. The snow loads are calculated based on a 50-year interval. The deflection for a beam with a uniformly distributed load follows the formula 5*q*L^4/384*E*I. This means that for a given beam type and beam dimension, the deflection increases exponentially with the span.