Water proofing basement (See Mod Edit on Post 6)

digestive

I am building a new house in a 'tight for space site" in the city. The new house will be semi detached to an existing semi detached house.

The site in question slopes down from the neighbouring house. As a result I will be building a basement under the new house.

The existing house has traditional strip foundations. I have 2 issues.

1. Supporting existing house next door while basement is been constructed.
2. water proofing the basement wall that runs parallel to the existing house's gable. As it will be unaccessable.

I am keeping an open mind on this and am open to suggestions. I am already looking at going in first with steel sheet piles to support the existing house's foundations. Then dig out for basement and let the new basement wall up against the steel piles. ( I would have plywood between concrete and sheet pile) Note that I only have an issue with building the basement wall where the basement abuts the existing house. All other elevations are ok.

My concern if I proceed with the sheet piles and building up against it is how do I water proof the wall. I won't be able to treat the outerface of the wall as it will be inaccessable.

I was wondering if a pretreated precast wall unit be the solution but have no experience in it. Any help or advise appreciated. I hope I have painted a proper picture of my scenario.

It is important that I build as close as possible to the existing house's footings as the width of the new house is already quite limited.

Conor

Moved to Construction & Planning. Help Desk is only for help with boards.ie itself.

Johnniep

digestive wrote: »

I am building a new house in a 'tight for space site" in the city. The new house will be semi detached to an existing semi detached house.

The site in question slopes down from the neighbouring house. As a result I will be building a basement under the new house.

The existing house has traditional strip foundations. I have 2 issues.

1. Supporting existing house next door while basement is been constructed.
2. water proofing the basement wall that runs parallel to the existing house's gable. As it will be unaccessable.

I am keeping an open mind on this and am open to suggestions. I am already looking at going in first with steel sheet piles to support the existing house's foundations. Then dig out for basement and let the new basement wall up against the steel piles. ( I would have plywood between concrete and sheet pile) Note that I only have an issue with building the basement wall where the basement abuts the existing house. All other elevations are ok.

My concern if I proceed with the sheet piles and building up against it is how do I water proof the wall. I won't be able to treat the outerface of the wall as it will be inaccessable.

I was wondering if a pretreated precast wall unit be the solution but have no experience in it. Any help or advise appreciated. I hope I have painted a proper picture of my scenario.

It is important that I build as close as possible to the existing house's footings as the width of the new house is already quite limited.

Hey Digestive,

What you are proposing to do is not an easy build and should be carried out under the supervision of a suitably qualified structural engineer with experience in in-fill basement construction (with PI obviously!)

I have done a few of these and each one presents its own problems, however the key thing is to get the basement water tight while avoiding effecting the neighbouring property.

First off, sheet piles may or may not be suitable depending on the ground conditions and the proximity of adjoining buildings. If there are boulders etc in the ground, it will deflect the sheet pile and cause problems. Also, generally sheet piles are rented however what you are proposing would cause difficulties in removing them and the cost would have to be included in your budget. Other solutions may be more appropriate, under pinning, mini piles etc. depending on the site constraints.

There are a number of options for tanking the basement but will depend on the buildup. I would avoid a precast system as you are introducing a lot of joints to the basement structure and invariably leaks occur at the joint, so fewer is always preferable. The extent and type of tanking would also depend on the use of the basement. An option might be to add a waterproofing admixture to the concrete in conjunction with a good quality water bar.

Hope this is of some help!

John

Cuauhtemoc

Some of this won't suit yourself and I'm not technical in this stuff
Our basement build consists of a poured concrete wall which is membraned(layer of bitumen and heavy waterproofing) on the outside of the wall.
This is followed by insulation followed by another waterproofing damp proof membrane which is essentially just a heavy sheet of plastic as a further precaution(just my paranoid addition not engineers and its cheap enough.)
Will probably membrane inside wall as well just to be sure(again my decision not engineer). Though if the water gets that far...probably a bit late.
.

C.

Edit @ John..What's this waterproofing admixture? Can it be added to the cement trucks prior to pouring? Thanks.

Johnniep

Hey Cuauhtemoc,

The admixture is available from a number of suppliers. I have used the "Grace Adprufe". Sika also do a similar product but the name escapes me.

The admixture is added to the conrete at the batching plant only. Don't allow admixtures to be added on site.

Poor Uncle Tom

OP AND OTHER POSTERS - PLEASE READ.

The Construction and Planning Forum does not allow discussion on structural issues. I am aware this thread did not start out on the C&P forum so I will not alter what has been posted to date, but, please read the forum charter before adding to the posts here.

OP, yours is a very specific case and generic references will not apply in your case as the ground structure and history of any intereference thereto will have a huge impact on any design solutions being used in your construction. Therefore it is paramount that you employ a suitably qualified Structural Engineer to answer your questions, specifically.