Damp proofing help! Tanking slurry and vapour barrier?

[Lassebakhansen]

Hello,

I am converting the garden brick shed into a garden office and music room.

It is built from brick walls with a concrete floor.

I’m planning to building a stud wall and insulate with mineral wool (rockwool).

the brick wall is essentially the garden wall, where they have popped a flat timber roof on top at about 7foot high.

I’m installing a vapour, so the composition would be:

Outside -> brick wall -> stud wall with mineral wool -> vapour sheet -> plasterboard

I understand the vapour sheet is needed on the inside, to prevent moisture building up in the stud wall.

But as it is using the garden wall, there won’t be any damp proof course in the bricks. Therefore, I want to use tanking slurry on the brick walls and floor, to stop water and damp getting through into the mineral wool and stud wall.

HOWEVER, then there will be TWO damp proof membranes, the tanking slurry on the brick and vapour sheet on the inside

is this okay and will help prevent damp? Or will this cause moisture to get trapped in between the two in the stud wall and actually cause more harm than good?

Considering I have the vapour barrier, there shouldn’t be much condensation happening between the two. So I’m hoping that is okay?

many advice here would be appreciated!!

cheers!

 

[Lassebakhansen]

Here are some pictures.

Another guy has recommended not to do that on a different forum, as you risk creating a literal tanked basin for water to collect.

Any thoughts anyone? would be a massive help.

 

[oakysmokyjoky]

Think about ventilation (in/out) and heating. We have an under-house garage built into a hill and suffer from condensation and efflorescence caused by moisture movement from the garden each side and our oil boiler. It didn't help that I had an insulated garage door fitted which wasn't as leaky as the old one so condensation has increased. I now leave the bottom of the roller door up a tiny bit to get some airflow and means I don't have to run a dehumidifer. Going forward I need to install I/O vents and some heating...then I will look at positive side waterproofing...and then some internal batten/insulation/vapour barrier/facing material on the inside. I will try and avoid tanking it as we don't have pooling water etc.