Liquid DPM instead of 1200 Gauge DPM for Timber Frame

[Gareth C]

First post here, although have browsed many a forum page in the past for answers to other queries over the years!

 

With a standard timber frame construction, utilising membranes internally and linking them with damp proof membranes is critical for the airtightness of the overall house.

 

If using a liquid DPM instead, I am wondering if this would make it harder to effectively seal the building from an airtight point of view or not. First thoughts are no, the areas requiring sealing, such as around openings and penetrations can still be taped and sealed.

 

Has anyone used liquid DPM in this scenario, and is this a good alternative to a membrane?

[JohnMo]

Why would you use a liquid DPM for a new build.  Your DPM isn't for airtightness it's to stop ground water transfer in to the building structure.

[Gareth C]

I didn't say DPM's are used for airtightness, linking the DPM to the VCL is though.

[Gareth C]

Why would you use a liquid DPM for a new build.

 

Partly my question.

 

Actually, I see many benefits if sprayed on, no need for folding membranes in corners or tricky junctions. Quicker, easier, no tearing.

 

Maybe it should be: why would you not use a liquid DPM for a new build?

[markc]

Really depends on where in the build, if you are tanking over old substrate then liquid will be much easier and forgiving, but for slab or over insulation etc then a sheet material wins hands down

[Iceverge]

I assume your airtightness layer is inboard of the external wall studs. 

 

On a typical build the floor slab will form the airtight layer. Normally a primer like Siga Dockskin will be used along with a specific tape like Siga Fentrim to join the masonry floor to the airtight membrane.

 

Alternatively you could use something like a layer of OSB as your airtightness layer, then you could treat this junction much like tanking a wetroom with a paint on membrane. Filler and mesh tape may be needed too.

 

If using the DPM as part of the airtight layer you need to return the DPM up the inside of the timber frame and tape it to the airtightness membrane. Tricky to detail in reality. 

 

TLDR. 

 

1.Joining solid substrate to solid substrate Tape or paint on membrane are both ok. 

 

2. Joining solid substrate to membrane or membrane to membrane use a tape. 

 

 

 

 

 

 

 

 

[Gareth C]

Yes, the airtightness layer is on the inside of the studs, in a typical timber frame arrangement.

 

I am unsure of site's way of sealing but I would imagine it isn't anything special.

 

Current detail is running DPM up back face and sealed to airtightness membrane from wall, as usual practice.

 

Those 2 points are good references!