Type of floor for Garage conversion

[moody_gaz 1]

Hi

I'm going to do a garage conversion in the near future and would like to use a suspended wooden floor over the original concrete garage floor which is not been DPC membraned. The span of joists from wall to wall is 3010mm but the house floor is only 240mm above the garage floor. The garage floor is one brick below DPC and the concrete is only around 3" thick over packed dolomite so I don't know if I can use sleeper walls without digging up the concrete and putting in deeper founds. Is there any easy way to do this or have I to resort to putting in a new concrete floor?

Cheers for any info given.

[verne 1]

i think this depends on what local building regs say and what you feel comfortable doing considering local conditions; water table, dampness, etc.

we moved in to our house in 1975. the house was built (and not very well) in 1864. apart from a small patch of tongue and groove the front room floor was probably original with rough cut and hewn joists and boarding adze shaped on the back.

someone had raised the level of the front garden around 18 inches above natural ground level/floor level and caused dampness in the front wall and this had caused the ends of the floor joists to rot along with some boards (also worm eaten) - hence the patch of tongued boarding. there was no damp course and yet the majority of the floor was still healthy after more than a century.

the surprise is the joists were loose laid on to a bed of sand over earth and rubble. there was no ventilation other than the gaps between the floorboards... i guess those joists had to be treated with something when they were laid but i have never heard of any wood preservatives being used as far back as that.

i imagine that if you used only treated timber and provided as much underfloor ventilation as possible your floor could easily outlast you and your children without taking any other special precautions.