Hello,
I'm in the starting blocks to add another floor to our one-story house with a basement. The house was built in 1956.
According to the stamp on the original drawings, it is a Gullringshus.
I realize that I will need to bring in a structural engineer to get all the calculations right, but I've done what I can anyway
I've noticed there's a wealth of knowledge on the forum, so I'm trying to post here.
Now I'm trying to figure out how the supports for the new roof trusses should be designed.
Am I thinking correctly according to the attached sketch?
White is existing, red is planned new parts.
In the attached file, there's also a calculation for a load-bearing beam, and I'm considering using 66x315 glulam resting on 90x90 or 115x115 glulam posts (length about 2.6 m).
Additional information that might be useful:
The roof will be mansard trusses with a 70/30 degree pitch.
The reason for the question mark on the existing wall plate is because I can't see the entire thing since the small 17x45 piece is on top. This is only between the existing trusses.
The 45x45 studs on the outermost part are for additional insulation.
Grateful for all wise insights
I'm in the starting blocks to add another floor to our one-story house with a basement. The house was built in 1956.
According to the stamp on the original drawings, it is a Gullringshus.
I realize that I will need to bring in a structural engineer to get all the calculations right, but I've done what I can anyway
I've noticed there's a wealth of knowledge on the forum, so I'm trying to post here.
Now I'm trying to figure out how the supports for the new roof trusses should be designed.
Am I thinking correctly according to the attached sketch?
White is existing, red is planned new parts.
In the attached file, there's also a calculation for a load-bearing beam, and I'm considering using 66x315 glulam resting on 90x90 or 115x115 glulam posts (length about 2.6 m).
Additional information that might be useful:
The roof will be mansard trusses with a 70/30 degree pitch.
The reason for the question mark on the existing wall plate is because I can't see the entire thing since the small 17x45 piece is on top. This is only between the existing trusses.
The 45x45 studs on the outermost part are for additional insulation.
Grateful for all wise insights
Do you not have a section on the future appearance for the entire roof structure? I think it's necessary to have a complete picture if one is to contribute anything meaningful. With a mansard roof, the largest roof loads are a bit in from the outer wall. How have you planned to bring these down?
OK. Are you going to discard the old trusses (fackverk?) and install new floor joists between the ground floor and the upper floor? It might be a bit tight with their dimensions if you also need to handle a point load from the bracing wall. What were you thinking? Where did you plan to place the glulam beam?
Thanks for the quick responseJ justusandersson said:
Yes, the old rafters will be removed and new rafters will be installed.
The lower arm is intended to be kept since the ceiling is hanging on it.
The new rafters will be placed next to the existing ones.
I gladly leave the dimensioning of the rafters to the rafter manufacturer
The glulam beam is for an opening in the heart wall visible on the section.
So what I'm after is partly whether the current exterior wall can handle the loads from the new rafters. (I suspect that a spliced plank wall can handle quite high loads)
And how the support on the current wall should be designed.
Maybe a new wall plate isn't even necessary?
The roof loads on the exterior wall are small, essentially just the weight of the lower part of the roof. Snow load is not considered for roof slopes over 60°. However, new loads arise from the floor joists. I think it's a good idea to add a new and wider wall plate to the exterior wall. It also ties together the different wall layers. The new floor joists, which have a span of 3.9 meters in each section, cannot be made of standard construction timber (maximum size 45x220 mm). They cannot meet the deflection criteria, even with screwed and glued particleboard. It must be glulam, preferably 66x225 or 42x270. Even though it is a bit difficult to calculate what the plank wall can withstand since I don't know how it is bound with the stud construction, I assume it can handle the loads. The total snow loads will be somewhat lower than before and half of the floor loads from the new upper floor will rest on the central wall.
Thank you so much @justusandersson! Very much appreciated!
I've tried to incorporate what you brought forward and done some more calculations,
Existing loads on the outer walls I calculated to 13 kN/m, below I've used as calculation basis:
Roof area (27-degree slope) 108 m2
Self-weight outer roof 0.6 kN/m2
Snow load 2 kN/m2
Outer wall length 11.2 m
Total load 281 kN
Line load outer walls 13 kN/m
The new loads I've come up with are:
Self-weight floor 0.85 kN/m2 71.4 kN
Self-weight outer roof 0.9 kN/m2 155.7 kN
Residential load floor 2 kN/m2 145 kN
Snow load outer roof 2 kN/m2 186 kN
Length load-bearing walls 11.2 m
Total load 558 kN
Total load-bearing wall 243 kN
Total outer wall load 315 kN
Line load bearing wall 22 kN/m
Line load outer wall 14 kN/m
If you managed to read through the novella, I have it that the load on the outer wall increases marginally.
I also haven't calculated any weight of insulation (sawdust) and inner ceiling of the existing house.
I've tried to incorporate what you brought forward and done some more calculations,
Existing loads on the outer walls I calculated to 13 kN/m, below I've used as calculation basis:
Roof area (27-degree slope) 108 m2
Self-weight outer roof 0.6 kN/m2
Snow load 2 kN/m2
Outer wall length 11.2 m
Total load 281 kN
Line load outer walls 13 kN/m
The new loads I've come up with are:
Self-weight floor 0.85 kN/m2 71.4 kN
Self-weight outer roof 0.9 kN/m2 155.7 kN
Residential load floor 2 kN/m2 145 kN
Snow load outer roof 2 kN/m2 186 kN
Length load-bearing walls 11.2 m
Total load 558 kN
Total load-bearing wall 243 kN
Total outer wall load 315 kN
Line load bearing wall 22 kN/m
Line load outer wall 14 kN/m
If you managed to read through the novella, I have it that the load on the outer wall increases marginally.
I also haven't calculated any weight of insulation (sawdust) and inner ceiling of the existing house.
I think your calculations are very accurate. Very small differences compared to mine. The snow load, 2 kN/sqm, which you can find on Boverket's website, is the value on the ground. Then you have to consider the shape factors that depend on the roof shape and slope. In your case, it gives slightly different values. Additionally, snow load is always calculated in the horizontal plane. In a comparison like this, you can disregard that. The important thing is to note that the line load on the outer walls is largely unchanged.