Foundations within RPA

[daltontrees]

There is supposed to be a Monterrey cypress here.

 

Would you have and not mind showing details of the cantilevered construction? That could be an idea if the foundations only just go into the RPA.

 

Cheers!

 

Phew, good luck if you're going to cantilever the whole extension, that's like hanging a new building off the side of an existing one. But a cantilever of only part of the extension is possible. The engineering of cantilevered buildings is always complex. For an extension of 2.7m it could be a disproportionate expense. Depends on the construction, if it's timber the loads are light but for masonry the dead loads add up rapidly.

[Chris at eden]

Phew, good luck if you're going to cantilever the whole extension, that's like hanging a new building off the side of an existing one. But a cantilever of only part of the extension is possible. The engineering of cantilevered buildings is always complex. For an extension of 2.7m it could be a disproportionate expense. Depends on the construction, if it's timber the loads are light but for masonry the dead loads add up rapidly.

 

The one I was involved with was a whole new building. Not an extension. I still think piling is easier but I'm no engineer so I leave that to them to sort out. I remember he had a photo of a building hanging over a waterfall to show what was possible. Very grand but expensive no doubt.

[Gary Prentice]

I've no idea, what's the differences in costs between piling and traditional mass pour foundations?

[Dave177]

Generally pilings are more expensive than traditional foundations, and cantelevered buildings are even more expensive. If it doesnt enter the RPA too much you could possibly look at a floating pad ontop of the soil? What percentage of the RPA will the building take up?

Arboraeration | Tree Healthcare Experts

[kevinjohnsonmbe]

Dave, I'm not sure if I'm thinking along similar lines to Gary but I'm wondering WHY piling may be more expensive.

 

It's like a conversation I'd have had with a builder we've used before (but no more) "Don't tell me it's more expensive, tell me WHY it's more expensive...."

 

Labour, machinery, materiels for traditional = X

Labour, machinery, materiels for piling = Y

 

The difference between the 2 is?

 

From an inexperienced, non-technical perspective it might be assumed that piling could be quicker, more efficient and cheaper or does it suffer from the 'because it's non-standard it comes at a premium' or are there tangible reasons why it could be more costly?

[Paul Melarange]

Thanks Chris. Just googled Abby Pynford system and it turns out the method statement is indeed theirs.

I will ask what the architect or engineer has in mind first as I think they already had this as an option. It is for a 2.7 meter single storey extension so there should not be too many piles and as such not much digging.

 

In these situations it is important to consider the existing ground and floor levels. If the floor level of the existing property is similar to the ground level within the footprint of the proposed extension, the slab or beams will have to be higher to avoid excavation, therefore creating a step up into the extension. For some this may be acceptable, for others it may not.

 

It is also worth discussing with the architect how the ground beam or slab will be finished off or hidden on completion of the project. How many houses do you see with a concrete ground beam or slab visible just above the ground?

 

Also how close will the extension be to the crown or the tree? Will there be future pressure to prune or remove the tree due to shading or leaves in gutters?

[Gary Prentice]

Generally pilings are more expensive than traditional foundations, and cantelevered buildings are even more expensive. If it doesnt enter the RPA too much you could possibly look at a floating pad ontop of the soil? What percentage of the RPA will the building take up?

Arboraeration | Tree Healthcare Experts

 

Thanks. My question is purely academic. Kevin's post creates some interesting questions.

 

Another question that comes to mind is after building over the RPA, is there any research into rootloss due to reduced moisture levels?

[Island Lescure]

Thanks for contributing everyone. I will be going on Monday so will update once I have surveyed tree(s) and spoken to client on site.

[Dave177]

In response to your question Kevin, im not sure why it is more expensive, however to take a semi educated guess I would say that because it is non standard would be a big factor. Its very easy to dig a big square hole and fill it with concrete, much harder to plot and accurately dig 12 small holes in the correct locations. I would then suggest the added cost of the lintles, bracing etc is where the extra money goes. Although as I said this is purely conjecture as Im not a builder or architect

[Island Lescure]

Well the RPA is overlapping their plans quite a bit and it turns out it is not only an extension being built but the demolition of the existing garage, as it has no foundations really, and then rebuilding.

They are now looking at other options. One of which is a wooden structure on the other side of the garden which makes me wonder; how much could you put over an RPA before needing to lay Geoweb or similar?