Basement Ideas....

PMI

Hi all, small question....

Im looking at building a house but am looking into have a basement level 1st, are there any extra rules that you know of when thinking of this?

Im really just at the beginning stage of looking and was also wondering as its underground what determines how large the lower floor could be? ie: couldnt it be larger than the footsprint of the house and re-lawned etc.. over the top?

Any ideas / help would be great

Cheers

Ed

gman2k

There are a few considerations - technical first,
Fire Safety - you need to be able to escape safely from a basement in the event of a fire, so the escape route needs to be protected from the rest of the dwelling by means of fire resisting construction.
Habitable space Requirements: You need a minimum of 2.4m from finished floor level to underside of finished ceiling to be a habitable room - one of the common fail points.
Lighting - natural lighting is hard to come by below ground, but not impossible! otherwise artificial lighting
Ventilation - usually needs permanent mechanical ventilation and humidity control.
Toilets at basement level need careful detailing and pumped solutions.
'Grade' of basement construction from wet carpark grade 1 to controlled archival storage area - grade 4. Grade 3 is usually sufficient for residential use.
Careful detailing is needed to prevent cold-bridging.
Basements are very expensive to build, as it's not simply a big hole with concrete walls and roof. You will need a good engineer with expertise in grade 3 at least, and a competent experienced contractor (which is hard at residential level in this country).
The size of the basement is up to you the owner and the designer - there is no restriction on just keeping within the building above footprint - but all will need to be planned correctly. A structural engineer should be retained at planning stage (in conjunction with your architect to advise on correct methodology, as there will be knock on effects on the rest of the design - wall widths, drainage etc. Unfortunately, there is not huge experience amongst many architects for basement construction at residential level.
I snagged a new built house (€2.7m) in a very exclusive development with a basement, and it was fubar, the architects were one of the most respected designers in the country at the time.

Mellor

It can be done. But it will cost.
For example, I'm currently involved in a addition and extension which includes an add on basement (for pool access). This extension will run to 6-7 figures

exaisle

++ to Mellor and gman2k.

I loved the idea of a basement but ultimately putting in all of the essential tanking/insulation, plumbing, electrical/lighting and safety features made the idea impractical. The inclusion of a basement affects everything above it...so that what were reasonable straightforward foundations became an engineering conundrum.
In the end, it would have cost more than the single storey building on top of it so instead, I just maximised the attic space at minimal extra cost. Perhaps a bit of lateral thought is required...lateral in an upwards direction, that is.

On the other hand, if you're the one who won the €16.7 million last week, then go ahead...

E