There are lots of reasons why customers are looking to dig down to create new space. The most typical layout we come across incorporates a combination of extra bedroom and ensuite, a utility room, plant room and an extra reception room/lounge area.
What makes basements special or grand for us would include, swimming pools, wine cellars, secret safe rooms and gun cabinets, fake live walls in the lightwells, water features, bars, saunas, media rooms, DJ stations, high ceilings (3m+), suspended staircase and bike stores. All of the above are features that we have built or designed with differing levels of difficulty and cost.
Going underground has issues, not encountered above ground, that limit ambition.
Apart from planning restrictions there are several limiting factors on how far you can dig down. Perhaps the most obvious is the increased cost of going deeper. An extra 10cm of ceiling height in a 75sqm basement costs approximately £3,500 just for the supply of reinforced concrete to form the underpins alone. Another factor is the contractor's insurance. BTL recently had to extend its policy to go down to a depth of 7m in the case of having to fit the sump pumps below an endless current pool on a project in Fulham.
Wine rooms, utility rooms, saunas, bathrooms and boilers all need extraction of various kinds to the outdoors and scope is obviously limited when the options are either to the front or back on a long house. In particular the running of these flues often requires a dropped ceiling beneath the floor above and for boilers can limit the choice of boiler available.
The difficulty of getting natural light to these underground areas becomes an advantage when creating a cinema room but puts limits on a designer when splitting the area into habitable and non-habitable space. This lack of light creates opportunities for designers to come up with clever glazed ceiling and lightwell solutions which are often adorned with plastic live walls and water features making one feel (with a bit of imagination!) outside.
Most basement require going below the existing sewers and drainage so pumps are required to bring back everything to a higher level. Normally a foul water pump and rainwater pump with back up are the basic requirements. Water features and pools take this basic requirement up a level literally.
Another limiting factor are the membranes that protect the basement from water ingress. The problem is that they must not be pierced or their integrity is compromised. This is a problem when you want to fix things to the walls of a basement that can't be supported by the typical metal stud and plasterboard that forms the walls. Special timber or steel supports are required if suspended stairs, heavy TV's, air con units, kitchen units and safes are planned for the walls.
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