membrane on top of floorboards

[davewizz]

Hi, i've just got a new house and am in the process of renovating.

This is what I want to do and further down is what i've discovered.

I want to put a sheet of pvc or a damp proof membrane on top of the floorboards and seal at the bottom edge of the skirting to stop any smells/draughts coming up from the crawlspace, then put underlay and laminate flooring on top.

I've discovered that the ground floor has a crawl space of about 3feet depth with joists and floorboards on top.

The crawl space has a strong musty earthy smell that seems to come through the boards and into the house.

I've found a hatch in a cupboard and have crawled about a lot of the house and it all seems dry enough with decent airflow, through the airbricks as daylight can be seen easily and it's pretty cold and draughty when your in there.. The joists and floorboards are also in pretty good condition. There's some traces of hard dry efflorescence on some brickwork.

So if there's good airflow in the crawlspace which would stop condensation on the floorboards and/or allow any condensation to dry, this would allow the membrane to be added on top of the floorboards ? And the insulation added on top of the membrane below any laminate flooring would help against condensation from the other direction ?

Any info would be much appreciated.

Thanks in advance

dave

 

[gregers]

why not use some expanding foam round the edges?.

 

[davewizz]

Hi, thanks for the reply. It lets air through. I tried using that in a flat before along the skirting and gaps between floorboards to stop cooking smells seeping up from the flat below.

It didn't work. I had to then scrape as much of it away as possible and put pvc over then seal the edges at the skirting with aluminium tape and caulk, that worked.

Hence my idea to in a sense repeat this method over the ground floor of the new house.

cheers

dave

 

[IJWS15]

Sounds like the crawl space is not ventilated, get that sorted out and the smell will disapear.

 

[Nige F]

Perhaps it was built on the site of a medieval charnel house, or midden

 

[davewizz]

Today I discovered two of the airbrick vents blocked. One with concrete the other with silicone from the back. I cleaned out all of the vents and they are all now clear. 8 vents in total. 2 on each wall of the house. Also cleared out some junk the other day from the crawl space and that seems to have helped the odour. Old bits of stinking underlay, etc. Today it wasn't as strong as last week.

I'm going to clear out some more of the junk in the crawl space this week. For example there's some bits of old plaster board left lying about that have fresh mould on them that smell. Everywhere else seems mould free.

I'll see what happens in the next few days if the cleared vents help. But for the sake of it I'm still going to get some plastic membrane and put it over the boards before the laminate gets put down.

 

[alittlerespect]

Get a breatheable membrane, not polythene. Polythene may encourage sweating to occur and if it occurs between the existing flooring and the polythene you could end up with timber decay problems.

Regards

 

[davewizz]

Thanks for the replies.

Do you know of any breathable membranes apart from Du-Pont Tyvek which is pretty expensive and just 1m wide ?

This is what I was goint to get originally from screwfix tomorrow :

Damp Proof Membrane 1000ga 4m x 15m Easy to lay, durable, high quality Damp-Proof Membrane prevents the ingress of moisture into buildings. Complies with all local building regulations.


And they do these too :

Vapour Barrier 2.5m x 20m Polythene 50m². Offers high resistance to the flow of water vapour.

Moisture Vapour Barrier 2.7 x 50m 2.7 x 50m floor to ceiling height. Stops the ingress of moisture. 135m² per roll, suitable for timber frame application. Transparent. Complies to NHBC recommendations.


Ideally 4m wide and a good length so it could be one piece per room.

I'm thinking about using the fibre board underlay on top of a membrane for the laminate flooring, maybe that would insulate the wooden floorboards enough from any room heat. The crawl space should have enough ventilation to dry out any moisture on the wood possibly. The house was built circa 1968.

Or just thought of this, paint whole floor with Zinsser BIN (I'm going to paint everything in the house with this to start with anyway, apart from the floor but that could be added in) and buy the 4mx15m damproof membrane (in bold above). That would be the floor sealed on the top side thereby no moisture could penetrate and the crawlspace would provide ventilation for the underside??

 

[huw169]

I'm glad you said that as I would have used polythene!

I have cleared my lower void, but there is a bit of moisture in certain patches. This is obviously below the dpc, but I am a little concerned.

As it is only a thin weak mix of cement & sand on top of earth, is it reasonable to assume that it will suck up a bit of moisture in wet conditions?

Was (now) planning to tag a tyvek roofing membrane under the joists and drop 150mm rockwool in between and pop the floor boards back on.
The void is quite well ventilated as I have cleared all the air bricks.

What do you think?

 

[davewizz]

The zinsser bin idea may be the answer to stop water /moisture ingress. I put that in an edit to my last post.

 

[davewizz]

Found this breathable membrane: (and its on ebay not much more than the damp proof membrane I was thinking about)

PERMAVENT ECO

Physical properties
Surface mass density 90 g/m2
Vapour permeability 1960 g/m2/24hr
Vapour resistance 0.11 MNSgm-1
Thickness 0.6 mm
Resistance to UV 3 months
Resistance to tear
— longitudinal: >189 N/5 cm
— transversal: >134 N/5 cm
Temperature range -40 °C +95 °C
Resistance at nailing point >188 N
Watertightness >5270 mm H2O !!!
Roll size: 1,5 & 1 m x 50 m 50m2 & 75 m2
Number of rolls per pallet 30

* Other roll sizes are available upon request



High Vapour Permeability
PERMAVENT'S high tech design will protect your home from damaging effects of condensation

Absolute watertightness
PERMAVENT SYSTEM ensures a dry home during prolonged construction or roof damage

UV Protected
PERMAVENT shows no degradation under sunlight for 3 month operation efficiently between 95 °C max<45 °C min

Light weight
PERMAVENT is easy to use, handle and store. Available in rolls of 1m x 50m (5.8 kg) and 1.5m x 50m (8.6 kg)

Any thoughts about this product ?

Cheers

dave