Difference between Vapour Barrier and Damp Proof Membrane?

[Paul_Thomas]

In terms of materials used what is the difference between a Vapour Barrier and Damp Proof Membrane?

I believe we need to use both to insulate and dry line our garage walls. These are 9" thick:- brick out and concrete block in and no cavity. Plan is to have DPM, 50mm battens with 50mm urethane insulation between then VB and 12.5mm plasterboard.

 

[noseall]

In terms of materials used what is the difference between a Vapour Barrier and Damp Proof Membrane?

.

nowt, other than gauge thickness. probably.

but there are breathable waterproof membranes which are used as an underslaters felt beneath roof tiles etc.

 

[Teahead]

A DPM stops water and water vapour from being transmitted through it. Ie 1200 gauge Polythene sheet.

A vapour barrier allows water vapour to pass through but not water droplets so it will breathe a bit like a waterproof coat made using goretex.

A big difference in Performance, useage and price

 

[markie]

A DPM stops water and water vapour from being transmitted through it. Ie 1200 gauge Polythene sheet.

A vapour barrier allows water vapour to pass through but not water droplets so it will breathe a bit like a waterproof coat made using goretex.

A big difference in Performance, useage and price

That depends what you mean by VAPOUR BARRIER, I use a v b in the job I do which is T P S

 

[Paul_Thomas]

So in my scenario I use a thick DPM on the concrete block wall, the 50mm battens with 50mm urethane between.

Then what should I use as a Vapour Barrier before applying 12.5mm plasterboard? (foil backed plasterboard is expensive)

 

[markie]

So in my scenario I use a thick DPM on the concrete block wall, the 50mm battens with 50mm urethane between.

Then what should I use as a Vapour Barrier before applying 12.5mm plasterboard? (foil backed plasterboard is expensive)

Use TPS as in clear plastic, thats what we/I use before plaster boarding, and the regs state the same up my way anyway.

 

[^woody^]

The difference is down to the terminology and usage.

Both are physical barriers and both may be the same material. But they are used in different parts of construction. They are both one way and intended to stop moisture either entering the structure from either the outside, or inside.

In literal terms their usage is as the name implies - a DPM stops damp (in the form of water from the ground or air), and a vapour barrier stops vapour (from internal air)

But in technical terms, they are both barriers or membranes - whichever you prefer

 

[Paul_Thomas]

Thanks for the confirmation.

what gauge would you recommend for my requirements?

 

[^woody^]

You could use the same as whatever you use as the DPM for the vapour membrane. Something like 1000ga which should be commonly available. It does not really need to be strong in this use.

If you use urethane foam (celotex, kingspan) with foil backing, then you need no additional vapour check. Likewise if you use foil backed plasterboard.

TBH, unless you are doing this under a building control application and they insist on it, then I would not bother with a vapour barrier layer - just the DPM. The is going to be minimal moisture ingress through the plasterboard.

 

[Paul_Thomas]

It is under a Building Control Application, at the initial pre-application discussions they asked for it so it is now on the submitted plans.

 

[^woody^]

If plans have been submitted, then why didn't the designer specify the construction?

 

[Paul_Thomas]

He did, it was me

During my initial pre-application discussions the BCO explained what he wanted to see; as in Vapour Barrier and DPM. I added the to the plans before submitting them.

I now have to start getting all of my materials together, priced and ordered. Hence the question, as although the likes of screwfix class some materials as Vapour Control and others as DPM they seem somewhat interchangable.