Period Property Sub Floor Ventilation
Walking along the high street in Bath, doing a bit of shopping, I couldn’t help but notice this hallway “vent” in one of the properties along the high street. Actually, it’s not one of the worse I’d seen but it struck me how much effort had gone into repairing the vent, which sadly had reduced its effectiveness considerably and how much nicer it would all look with a proper grille and a lick of paint on the door. I’m often drawn to the architecture and the construction and ventilation of the ancient properties in this lovely Roman city but it’s sad to see signs of neglect that create damp within buildings that have lasting consequences. Suspended wooden floors were the main battle against damp within the rooms of properties of the Georgian, Victorian and Edwardian eras. A solid floor requires a physical barrier to prevent moisture whereas suspended floors utilise dry air flowing underneath the floor boards . This air is fed naturally by wind and flows under the house, in one side and exhausting out the other. In a double fronted house, with rooms either side of the front door, the steps leading to the door quite often have a long cast iron vent grille that is essential to the health of the property. The grille allows the equivalent of 4 or 5 air bricks of air to ingress or exhaust under the hall and permeate beneath the living rooms either side. If this is blocked or has been replaced with bricks, plywood or a single brick vent then moisture can build up under the floorboards and lead to serious problems causing the underside of the wooden boards to become saturated leading to damp, wet rot and more seriously, dry rot. The hallway grille is part of a system of sub floor ventilation linked with air bricks at the front and back and possibly the side of the property designed to keep the property habitable and ensure the longevity of the building materials supporting the ground floor. When inspecting a property with rotten floor boards or damp in the floors ensure the sub floor ventilation is clear but also ensure that it exists or hasn’t been reduced. If in doubt as to the original layout of ventilation it can be a good guide to look at other similar properties in the street and see what they have, especially the well maintained properties. An extensive inspection of the ground floor vents and lifting of a few boards to check the sub floor cavity is clear would be the first place to start. Don’t forget to check the hallway vent !