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I'm piggy-backing off another thread here which has inspired me to attempt to build a free-standing mezzanine storage in my single brick wall lock-up garage in a strata building, as a replacement for the very basic shelves left from a previous owner.
The Initial response given by JacobZ in that thread made a lot of sense to me and I've sketched out a few options based on the information provided about span tables and deck planning.
The space I have to play with at the rear of my garage has a width of 2860mm and depth of ~2600mm. The ceiling is about 2600mm, so I'd be looking at shelf heigh of ~2100mm. The mezzanine would be entirely for storage, and the total live weight of storage items would typically be 150kg - mostly consisting of camping gear and roof racks.
There is no option for a centre bearer so the joists will need to span the full width of 2860mm. I have flexibility with the length of two bearers, with the only constraint being that they must be less than 2600mm.
The garage has my car and bicycle parked next to each other - it is pretty tight as it is - so I would prefer if the posts of this structure were narrow, or at least placed in such a way that they aren't getting in the way.
I am 194cm tall so ideally the joists would be at least 1950mm off the ground so I'm not banging my head all the time.
Looking at span tables I think I have a few options:
- For joists to span that distance I would need at least 1900 x 35 mm MGP10.
- I could use 1900 x 45 mm MGP10 bearers up to 2000 mm to bear the floor width I'm planning (i.e. half of 2860mm). I would need five joists for a bearer of the full 2000mm, or I could reduce it to 1900mm and use four joists.
Correct me if any of these calculations are wrong, but this seemed relatively straight-forward bit of planning.
I have a few questions about the posts for this project.
- In the example given in the thread I linked it was suggested to use 90x90 posts. Given I want to minimise the post width, is there any reason I couldn't use non-square timber as posts for this project, for example 750 x 45mm MGP10? The height of the posts would be somewhere between 1800mm and 2000mm depending on whether joists are hanging or on top of bearers.
- Another suggestion in the previous thread was to fix the posts to the concrete using downpost anchors. One of the complications of this for me is that I would need to fix those anchors right on the edge of the concrete slab on both sides - which doesn't seem to be advised. Would it be a poor idea to leave the mezzanine free-standing, without any post anchors? Or should I at the very least attempt to fix the posts to the brickwork? The garage is fully indoors and there is no wind.
Welcome to the Bunnings Workshop community @termbornus. It's wonderful to have you join us, and many thanks for your question about creating storage.
For a free-standing mezzanine storage like you’re planning, the load you’ve described—around 150 kg—is relatively light compared with a floor or deck designed for people walking on it. That means your timber spans don’t need to be built to full floor specifications, just strong enough not to deflect under your storage load.
Your material choices are generally fine. I’d suggest using 90×45 mm MGP10 posts rather than the narrower 70×45 you mentioned. As long as these posts run from the storage platform down to the ground, they’ll carry the load adequately. At the base, you don’t strictly need heavy post anchors; simple L-brackets bolted to the concrete should suffice. If the posts are close to the slab edge, I’d use concrete anka screws instead of Dynabolts, as they’re less likely to crack the edge.
Fixing the posts to the wall every 600 mm or so will help stabilise the structure sideways, which is a good idea even in an indoor garage with no wind. For the joists, sticking with your 190×35 mm MGP10 is sensible; you could theoretically reduce to 140×45 mm, but there’s a higher chance of deflection over your 2860 mm span, so over‑engineering slightly is safer. The other option you have is to tie the middle of the structure to the concrete ceiling. So, instead of a post to the ground, you'll have a short length of timber to the ceiling bracketed in place.
In summary, your plan looks solid. Focus on making sure the joists can span the width without sagging, use 90×45 posts to carry the load down, and fix the posts lightly to the concrete and periodically to the wall for stability. That should give you a safe, functional storage mezzanine.
Please let me know if you have any questions.
Mitchell
