About to start garage conversion, but found a puddle of water?

The damp proof membrane needs to run over the floor and up and behind the studs, the idea is to encapsulate the space you are inhabiting to prevent water migrating into the structure.
Dpc, the black stuff is not needed in your case.
Lapping the dpm under the dpc wont work as moisture is penetrating between the slab and brick.
 
Sponsored Links
The actual full floor DPM hasn't been put down yet.
That's the problem

The idea is to line the walls and floor first to form a continuous barrier to damp before doing any of the internal work.

That DPC is doing nothing, and the concept of lapping and joints at the location of where the water will be trying to get in under the most pressure, is a bit of a fail.

That damp wont go away and unless you take that timber out and do it properly, it will be permanent damp, mould and rot in no time.
 
The damp proof membrane needs to run over the floor and up and behind the studs, the idea is to encapsulate the space you are inhabiting to prevent water migrating into the structure.
Dpc, the black stuff is not needed in your case.
Lapping the dpm under the dpc wont work as moisture is penetrating between the slab and brick.

That's the problem

The idea is to line the walls and floor first to form a continuous barrier to damp before doing any of the internal work.

That DPC is doing nothing, and the concept of lapping and joints at the location of where the water will be trying to get in under the most pressure, is a bit of a fail.

That damp wont go away and unless you take that timber out and do it properly, it will be permanent damp, mould and rot in no time.

Just to clarify, the DPC IS running up the walls so it's encapsulating the battens. It runs up the walls between 150mm and 200mm and the rest can be seen on the floor, the width of the DPC is about 600mm. The DPM will be seated underneath or above the DPC (and butt up just before the battens start) when installed so it's impossible for any moisture to make it to any of the internal structures. See the attached diagram I prepared before starting out which shows the DPC up the wall and the tails visible with the DPM lapping over these.

The battens are lined with a moisture membrane on the other side of the battens - it's not bare wood against the brick wall.

The mystery here is how the water has come in contact with the bottom plate batten. I think it has trickled down into the other side where the DPC runs up the wall and is now sitting.

Flooring View.JPG
 
Sponsored Links
The moisture is tracking under the dpc.
The membrane should go under the stud in a single unbroken sheet and return up the back of the stud, any penetrating moisture from the external wall or slab will not cause any problems.
 
What have you lined the wall with?

Waterproof, breathable membrane. Stapled to the battens and pressed against the brick wall.

The moisture is tracking under the dpc.
The membrane should go under the stud in a single unbroken sheet and return up the back of the stud, any penetrating moisture from the external wall or slab will not cause any problems.

If the water is trickling down at the back and entering where the membrane is going up the wall, the water would still enter the enveloped area as it is doing now with a DPM, that's my concern.
 
The floor dpm goes up and behind the stud, nothing can penetrate if done properly as it would be sitting in isolation from any external influence.
 
The floor dpm goes up and behind the stud, nothing can penetrate if done properly as it would be sitting in isolation from any external influence.

How far up the wall?

This is part of the mystery, because I cannot see any evidence to suggest that there is moisture creeping in from any break in the DPC laying on the concrete floor, my only explanation is that it's coming from behind some how and trickling down. I will only be able to be sure I move the stud wall out of the place and see what's happening on the outside of the wall.
 
Polythene against the wall, down to floor level
DPM across the floor, turned up the wall at least 300mm on the inside face of the vertical polythene and then taped with butyl tape to seal the joint.

Not breather membrane on battens. Wrong material and wrong place to fit it.

No DPC anywhere. No need
 
How far up the wall?

This is part of the mystery, because I cannot see any evidence to suggest that there is moisture creeping in from any break in the DPC laying on the concrete floor,
Screenshot_20200629-135220_Chrome.jpg
 
Polythene against the wall, down to floor level
DPM across the floor, turned up the wall at least 300mm on the inside face of the vertical polythene and then taped with butyl tape to seal the joint.

Not breather membrane on battens. Wrong material and wrong place to fit it.

No DPC anywhere. No need

I'm quite confused by this as I've never seen any resource guides I've consulted use a poly-barrier against a brick wall.

By fixing in polythene against the wall wouldn't this will prevent the movement of air and trap in air moisture that builds up inbetween the battens? We are fitting a vapour barrier sheet to the inside to prevent moisture transfer onto the insulation and battens.

The breather membrane we're using is waterproof so is supposed to safeguard against water ingress but allow for air movement.

Can you elaborate on the science behind installing two poly membranes to sandwich in the battens?
 
I'm quite confused by this as I've never seen any resource guides I've consulted use a poly-barrier against a brick wall.

By fixing in polythene against the wall wouldn't this will prevent the movement of air and trap in air moisture that builds up inbetween the battens? We are fitting a vapour barrier sheet to the inside to prevent moisture transfer onto the insulation and battens.

The breather membrane we're using is waterproof so is supposed to safeguard against water ingress but allow for air movement.

Can you elaborate on the science behind installing two poly membranes to sandwich in the battens?
A breather membrane can/should only be used where there is a ventilated cavity so that it can actually allow evaporation. If it is pressed up against a wall it will stay wet, allow water to pass through it the wrong way and not permit moisture to pass through it the right way either.

Lots of people misunderstand the concepts behind what needs to breathe and what does not. Not all timber walls need to breathe. You are not constructing a timber frame so what you are doing there does not need to breathe - if it did you need a ventilated cavity.

What you should be doing there is preventing moisture from coming in through the wall from the outside and into the wall from the inside, and then that timber stud wall does not need to breathe or be ventilated. So you put an impermeable layer, not permeable layer, on the back of the brick wall, and another on the front of the timber wall.

And for this to work, you need to ensure that there are no air voids within the wall, so it needs to be filled with insulation.
 
A breather membrane can/should only be used where there is a ventilated cavity so that it can actually allow evaporation. If it is pressed up against a wall it will stay wet, allow water to pass through it the wrong way and not permit moisture to pass through it the right way either.

Lots of people misunderstand the concepts behind what needs to breathe and what does not. Not all timber walls need to breathe. You are not constructing a timber frame so what you are doing there does not need to breathe - if it did you need a ventilated cavity.

What you should be doing there is preventing moisture from coming in through the wall from the outside and into the wall from the inside, and then that timber stud wall does not need to breathe or be ventilated. So you put an impermeable layer, not permeable layer, on the back of the brick wall, and another on the front of the timber wall.

And for this to work, you need to ensure that there are no air voids within the wall, so it needs to be filled with insulation.

Thanks for that, but I've got a few more questions in response to this:

As this is a single leaf construction, aside from the ventilated cavity (which is absent here), wouldn't the vapour still evaporate (cavity or not) as the air will pass through the outer wall? My understand is that so long as there is positive pressure internally there will always be vapour wanting to escape via the walls, but if it ends up being trapped in the cavity there is no chance of evaporation due to an impermeable layer. The permeable layer in this scenario would allow the evaporation of the vapour via the negative outside pressure and prevent the moisture ingress through its own membrane properties.

When you say timber frame - what are you referring to - isn't what has been built a timber battened frame?

There's a couple of links I've looked at which come from possible credible sources:

https://www.proremodeler.com/building-science-do-houses-need-breathe
https://www.architectsjournal.co.uk...tions-all-timber-walls-breathe/780911.article
 
Thanks for that, but I've got a few more questions in response to this:

As this is a single leaf construction, aside from the ventilated cavity (which is absent here), wouldn't the vapour still evaporate (cavity or not) as the air will pass through the outer wall? My understand is that so long as there is positive pressure internally there will always be vapour wanting to escape via the walls, but if it ends up being trapped in the cavity there is no chance of evaporation due to an impermeable layer. The permeable layer in this scenario would allow the evaporation of the vapour via the negative outside pressure and prevent the moisture ingress through its own membrane properties.

When you say timber frame - what are you referring to - isn't what has been built a timber battened frame?

There's a couple of links I've looked at which come from possible credible sources:

https://www.proremodeler.com/building-science-do-houses-need-breathe
https://www.architectsjournal.co.uk...tions-all-timber-walls-breathe/780911.article
You can ignore the yank site, or any site or person that mentions "remodelling" for that matter.

From your other link

"The breathing aspect of any timber-frame wall is about eliminating the risk of interstitial condensation. This is done by controlling the flow of water vapour from the high-humidity interior"

Which is the principle to follow and means - stop the vapour getting in, then there is no need to allow for it getting out the other side.

Then, to stop any interstitial condensation, you ensure there are no voids within the wall, therefore no cold surfaces for any residual air to condense on.

Those are the two concepts you need to know and deal with. You don't need to read much else.

Timber framing is a specific method of construction. You have done some lining in timber, and the concepts are different.
 
"The breathing aspect of any timber-frame wall is about eliminating the risk of interstitial condensation. This is done by controlling the flow of water vapour from the high-humidity interior"

Which is the principle to follow and means - stop the vapour getting in, then there is no need to allow for it getting out the other side.

Then, to stop any interstitial condensation, you ensure there are no voids within the wall, therefore no cold surfaces for any residual air to condense on.

Right, I understand the former concept of vapour moving into the walls and the poly vapour membrane on the warm side underneath the plasterboard helps prevent this, but when you say there's no need to allow it getting out the other side - this is what I can't grasp - if it doesn't escape wouldn't it just start to rot the insulation and timber over time (assuming the poly membrane was in place to prevent it evaporating outwards, through the brick wall?
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top