I'm building a house with a terrace above the kitchen/living room and want to know if I can put a hot tub there sometime in the future. The house supplier says "yes, it should be possible but we offer no guarantees."
Is there any way I can get an answer without hiring a structural engineer? The drawing states that the floor consists of beams measuring 45x220 and they are placed in pairs with 40 cm centers. The span is 5 meters.
How do I find out what load this can support?
Is there any way I can get an answer without hiring a structural engineer? The drawing states that the floor consists of beams measuring 45x220 and they are placed in pairs with 40 cm centers. The span is 5 meters.
How do I find out what load this can support?
What matters is how big it is and how much water there will be, a 5-meter span is quite long even if there is 45X220, doubtful if it's good, even with 40C/C there will surely be deflections, but that's my opinion, I don't calculate such things, go with thumb and forefinger, but others will surely come in and know better.
It's wobbly to walk on that terrace even without a hot tub. A joist with a span of 5 meters doesn't work with regular construction timber even if you screw the beams together in pairs. It requires glulam. What kind of house supplier is that?
A 5-meter span seems to be the max before needing to switch to glue-laminated timber, lightweight beams, or similar.J justusandersson said:
https://www.traguiden.se/konstruktion/dimensionering/barverk/barverk/balkar-och-ytbarverk/
Heij83
Stick-builder
· Västra Götaland
· 1 037 posts
Heij83
Stick-builder
- Västra Götaland
- 1,037 posts
When I built a deck to support a hot tub, I used double 195 joists at 60 cm centers and 9 concrete pillars under the tub. I may have gone a bit overboard, but a tub weighs quite a bit.
Normal tub about 400 kg
Water amount about 1000 l
People in the tub 5-6
Weight at least 2000 kg on an area of about 6 square meters.
I wouldn't have taken chances.
Normal tub about 400 kg
Water amount about 1000 l
People in the tub 5-6
Weight at least 2000 kg on an area of about 6 square meters.
I wouldn't have taken chances.
I think the wood guide expresses itself carelessly on the page you refer to. If instead you look at the page containing construction examples for floor structures, you will notice that none have a span over 3.5 meters. https://www.traguiden.se/konstrukti...uktionsvirke-i-ett-fack/?previousState=101000. If you are building a terrace floor structure with a span of 5 meters (i.e., the beams have no support in the middle), beam dimensions in the range of 70x300 mm are required, and it's difficult to obtain such sizes today.
If the 45x220 beams are paired and both glued and screwed, they effectively become a type of glued laminated beam at 90x220. Now, it doesn't specify if they are both glued and screwed together, but if done properly, they can certainly support a lot of weight. And they are laid at cc40. I am currently insulating a house frame where the manufacturer has placed 45x195 between floors glued in pairs at cc60 over a 6-meter span. Admittedly, there won't be a spa bath on the upper floor, but the intention is to furnish it with a bathroom and various other things that weigh quite a bit. And it should have an open plan under. These house modules have been manufactured for a long time, and nothing has collapsed yet.
But if you want to be extra cautious, you can reinforce by supporting it in some way.
Edit: According to the handbook (Swedish wood), a 45x220 at cc40 can handle a free length of 4.72. Then double glued 45x220 should absolutely handle five meters and carry a significant weight. So from a construction standpoint, I don't see anything wrong with it. However, as mentioned, you might want to be extra sure if placing a spa bath on top.
But if you want to be extra cautious, you can reinforce by supporting it in some way.
Edit: According to the handbook (Swedish wood), a 45x220 at cc40 can handle a free length of 4.72. Then double glued 45x220 should absolutely handle five meters and carry a significant weight. So from a construction standpoint, I don't see anything wrong with it. However, as mentioned, you might want to be extra sure if placing a spa bath on top.
Last edited:
The most limiting requirement for joists in floor frameworks is the deflection criterion. There, it is the joist's dimension, type, and span that are crucial. Reducing the c/c distance has only a limited effect on this. However, static loads can be distributed over more joists by decreasing the c/c distance. A floor framework can withstand a lot of load but still not meet the deflection criterion. Some quick comparisons (dimension and instantaneous deflection at a 5 m span): 45x220 - 5.8 mm, 90x220 (screw-glued) - 2.9 mm, glulam 90x270 - 1.3 mm.
Interesting. Where can this table be viewed?J justusandersson said:
I made the table myself just before I wrote the text. They are very simple calculations if you know a little building statics.
Why don't you want to hire a structural engineer? If it's important for you to be able to place a bathtub there in the future, then you should just make sure it's built that way. The house supplier's "yes, it should go, but we leave no guarantees" should probably be seen as the person you're talking to, at best, having no clue (i.e., a salesperson without technical knowledge).Krokkodriljo said:
Regarding a wobbly terrace, I would be more worried about the waterproofing than the wobbliness. If I understand correctly, this is the roof over the kitchen and living room. Deflection there could cause water leakage, e.g., where it connects to the rest of the house.
Would love to learn.J justusandersson said:
The formula to calculate the deflection from a point load placed at the middle of a beam is as follows: Q*L^3/48*E*I. Q=the point load, L=the span, E=the modulus of elasticity for the material in question, and I=the moment of inertia of the beam. For a rectangular beam, the moment of inertia can be calculated using the formula b*h^3/12 (b and h refer to the dimensions of the cross-sectional area). When it comes to steel beams, it is easiest to look up the value in a table. You can use any units (e.g., meters, mm, kg, kN [kilonewton]) as long as it is done consistently.
If we take the current example, a 5-meter long beam with dimensions of 45x220 mm subjected to a point load of 100 kg (0.98 kN), the calculation is as follows: First, we calculate the moment of inertia, which is 0.00003993 m4. E for C24 wood is 11000 MPa [megapascal], i.e., 11000000 kN/m2 for deformation calculations. Inserting all values, we get the following calculation: 0.98*5^3/48*11000000*0.00003993=0.0058 m, i.e., 5.8 mm. You can make it easier by entering the formula into an Excel sheet so you only need to input the span, point load, and cross-sectional dimensions.
If we take the current example, a 5-meter long beam with dimensions of 45x220 mm subjected to a point load of 100 kg (0.98 kN), the calculation is as follows: First, we calculate the moment of inertia, which is 0.00003993 m4. E for C24 wood is 11000 MPa [megapascal], i.e., 11000000 kN/m2 for deformation calculations. Inserting all values, we get the following calculation: 0.98*5^3/48*11000000*0.00003993=0.0058 m, i.e., 5.8 mm. You can make it easier by entering the formula into an Excel sheet so you only need to input the span, point load, and cross-sectional dimensions.