Weight capacity of wooden joists

breanting

I’m looking into buying a recording booth to put into my home studio in a first floor flat. The booths I’m looking at weigh from 611kg up to 886kg (138x175cm) and I’d like to know if my floor can take that kind of weight.

The wooden floor joists are 370cm long, 5cm thick, 15.5cm wide and 40cm apart, meaning the booth will be sitting on roughly 4 joists, and will be situated in the corner where the joists meet a supporting wall.

I have a heavy-ish large table, a sofa bed and a bunch of recording equipment in the room, and will have usually no more than three people in the room at a time.

Is there any danger at all of the floor not being able to hold all of this weight? Anyone who has experience with this kind of thing would be much appreciated.

I’ve attached a floor plan below.

jimi_man

Hi
I'd think you'd have to speak to a structural engineer for that. From memory, UK floors are designed around 150kg per square metre, however that's the sum total of my knowledge. It does seem quite heavy and I imagine you'd need to allow extra for any equipment/the artist themself, inside the booth as well, potentially adding another 100kg or so, from 886kg up to 1000kg. 

GDB2222

My gut feeling is that it will hold up easily. However, you should be able to find a table of weights that joists can take. 

A bigger issue is not so much whether it will collapse but whether it will sag a bit, and the ceiling below will crack. Or the floor will bounce around a bit with several people in the room. 

A couple of gotchas are how strong the joist hangers are that attached the joists to the wall, and whether the joists are notched at all for central heating or electrics. There’s no point calculating for a 15 cm joist if the plumber has cut a 5 cm notch in for his pipes. The joist is only as strong as the weakest part.

GDB2222

Having said that, your joists are a bit undersized, anyway. They are, in inches, 2 x 6 joists spaced at 16 inches apart. According to the table I found, the maximum span is 10 feet, whereas your span is 12 feet. 

GDB2222

https://www.rightsurvey.co.uk/floor-joist-span-tables-for-surveyors-floor-construction/

This shows the max span for your joists as 3.06m

breanting

Thanks a lot for the replies. You're right jimi_man about having someone inside the booth, it would indeed go up in weight too, so that's definitely to factor in.
My gut feeling was that it would be fine too, but then on trying to find some information online, it didn't seem as clear. The kN/m2 numbers are a little difficult to translate into kg for me.  When I was putting the floor on, there were a few very small notches in the joists, but nothing major at all. From memory, I think the joists were just resting on the bricks at each end, but I could be totally wrong. Anyway, it's slowly starting to look like it may be a little too heavy...

ComicGeek

To put it into perspective, the booth with a person in is equivalent to 4 large hot water cylinders grouped together, or 3 large baths full and occupied. Sounds far too heavy in my view across the joists, even if you can spread the weight across them - I wouldn't risk doing it. How does the booth get installed as well, as you won't be able to get it up to first floor and through doors unless it can be completely broken down and rebuilt?
Only way to know is to get a structural engineer to look at the existing joists, but they will want to view the joists themselves so the floor would need to come up.

breanting

Thanks ComicGeek. The booth comes in either panels that are joined together or brick-like panels, so they can be fully broken down for transportation. Studiobricks and WhisperRoom are two companies that make them. The people selling the booth said they think the weight would be okay but can't take responsibility for any damages of course. It may be best to get professional help just to make sure. Luckily there's a section of my loft I have access to which has the same joists as the floor.

Rosa_Damascena

Have you permission from the freeholder / management company? I sure as heck wouldn't want to live in the floorspace above or below you!

breanting

Thank you for your comment Rosa_Damascena. Yes, I do indeed have permission. This booth is also to partly to ensure that everyone else living nearby is 100% happy, that's why it's so heavy!

weeg

50x150 joists at 3.75m will take a load of 1.75kN/m2 (as per the load tables in the Structural Engineers pocket book, which I have to hand). Which is 175kg/m2, and allows for the weight of the floor construction as well as an imposed load, which in domestic houses is indeed 150kg/m2. Your booth (without a person inside) is 382kg/m2. Ok, it's against the wall which is in your favour, but it's still more than double the design imposed load.
You need someone to actually run the numbers on this, but in my professional opinion, the answer is no. Especially as it's a flat. The joists are already pretty much at the acceptable limit for span. This boothis going to cause, at a minimum, unacceptable deflection and crack the ceiling downstairs, in all probability. I think you are looking at doubling up the joists locally, but you need a local structural engineer.