Hello, I have an entrance roof with four posts in each corner.
They are attached to the facade at the back, but have sunk at the front since they are only standing on an old sleeper. I'm considering building a deck adjacent to the entrance, so I wondered if it's possible to replace the front posts with a bracket/brace instead. This way, there would be no post in the middle of the deck.
The posts are 90x90 and I'm thinking the brackets would be double 45x90 or alternatively 45x120.
The current dimension between the posts is 97 deep and 195 wide.
Is there anyone who dares to say whether it works from a construction and durability standpoint?
I live in Stockholm, so there are no extreme snow loads, although of course I want to be sure that it holds even if it snows heavily.
I checked the building description for the canopy at Svenskt Trä and they seem to use simple 45x120 brackets on similar constructions, so I think using double 45x120 "should" be fine
What kind of roof do you have? There is a difference between tile/concrete and felt as in the picture. Then there's the measurement of the roof itself, the roof pitch, etc., that also affects it.
That wasn't your question, but should you even have the roof? It doesn't feel original
What type of roof do you have? There's a difference between tile/concrete and felt like in the picture. Then there's the size of the roof itself and the slope, which also affect things.
That wasn't your question, but do you even need the roof? It doesn't feel original
It's metal, like the kind that looks like roof tiles, so not super heavy in other words. The slope is steep, haven't measured it but haven't seen any significant accumulation of debris on the small area.
Unfortunately, I probably need to let the roof stay, townhouse row where all the neighbors have similar roofs, but as you say, it deviates a bit from the style...
One thing to consider regarding the loads for the fastenings is what happens to the screws that hold the roof against the facade if you replace the front posts. Today, the roof is supported at four corners and then probably attached at the rear edge to the facade to prevent it from "falling out/to the side," and that fastening doesn’t need to be very strong if it only needs to stabilize the roof standing on four posts.
If you replace the front posts with braces (and the dimensions you are talking about will likely work), then the roof will stand on two posts at the inner edge, creating a significant moment around the point where the post stands. This will cause the roof to want to fall away from the facade, and it’s crucial that there are screws in the roof construction and into the house frame to hold it.
It might also be good to look at how the posts are attached at the top to the roof frame, which likely requires removing more of the ceiling to see. Today, the forces are essentially straight from above down into the post, but if you install braces, it will be different with tension/lift/pressure at various points.
I won’t even guess how that fastening needs to look, but it needs to be substantial, something I would certainly ask a structural engineer to calculate. Calculate the weight of the roof (self-weight) and snow load to see if you can find a formula to calculate the moments that occur at different points. Then maybe you can find information on how many screws are needed in a certain dimension to handle those loads.
Once you have checked if it’s even feasible to make the change, it might be time to find a structural engineer who really knows this.
One thing to consider about the loads for the fittings is what happens to the screws that hold the roof against the facade if you replace the front posts. Today, the roof is supported at four corners and then probably attached at the back to the facade to prevent it from "falling out/to the side," and that attachment doesn't need to be very strong if it's just to keep a little control over the roof standing on four posts.
If you replace the front posts with braces (and the dimensions you're talking about will probably work), the roof will stand on two posts at the inner edge, and there will be a fairly large moment around the point where the post stands. This will cause the roof to want to fall out from the facade, and it's crucial to have screws in the roof structure and into the house's frame that can withstand that. It can also be good to look at how the posts are attached at the top against the roof frame, which likely requires you to remove more of the ceiling to see. Today, the forces are essentially directly up and down in the post, but if you place braces, it will be different with tension/lift/compression at different points.
I'm not even going to guess what that attachment needs to look like, but it must be substantial, and something I would have an engineer calculate. Estimate the weight of the roof (self-weight) and snow load, and see if you can find a formula to calculate the moments at different points. Then maybe it's possible to find information on how many screws are required in a certain dimension to handle those loads.
Once you've checked if it's even feasible to make the change, it might be time to find an engineer who really knows this.
Thank you very much for the informative response; you're absolutely right, I hadn't thought all the way regarding the changed load points. Based on what you say, I think I'll try to solve a better foundation than the semi-rotted sill supporting the front posts today and maintain the original construction, which has proven to work. The original idea actually came from the fact that the front posts have sunk.
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Viktor.J said:
What type of roof do you have? There's a difference between tile/concrete and felt like in the picture. Then there's the size of the roof itself and the slope, which also affect things.