The Brew Cabin

Posted: **Thu Jul 06, 2006 2:19 pm**

I am having a new driveway and path laid at the front of the house. The problem is that there is a shallow bank from the pavement down to the house which is currently laid to grass over a very shallow layer of topsoil benath which is clay. The existing path was laid by the original bryant builders (10yr old house) with 24"x18" concrete slabs that just kept flooding (2" water)everytime it rained- hence we decided to have a new path and driveway to match. There is currently gravel from the side of the slabs upto the house brickwork and no aco drains or formal soakaways. There is a manhole cover with an 8 foot deep soil drain in the proposed pathway to the far right of the house which the downstairs loo drains into. Currently the drive is tarmac'd and drains to an aco drain and main sewer.
Right now for the difficult bit- the driveway and path will be done in clay blocks and the FMB registered and guaranteed builder doing the job says that they will slope the path TOWARDS the house with runoff into a soakaway at the foot of the brickwork. The argument being that the the clay soil is wet anyway so draining it there shouldnt be a problem. This goes against my common sense which says you should always drain away from buildings.....and I thought was standard practice when building. He also says that the standard 2 bricks depth below the dampcourse is not essential these days as used to be common practice- because rain does bounce higher than 8 inches and the disability act makes for buildings that dont have steps 2 courses below the dpc...... Is this all a crock of BS?? I would prefer a solution using the existing drain that is in the path and running it into there rather than a soakaway right at the foot of the house..... Like I said these guys have the FMB and masterbond trustmarks etc so maybe I am wrong but I'd just like reassurance please!

Edit: The gradient of the drive/front is approx 1/12 (.75 m drop over 9m) and the width of the drive is 6.9m so I presume an intermediate restraining course of concrete is required at halfway?
property width is 11metres.

Posted: **Thu Jul 06, 2006 11:38 pm**

Somebody please help!!!! Have I posted incorrectly ? :O

Posted: **Thu Jul 06, 2006 11:51 pm**

I'm not sure about the rest of it but the soakaway advice is not sound. Firstly, you shouldn't really have a soakaway within 5m of a building foundation, so having it right next to the house would be a big no-no. This is a British Standard that has been around for quite some time and all the engineers I know try not to violate this rule.

Second, using the argument that "the clay is wet anyway" is invalid. Clay is not very permeable and can retain (hold on to) relatively large volumes of water compared to other soil types. So even if there is a lot of water in the clay at the moment this does not necessarily mean that it will flow out of the clay and damage your house....think about it, if you grab hold of a handful of wet clay, you can feel that it's wet right? But how much water drips from it? Not much, if any at all.

However, if you try to force more water into the clay then all that's likely to happen is that it will flood all over the place. Once the clay immediately surrounding the soakaway reaches saturation point (if it's not there already), the soakaway is going to stop working. I would expect you would see surface flooding during any major storm event.

I would question whether you should be using a soakaway in a clay soil anyway as they are generally not suitable (the hydraulic conductivity is often too low...whilst clay is good at retaining water it is pretty bad at conveying it anywhere). In your post you state that you already have surface flooding problems due to the presence of clay soils. Simply digging a hole in the ground and draining your surface water into it is not likely to help, since it will still have nowhere to go and you'll likely just end up with a hole permanently full of water.

Posted: **Fri Jul 07, 2006 12:54 pm**

Thanks Robster so I was right and it should be drained into the existing drain if possible?

Posted: **Fri Jul 07, 2006 3:33 pm**

Yes, if it's possible to utilise the existing piped drainage system then this would be a better solution.

Posted: **Fri Jul 07, 2006 11:44 pm**

Thanks mate I really appreciate your thoughts and advice. Clearly FMB membership doesn't guarantee sound advice and practice in all cases eh?

Posted: **Sat Jul 08, 2006 12:15 am**

This is often the case with soakaways. I find that a lot of people who should know better often don't understand the underlying principles well enough. I'm willing to bet that the builder didn't even try to investigate the ground permeability, which is one of the key factors in whether or not a soakaway will be successful!

Posted: **Sun Jul 09, 2006 1:23 pm**

Robster has guided you correctly re the soakaway, so no need for me to repeat his excellent comments.

However, regarding this FMB's comments regarding the '150mm below dpc advice', they are correct in saying that this 'rule' is waived when it comes to creating level thresholds for disabled access, but they've misunderstood the intention of this waiver. It's OK to pave up to DPC level for a threshold, but the rest of the paving should be at or below 150mm from DPC - just because it's waived at a threshold does not mean it is waived everywhere.

As this crowd are FMB registered (which means buggerall anyway!), I'm guessing they are jobbing builders rather than paving specialists, which would explain (but not excuse) their lack of understanding regarding the soakaway and the paving levels. I recommend you get at least a couple of paving specialists to take a look at your project.

Posted: **Sun Jul 09, 2006 3:58 pm**

I still think Tony ought to create a sticky'd thread about soakaways....especially about (not) using them in clay soils since most soakaway questions seem to be about this!

Posted: **Sun Jul 09, 2006 5:50 pm**

Maybe I should, but I've always felt that as this info is given several times on the main website, and is mentioned in what seems like every other post, somehow, the message would finally get through, but maybe you're right and I have too much faith in my fellow man.

Posted: **Sun Jul 09, 2006 6:52 pm**

That's not how some people use websites such as this though...they just go straight to the forums and ask everyone else. :p

Posted: **Sun Jul 09, 2006 11:16 pm**

Absolutely Robster- I remember this site being 3 or 4 pages, which helped me immeasurably - never occured to me to use a forum - forum? what forum? - something funny happened on the way to the forum.
Surely using the forum is a last resort? - when you're seriously stuck - shouldn't be an easy option.
Do I sound sanctimonious?
I DO love the Brew Cabin.

Posted: **Wed Jul 12, 2006 10:41 am**

Hi again and thanks for all the sound advice. Just a thought on some of your comments regarding the use of forums though...

Yes a lot of people do jump straight to an advice forum to ask questions regarding the issues which they feel are specific to them. A lot also goto the forum after getting frustrated at reading through loads of detail on the main site but finding it still doesn't answer their little niggles and problems. Obviously you cannot cater for every nuance and minor detail in your general info on a topic on the main site!
Furthermore, somebody who is inexperienced may not be able to sort the wheat from the chaff, on the broader detail and feel the need for asking more specific detail. Do you get where I am coming from here?

Unless you limit joe publics access to these forums you will always get this happening, but you surely know that already, so I am no doubt teaching granny to suck eggs.

I think robsters idea of making the thread 'sticky' is a great one. To be honest the best way of learning is asking questions (in any profession).Also, reading the forum questions teaches far more than just reading the topic on the main thread, as it covers the more unusual situations that do arise.
I think this site is absolutely superb and cannot commend it highly enough, but don't want to feel unwelcome from vitriolic comments from the pros on here.

PS My question regarding the intermediate restraining course on the drive still hasn't been answered(and I did read the site!) :p

Posted: **Wed Jul 12, 2006 11:20 am**

Relax Salvador, my comments weren't aimed at you.

You obviously have site-specific issues so yes in that case asking in the forum in the wise thing to do. They were more aimed at people who know they have drainage problems due to clay soils who then start asking about how to build a soakaway to solve the problem. This quite clearly won't work in the conditions they are working under!

Posted: **Wed Jul 12, 2006 10:12 pm**

Rob- I didn't mean it to sound like I was getting annoyed at anyone! Just proposing some ideas as to why people do what they do.... Apologies if it sounded sanctimonious of me, and I am very grateful for all your and others advice!

The Brew Cabin

Drainage problem