Upper Floor Garage Gym 1

[MegaStructures]

Hello,

I am a licensed structural engineer specializing in steel and reinforced concrete, but my question is related to wood framing.

I have a friend building a residential home (CMU walls and wood-framed floors) who asked my opinion on placing a home gym on the second floor. I don't plan on stamping drawings or interjecting in the design process, but the topic got me thinking about how I'd approach the design myself.

Loading:
The plan is to frame the floor with engineered joists and a plywood subfloor. The EOR has stated that the equipment type and location must be known before designing the floor. While I agree it's ideal to know exact point loads, it’s unrealistic to assume the owner (or future owners) won’t move or add equipment. Instead, I think a more practical approach would be designing the entire gym floor for an increased live load (125-150 psf) and ensuring the subfloor can withstand a 2,000 lb. point load at any location.

Structural System Selection:
From reviewing the plans, it seems feasible to meet these loading demands using a wood joist system with joists at 16" o.c. and two layers of 3/4" plywood subfloor, fully glued and screwed. I would also recommend a thick rubber floor covering above the subfloor to absorb sound, vibration, and impact. My quick back-of-the-napkin calculations suggest that the plywood would be sufficient for both distributed and concentrated loads in terms of strength and serviceability.

Question:
For those with experience designing similar systems, I’d appreciate your insight on the following:

1. Does the assumed loading sound reasonable? I’ve seen 100 psf commonly cited for gymnasiums, but I aimed for conservatism with 125 psf.
2. Does the proposed structural system seem sufficient for this application, or have you used a more suitable system in the past?

 

[XR250]

What does "home gym" mean to this guy?
An eliptical and a few yoga mats or is he doing 300 lbs free weight clean and jerks?

 

[milkshakelake]

1. I designed a slab for a commercial gym with concrete slab. Live load was 125 psf. Home gym for a family, with 1 or 2 jacked people and some kids? I'm skeptical it will ever see that load, and I'm willing to bet that 100 psf is more than enough.
2. If the joists can support the load based on NDS calculation, it sounds reasonable to me. You might also want to calculate a concentrated load of assumed number of plates on a rack. I don't know what that will be; it depends on the user. But 2000 lbs sounds...insane. Your buddy has to be Arnold Schwarzenegger or Larry Wheels for that to take effect. It's a good number if you want to be conservative. There are some rare exercises where you drop weights from high places but those need a special platform designed to absorb the impact.

Based on my experience, gyms need more blocking/bridging than usual framing. But that's for a commercial crossfit or aerobics gym. For a single family, it should be fine. I also do recommend a gym floor mat as you mentioned; I use it in my own home gym. It protects the subfloor. There should also be some consideration for noise beyond the mat, though the mat is the best way to reduce it at the source. It might involve two layers of fire code gypsum board on the ceiling below, plus resilient channels, and maybe some acoustic foam between the joists, and acoustic sealant to glue the two layers of gypsum together, but all that is $.

 

[XR250]

Even 40 PSF is fine for most "home gyms" in my experience.

 

[MegaStructures]

Thanks for the comments. In this case, a home gym refers to free weights used primarily for powerlifting (squat, bench, and deadlift), with the potential for dropping a bar from a standing deadlift. While they won’t be lifting 2,000 lbs, using reasonable assumptions for stopping time, a 500 lb drop could generate peak forces exceeding 2,000 lbs, depending on flooring and damping.

This is outside my typical design scope, so I’m unsure how liability would be handled if the floor were designed assuming no dropped weights, yet someone later decided to conduct their own "dynamic load test." In an industrial setting, I could mitigate risk with placarding and operational controls, but in a residential setting, there's no way to control how the space is used once designated a home gym. So, who bears responsibility when an Olympic plate ends up poking through the ceiling below?

 

[XR250]

Seems like a bad idea. Might have to put some steel plates down in certain areas but 2 layers of 3/4" is pretty tough. 100 PSF for sure.

 

[milkshakelake]

If you want to account for that eventuality, then yes, you'd have to design it for that level of concentrated force. There's a reason why we do commercial gyms with concrete, and run 1/4" steel plates on top, and still use a platform for the clean and jerk stuff on top of that. However, the heavily designed joists and floor come with significant cost, like double to triple what a homeowner is expecting. The way I'd handle it is to have a conversation with the owner and explain the outlier cases to them, which can cause real damage, and they should know the cost implications. You're right that it's not feasible to ensure that nobody will drop such a weight, or to have placards in a home gym.

Based on that, I'd sign a contract where it's clear what you're designing for. It should also be noted on the drawings. If you don't do this, you're going to have a very expensive design and an unhappy client. Or if you design unconservatively, you'll have real life results of a dynamic load test and you get sued, and you don't have a contract to protect you.

 

[XR250]

If you want to account for that eventuality, then yes, you'd have to design it for that level of concentrated force. There's a reason why we do commercial gyms with concrete, and run 1/4" steel plates on top. However, the heavily designed joists and floor come with significant cost, like double to triple what a homeowner is expecting. The way I'd handle it is to have a conversation with the owner and explain the outlier cases to them, which can cause real damage, and they should know the cost implications. You're right that it's not feasible to ensure that nobody will drop such a weight, or to have placards in a home gym.

Based on that, I'd sign a contract where it's clear what you're designing for. It should also be noted on the drawings. If you don't do this, you're going to have a very expensive design and an unhappy client. Or if you design unconservatively, you'll have real life results of a dynamic load test and you get sued, and you don't have a contract to protect you.

Honestly, with all that, it is likely not worth the fee.

 

[milkshakelake]

Honestly, with all that, it is likely not worth the fee.

It could be worth it. You just have a conversation, agree on the loading (as best as you can explain to a layperson), and move forward.

 

[XR250]

Risk-Reward would not be there for me. Good luck in court proving that the loading was exceeded.

 

[jerseyshore]

Based on my experience, gyms need more blocking/bridging than usual framing. But that's for a commercial crossfit or aerobics gym. For a single family, it should be fine. I also do recommend a gym floor mat as you mentioned; I use it in my own home gym. It protects the subfloor. There should also be some consideration for noise beyond the mat, though the mat is the best way to reduce it at the source. It might involve two layers of fire code gypsum board on the ceiling below, plus resilient channels, and maybe some acoustic foam between the joists, and acoustic sealant to glue the two layers of gypsum together, but all that is $.

This right here. We've done a lot of gyms, including a home gym above a garage very recently.

The floor mat is the most important part. Blocking, bridging, anything else that distributes loading but most importantly vibration. There is only so much you can do with wood framing and impact type loads. You drop two dumbbells you're going to feel it.

 

[milkshakelake]

Risk-Reward would not be there for me. Good luck in court proving that the loading was exceeded.

This is getting off topic a bit. But I find that I'm on the other side of this compared to most engineers. I've taken risks and it usually pays off. When something goes wrong, I've always been able to negotiate with the client or explain the situation. Never had a lawsuit yet. When there's threat of one, I talk it out. I think I have yet to get that really nasty client that will sue at the drop of a dime.

 

[XR250]

I've taken risks and it usually pays off.

For me, maybe if it is a good, repeat customer with tons of billings. For a rando homeowner - hard pass unless I could negotiate a huge fee for the risk.

 

[Eng16080]

I might consider using LVL floor joists instead of I-joists as the latter is prone to vibration issues even under normal conditions. Certainly use lots of blocking/bridging either way.

Dropping a loaded barbell on a wood floor seems like a bad idea. The whole structure will shake from that. Maybe it's not a big deal, though, if it's above the garage. For crossfit level stuff where people and weights are being thrown around recklessly, I think I'd want a concrete slab instead.

 

[XR250]

I might consider using LVL floor joists instead of I-joists as the latter is prone to vibration issues even under normal conditions. Certainly use lots of blocking/bridging either way.

I am not sure i-joists would even hold up to this abuse.

 

[MegaStructures]

This right here. We've done a lot of gyms, including a home gym above a garage very recently.

The floor mat is the most important part. Blocking, bridging, anything else that distributes loading but most importantly vibration. There is only so much you can do with wood framing and impact type loads. You drop two dumbbells you're going to feel it.

What structural system did you use for the home gym you did above the garage?

 

[GaStruct]

I would throw commercial loading criteria per ASCE at this based on the power lifting intended use you described. The load could end up being a lot. Maybe he invites all his buddies over who can also throw around a lot of weight and they all dead lift at the same time. You also need to think about storing all the weights on a plate tree and how that load gets distributed. Maybe there is a dumbbell rack and maybe later on they move it to be parallel with a joist.....I could go on.

I see a lot of potential for overstress and localized failures so I wouldn't try to reduce loads to save money on framing. They can always put the gym on the basement slab to cut costs.

 

[MegaStructures]

Thank you, everyone, for contributing. It was fun to consider this scenario, and I think we reached a general consensus that the entire gym area would need to be designed for significantly elevated loading (whether that's 100 psf, 125 psf, or more) as well as concentrated loads from dropping weights. A high-quality rubber floor, additional blocking, and increased insulation would also be necessary to reduce noise transmission to the floor below.

Given these factors, the cost of the floor framing would be at least double that of a typical room, and even with these reinforcements, noise would still be a concern. For this particular project, I recommended placing the gym on the ground floor, as it simplifies the structural design and eliminates these challenges. The recommendation was well received.

It's too easy to handle thse weights with a slab on grade - no fancy engineering types needed

 

[milkshakelake]

Good call @MegaStructures . I have my home gym on a slab on grade, and it costed no more than a slab on grade should.

 

[jerseyshore]

What structural system did you use for the home gym you did above the garage?

We did TJI's with steel beams around the perimeter. Designed it for 100 psf I believe. Framing just wrapped up so looking forward to seeing the finished product.

But can't go wrong with a gym on the SOG vs elevated structure. Vibrations are always going to be a challenge when a gym is on a raised level.