What shed base for a balcony installation?

[minklet]

I have brought a metal flat roof shed to put up on my terrace balcony. It's 9th floor, so it get some strong wind gusts, but it's against 2 walls and covered, which should make it slightly less prone. However, I'm still keen to make sure the base is heavy enough.

The shed dimensions are 2.8m width x 1.07 depth x 1.8 height

My first thoughts are to use 200x50mm sleepers laid flat in a criss cross shape (5x 3m sleepers along the length on top of maybe 6-8 1.2m sleepers) and then some marine plywood on top of that for the floor. I think this should be suitable weight at 180-200kgs?

I've read a bit around that states that base should be the same size as the shed floor to minimise water getting in. Would this be doable with just the plywood or should I cut the sleepers to size too? And would it be useful to wrap the underside and edges of the plywood with builders plastic to minimise moisture getting in, or would that make it worse by trapping vapour?

It's undercover, but it does get wet as it's southerly facing.

[JacobZ]

Hi @minklet,

Thank you for your question about installing a shed on your balcony.

Do you have some photos of the area where you are looking to install this shed? It would certainly help our members offer their best advice possible, based on your specific circumstances. 

While a timber base can be a good solution for a shed, it should still be anchored to the ground beneath, especially when it is at such a great height. The weight of the base is important, but if you experience particularly strong winds that grab hold of the shed, get up under it and lift it, then all it is doing is adding weight to a projectile.

I'm assuming the terrace balcony is made of concrete? Is that correct? Is there a reason you couldn't attach the shed directly to the concrete?

I would be much more inclined to recommend anchoring the shed directly to the concrete with DynaBolts or AnkaScrews.

Is there a reason you couldn't do this? If so, please let me know so I can assist further.

I am very wary of using a timber base without seeing the circumstances, especially considering the height.

Allow me to tag our experienced members @Nailbag and @Dave-1 for their thoughts.

Jacob

[Dave-1]

Good Evening @minklet 

This would be a yeah, nah type situation I am afraid. The ninth floor, metal shed and balcony all add up to some serious issues. I would check with your strata group to find out what is allowable but really I would be changeing from a shed to a box. A shed would be a huge sail and no matter what you fill it with/lock it down the door and roof may not be rated to handle winds at that point. 

Thats a large shed for a 9th floor balcony, how big is your balcony?

Dave

[Nailbag]

Hi @minklet is there any reason you can't fix the shed directly to the tiled over concrete balcony or is this a rental?

Regards Nailbag

[minklet]

It's not a rental, but it's a strata property so basically can't fix anything at all to the tiles as it would pierce the waterproofing underneath. 

[minklet]

Yeah I can understand the reticence I've been umming and ahhing for a long while about it. 

The balcony is massive, it's more of a terrace really. But it's also largely wasted space, and I've been putting things in this area in storage boxes for the last year but I want a place to store bikes, larger tools like a table saw, and a workbench.

I've added the shed in blue, it's pretty close to scale. With it being undercover and in the corner, the wind load should be reduced. The height of the balcony is 3m, and there are solid glass balustrades of 1.1m along the edge. 

The door and roof should be rated to these levels, I'm in the Illawarra which does get some strong winds, and we've had some grim storms, but it's still only in wind region A - I know that is made different by the altitude, but we definitely don't get cyclonic winds here. The shed is rated for Region A, Region B & Region C

[MitchellMc]

Hi @minklet,

That’s quite a significant structure to be installing on a balcony—especially on the 9th floor. Do you know roughly how much weight you expect the shed and its contents to be once installed? Balconies are generally designed to support the weight of people and light items like outdoor furniture, potted plants, or a barbecue. They’re not typically engineered to hold the concentrated load of a full timber-framed base, a shed, and the items stored inside.

Our shed suppliers would not recommend installing a metal shed on a balcony, especially of this size. Aside from the weight concerns, wind uplift on a metal shed—even one positioned between walls—can be significant, and it poses a serious safety risk if not securely anchored. Since you’ve mentioned you can’t anchor it to the balcony due to waterproofing, that risk becomes even more problematic. It's important to note that the N2 wind rating (which sheds are typically constructed to comply with) is designed for low-rise, non-cyclonic areas, typically for buildings no higher than a couple of stories. On a balcony, especially one on a higher floor, wind speeds can exceed the N2 rating, and the shed may not be suitable for the conditions at that height.

A safer and more practical option might be a smaller vertical plastic storage unit—something like the Lifetime 1.42 x 0.73m Vertical Plastic Storage Shed —which can be raised slightly on pavers to allow airflow and drainage without requiring a permanent base or fixings. 

Unfortunately, we could only go on the advice that our supplier offers for our sheds, and that would be that this is not a suitable location. Our sheds also require them to be attached to a concrete slab or a suitably constructed timber base, which is then anchored to the ground. If this is a shed you've purchased elsewhere, I would encourage you to contact the supplier to verify whether your location is suitable for their product. If it is one of our sheds, I'd be happy to reach out to the supplier for a more detailed assessment.

Please let me know if you have any questions.

Mitchell

[minklet]

Yeah I engaged an engineer about a similar request a while ago. It's supported from underneath, it's not a cantilevered balcony, the rated weight limit is minimum 200kg/m2, but actually much higher than that (not that I would want to go higher than 600kg

> poses a serious safety risk if not securely anchored

Yeah I realise that, which is why I'm looking for ways to securely anchor it, possibly to heavy sleepers, possibly also anchor the base to the walls aswell. Possibly even some ceiling to base posts! I'm keen to make this space usable. 

 Lifetime 1.42 x 0.73m Vertical Plastic Storage Shed
I feel like this would be just as likely to blow away. I know the surface area is smaller, but do these things even support anchors properly? Whenever I see them I think they feel and look very flimsy

[EricL]

Hello @minklet 

I understand that you are very keen to install this shed in your balcony, but I can only suggest the same thing my teammate has recommended and that is to get in contact with the supplier of your shed to verify whether your preferred location is suitable for their product. If it is one of our sheds, we'll be happy to contact our supplier for their recommendation.

If you need further assistance, please let us know.

Eric