We are finalising the plans for our first straw bale house - a simple, rectangle with a bedroom and bathroom, the rest open plan. We are building in the centre of France. We have (finally) decided on using a shallow trench filled with stone for the foundation - if we use the perforated pipe for drainage, should we still use a plastic barrier between the stone and the straw? Any reason why we can't use the water collected for the garden? I'm planning a permaculture system so the closest plants will be flowers, herbs and the veg patch.
Our plan is to be as autonomous as possible so we are trying to build to last - any advice or suggestions, do's and don'ts would be really appreciated.

From my understanding the straw bales should be on an elevated foundation and protected from moisture, so yes a plastic barrier between the stone and bales (maybe elevated if possible).

Can you collect your rain water from the roof into a cistern?  That would keep it away from the foundation and allow you to water your garden.

From your description it sounds as if you are planning on putting the bales directly on the stone? 
Of the stone rubble foundations I have seen being used in straw bale construction there is a thin concrete cap on top of the rubble,  The rubble being used to reduce the amount of concrete required.
A vapor barrier should be used.
Substantial overhang of the roof would help moving the water from the foundation.
French tile at the drip line to harvest the water if roof gutter collection is not an option.

Apologies for not saying thank you earlier - Thank you both for your replies. We are storing all the rainwater from the roof for use in the house / garden and will be reusing all the greywater. We hadn't thought about the cement top on the foundation - we will probably do that and put a barrier between just to be sure.
Thanks again.

http://weblife.org/cob/index.html

This is a link to the Cob Builder's Handbook. I am drawing up plans right now for a similar house (just a bedroom and bathroom)... but it is likely only my north wall will be straw bale. My south wall will be cob so it can absorb the heat from the sun and slowly release it at night during the winter. Any reason you are doing all the walls straw bale and not combining with any other methods?

hey, ruthg
also am planning on building strawbale.  started digging the rubble trench foundation recently. we plan to use old discarded auto tires rammed with earth over the fabric-lined trench to set the bales on.  this will be the stemwall to keep the bales off the ground by 6 inches or so. tires will not outgas once they have been covered with earth or mud plaster.
the french drain at the bottom of the trench (at frost line) will carry off excess water that will not quickly soak into the clayish soil.

Hi Ruthg!

We just completed our first year in our straw bale house with a rubble trench foundation and so far so good!

We put a concrete beam on top of the drained rubble trench, sealed it and then built a 6"-8" "toe-up" out of wood where we ran all our wiring and then packed it with cellulose insulation. This keeps the bales off of the concrete and higher off of  the ground and kept our wiring out of the walls. Just food for thought!

Good luck and all the work is SO worth it!

hi bildeen,

i'm no means an expert but i've heard that tires leach into the earth. don't want to see you get sick down the line. worth looking into if you haven't already.

have fun building!

Sorry to keep going but I'm excited to finally be able to share my experiences with people on the same path! My neighbors were taking bets that I'd never finish or it wouldn't work, HAH!

To all of you planning or building if you haven't considered or decided on an exterior earth plaster I say go for it! We live in Vermont and just experienced the snowiest winter in ages and a super wet spring and with our overhangs (around 30") our plaster is absotootely 100% FINE. It's been hit very little by moisture and even in the driving snow/rain the one wall that got hit is totally fine, no erosion. Earth plaster is so much fun to play/work with and there is NO gloves needed and it is the least energy intensive of all the plasters.

Whatever you decide is what will be right for you and whenever you have decisions to make while in the building process my advice is to always go with what your "gut" is telling you. There were several times I listened to so called "experts" in different fields where I listened to them and REGRETTED it because they weren't familiar with straw bale building.

Have fun!