Hello

I am a Newbie to the forum so apologies if this is in the wrong place.

I am currently designing a garden room. I plan to use Easypad plinths for my foundation and sit the timber frame on these. I want to insulate the floor with Rockwool between the joists. I will then place OSB board on top of this.

What I am unsure of is where I need to place a breathable membrane or vapour seal.
If I put a membrane over the ground and then a vapour seal between the joists and OSB, is this correct. I would also like to deter any pests from getting under the floor and into the insualtion. Should I put an additional breathable membrane on the bottom of the joists?

Thanks for your help!

Posted By: atmos74What I am unsure of is where I need to place a breathable membrane or vapour seal.
If I put a membrane over the ground and then a vapour seal between the joists and OSB, is this correct. I would also like to deter any pests from getting under the floor and into the insualtion. Should I put an additional breathable membrane on the bottom of the joists?

A membrane on the ground is just to discourage plants from growing, but they won't grow very much if there's no light. Concrete or sand blinding is another approach.

The vapour barrier needs to go above the insulation, as you and Tony say. You might be OK using just the OSB as the vapour resistance, especially if it is designed for that purpose, like e.g. (first hit) http://www.smartply.com/products/vapairtight If you use a separate membrane then it goes over the joists and under the OSB as you say.

You will want a membrane or a vapour-open board like Panelvent on the bottom of the joists to contain the insulation. Pests come in various sizes from the very small to the quite large - ants, woodworm, mice, rats all come to mind as liking the inside of an insulation-filled timber box and being capable of making their own openings. I suspect you'd be best to have a solid curtain around the perimeter of your building - perhaps brick or paving slabs on edge.

Or as Tony says, a different construction with no underfloor void.

The Easypad system raises the floor off the ground which is a good idea. I think I would go for an easy if more expensive route than others have suggested.

Level and compact ground.
Lay a weed barrier.
Put the Easypads on top.
Build the timber floor with OSB on top
Errect timber walls
Then lay rigid insulation inside.
Vapour barrier and more OSB or engineered wood floor (>18mm thick)
Lap vapour barrier up walls.

Many thanks for your replies, very helpful. I was thinking of the rockwool insulation as I am trying to make the room fairly soundproof and this seems to be recommended as good for Thermal and Acoustic.

I was considering putting a metal mesh around the timber frame which is then buried around 200mm into the ground to stop any vermin. Hadn't really considered ants!

Liked the Easypad and raised solution as consensus seemed to be that it was good to have airflow under the frame?
Also not a massive fan of the concrete base, we have to remove a tree for this garden building and concerned about the roots ruining the base in years to come.

Again, any thoughts much appreciated!