Question on land drainage/tanking/retaining wall

[damanpunk]

Fella's,

I've finished drawing up my garage and had decided on internal tanking but I'm looking for second opinions. The garage is 10m long and the adjacent properties ground level starts 200mm above my FFL at the front and ends up 800mm above FFL at the rear. The houses are built on a hill so it's unavoidable unfortunately. The wall of my property is 50mm back from the boundary line so I don't have much, if any space for land drainage. I could put a geotextile double drain sheeting down the external face of the blockwork but will this just move the problem elsewhere?

Any suggestions?

In NE Scotland if it makes any difference.


Here's the current design without any changes:

 

[pinenot]

As you will be digging out the neighbours ground anyway as enabling works to the strip founds, you could put in a field drain panel to the external wall, to the height of the DPC, or just ground level. This would require a geocomposite panel which was porous on the open side but closed to water on the side of your wall.

Something like this -

Untitled

• pinenot
• 15 Apr 2013
• 1

...pinenot

 

[damanpunk]

I did consider this as I found 50mm perf pipe, my only concern was the rubble fill as it'd then be stepping over the property boundary, perhaps it's no concern as it's only rubble and it'll be covered with turf again?

Not sure what to do

 

[freddiemercurystwin]

How thick is your wall? If double skinned then you could just take the RIW up the middle between the leaves.

As you have currently drawn it there is a chance the RIW will get blown off the wall by any moisture getting through it. It really needs a skin of blockwork inside to hold it there/protect it. Standard tanking detail. A bit like this:

Otherwise if you really want to tank on the outside then your wall tanking needs to link with your membrane underneath the slab a bit like this:

 

[damanpunk]

The cementseal is what RIW recommend for internal tanking basement refurbishment, it's good for 100m head positive/negative water pressure apparently. I don't know much about this but building control thought it was quite a lot? In all honesty if I can't get something to work here then it's as good as a re-design

I keep thinking surely it can't be this difficult for a soil build up of 800mm!!

 

[damanpunk]

Sorry, in my haste I forgot to reply to your question. Wall is single skin 215mm block.

 

[pinenot]

I did consider this as I found 50mm perf pipe, my only concern was the rubble fill as it'd then be stepping over the property boundary, perhaps it's no concern as it's only rubble and it'll be covered with turf again?

Not sure what to do

Speak to your neighbour re the proposal, keep the rubble trench as narrow as poss, there's no point filling the sub base area with compacted earth and top earth, surely your neighbour won't want his grass hart to your wall??...pinenot

 

[freddiemercurystwin]

If you are confident of being meticulous with the instructions then go ahead watch the detail at the base, note how it differs from your proposal. http://www.riw.co.uk/documentDownload.aspx?docnam=RIW.Cementseal-DS-2

Personally I don't like any membrane systems applied without something to hold it in position, seen it poorly applied and fail too many times.

 

[damanpunk]

I did consider this as I found 50mm perf pipe, my only concern was the rubble fill as it'd then be stepping over the property boundary, perhaps it's no concern as it's only rubble and it'll be covered with turf again?

Not sure what to do

Speak to your neighbour re the proposal, keep the rubble trench as narrow as poss, there's no point filling the sub base area with compacted earth and top earth, surely your neighbour won't want his grass hart to your wall??...pinenot

That's a good point, she's pretty decent so probably wouldn't mind what I get up to!

 

[pinenot]

Untitled

• pinenot
• 15 Apr 2013
• 1

...pinenot

 

[damanpunk]

If you are confident of being meticulous with the instructions then go ahead watch the detail at the base, note how it differs from your proposal. http://www.riw.co.uk/documentDownload.aspx?docnam=RIW.Cementseal-DS-2

Personally I don't like any membrane systems applied without something to hold it in position, seen it poorly applied and fail too many times.

The linked detail is very similar other than the base, where theirs has the DPM sandwiched between two concrete layers. It was RIW technical that advised on the detail I've used but I've still got my doubts hence why I keep ending up back here I draw steelwork for oil rigs as my day job but this garage has almost driven me insane

 

[damanpunk]

That looks good pinenot!

Last question, I promise. There's no problems that can occur from tanking both sides of the wall are there? I'm guessing what I'm talking about doing externally may not count as tanking as it's just directing water away from the wall rather than waterproofing it like inside?

 

[pinenot]

Don't see any problem with this, but I would only bring your dpm up sufficiently beyond the slab floor to allow for a self adhesive dpm strip up to dpc height...pinenot

 

[freddiemercurystwin]

I don't understand why you would bother with the drainage if tanking anyway, if you are confident the tanking is sound the drainage is pointless and a waste of effort/money.

 

[damanpunk]

I don't understand why you would bother with the drainage if tanking anyway, if you are confident the tanking is sound the drainage is pointless and a waste of effort/money.

In all honesty it only came into my head as I don't know myself how good 100m head positive/negative protection is. As mentioned the building control guy reckoned it was a hell of a lot but it's not my game, I'm just learning bit by bit as I move along.

The interests there now though, I'm building a house next time I move and it's having a basement