| Unlike a lot of cellars, pavement vaults only have | | | | butyl rope or other material, which will be supplied by |
| their back wall built into the ground but they also | | | | the specialist supplier of the system. |
| have ground over their roof. Consequently most | | | | When the water reaches the bottom of the |
| water ingress occurs as percolation of rainwater | | | | membrane it is best to have an under floor channeling |
| through the brickwork at a high level, usually the | | | | system that acts a bit like a guttering system, this |
| arched roof itself. The structures have very little in | | | | will run around the whole perimeter of the vault and |
| the way of foundations and do not have the weight | | | | discharge into a sump chamber. In many cases a |
| of the house pressing down on them so they move | | | | perforated sump chamber will act as a soak-away |
| differentially to the house and are also subject to a | | | | especially if the ground is absorbant and the water |
| lot of vibration from traffic. Any attempt at using a | | | | ingress is slight - which it usually is. However the |
| rigid bonded coating to hold water back is doomed to | | | | inclusion of an automatic submersible pump in the |
| failure due to this differential movement, vibration | | | | sump chamber will add reliability in the eventuality of |
| and the inherently weak tensile strength of the | | | | a larger rate or water ingress or the ground |
| brickwork from which they are most usually | | | | becoming waterlogged itself. |
| constructed. | | | | To waterproof the floor, another similar membrane |
| The best method that will provide reliability over time | | | | can be used which will require a concrete screed or |
| is the drained cavity method, although there are | | | | board overlay. This will consume a few inches of |
| some differences between the details of a drained | | | | headroom which is often at a premium. The use of a |
| cavity system in a vault as compared with a regular | | | | plastic floor tile system can be used to provide the |
| cellar with all vertical walls that is under a house. The | | | | waterproofing and floor finish in one go thus saving |
| main difference stems from the fact that water | | | | headroom, but such systems are a little harder to |
| ingressing from the arch itself will drip onto the | | | | find. If more headroom is required the whole process |
| membrane and, if the system is installed correctly, | | | | will have to be preceded with an underpinning |
| run down on the back surface of the membrane | | | | operation which will add significantly to the cost, but |
| rather than running down the surface of the brick | | | | is non-the less a possibility. Some people consider |
| wall behind the membrane as is the case in most | | | | joining two adjacent vaults together but this is a |
| other cellar conversions. This truly tests the | | | | tricky process and will require the services of a |
| perfection of each of the sealed fixings that have to | | | | structural engineer. |
| be used to hold the membrane in place. Furthermore, | | | | As regards finishing works, the vault could be lined |
| the use of a semi-rigid membrane is necessary as is | | | | with plasterboard supported by timber battens, which |
| the presence of dimples on the membrane as this | | | | are in turn fixed into the same fixings that hold the |
| example of a drained cavity system is one in which | | | | membrane in place. Alternatively the membrane can |
| the space between the dimples is truly the means of | | | | be rendered over using a special type of plaster such |
| draining the water down. | | | | as whitewall renovating plaster. If rendering a mesh |
| Basically this membrane behaves like a big umbrella, | | | | will be required to form a key, this can be ribbed |
| shedding water to the sides and thus protecting the | | | | expanded metal lath of you can get a membrane |
| space underneath. It is normally fixed to the internal | | | | with a mesh pre-attached. |
| masonry surface with plastic fixings, a bit like over | | | | If it is a little difficult to visualize the process, there is |
| sized drawing pins and the hole where the pike of | | | | a three dimensional animated diagram of the vault |
| the pin goes through the membrane is sealed with | | | | cellar conversion process on our website. |