DPC / DPM and retaining wall question. (picture)

[mattysupra]

hi im building a garage, building regs need to come out and inspect as usual but i want to clear a few things up before we make a mistake.



1- First of one of the walls needs to retain a gully way that is 1 meter higher than the ground level on my side. As i understand i need to have the wall double skin here and void filled with a weak mix concrete.

so it works out the height (wall) is no greater than 4x the thickness (wall) ? is that correct?

2- I need the dpc to be 150mm higher than ground level, and the dpm sheet under the concrete should ty into the dpc, so what do i do as the concrete base will be 1 meter lower than the dpc in the wall?


3- can the whole lot be built out of concrete block? or do i need enginnering bricks below the DPC?

Thanks for any help.

 

[freddiemercurystwin]

Edit: Thanks, your welcome!

 

[Static]

Your retaining a "gully way", not a term im familiar with.. please explain

Firstly why do you want a dpm in the external wall? Its gonna get wet no matter what..

Retaining walls need good sized footings and heavy walls to resist overturning and slidding.. so wall and footing sizes depend on soil and load on higher level ground etc..

 

[mattysupra]

Edit: Thanks, your welcome!

ye thanks, give me chance! I have been trying to source the product and check the specs before i came back here to see if i was to ask more questions etc.

Plus i had already said thanks for any help in my first post.

 

[mattysupra]

Your retaining a "gully way", not a term im familiar with.. please explain

Firstly why do you want a dpm in the external wall? Its gonna get wet no matter what..

Retaining walls need good sized footings and heavy walls to resist overturning and slidding.. so wall and footing sizes depend on soil and load on higher level ground etc..

Gully as in a walkway up the side of my house.

The footings are 1 meter deep and 60cm wide. I need to tank the exterior wall to stop moister passing through to the inside of the building.

 

[Static]

Ah yes.. garage..

1. Cavity filled retaining walls are pretty common but dont use weak mix.. use a nice RC30 and put some rebar in the cavity into the footing..

2. Either tank the inner face of the wall (prone to problems as its exposed) or run the sheet up the face of the concrete (inner side) and lap with dpc (again exposed on exterior side).. never run the dpm through the whole retaining wall..
Why not make it cavity wall all the way up?

3. Engineering bricks resist moisture transfer through them better than spongy concrete blocks.. so avoid frost damage better..


And lastly.. who owns the walkway (gully way)?

 

[mattysupra]

All sorted now, spoke to Synthaprufe and they have recommened a product called Synthaprufe Original. Its designed for what i need to do.


Thanks for the help!

 

[mattysupra]

Ah yes.. garage..

1. Cavity filled retaining walls are pretty common but dont use weak mix.. use a nice RC30 and put some rebar in the cavity into the footing..

2. Either tank the inner face of the wall (prone to problems as its exposed) or run the sheet up the face of the concrete (inner side) and lap with dpc (again exposed on exterior side).. never run the dpm through the whole retaining wall..
Why not make it cavity wall all the way up?

3. Engineering bricks resist moisture transfer through them better than spongy concrete blocks.. so avoid frost damage better..


And lastly.. who owns the walkway (gully way)?

sorry missed your post.

The gully is council land. they fitted some gates of late that are to tight to get a car through so we had a meeting and i told the lady from the council im building a garage and they can hang one of the gates off the corner of my garage wall when built and they are all happy with this.

Why? is there something i need to know?



The reason why it is only 100mm thick wall (apart from where it is retaining) is down to i need the extra few inches. If i had more space i would of opted for a cavaty wall.

 

[Static]

As the land is owned by others and as youve just said was once vehicled area the wall has massively different design criteria.. you cant be sure they wont remove the gates in a year or two.. and a 30t garbage truck reverses down there..

Also ALL of the retaining wall including foundations will need to be on your land.. if any is over the boundry they could happily pop round and ask you to remove it.. even if you garage is up and complete..

You might wanna look at getting it properly designed as this is more than a simple job

 

[mattysupra]

no chance of a bin lorry or something big going up there. You can only just fit a berlingo van up. (it gets wider as you go up where my garage is being built)


All the foundations will be on my side. But if i was to contiue the wall up (cavaty) then my gutters etc would over hang onto the council land.


Anyway, im going to dig the foundations as suggested on my plans (1m deep filled 750mm x 600mm) Unless you disagree!

I take it that is still o.k? I have just measured properly and the wall needs to retain 800mm soil/ gravel. My wall will be 275mm thick i think? My calculations indicate that the wall would only have to be 200mm thick to take the load so the etra 75mm thickness should deal with the 1.5 ton vehicle that goes up and down once in a blue moon i hope!


Or would you say its needs to be stronger?

should my architect of shown better on the plans what should be done? When i asked him he said the builder will know. My bricklayer has asked me to get it confirmed and the BCO have been no help!

Cheers.

 

[mattysupra]

would pictures help?

 

[Static]

Be wary your stepping into potential liability problems.. ask your builder if he is liable for the retaining wall design if he builds it.. and do the same with the architect.. both will probably turn a little white and not give an answer.. IF a problem occurs and a car lands in your garage more than likely you will suck up the bill for a new berlingo van and garage.. as well as the law suit from the van owner and council..

That said its late today, i'll try and run a few numbers tomorrow and check your wall against a berlingo loading

ps. why didnt your architect specify the dpm tanking detail?

 

[mattysupra]

ps. why didnt your architect specify the dpm tanking detail?

You tell me! The plans state that the dpc needs to be 150 min above ground level but nothing else!


Its the first time i have had something built. I will use a different architect if i have something else done in the future as im now starting to realise the lack of details the plans have.

I have had 3 different builders out and they all say different stuff that i know is not correct so i have given up and sourced different people to do different parts of the build. But my problem is they all say the other person will do this and vs versa.

Im pretty stuck and trying to get the correct info, problem is they are coming to start digging tomorrow so need to work things out so i can instruct how deep and wide they dig


Not sure if it makes a difference but they are removing 1 meter of soil out of my drive before they dig down another 1 meter for the footings. It does not have a drop where the wall is going at the moment.


P.s, it will be a great help if you can work out the load against the wall for me. Tomorrow will be great. Thanks

 

[mattysupra]

after speaking on the phone to a mate it seems im missing engineer calcs and my plans are wrong! They have however been passed so im confused as what the council used to check my plans?

 

[Static]

after speaking on the phone to a mate it seems im missing engineer calcs and my plans are wrong! They have however been passed so im confused as what the council used to check my plans?

Well urm yes..

When you say plans have been passed.. by whom.. building control, planning, other??

If its building control they dont design the retaining wall they will check for building compliance its down to you to design it.. or employ a professional to take responsibility for the design..

ps.. unless your into some pretty solid material then you may end up with some movement in the bearing of the retaining wall footing and a berlingo in your garage or more likely some cracking in the wall and the "gully way" above