Excavating a basement - Perth - Cost ideas ?

[harvnicm]

Hi,

We have just finished putting together rennovation plans for our house. I got a scary phonecall from the builder suggesting the basement part has increased the cost by about 40% maybe more. :(

We live in the hills and have a double carport that we are turning into a kitchen.

We intend to excavate underneath this to put in a laundry and wine cellar/storage room. The land slopes steeply from front of the carport to the back andthe wall at the backis tall enough for laundry to have door to the outside and window. The laundry would roughly take half and cellar the front half underneath carport. This project involves demolition of carport and exising retaining walls then replacment with new retaining walls.

When we had the initial sketches of the basement we only had the laundry which went half way towards the front and no demolition was needed and the plan was to use exisiting retaining walls and only the demolition of the concrete slab in carport. The initial estimate was quite reasonable for this.

The structural bearers 3 and retaining walls (3) for basement go 500mm into the ground. The Ret walls are concrete filled with waterproof membranes etc.

Can anybody tell me what sort of cost per sq metre putting in such structurally sound basement would be ? Are we better off forgetting the cellar and going with the much simpler plan that involves less retaining wall building and will use the existing walls and retaining walls of carport with only two additional retaining walls at the back (approx halfway along carport) and down house side under carport.

[journeyman Mick]

Originally posted by harvnicm
Can anybody tell me what sort of cost per sq metre putting in such structurally sound basement would be ?

Yep, your builder, price per M2 = 40% of initial cost divided by M2 of basement. Sorry couldn't resist, this doesn't sound like the sort of job that estimating packages give M2 rates for and while your builder may have been stabbing in the dark a bit quotes like this take a long time to work out.

Mick

[Bob Willson]

Have you thought of using micro dynamite blasts to blow the dirt and rock out. I believe that this could reduce your excavation costs considerably. :) :) :) :)

[fxst]

nah miss the micro go for the big bugger .......plans for a new house to fit expanded basement cant be that dear :D
Pete

[harvnicm]

Dynamite or micro dynamite ?

Thats what we thought - but it is. We had it costed up and to rebuild to the specification let alone the addition was at least 3 times the cost we paid. Economically it is cheaper to add on.

I have a friend who is a shot firer and yes it can be done with blasting. In fact with shaped charges and the like you can do it. There arehowever issues with what might happen to the existing fundations.

Anyway, I spoke again to the builder and the quote would revert back to something more reasonable if we renounce the wine cellar..... I guess I will have to drink it quicker.

[dale]

Whatever you do, make sure you make allowance for the -inevitable- :-) desire to start digging under your house. Perhaps put a door in your laundry wall to underhouse space so that you -can- start digging (you know you just want to... :-), perhaps as well as providing piers on the internal wall (if you do it in brick) so that you can hang beams on to extend the open space underneath.

I remember an episode of Burke's Backyard which featured a guy who had dug out almost all of his underhouse space, and even extended it out into the courtyard (which remained in place!). Very, -very- dedicated to his hobby...