If the exterior of our house has a cement render is it worth using a breathable paint for interior walls?
It all depends on what the interior of the house is coated in. If moisture is able to escape through the internal mortar or plaster then a breathable paint will be beneficial. If moisture is unable to escape, a breathable paint will not help this as the underlying coating is not able to breathe. However, even if the wall is non-breathable, a breathable paint can offer other benefits such as a dramatically lower chemical content, low VOCs and a more environmentally friendly wall coating.