Shepherds hut floor and vapour barriers? (preventing mould and rot)

[cowboy25]

So my Shepherds hut build is stalling a little regarding the floor, I have sorted the mould problem on my plywood to be used on the floor but this has got me thinking how to I prevent further mould when the hut is built and out in the field. I am also concerned about rodents eg mice and rats being a problem entering the space from underneath and causing damage eating insulation and wood. Looking around on youtube I see a lot of Shepherd hut builds have a timber frame floor with plywood attached to the bottom and top of the frame, however my floor frame has only plywood on top with a some kingspan insulation underneath this as pictured.  I could double the thickness of the insulation if needed as I have more kingspan boards.

 

My plan is to use some weld mesh below the kingspan insulation to prevent the rodent problem, but what about mould problems further down the line regarding the floor? I am really worried (rightly or wrongly) about the plywood rotting as it will be quite exposed to the air with it being only a single sheet. I have painted the side facing down to help with this worry but should i put a damp proof barrier below the plywood as well?  This would mean the layers of materials from nearest the ground upwards would be as follows: weld mesh, 2.5cm thick kingspan insulation board, damp proof barrier, plywwod and then the interior tongue and groove flooring (yet to be purchased).  Does this seem ok? Or is the damp proof barrier not a good idea? I ask as would it trap moisture and cause the problem I am trying to prevent?

 

 

 

 

 

 

 

 

 

[JohnMo]

I have some marine ply outside for 5 years, apart from discoloration no real issue. Mould and rot, can all be controlled by good ventilation. If you are off the ground I would add a waterproof layer below the wood as it will not get ventilation and will rot if it gets damp etc

[Redbeard]

1 hour ago, cowboy25 said:

My plan is to use some weld mesh below the kingspan insulation to prevent the rodent problem,

 

'Weld mesh' to me summons up a picture of 100mm squares. This won't be what you mean, I think. Do you mean 'expanded metal'? If so (based on 'mice men' having told me on the past that mice can squeeze through a hole the diameter of a ball-point pen) that may not keep mice out. I was considering it recently re rats.

 

I definitely do not think an extra layer of PIR will help keep rodents out. If they will eat one layer they will eat 2. I am not 100% certain I have seen mouse damage to PIR (maybe they don't like the foil?...) but maybe I have. I would not risk it with the foil/PIR itself as the only barrier below the floorboards.

[cowboy25]

1 hour ago, Redbeard said:

 

'Weld mesh' to me summons up a picture of 100mm squares. This won't be what you mean, I think. Do you mean 'expanded metal'? If so (based on 'mice men' having told me on the past that mice can squeeze through a hole the diameter of a ball-point pen) that may not keep mice out. I was considering it recently re rats.

 

I definitely do not think an extra layer of PIR will help keep rodents out. If they will eat one layer they will eat 2. I am not 100% certain I have seen mouse damage to PIR (maybe they don't like the foil?...) but maybe I have. I would not risk it with the foil/PIR itself as the only barrier below the floorboards.

No I am on about weld mesh with holes that are 1/4 inch (6.5mm) big which should keep mice out. The website I was looking at said it would in any case.

[cowboy25]

The other option is to buy more ply boards cut them up into the correct size squares and slot them in under the kingspan PIR insulation but this would be more expensive and there is still the issue of rot/mould and is ply board totally rodent proof anyway? 🤔 I'm not sure.

[Crofter]

I hope I'm understanding you correctly, but are you saying that you're worried that a layer of ply underneath the kingspan would rot? I'd have thought it would stay pretty dry, it't got an entire hut on top of it.

 

If it helps at all, the little place I little place I built has a floor build up of (from bottom to top): 9mm OSB, 300mm glass wool, 22mm moisture resistant chipboard (glued and screwed), bamboo flooring bonded down.

This is completely exposed underneath as the building sits on piers. I'm in NW Scotland and we get our fair share of driving rain here. The underneath of the building remains perfectly dry. It's been up nearly ten years now and it looks the same as it did on day one.

 

Glass wool is obviously going to be a bit more permeable than PIR, but I imagine you'll be fine. And OSB could be slightly more permeable than ply. Maybe.

[SteamyTea]

Why not coat the PU/PIR sheet with GRP, then fit into place.

Works well on boats.

[cowboy25]

1 hour ago, Crofter said:

I hope I'm understanding you correctly, but are you saying that you're worried that a layer of ply underneath the kingspan would rot? I'd have thought it would stay pretty dry, it't got an entire hut on top of it.

 

If it helps at all, the little place I little place I built has a floor build up of (from bottom to top): 9mm OSB, 300mm glass wool, 22mm moisture resistant chipboard (glued and screwed), bamboo flooring bonded down.

This is completely exposed underneath as the building sits on piers. I'm in NW Scotland and we get our fair share of driving rain here. The underneath of the building remains perfectly dry. It's been up nearly ten years now and it looks the same as it did on day one.

 

Glass wool is obviously going to be a bit more permeable than PIR, but I imagine you'll be fine. And OSB could be slightly more permeable than ply. Maybe.

You are probably right it would stay dry from the rain, still I would be wary of rats as the hut will be sited close to a working farm. I'm not even sure a second layer of ply is necessary if I am honest, it would help with insulation but really I don't worry about floor insulation especially when the hut will have a nice wood burner for warmth. 

 

26 minutes ago, SteamyTea said:

Why not coat the PU/PIR sheet with GRP, then fit into place.

Works well on boats.

 

Interesting. Do you have a recommended vendor/ product you could point me to? 

[SteamyTea]

3 minutes ago, cowboy25 said:

Do you have a recommended vendor/ product you could point me to

These people could supply all the kit needed.

Any GRP fabricator could do it, but no reason what you could not do it yourself.