Building on bedrock, light straw, roofing materials, and more...

Hi all, new member and relatively new permie. I've recently been asked to build a small structure with an interior of 4m x 5m to be used as a sleeping space. This will be the first building for which I design and lead construction. The lot selected is flattish and directly on limestone bedrock. There are tons of rocks in every size around here, but not much in the way of other resources. We have very strong winds out here, 0% humidity in the summers with temperatures of up to 39°C.  I haven't been here in the winter yet, but I understand that it can get pretty cold (down to - 5°C) with up to 30cm of snow, although above freezing is much more usual.

Frankly, I'm a little at a loss in terms of where to start. I'd like to build stone walls directly on the bedrock and lay a wood floor, but am struggling with what kind of insulation to use and what to do about the roof. From what I understand, light straw may be my best insulation option,  but I'd prefer something more efficient. I prefer to design around the materials rather than trying to work against them, so I have to get these down before actually getting started.

Any and all input is appreciated!

I don't have practical experience and I'm a little rusty with theory, but when I see stone and bedrock I think thermal mass. My first thought would be to take advantage of that mass to store heat and cold. I believe that means thick stone walls with shade in the summer and solar gain in the winter.  A rocket mass heater bench as a bed would keep it toasty in winter.

Other considerations:

Is this going to be regularly occupied or is it more of a guest room?

With that low humidity, does it get pretty cool at night in the summer?

Is that wind good or bad for heating and cooling (would a windbreak be a good idea)?

Thatch roof (decent insulation but might be a bad idea with the strong winds)?

Slate roof?

If there's clay anywhere nearby, perhaps an earthen floor instead of a wooden floor? This could help with storing solar gain in winter.

Stone cottages might be a good inspiration.

Thanks Thyri. I had thought about the thermal mass aspect with a heater bench at the beginning and had nixed it as being too complicated for a first project,but you're probably right and it's at least  worth reconsidering.  

The room will have one full time occupant and some occasional volunteers passing through.

It does get chilly at night.

Not sure what impact the wind has on interior temperature, but it does make it colder at night. It generally comes from the northwest. There's a vinyard directly to the west and we need the visibility on the northern side, so no chance of a windbreak.

Haven't checked the valley yet for clay, but I may end up bringing some in -apparently it's a waste product from the water company?

Again, I'm not an expert, although I've gotten the impression that there are some instructions for rocket mass heaters out there that are pretty reliable as long as you don't try changing the design. You might want to see if you can get The Rocket Mass Heater Builder's Guide or borrow it from a library before you make your decision.

The chilly nights and wind might be good on those hot days. It might even be worth building in low/high ventilation. That is a window or vent that can be opened low and another that can be opened high to let the heat out. Then all that mass can help keep the interior cool during the day by being cooled down at night. Another thing to consider with mass is that if it gets hot or cold, for instance if it's unoccupied for a while, then it will take a while to change the temperature. In other words, if it's unoccupied and unheated for part of the winter, getting it warmed up is going to be a slow process because of all of that mass. If it's closed up and gets a lot of solar gain in the summer, it will take a while to cool down.

I'm hoping someone with actual experience will pipe in here. I like reading about this kind of thing, but it there's nothing like doing it for really understanding how things work.