Hello!
I am working on a deck and possibly in the future, we want the option to install a lightweight sliding "pergola" roof.
The deck is 3.6x8 meters and adjacent to one side of the house facade. I have placed 3 pieces of 95x95 posts, one at each end and one in the middle. Now, I am going to attach joists between the house/facade and the posts, and considering you can use a 45x195 that supports the load, but I'm wondering if I should screw together 2 pieces of 45x145 or 2 pieces of 45x170 instead, as that would make the joists almost the same width as the post.
The question is, which provides more load-bearing capacity: 1 piece of 45x195 or 2 screwed together 45x145 or 45x170? The length between the posts and the facade is about 3.6 m and I am installing them with at least an 8-degree slope.
I am working on a deck and possibly in the future, we want the option to install a lightweight sliding "pergola" roof.
The deck is 3.6x8 meters and adjacent to one side of the house facade. I have placed 3 pieces of 95x95 posts, one at each end and one in the middle. Now, I am going to attach joists between the house/facade and the posts, and considering you can use a 45x195 that supports the load, but I'm wondering if I should screw together 2 pieces of 45x145 or 2 pieces of 45x170 instead, as that would make the joists almost the same width as the post.
The question is, which provides more load-bearing capacity: 1 piece of 45x195 or 2 screwed together 45x145 or 45x170? The length between the posts and the facade is about 3.6 m and I am installing them with at least an 8-degree slope.
I don't know if you are most interested in the stiffness or strength of the studs, so you get both comparisons here:
90x145 has lower stiffness (moment of inertia) than 45x195.
90x170 has higher stiffness than 45x195.
Both 90x145 and 90x170 have higher strength (bending resistance) than 45x195.
90x145 has lower stiffness (moment of inertia) than 45x195.
90x170 has higher stiffness than 45x195.
Both 90x145 and 90x170 have higher strength (bending resistance) than 45x195.
Last edited:
You mean 2x45x170 I suppose. In terms of stiffness, yes, maybe not in terms of price...T A said:
Maybe I should elaborate on my latest brief and somewhat cryptic answer, (I'm a man of few words).
The winner is usually the option that meets the requirements at the lowest cost.
45x195 meets the requirements according to the thread starter, unclear with what margins regarding strength and deflection.
Both proposed alternatives to 45x195 meet the strength requirements as they both have greater strength (bending resistance) than 45x195, (as previously noted).
Regarding stiffness, 45x195 has a moment of inertia of 2781E4 mm4 while the alternative 2x45x145 has a moment of inertia of 2286E4 mm4.
2x45x145, in other words, has a stiffness equivalent to 82% of the stiffness of 45x195, (if my calculations are correct).
If the design calculation of 45x195 shows that the deflection requirement is met with such a good margin that a lower stiffness (<82%) is sufficient, then the alternative 2x45x145 might be the winner.
Otherwise, that alternative is shaky, and 2x45x170 becomes the winner. It's TS who has the calculation of 45x195, so TS is the jury!
I hope this is more explanatory than confusing! 🙂
The winner is usually the option that meets the requirements at the lowest cost.
45x195 meets the requirements according to the thread starter, unclear with what margins regarding strength and deflection.
Both proposed alternatives to 45x195 meet the strength requirements as they both have greater strength (bending resistance) than 45x195, (as previously noted).
Regarding stiffness, 45x195 has a moment of inertia of 2781E4 mm4 while the alternative 2x45x145 has a moment of inertia of 2286E4 mm4.
2x45x145, in other words, has a stiffness equivalent to 82% of the stiffness of 45x195, (if my calculations are correct).
If the design calculation of 45x195 shows that the deflection requirement is met with such a good margin that a lower stiffness (<82%) is sufficient, then the alternative 2x45x145 might be the winner.
Otherwise, that alternative is shaky, and 2x45x170 becomes the winner. It's TS who has the calculation of 45x195, so TS is the jury!
I hope this is more explanatory than confusing! 🙂
A little confusing, but I am a person who likes to use both belt and suspenders... And since I don't really know what weight might come on the pergola etc. and I don’t even want to risk it bending and starting to sag over time, 2x45x170 feels like the safest bet 😃 thanks 🙏G Granngubben said: