I have two 95*95 posts that stand 1800 from the house, with 4000 between them. I would like to create a slanted roof (like a veranda roof) covered with roof tiles on coarse battens (around 45*45) so that the tiles are visible from underneath. I need some guidance on dimensioning and material choice. Is it sufficient with 45*220 C/K rated as top plate, or do I need to use glulam for it to hold the roof tiles and snow? Roof joists 45*170? I believe we're in snow zone 2, the house roof has a mansard roof so some snow might slide down where the entrance roof will be...
Come on, someone should dare to give me some advice, right? I shouldn’t have to "ask someone who knows"...
Come on, someone should dare to give me some advice, right? I shouldn’t have to "ask someone who knows"...
Last edited:
4 meters is quite a stretch for a single 2*9 beam. I feel, without really having a solid grasp, that it seems weak. The roof weighs quite a bit: 10 sqm * 10.7 pcs/sqm * 3.9kg (benders.se) = 417kg + the weight of the roof beams. And then there's the snow too; here the roof pitch is obviously crucial for the snow load, and an entrance roof usually doesn't have a particularly steep pitch. There are tables for this but I don’t really know where. I think you should put up another post in the middle, or does it end up right in front of the door then?
Now I have received suggestions from elsewhere for 70*195. Will probably try with that, otherwise it will simply have to be some sort of limträ.
Extra pole is out of the question.
Trying to achieve at least a 10-degree slope.
Extra pole is out of the question.
Trying to achieve at least a 10-degree slope.
A cheaper way than laminated timber is to glue-screw together two 45x195, then you have a stable beam. Good luck!
If one ventures to compare with constructions where one typically uses 45x220. It is a dimension that is quite common in intermediate floors. The beams there are often spaced at cc60. And often with a span of about 4-4.5m.
An intermediate floor in residential buildings is dimensioned to withstand a load of 200kg per sqm plus the structure's own weight. So roughly, one might assume that such a construction should withstand 230kg per sqm.
Now you have 1.8 m out from the wall, which corresponds to 3 bays in an intermediate floor. You have supports both on the wall plate and where the roof is attached to the wall.
The beam in the intermediate floor takes up load from 0.6 sqm per linear meter (30cm on both sides), your wall plate takes up load from 0.9 sqm per linear meter. That is, if your snow load plus self-weight is lower than about 150 kg per sqm, you get exactly the same loading case as in an intermediate floor (I have no idea how much snow load one should account for).
At the same time, the intermediate floor is primarily dimensioned not to bend down too much, as I understand it, there is a fairly large margin to failure. An entrance canopy should be allowed to bend down significantly more than an intermediate floor.
If it is aesthetically okay, I would probably suggest that you rather go with 225mm than go down to 195 as you had been suggested, the extra height does quite a bit for deflection. But it is clear that if it turns out you don't need to account for more than about 50kg snow load, then the slimmer beam should be okay as well.
An intermediate floor in residential buildings is dimensioned to withstand a load of 200kg per sqm plus the structure's own weight. So roughly, one might assume that such a construction should withstand 230kg per sqm.
Now you have 1.8 m out from the wall, which corresponds to 3 bays in an intermediate floor. You have supports both on the wall plate and where the roof is attached to the wall.
The beam in the intermediate floor takes up load from 0.6 sqm per linear meter (30cm on both sides), your wall plate takes up load from 0.9 sqm per linear meter. That is, if your snow load plus self-weight is lower than about 150 kg per sqm, you get exactly the same loading case as in an intermediate floor (I have no idea how much snow load one should account for).
At the same time, the intermediate floor is primarily dimensioned not to bend down too much, as I understand it, there is a fairly large margin to failure. An entrance canopy should be allowed to bend down significantly more than an intermediate floor.
If it is aesthetically okay, I would probably suggest that you rather go with 225mm than go down to 195 as you had been suggested, the extra height does quite a bit for deflection. But it is clear that if it turns out you don't need to account for more than about 50kg snow load, then the slimmer beam should be okay as well.
Thank you for the post. Nice to get some references.
The Hammarbandet will probably also be topped with a horizontal 45*195 since someone with some design influence in the project has decided that there should be round glulam posts at 1200 kr each, and these are hollow and need a cover.
The Hammarbandet will probably also be topped with a horizontal 45*195 since someone with some design influence in the project has decided that there should be round glulam posts at 1200 kr each, and these are hollow and need a cover.
I have learned that the load-bearing capacity is linear with the width and squared with the height. So 1.95*1.95 = 3.8 and 2.25*2.25=5.06, i.e., more than thirty percent stronger with a 45*225. If you don't want an unsightly high beam, you can follow the earlier advice and glue a nail together with two 45*195 or 45*170. 4 extra meters of timber don't cost that much.hempularen said:
Now there is a 45*225, but it would have looked better with 70*195... Let's see how it feels. It can always be redone if it looks ugly. That will have to be next year....
I'm a bit curious about your nice formula. Why do you divide by 6? What unit do you get out of a calculation?Krawk said:
If you're good at physics, I'd be grateful if you could elaborate on this a bit, so that at least I can convince myself that I understand...
Last edited:
The magnitude is "Elastic section modulus"
The unit is "mm^3"
http://sv.wikipedia.org/wiki/Böjmotstånd
More detailed but in English:
http://en.wikipedia.org/wiki/Section_modulus
Used to calculate the stress in elastic deformation according to:
Stress = Moment / Section modulus
The unit is "mm^3"
http://sv.wikipedia.org/wiki/Böjmotstånd
More detailed but in English:
http://en.wikipedia.org/wiki/Section_modulus
Used to calculate the stress in elastic deformation according to:
Stress = Moment / Section modulus
Thank you!