You should thicken the edges of the base to a depth to suit the ground conditions. e thickness of the
concrete in the base will also depend on the soil conditions. e concrete mix design should be suitable for
a garage base – speak to your supplier and tell them what the concrete is intended for so they can provide
the correct mix. A minimum concrete thickness of 100mm (4”) is normally recommended, laid over at least
the same thickness of well compacted clean hardcore. e hardcore should be “blinded” with sand if you are
going to lay a damp proof membrane (dpm), normally 1200g polythene sheet. Steel reinforcement mesh will
further strengthen your base, your local agent or local builder will advise.
If you intend to store items in your garage once it has been built, we recommend the inclusion of a dpm.
Without the dpm there is no guarantee that damp will not spread into the building. Don’t forget that the base
will need time to “go o” or cure, before it is built on; allow at least a week, or more in winter.
e concrete base should be square. e garage is a rectangle, and needs to sit on a base about 75mm (3”)
larger all round. (In any doubt, seek advice and conrmation of the size of your building from either the
company or from your local agent.) When setting out your base, make sure that the shuttering is square. To
make sure your base is square, measure the diagonals AD and BC – they should be the same. If not, adjust
your shuttering until they are – your base will then be square.
e concrete base should be level. ere must be no slope from side to side, back to front or front to back.
If you build your concrete garage on an unlevel base, the panels may not t together properly, the roof wont
t it may be dicult to lay the necessary concrete llet, there could be a gap under the Up and Over door,
and the roof may not t properly. If the fall is to the rear, you may well get puddles forming at the back of the
garage.
e base must be higher than the surrounding area. It should stand out of the ground by at least 25mm (1”).
If not, water may stand on the base and leak under the panels.
If the ground slopes down to the base, you should ideally dig out a trench 150mm (6“) around the base,
backlling with gravel or pea shingle, aer retaining the existing ground. Don’t forget to take into account
surrounding ground levels when you position your personal door – if the ground is higher than the base, the
door will catch as you open it. Obvious when you think about it, bit late when you have built the garage! If
your concrete garage is at the bottom of a sloping drive, you need to put in a gully to take rainwater away to
a suitable drain. We can provide a timber weather bar to help prevent water getting under the Up and Over
door, but where there is a sloping driveway, a gully is essential.
So, your base should be designed to suit your local conditions. It should be strong enough, at, square and
level, higher than surrounding ground and 150mm (6”) larger than the building size (external dimension).
Finally, your concrete base should be positioned properly. Don’t forget that the Up and Over door can project
up to 1220mm (4) in front of the building when it is being opened, so position the base so that the door
doesn’t foul a wall or other building when you open it. A standard 1981mm (6’6”) Up and Over door projects
910mm (3).
Leofric Building Systems - Broadway Instruction Manual Page 5
