I have a 12 x 12 cellar which isn't wet and has never flooded in the 9 years we've lived here, but as all old cellars are a bit moist, I'd like to line it and add ventilation before I move a metalworking workshop in, consisting of a lathe, a mill, bandsaw, media blasting tank and many hand and power tools, all no doubt prone to rust in damp air! The cellar stays between aroun 15 - 18 C regardless of the ambient temperature, so it is much prefereable to my current workshop (garage) which varies between about 5 degrees lower than ambient in the winter, and 300 degrees higher than ambient when the sun's on it!
The cellar is typical of a mid 1800's type. Double brick walls, no cavity, with around the upper 2ft of wall being above ground (the house is built on a slope at the foot of the Malvern hills). The existing floor is red brick, laid on their side so taking around 4" of height. There is an old wooden exterior door and a small cast iron window at head height. I plan to replace both of these during the update, perhaps with a small extractor fan in the window / vents in the door to allow airflow. As the house is on a gentle hillside, there is already a drain in the corner of the cellar which exhausts into the main drain going down hill from the property, even though as I say there is never any sign of puddles.
The route I am leaning to following is a membrane liner (the dimpled type which allows air movement) and a concrete screed floor.
I plan to take up the loose brick floor before screed / membrane, but obviously the membrane needs to sit on a hard surface. So my first question to the experienced folk here is -
Do I put down a thin screed (say an inch?) in order to give the membrane a hard surface to sit on, and then another screed on top of the membrane? Currently, the drain is below the level of the brick floor so I can leave the edge of the membrane open around that point for airflow.
As this will be a workshop rather than for habitation, I'm assuming that regs are not required?