Thinking of a basement, water table info?

pauldavis123

Is water table depth information collected by any agency in Ireland, is there maps or logs that can be referenced?

Thanks,

kieran.

Not that I know of as it would be very much site specific. You'll need to dig a hole and monitor it and then adjust it for seasonal factors.

No matter what the water table level is I would be tanking from base level right up to ground floor finished floor level anyway.

murphaph

pauldavis123 wrote: »

Is water table depth information collected by any agency in Ireland, is there maps or logs that can be referenced?

Thanks,

We built a cellar here in Germany and even though there is fairly good info about general levels, no builder will go near you unless you've done a site investigation and this includes details on the actual water table level on your site. Our report noted that the level was 2.65m below the surface when measured in September but also stated that it is at its highest around March. We ended up getting a second investigation done after we changed our minds about the position of the house on the site and it was done in March and the level was at 2.2m below ground.

We had to go for a waterproof cellar obviously given the very high water table.

pauldavis123

https://www.engineersireland.ie/EngineersIreland/media/SiteMedia/groups/societies/geotechnical/Soils-of-Dublin.pdf?ext=.pdf

Page 20 here shows bedrock, there must be something for watertable!

The bedrock info seems a bit weird, as if it pops out of the ground. Is it not the ground ;-)

Johnnyhpipe

You can still have a basement with a high water table.

If you're serious about it then you need a geotechnical investigation including boreholes with standpipes.

Suggest you get prelim costs for basement construction first... Generally works out at over 3xcost of normal build, so you could be in the order of 6k per sq m in my experience.

murphaph

I think basements are a niche/luxury item in Ireland right? We paid 60k for our 100m² waterproof (not tanked, the actual concrete the thing is made of is waterproof) prefabricated one. That was including 5 triple glazed windows, the internal plasterwork, a reinforced concrete stairs, all earth works and disposal of excess top soil, chasing walls for services, core bores for services. It did not include the floor or floor insulation.

Most people around Berlin don't build cellars any more because of the water table and the added cost of waterproofing but it is only around 10k more than a non waterproof one and you gain 50% more area and it doesn't cost 50% more to build.

Johnnyhpipe

murphaph wrote: »

I think basements are a niche/luxury item in Ireland right? We paid 60k for our 100m² waterproof (not tanked, the actual concrete the thing is made of is waterproof) prefabricated one. That was including 5 triple glazed windows, the internal plasterwork, a reinforced concrete stairs, all earth works and disposal of excess top soil, chasing walls for services, core bores for services. It did not include the floor or floor insulation.

Most people around Berlin don't build cellars any more because of the water table and the added cost of waterproofing but it is only around 10k more than a non waterproof one and you gain 50% more area and it doesn't cost 50% more to build.

€600 per sq m for a basement????????

murphaph

Johnnyhpipe wrote: »

€600 per sq m for a basement????????

Ah a bit more. I rounded off both ways. 95m² for 62k.

But it was a simple rectangular basement with a cantilever in the ground floor slab to go under the bay window. Our house is rectangular.

Johnnyhpipe

murphaph wrote: »

Ah a bit more. I rounded off both ways. 95m² for 62k.

But it was a simple rectangular basement with a cantilever in the ground floor slab to go under the bay window. Our house is rectangular.

Still...I would have expected an axtra zero on the end of that! Then again I'm thinking of secant piles etc which I guess you didn't need. Still seems extremely cheap considering earthworks etc.

pauldavis123

The reason the water table is an issue is if i need secant or contiguous piles.

Secant is basically the dearest option out there and needed if the water table is above the foundation.

murphaph

Johnnyhpipe wrote: »

Still...I would have expected an axtra zero on the end of that! Then again I'm thinking of secant piles etc which I guess you didn't need. Still seems extremely cheap considering earthworks etc.

I suppose it's a matter of competition. Cellars are common enough creatures in Germany, especially down south, maybe not so much up here in recent years.

I should state that we built what they call a "high cellar" so you have 5 steps up to your front door. This is quite traditional around here due to groundwater levels. We went for this because it enabled us to put our windows in above ground level to maximise natural light as the cellar is living space. This obviously saves some excavation and you don't need waterproof light wells around the windows.

Our cellar has a poured raft foundation and sandwich Prefabricated exterior wall panels (they are cast off site and poured waterproof concrete goes in between the inner and outer skins to form one solid box) and prefabricated ground floor panels again all bound together with poured concrete on site. Because the structure itself is waterproof, we don't need to worry about draining water away from the outside surfaces. It would float if put in a lake.

PMBC

pauldavis123 wrote: »

Is water table depth information collected by any agency in Ireland, is there maps or logs that can be referenced?

Thanks,

Geological Survey Ireland, GSI, collect information on water table levels from boreholes afaia. I think its more rural related as well drilling is not that evident in Dublin. Anyway its worth a try.

Johnnyhpipe

pauldavis123 wrote: »

The reason the water table is an issue is if i need secant or contiguous piles.

Secant is basically the dearest option out there and needed if the water table is above the foundation.

Is this for the 5 storey inner city site mentioned in your other thread?

5T3PH3N

pauldavis123 wrote: »

The reason the water table is an issue is if i need secant or contiguous piles.

Secant is basically the dearest option out there and needed if the water table is above the foundation.

What are you building on top of the basement?
If it's a normal house just spec the basement structure to carry the weight of the house.
We usually did basement walls 440mm in this case with internal walls 215mm to carry the precast or in situ slab. Tanked externally.
The only piling we ever had to get was sheet piling solely for shoring when necessary.

5T3PH3N

murphaph wrote: »

I think basements are a niche/luxury item in Ireland

Yeah, i only ever did them around the most affluent areas really.

hexosan

I priced my basement originally with a well known Dublin based company who specialised in basement construction 3 yrs ago when the bubble had well and truely burst (someone clearly hadn't made them aware) they came back with a quote of €160k for a square concrete box tanked. He was then really sound and informed me how lucky I was this wasn't a few years ago when they'd of been asking well over €200k. He Rang back twice wanting to know if I was going ahead with them. Got a giggle out of both those calls.

Needless to say I built for a faction of his price. I will say basements are expensive when you factor in everything. Almost no one has a clue about them, architect, engineer, builders. Be prepared to be on your own doing all the research.

hexosan

P.S the shuttering is not a job for the fella with a few panels that fires up slatted tanks for local farmers.

Sika have some good products, both admixtures for concrete and tanking products with long (20yrs it you use two products) guarantees. Make sure and step the joint between the raft and walls & install a water bar. Tank from the base of the raft slab up the shuttered walls. Install French draining around the basement piped away to your drainage area or into a storage tank to be pumped to the surface if natural drainage isn't an option.

Johnnyhpipe

hexosan wrote: »

I priced my basement originally with a well known Dublin based company who specialised in basement construction 3 yrs ago when the bubble had well and truely burst (someone clearly hadn't made them aware) they came back with a quote of €160k for a square concrete box tanked. He was then really sound and informed me how lucky I was this wasn't a few years ago when they'd of been asking well over €200k. He Rang back twice wanting to know if I was going ahead with them. Got a giggle out of both those calls.

Needless to say I built for a faction of his price. I will say basements are expensive when you factor in everything. Almost no one has a clue about them, architect, engineer, builders. Be prepared to be on your own doing all the research.

...that sounds very worrying that your engineer had no clue about basements..

Such a generic statement sounds foolish. I've designed many single storey and multi storey basements over the years and the design/construction team had full knowledge of basement construction.

hexosan

Johnnyhpipe wrote: »

...that sounds very worrying that your engineer had no clue about basements..

Such a generic statement sounds foolish. I've designed many single storey and multi storey basements over the years and the design/construction team had full knowledge of basement construction.

Just because you know doesn't mean everyone else does.

There are plenty of archs & engineers that phone in there preformance on builds you only have to look at the quality of what was built in the last 10/15 yrs.

I've corrected more than one glaring error made by my "professionals"

I'm not saying all archs and engineers are bad but making generic statements that all know what their doing sounds foolish.

murphaph

Over here it's common for a firm to specialise in below ground or above ground construction. My cellar man is a Tiefbauer. He only builds cellars, roads, pipes etc.

We were very pleased with our concrete box in the end. It was within 1cm tolerance which was important because the timber frame house that went on top of it was built to mm accuracy as it was prefabricated in a factory so making little adjustments is tricky.

Over here the trend is towards waterproof concrete rather than applying tanking. If you get a leak in a waterproof concrete wall then it's reasonably trivial to exactly locate it and inject resin from inside the building. If your outside tanking fails the water can come into the cellar somewhere 10 feet away from the failure point. You have to excavate and painstakingly look for the failure from outside. There is very little cost difference here between the 2 methods but the waterproof concrete solution needs experience by the lads building it or a leak is guaranteed. They have to be very careful with the additives. So far our cellar is bone dry, touch wood, and we've come through a winter and spring with it.

With a truly waterproof cellar you don't need and special drainage to divert water away from it. Given land prices in Ireland it's a bit strange that cellars aren't more popular, at least in urban areas. Just not enough companies doing them I reckon.

murphaph

hexosan wrote: »

I'm not saying all archs and engineers are bad but making generic statements that all know what their doing sounds foolish.

Same over here. Our architect had very little experience with cellars because he is responsible for northern Germany, where they are less common these days. He had to ask his colleagues who deal with Bavaria etc. to help him as they build them all the time down there.

My tip for anyone building a cellar...make sure you have a vertical services shaft from the utility room all the way up to the attic. Very handy for future cable pulling.

pauldavis123

Great basement info here, not much water table info though ;-P

pauldavis123

Johnnyhpipe wrote: »

Is this for the 5 storey inner city site mentioned in your other thread?

Well spotted, 330m site.

Double basement would add a lot to the building!

Markcheese

hexosan wrote:

P.S the shuttering is not a job for the fella with a few panels that fires up slatted tanks for local farmers.

I'm gonna sound a bit of a dope here but whats the difference between a (properly designed and built) ,slatted tank and a basement..

onrail

For a 5-Storey development, incorporating secant or contiguous bored piles you're really going to need a formal ground investigation anyway - say 1 - 2 boreholes to adequate depth below the deepest pile.

As part of this GI, it would be straightforward to install a standpipe and monitor groundwater levels for as long as possible.

It might be worth consulting the GSI borehole database to see if any GI has been carried out in close proximity to your site - generic reports are close to useless.

hexosan

murphaph wrote: »

Over here it's common for a firm to specialise in below ground or above ground construction. My cellar man is a Tiefbauer. He only builds cellars, roads, pipes etc.

We were very pleased with our concrete box in the end. It was within 1cm tolerance which was important because the timber frame house that went on top of it was built to mm accuracy as it was prefabricated in a factory so making little adjustments is tricky.

Over here the trend is towards waterproof concrete rather than applying tanking. If you get a leak in a waterproof concrete wall then it's reasonably trivial to exactly locate it and inject resin from inside the building. If your outside tanking fails the water can come into the cellar somewhere 10 feet away from the failure point. You have to excavate and painstakingly look for the failure from outside. There is very little cost difference here between the 2 methods but the waterproof concrete solution needs experience by the lads building it or a leak is guaranteed. They have to be very careful with the additives. So far our cellar is bone dry, touch wood, and we've come through a winter and spring with it.

With a truly waterproof cellar you don't need and special drainage to divert water away from it. Given land prices in Ireland it's a bit strange that cellars aren't more popular, at least in urban areas. Just not enough companies doing them I reckon.

I used a waterproof admix and fully tanked the raft base & walls. The single biggest threat to a basement leaking is hydrostatic pressure. If you can prevent the water pressure building up around the basement the chances of it ever leaking are slim.

hexosan

Markcheese wrote: »

I'm gonna sound a bit of a dope here but whats the difference between a (properly designed and built) ,slatted tank and a basement..

Theyre rarely properly designed around my way.

Plus it's easier to design something to hold water in than hold out water.

murphaph

hexosan wrote: »

I used a waterproof admix and fully tanked the raft base & walls. The single biggest threat to a basement leaking is hydrostatic pressure. If you can prevent the water pressure building up around the basement the chances of it ever leaking are slim.

Our groundwater is above the raft in spring so we can't keep the water away anyway with any kind of drainage. We had to build in September when the groundwater was 45cm lower so as to avoid having to pump out during construction €€€€. It was that tight with us!

PMBC

hexosan wrote: »

I priced my basement originally with a well known Dublin based company who specialised in basement construction 3 yrs ago when the bubble had well and truely burst (someone clearly hadn't made them aware) they came back with a quote of €160k for a square concrete box tanked. He was then really sound and informed me how lucky I was this wasn't a few years ago when they'd of been asking well over €200k. He Rang back twice wanting to know if I was going ahead with them. Got a giggle out of both those calls.

Needless to say I built for a faction of his price. I will say basements are expensive when you factor in everything. Almost no one has a clue about them, architect, engineer, builders. Be prepared to be on your own doing all the research.

Would you mind giving (an indication) of the basement construction cost per sq metre floor area. I'm not doing anything like this but am very interested.
From education forty years ago I recall that basement wall is just a form of retaining wall and that the problems arer as identified on this site, not structural water ingress. Another issue (that I learned then) was that tanks e.g. swimming pools often had problems not with watertightness but with flotation before they were filled with liquid. Years back I was involved with a high level water retaining structure i.e water tower which had about four construction joints on the tank portion and water bar was expressly not used. Instead each wall joint had a rebate cast at the top, that was 'sparrow picked' before the next concrete pour and a grout was poured before the concrete. It was completed in 1975 and when I last saw it in 2008 it still had no leak or weep. Having said that, water bar for underground is wise but make sure its not allowed to be turned over or flattened by poured concrete.
Finallly, and now Ill go back to sleep, I would be astonished if civil engineers did not know the basics of basement and tank construction. I know, but only because I asked years ago, what a secant pile was; but ive never seen one being placed - seems to me sheet piling for single storey basement would be adequate.
Thanks to all the contributors; you've made an old man happy. This stuff is what civil eng is all about - not spreadsheets and 'mining data'!!