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Hi all,
I'm hoping to get some advice/info in regards to subfloor structure to support an elevated 'room within a room' idea I'm considering.
We've got a 70's/80's addon room at the back of the house, that's a bit of a walkway/sunroom, a landing about 1.4m high and stairs down to a tiled floor and our back door. There's a lot of wasted vertical space (roof is 4-4.2m high) that I'm looking to take advantage of, essentially I'm looking to build a 2nd toilet/laundry room over the steps, at the same level as the landing, add some new stairs to get down to the back door, and have a bit of storage space underneath the new room/stairs. Eventually we'll knock out the back room and extend the house and the couple of quotes we've gotten so far are quite a bit more than we were hoping to spend on something that'll probably be pulled down in next 3-5 years, so I'm looking at the feasibility of doing as much of this myself as possible.
I'm comfortable with building/lining the 'box' itself and getting a plumber/electrician in, but the bit I'm not sure about is the subfloor structure for the new room when it's going to be as much as ~1.4m high. Bearers will be in part rest on the existing concrete steps and can be anchored into the existing brick walls, but what sort of piers/posts would I potentially need to consider - my mind goes to decks I've built and thinks well it's just a much higher raised deck, chuck a bunch of 100mm timber posts in with lots of bracing and that'll do, but once you consider the washer/dryer/toiler/timber frame/ceiling/lining etc I wonder if timber posts would be insufficient at 1.4m. Then on the flipside I think brick piers like under the house might be overkill for a 3m x 2m timber framed internal room - it's not supporting a tile room and a whole house worth of 'stuff'. I've seen those Hebel load bearing panels or blocks, would something like that potentially be suitable and less hassle than trying to do some bricklaying for the first time if timber posts are a definite no go.
Happy to be pointed in the right direction from the experts here.
Welcome to the Bunnings Workshop community @benholmes. It's terrific to have you join us, and many thanks for your question about flooring.
I don’t see any reason why you couldn’t use timber posts to support your structure. As long as you have enough posts to adequately distribute the load across the bearers and joists, timber can work well for an elevated internal room like this.
Since you’ll have the weight of the washer, dryer, toilet, and timber framing to consider, it’s important to follow standard load-bearing guidelines. Using 100mm timber posts with proper bracing and securing them to concrete footings should provide sufficient support.
If you’re concerned about stability at that height, you can add cross-bracing between the posts to reduce lateral movement. Treated pine rated for structural use would be suitable here, and using stirrups embedded in or attached to concrete will help prevent movement over time.
While brick piers would certainly provide robust support, they’re probably overkill for a structure of this size. Hebel blocks could be an option if you want a simpler installation, but they might add unnecessary complexity compared to timber posts.
It might be worth consulting with a structural engineer to confirm your project's span and post requirements.
Please let me know if you have any questions.
Mitchell
