garden shed built with cavity blocks/ waterproofing options?

beolight

hi guys

done a self build on garden shed after getting quotes in the region of 12 top 18k

however i think i made a mistake using cavity blocks :eek: . as my back garden is at least 2 foot lower than adjoining neighbours i think his garden is simply draining into mine and where shed is the water is pooling because of shed foundations.

the roof is not o the shed yet but below damp course the blocks are very wet

is there anything i can do now to prevent trouble later on

thanks

kadman

Do you have a damp proof layer/polythene in the subfloor of the shed , that runs up the inside of the wall, to the block damp course layer. The blocks under the damp course being wet is not a problem, thats the idea of the dpc, to stop it rising further up the wall. If you ave a damp proof layer/ polythene in the floor, that rises up to meet the block dpc, then there should not be an issue. How far above the surrounding garden is the block dpc, should be at least 150mm. Before you go further, any library will have good building construction books to give you advice. No need for panic at this stage.Getting good advice is the right approach now.

kadman

rooferPete

Hi,

I presume you mean 9" cavity blocks ? in my opinion that was no mistake because it gives you a good stable base for any roof you choose to put on it.

Also solid blocks will help rising damp every bit if not more than a cavity block, the usual way is to bring your rising walls to sub floor level in solid blocks on flat.

If you are concerned you could look at laying a land drainage pipe along the side of the wall and allowing it to drain into a soak pit or the fresh water drain system if you have one.

The fact that you can see damp blocks is ok as long as they are below the damp course level, when plastering make sure to carry the plaster as low as you can, with a plinth not higher than the DPC level, if you are still concerned you could use a waterproofing admix in the plaster mix like Sika.

Unless you have broken the basic damp course rules I think you should be OK.

beolight

thanks for replies

yes 9" cavities

i havent laid the floor yet

the brickie put the damp course after two courses of 9 inch solids on their flat, i think it should have been 3 or 4 courses before he put dpc course in as now the floor in shed will still be below ground level of next door garden at rear of shed.

as next door garden is at higher level i need to do something

any ideas?

kadman

Doesn't matter how low your floor is in relation to your neighbours garden. The main points for you need to be concerned with is,
is the floor
1 damp proofed
2 Damp proof of your floor. adjoining the damp proof of your block course.
3 Ideally your lowest damproof level , above surrounding area.


kadman

beolight

thanks again guys

@kadman

points 1 and 2 you raised will be dealt with when putting floor in. however point 3 is a problem as final floor level(ie damp course level) will be below neighbours back garden.

@ rooferPete i have used land drainage in other parts of the garden but in this case if i put it in it will be lying on top of foundation plus bed of drainage stones and if i raise it at one end to create fall it will be above the damp course covered with drainage stones creating a route into cavity for water

is there any way i can get this to work? was thinking of putting layer of dpc on exterior of wall before plastering plinth up to dpc level acting as a further waterproof barrier of sorts

or perhaps using sand and cement to create drainage channel keeping it below dpc course?

there is quite a lot of still water lodged in this space at the moment

cheers

kadman

You seem to be overly concerned with the level of next doors garden, it really has no relevence to your situation, if your blockwork damp proof course is above your own garden level. As stated before, if your floor dpc adjoins or rises above your block dpc, then there should be no problem.

Picture this, if you dig 2 holes, 24" diam, and 24" deep.
Fill hole one with concrete.
Place a bin bag in hole two, and fill hole 2 with concrete.

Capillary action around hole one will force water into it's concrete.
Concrete in hole two will remain dry, because it is enveloped in a dpc.
Hope this clarifies things.

kadman

rooferPete

Hi,

If you put a sheet of DPC or any plastic type material tight against the wall you could cause a worse problem than rising damp, because you would be creating capillary attraction between the wall and the DPC.

These systems only work when engineered and planned into the wall as part of the overall damproofing such as for basements.

What you could look at doing is putting in a foot path at the side and forming a channel in the centre to carry the water away from the building.

As we are guessing the extent of the problem and none of the above appear suitable you could go to the expense of buying 25 litres of Syntapruffe and coating the walls with it.

This may be over the top but you are the one who can see the exact problem, as far as I and I think Kadman are concerned it's usually looked after by the DPC above your ground level not your neighbours.

kadman

I agree with Rooferpete, in that we are guessing somewhat as to the particular type of condition you are faced with, if maybe you could post a picture , it would clarify everything. Is it not possible for you maybe to get some professional close to you , to have a quick look and advise you ?
You never said how far above your garden level your dpc is, you said you thought it was too low, how far up is it?

kadman