Currently building a pergola.
Upright studs = glued, screwed 45×95
The distance between these studs is 4600mm.
Is it enough to have 45×120 studs resting on the posts, or are larger dimensions required to prevent these boards from bending?
There will be no weight on these boards.
Possibly (less likely) there will be studs crossing over these studs.
Your question is: Will 45x120 with a span of 4.6 m with only its own weight as the load sag?
One should consider that the own weight is a long-term load and that the properties of the wood deteriorate due to the construction being outdoors without a roof. Although the own weight increases with the dimension, since the moment of inertia (as the most important static parameter) increases with the cube of the beam height, the deflection decreases with increased construction height. Then it is primarily an aesthetic question of how much deflection one accepts. My experience is that this type of construction (like, for example, horizontal fence slats) is sensitive to even small deformations. It is also a question of proportions. My answer is that 45x120 C 24 can handle the span with limited deflection. However, I would choose a slightly larger dimension for better proportions.
Your question is: Will 45x120 at a span of 4.6 m with only its own weight as load sag?
One should consider that the self-weight is a long-term load and that the properties of the wood are deteriorated by the construction being outdoors without a roof. Although the self-weight increases with dimension, the moment of inertia (which is the most important static parameter) increases with the cube of the beam height, thus reducing deflection with increased construction height. Then it is mainly an aesthetic question how much deflection one accepts. My experience is that these types of constructions (as well as, for example, horizontal fence slats) are sensitive to even small deformations. It is also a matter of proportions. My answer is that 45x120 C 24 manages the span with limited deflection. However, I would choose a slightly larger dimension for better proportions.
Ok, thanks for the answer.
Then I will move up a dimension to 45×145 or alternatively, there will be a post in the middle.
I have plans to set up a pergola, or a slatted roof or whatever you choose to call it.
The pergola/slatted roof will be over the patio deck and I was thinking of a total of 6 posts, dimensions 95x95, placed about 3.6 m apart. So it will be a slatted roof approximately 7.2 x 3.6 m.
My idea is to unscrew a number of decking boards from the deck, dig down and cast footings for the posts between the screw joists. Then notch out for the posts in the decking and put them back.
I haven't gotten further in my thinking, to be completely honest. I'm unsure how to continue thinking to create a durable, yet somewhat sleek construction.
The only given thing is that the slats on top should be placed along the longer side, a total of 7.2 meters. I'm thinking of slats with dimensions 45x70, placed on their edge with a 45-50 mm gap. So it would be 35-40 slats. Is this overkill? Perhaps unnecessarily dense? Or maybe smarter to increase the dimension to 45x95 or 45x120 and place them more sparsely as the original poster did?
I also (like otherwise) have poor knowledge on how to best connect the posts with the slats. Some form of frame/beams is obviously needed. Dimensions for these? Should diagonal braces be placed between the posts and beams? Like a Y shape. If so, is it needed in all directions? Or is it enough with angle brackets of suitable size to hold it together?
As mentioned, the idea is to attach slats on top like a sparse roof/pergola, but in the future, one might want to add a plastic roof on top of the slats to make it a real roof. I assume this will increase stability requirements considering the wind load this entails on a relatively exposed site?
Even if it's not time to start building yet, I wonder if there is a specific work order to follow for such a construction. Mainly thinking about how to get it straight and good-looking and to avoid building oneself into a corner, for example.
All help, info, and guidance are gratefully received!
If more info is needed, please respond.
If it is to be a completely standalone pergola, it needs to be stabilized with diagonal braces or similar arrangements. Cross-braced wires on two of the sides are an option. The pergola in the picture is braced by wall pieces in the corners. How closely the slats should be placed depends partly on the orientation in the cardinal directions. If the long sides of the slats are facing south, you can calculate the appropriate distance between them to get shade at midday. I believe that 45-50 mm is unnecessarily tight for 45x70 under all conditions. Slats that are 45x70 C 24 should not have a span as long as 3.6 meters. Half the distance, i.e., 1.8 meters, is more suitable. The framework supporting the slats should be 45x170 C 24. Horizontal posts with a square cross-section like in the picture should be at least 120x120 C 24. There are many design variations. The most important thing is that it stays aesthetically pleasing in the long term, and for that, high quality timber is essential.
If it's going to be a completely free-standing pergola, it needs to be stabilized with diagonal braces or a similar arrangement. Cross-linked wires on two sides are an option. The pergola in the picture is braced by wall pieces in the corners. How closely the slats should be spaced depends partly on the orientation concerning the cardinal points. If the long sides of the slats are facing south, you can calculate the appropriate distance between them to get shade in the middle of the day. I think 45-50 mm is unnecessarily close for 45x70 in all conditions. Slats measuring 45x70 C 24 should not have a span as long as 3.6 meters. Half the distance, i.e., 1.8 meters, is more appropriate. The framework that supports the slats should be 45x170 C 24. Horizontal posts with a square cross-section like in the picture should be at least 120x120 C 24. There are very many design variations. The most important thing is that it looks good in the long run, and high timber quality is key.
Thanks for the response! I brainstormed further and concluded that it would probably be wise to add another row of posts, and then make my own version approximately 120x120 using 3 beams of 45x120. I put together a simple model in Excel to illustrate the whole thing, see the image.
Would a construction like this work, or is it still somewhat questionable?
For example, do the total of 8 green beams that are attached to the blue beams serve any significant purpose, or would 4 be enough? They're mostly intended to provide some stability north-south and to have something to screw the slats into, which will run west-east.
Considering that the blue beams are to be placed in the U of the post, maybe the posts should be made of 3 beams of 45x145 instead to provide an extra centimeter for resting? I'm mainly thinking about the three middle posts where two blue beams would share a U.
The questions are still many, and the knowledge is limited, so any feedback is gratefully received.
I have made a simple image to illustrate the principles. I think 6 posts are enough. What is not visible are the diagonal braces that need to be present in two sections, one on one of the long sides and one on one of the short sides. Preferably gathered next to a corner.
Joist hangers are not attractive in visible assemblies. You should think of other solutions, such as notching in the posts. It's not a matter of large loads. The ribs should have rectangular cross-sections, so that the height is greater than the width. I wouldn't use too small dimensions if I don't have access to a surfacer. The wood quality easily becomes too low. Use no less than 45x70 mm.
I have made a simple illustration to demonstrate the principles. I believe 6 posts are sufficient. What is not shown are the diagonal braces that must be present in two sections, one on one of the long sides and one on one of the short sides. Preferably gathered near a corner.
Beam hangers are not attractive for visible mounting. You should consider other solutions, such as indentations in the posts. It is not a question of large loads. The ribs should have rectangular cross-sections, so that the height is greater than the width. I would not use too small dimensions unless I have access to an adjuster saw. The quality of the lumber tends to be too low. Do not use less than 45x70 mm.
[image]
Nice illustration! Just something like that is in mind.
So 6 posts are still sufficient? That means about 3.6 m between each post then. Are 95x95 posts (2 pieces 45x95) or 120x120 (3 pieces 45x120) sufficient with 6?
Unfortunately, I don't understand the diagonal braces. Googling only gives me various metal constructions. How are such mounted in a wood construction in a good and aesthetically pleasing way?
Aesthetically, I probably have no problem with visible beam hangers. The idea is to build in common pressure-treated wood to be painted the following year. I also thought of painting the beam hangers in the same color. Bad idea?
I have (also) no good understanding of lumber quality. How do I know what's good enough or not? What should I look for or avoid?
Ribs on edge with dimensions 45x70 sound good to me, that was my initial thought.
Are the other dimensions in my simple drawing OK or is there something else that should be adjusted?
Posts can support very large loads. Considering only their load-bearing capacity, 4 would be sufficient, but that would result in spans that are too long for the horizontal material. Therefore, 6 posts are suitable. Pressure-treated 95x95 is sufficient.
Regarding wood quality and pressure-treated wood, there are two quality systems to consider (besides the pressure treatment itself). Posts and larger beams are strength graded. Choose C 24 wood. C 14 is common but unsuitable for this type of construction. Other wood (mostly applies to the slats) is sorted based on the presence (and type) of knots. The best grade is called G4-0 and the worst G4-3. In this case, I would not buy anything worse than G4-1.
Visible joist hangers should absolutely be avoided. It is not difficult to inset the beams into the posts. See sketch.
I have added some diagonal braces to the old picture. They can be made of wood, but also steel wires.
My suggestion for dimensions: posts 95x95, beams 45x170, slats 45x70.
Posts can handle very large loads. If you only consider their load-bearing capacity, 4 are enough, but then the spans for the horizontal material become too long. Therefore, 6 posts are appropriate. Pressure-treated 95x95 is sufficient.
Regarding timber quality and pressure treatment, there are two quality systems to consider (in addition to the pressure treatment itself). Posts and larger beams are strength graded. Choose C 24 timber. C 14 is common but unsuitable for this type of construction. Other timber (this applies mainly to the battens) is sorted based on the occurrence (and type) of knots. The best grade is called G4-0 and the worst G4-3. In this case, I would not buy worse than G4-1.
You should absolutely avoid visible joist hangers. It's not difficult to recess the beams into the posts. See sketch.[image]
I have added some diagonal braces on the old picture. They can be wood, but also steel wires.[image]
My suggestion for dimensions: posts 95x95, beams 45x170, battens 45x70.
Thank you very much for your engagement!
I have updated my drawing, see picture.
I now understand what is meant by diagonal braces, but it becomes very impractical with those considering how the deck is designed overall. Can I replace diagonal braces with an extra post on the short sides (see drawing)?
If extra posts on the short sides are not enough, I can also consider some form of "Y-bracing" (I don't know what it's called in technical terms) between the posts and the beam on top (see picture). Does this provide the necessary stability, I wonder?
Another possible solution could be to build some form of trellis at the bottom on one of the short sides, if it can help to support it (see picture).
Is any of these alternatives able to do the job instead of diagonal braces?
I have also changed back to 95x95 (90x95) posts and fully understand how the corner posts should support the beams (blue). However, when it comes to the posts in the middle of the long sides, I wonder if it's meant to look like in my simple drawing of a post from above (see picture). Is this the best way to join three beams resting on a post?
Regarding the beams (green) running N-S that do not rest on posts, I don't know how to proceed without using joist hangers. I assume these beams also need to be 45x170, just like the frame of beams around (blue)?
Simply screwing these through the blue beam, or skew-screwing, doesn't seem sufficient to me as a layman, or am I wrong? Here, I would have gone for joist hangers if nothing else.
Then I haven't understood what's so negative about joist hangers; is it a bad construction detail in a "roof" or just considered ugly? Would an internal joist hanger be considered more attractive, or is such a thing too weak? Here I feel I need more info on how to think.
And as I said, any joist hangers would be painted along with the wood in time. Still a big no-no?
As a layman, I typically look at timber at places like Byggmax. I recall they usually state that their treated timber is mainly G4-3 or G4-2, so this is off the table regarding quality? I'll have to scrutinize their labels next time to see what's actually available.
Is it usually difficult (and expensive?) to find better timber qualities like G4-1 and G4-0, or is it something all well-stocked building supply stores can offer at a reasonable price?
Extra posts do not add to the stability. I have updated my image with the three methods that can be used. 1) Diagonal bracing (can also be done with steel rods or wires), 2) Angled supports, and 3) Wall segments.
If you have to use brackets, check at a well-stocked hardware store or go to a blacksmith/mechanical workshop and ask them to make some in flat steel. Sturdy fittings that are visible. Joist hangers are ugly and significantly detract from the impression of your now quite expensive pergola.
Byggmax is the wrong place to go if you want higher quality wood. They typically only have G4-3. For posts and beams, you should use strength-graded wood of C 24 class, which also considers that there are not too many edge knots. (C 24 wood can, however, be found at Byggmax) If you choose a poor sorting for the slats, the whole project could become a failure and thus expensive. Preferably G4-1. Check at any XL-Bygg store or Beijers. Higher sorting becomes more expensive but also results in less waste.
Time to dust off this project, at least in theory for now. I've been bouncing around different ideas and designs with sellers at the hardware store and carpenters. I have yet to decide the best way to design this due to various responses and opinions from these professionals.
Anyway, a question that has arisen/discussed is the maximum distance between two posts that a 45x170 beam (C24 grade) can handle without sagging too much (i.e., what the thread originally dealt with...) so that it doesn't end up looking too bad or unstable.
The idea, as described earlier in the thread, is to have a number of beams inside the 45x170 frame to screw the slats into. The screw beams are estimated to be 45x95 and the slats either 45x45 or standing 45x70. The appropriate distance between the slats is also unclear. Let's say reasonable...
The big question is the maximum distance between the posts (95x95) that support the 45x170 frame. Too many unknown variables to give an exact answer, but perhaps someone knowledgeable here would like to venture a guess in 0.5-meter intervals?
To increase stability, the intended solution is braces. The question is what dimensions should be used for these and how long they should be to have an effect.
Time to dust off this project, at least in theory for now. Have been bouncing various ideas and designs with sellers at the building supplies store and carpenters. I still haven't decided on how this is best designed due to some differing responses and opinions from the mentioned professionals.
Anyway, one question that has arisen/discussed is the maximum distance between two posts that a 45x170 beam (C24 class) can handle without sagging too much (i.e., what the thread was originally about fittingly...) so that it either becomes too unattractive or unstable in the end.
The idea, as previously described in the thread, is to have several beams inside the 45x170 frame to screw the slats into. The screw beams are estimated to be 45x95 and the slats either 45x45 or standing 45x70. The appropriate distance between the slats is also unclear. Let's say just right...
The big question is thus the maximum distance between the posts (95x95) that support the 45x170 frame. Too many unknown variables to give an exact answer, but an approximate answer in 0.5-meter intervals perhaps someone knowledgeable here would like to attempt to estimate?
To increase stability, braces are the intended solution. The question is what dimension should be used for these and how long they should be to have any effect.
Thanks in advance!
We used standing beams 45×95, glued and screwed.
For horizontal, we had 45×145.
We have about 4.20 between the posts without it sagging. But no additional load from above.
We used standing studs 45×95, glued and screwed.
As horizontal, we had 45×145.
We have about 4.20 m between the posts without it sagging. However, no additional load from above.
So you have a frame with 45x145 and on this frame have 45x95 standing as "slats" in the roof of the pergola? And about 4.20 m between the posts?
Interesting!
As I said, I'm considering 45x170 as a frame and 45x95 as studs in the frame and then slats on top of that.
Let's say the distance is a maximum of 4.50 m between the posts. Can the 170-frame withstand additional weight in the form of slats on top of everything?
So you have a frame with 45x145 and on this frame have 45x95 standing as "slats" in the pergola ceiling? And about 4.20 m between the posts?
Interesting!
As I mentioned, I'm considering 45x170 as the frame and 45x95 as the beams in the frame and then slats on top of that.
Let's say the distance is max 4.50 m between the posts. Can the 170 frame handle additional weight in the form of slats on top of everything?
I should probably turn it around.
Standing beams 2x 45×95 glued and screwed. On these posts, there are slats 45×145mm.
Here is a picture, so it's easier to understand what I mean hehe
I don't think you can add more weight on the 45×170 without it starting to sag.
But I'm sure there's someone who knows better about that than I do.
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