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How to set up under-house storage with raised timber floor over soil?

Ben_G

I'm planning to convert the space under my house into storage. There's about 1.25m of headroom across roughly 5 sqm. My idea is to build a slightly raised timber floor on a joist/bearer subframe sitting on the soil, to keep stored items up off the ground.

A few details: the ground is soil over clay, and there's good existing sub-floor ventilation that I don't intend to block or reduce. I'd mainly be storing things in sealed tubs (seasonal gear, that sort of thing) rather than anything moisture-sensitive.

Does this approach seem reasonable? In particular I'd like advice on:

whether I should lay a vapour barrier (polyethylene sheeting) over the soil first to manage ground moisture from the clay
the best way to support the timber frame on soil without it sinking or sitting in damp
anything I should do to keep termites and damp in check
whether there's anything structural I need to watch (footings, stumps, clearances)

Or should I install a concrete base?

Any tips from people who've done similar would be appreciated.

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Accepted answers

EricL

Hello @Ben_G

Welcome to the Bunnings workshop community. It's sensational to have you join us, and thanks for sharing your question about under house storage.

Placing a vapor barrier is a great idea as it prevents rising moisture from the soil to condensate under your timber flooring. This also applies to a concrete slab if you are putting one in. You can use a combination of a https://www.bunnings.com.au/builders-edge-35-60mm-smallfoot-pedestal-feet_p2450074 along with a Brighton Masonry 300 x 300 x 40mm Charcoal Mypave 334 Paver. This prevents direct soil contact with your timber frame and flooring.

On the condition that there is no residual water flowing through the area, your layout idea is very sound. I'm a firm believer in over engineering things and therefore would suggest adding a powered ventilation fan for active air movement. I also recommend adding a Wi-Fi controller to the fan so that you can have it turn on and off when necessary. Termites love warm damp spaces so keeping the area dry is one way to keep them away.

I'm a fan of both timber and concrete base flooring. From a long-term perspective, the concrete slab would probably provide a longer service life.

Here are some handy step-by-step guides:

Let me call on our experienced members @Dave-1, @Nailbag, @TedBear and @JoeAzza for their recommendations.

If you need further assistance, please let us know.

Eric

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EricL

Hello @Ben_G

Welcome to the Bunnings workshop community. It's sensational to have you join us, and thanks for sharing your question about under house storage.

I'm a fan of both timber and concrete base flooring. From a long-term perspective, the concrete slab would probably provide a longer service life.

Here are some handy step-by-step guides:

Let me call on our experienced members @Dave-1, @Nailbag, @TedBear and @JoeAzza for their recommendations.

If you need further assistance, please let us know.

Eric

Dave-1

Good Afternoon @Ben_G

I like the idea of pavers for the ground instead of timber, less chance of moisture issues and creates a nice solid base to work with.

That said, if your soil under the house stays dry always then Id go the route of chocs (bricks) with timber rails sitting on them on which you place your sealed containers. I have found that once we put things away under the house, they stay there for a Loooong time :) Maybe pave the pathways (Just rest the pavers on smooth soil and tamp them with a mallet) and go for the slightly raised rails to keep the containers off the ground.

Dave

Nailbag

Hi @Ben_G

For this project, I would keep it simple and effective. Constructing essentially a low-lying deck is over-kill. Especially with the added complication of a clay base which is a moving sub-structure between the seasons. And similar reasoning for not pouring a concrete slab.

Some manual labour in clearing a relatively level ground would be the first step. Then laying down a crushed rock road-base and doing your best within the limited height to compact this down. Add 50mm of washed sand and screed this level. Now you're ready to lay 450mm x 450mm x 50mm pavers to finalise a solid base ready for your storage tubs.

Unless the area is subject to extreme dampness, I don't see the need to install an expensive automated air-flow system and as it's a masonry build you have a termite-free environment.

Nailbag

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