Damp proof membrane over floorboards ?

[jonny_throstle]

Hello,

Now that i've decided to lay laminate flooring through my hallway and dining room, i now have to decide on which underlay to buy.

All the laminate manufacturers recommend using a damp proof membraine when laying over ground floor floorboards with no heating below, otherwise this invalidates the warrantee.

Is a dampproof membraine really needed ?
I was told by a damp expert not to seal or varnish floorboards and that it is much better to let the house 'breath' (especially wood), otherwise you cause more problems (house is 1900's and he also said not to cavity fill the walls) When I pulled up the carpet the boards were perfectly 'dry'.

i was planning to use 6mm softboard to level and insulate the floor followed by 3mm underlay on top and then laminte.
- Does anyone know if a damp proof membraine is neccessary ?

 

[WoodYouLike]

All the laminate manufacturers recommend using a damp proof membraine when laying over ground floor floorboards with no heating below, otherwise this invalidates the warrantee.

Is a dampproof membraine really needed ?
I was told by a damp expert not to seal or varnish floorboards and that it is much better to let the house 'breath' (especially wood), otherwise you cause more problems (house is 1900's and he also said not to cavity fill the walls) When I pulled up the carpet the boards were perfectly 'dry'.

Your expert is absolutely right and the manufacturers are completely gone mad!
Don't use DPM on wood be it floorboards, chipboard, plywood or whatever.

 

[JohnD]

Surely the manufacturers say you should use the DPM on a concrete subfloor, not a wooden one!

 

[jonny_throstle]

JohnD wrote:

Surely the manufacturers say you should use the DPM on a concrete subfloor, not a wooden one!

No, all the laminates and softbords i have looked at all say to use DPM on existing plank floor and floorboards on lower ground levels when the room below is unheated. See here for example: http://www.quick-step.com/faq.aspx?id=1

I guess its their way of protecting themselves against warrantee claims.

I think it would be best just to run a small width of plastic sheet under the outer laminate where it meets the wall.

 

[Bazdaa]

Hello,

I was told by a damp expert not to seal or varnish floorboards and that it is much better to let the house 'breath' (especially wood), otherwise you cause more problems (house is 1900's and he also said not to cavity fill the walls) When I pulled up the carpet the boards were perfectly 'dry'.

OMG, does this mean that I should buy shares in damp companies (joke). Theres a lot of people with varnished floorboard including me.

Is this a problem waiting to happen?

Bazdaa

 

[WoodYouLike]

Is this a problem waiting to happen?

Bazdaa

No, don't think so. Floorboards on cavity areas have been around for ages. The problem starts when they are 'rediscovered' by (new) owners who think they have found an instant proper wooden flooring underneath their carpets. They start sanding the boards, try to fill the 'normal' gaps and then find it is still a bit drafty. Then they board up any ventilation bricks to stop the draft and problems will start I'm afraid.
As long as you understand the ventilation principle and 'treat' your original floorboards accordingly everything is fine.

 

[Bazdaa]

As I said OMG!!!

I've gone as far as sanding and varnishing the floorboards (got a company in). But have not and would not dream of blocking airholes (apart from one maybe, but thats another thread entirely).

Is this OK, or are you saying using old floorboards is bad. Heck how do I break the news to the misses?

Bazdaa

 

[WoodYouLike]

Don't panic!
What you're doing is fine, like I said, as long as you understand the ventilation principle. You can reduce the 'draft' (if any, but we know from experience most will have draft) by insulating the ventilation area. That's something different then blocking the air bricks to stop draft (as we have seen so many times).
I presume you had carpets on the boards before? You just have to see (feel) what the 'draft' result will be, could be very acceptable.

 

[Bazdaa]

Thanks for the clarification.

As I always say when it comes to houses. Things were put there for a reason!

I have 2 questions however;
1)How do you insulate the ventilation area. Infact what is the ventilation area?

2) What do you think of filling the gaps with a clear sillicon?

Bazdaa

 

[WoodYouLike]

Well Bazdaa, since we're original from The Netherlands where house were/are build very differently we're not really the right persons to advice you on how to insulate the 'cavity' area. We only see the problems when things go wrong I'm afraid and then advice our customers to a builder.
The ventilation area is the area beneath your original floorboads with air bricks in the walls to keep it dry. Those floorboards are in fact the underfloor, where now concrete is used.
Silicon sealer would do the trick only temporarily (but longer than other products) cause of the normal seasonal movement of wood.
Really hope I didn't put my foot in

 

[Bazdaa]

No thats cool and very helpful, thanks.

Dont worry about the advice thing, People need to remember that its advice and its down to them to implement if happy. What works for one, might not work for another!

I've a friend who used clear silicon, and it has held up quite long (years). She has to fill a gap evey now and then, but hey.

Bazdaa

 

[Nige F]

Insulate the cavity If you can get under the floor......... cut to size celotex (kingspan) insulation between the joists agin the underside of the boards. a big IF otherwise the whole floor has to come up to insulate between the joists