The trenches of the Western Front were primarily designed to protect soldiers from enemy artillery and small arms fire while they were guarding the frontline. The most effective trenches in this regard were narrow and deep ones and so this tended to be the design used wherever possible. That said, the soil in some areas was too soft or waterlogged to allow this and in such places comparatively broader and shallow trenches had to be used instead. Most frontline trenches were not designed to be places where a soldier was expected to live for any significant length of time - in the British Army (and by extension the New Zealand Division) a rotation system was used where an infantry battalion would man the trenches for 48 hours and then be relieved by another battalion. So normally (big battles excepted) no soldier was expected to be in the trenches for more than two days at a time. Given this there was no real need to try and build 'creature comforts' such as permanent cooking, sleeping or washing facilities in the trenches. Instead these sorts of things were taken care of in camps and billets immediately behind the lines (usually just far enough back to be out of range of all but the heaviest enemy guns). Furthermore, experience early on in the war had demonstrated that cramming as many soldiers as possible in to the frontline trenches just led to greater casualties without really adding anything to the defence. So if a battalion (approximately 1000 men) could adequately defend a sector of the line there was nothing to be gained by trying to squeeze another battalion into the same trenches - this would achieve nothing other than to provide more targets for enemy snipers and artillery fire during the battalion's 48 hour 'stint' in the line.