Calculating roof pitch

Slope pitch conversion, % pitch to degrees pitch can be found here.


I’m calculating a suitable roof pitch (truss roof) to allow at least 30cm of insulation to exist at the inside of the bale wall (interior) to minimise heat loss on this area of the house. The solution can be a raised heal but alternatively the slope of the roof can be formed so that insulation can be maximised.

I just read on https://www.leroymerlin.fr/v3/p/produits/tuile-imerys-toiture-rouge-romane-sans-e46534#questions-answers-details that the Romane tile can have a minimum of 15 05 degrees pitch (27%).

I’m just going to work the numbers with a 25 degree pitch to make the roof above more shallow.

tan(25)*4.45
25-degree pitch would give 2.07 metres to the eves

tan(25)*0.95
0.44 meters at the internal edge of the bale in the roof

25 degree pitch is 46.6308%

A Simple Woodburner or a Boiler Stove?

Someone in a self-build group suggested a boiler stove instead of just a burner requiring separate water heating. The oone they linked to had a heat output of 2kW with 8kW going to the water. That seems low given we’ve been told we need a 10kW stove for m2.

Cost wise they’re not much difference though. Something to consider?

This one, the Stratford EBW12, has a total output for 24kW, of which 6kW goes into the room and 11.8kW into the water.

It has a direct air supply (required by RT2012).

£1,912.00

Stratford EBW12 wood boiler stove

Trying to find out why you’d choose a water heating stove and the Centre for Alternative Technology have an article suggesting that it’s not worth it unless you have a super-duper stove such as the Broseley eVolution 26 boiler. With this you get 10kW for heating and 15.8kW for hot water heating. I can’t find a price for it though!

Floor screed


A floor screed is usually a cementitious material made from a 1:3 or 1:4.5 ratio of cement to sharp sand. It may be applied onto either a solid in-situ concrete ground floor slab or onto a precast concrete floor unit.

Source: Concrete centre

I just read that apparently you don’t use rebar in screed… don’t know why or if this is correct.

Free building advice

The following are links to free building advice from various manufacturers.

We are investigating the use of Rockwool for under the slab insulation and Rockwool provide access to scientists for advice on the usage of it in this application (and other applications) – 
https://www.rockwool.com/technical-resources/building-science-support/
(I believe Rockwool Comfortboard is known as Rocksol in Europe) 

Good information here https://www.apawood.org/buildabetterhome

Choosing the Right Type of Foundation

Slab vs. vide sanitaire? Discussion here along with info on how to layer with the moisture barrier and insulation.

https://www.ecohome.net/guides/2370/slab-on-grade-or-foundation-and-basement/

Some other useful articles here:

Tips from these pages:

  • Dig out the earth and then pack it tightly before pouring any concrete.
  • You can – if you’re crazy enough – do this without using any rebar (as if!)
  • You can literally make it up as you go along. These guys used rockwool under the slab and EPS under the footings. How does that not compress when under concrete and with the weight of the house on it. 
  • It IS important to use a Radon/vapour barrier before pour cement.
  • Remember to put the rebar over the vapour barrier!
  • Polished concrete is a good idea – but who is capable of doing this here in France?

Reaching Out

I got a message back from someone else about an hours drive away building a GREB house with a similar budget to us. They have a new baby so are pretty busy right now but are happy to be in touch so I will email him back asap.

He recommended getting in touch with the free architect, CAUE, and also with Ariege Conseil Energies Renouvenables (http://acer09.fr). I’ve seen that site before and now I have a recommendation I’ll follow up with them. I’d sent an email to the CAUE in Carca back on 10/10 so have sent a chaser message to them.