Warm (& Humid) Room Insulation

[Manhattan63]

My debut post, so firstly HELLO!

I'm building a 20x10foot warm room (for fish tanks) inside an outbuilding of my home. The unit has a decent kingspan roof and the walls are plasterboarded (the stuff with 20mm of polystyrene) over 9" brickwork (with a dot and dab size 'cavity'). The floor is concrete (with cheapo carpet over it). It's a large room so heating a smaller area makes sense. I will build this room in the corner of the large building to utilise 2 of the existing walls.

I plan to build the two new walls from 3x2 timbers at 600 centres. The walls need to be insulated and this is where I am hoping for some advice. Celotex/Multi-Foil/Frame Therm/Fibre Glass? The outside of the room can be plasterboarded (for aesthetic reasons) and the inside will have plastic cladding - then siliconed down to a lino floor.

Now, this room will be very humid because of the warm water within it, whereas the main room gets pretty cold in the winter. So I'm unsure if I need to leave a cavity in the timer (and against the existing plasterboard walls). Celotex is so expensive that if I can get away with 25mm (also gives me the option to add more later if it's an epic fail) then that would be great.

There also needs to be an insulated roof (at 2300mm approx), but I was thinking about just chucking down loads of loft insulation as have the space and it helps the budget.

Any advice for insulating the walls (both over the existing plasterboard and timber stud walls) and how to build such a 'warm' (and damp) room within a colder environment would be appreciated.

The room will be heated rather than the water directly so needs to hold heat very well, but also remain budget conscious.

Many thanks

 

[^woody^]

Avoid any cavity in the wall, or indeed any air pockets at all, and maybe best to use treated timber.

Full fill the wall with whatever insulation you prefer (board or quilt but not multi-foil), and make sure to use a proper vapour barrier (eg polythene) behind the plastic cladding to prevent moisture getting through to the frame

Same principle for the ceiling

 

[Manhattan63]

Thanks for the reply. The plastic cladding is the double layer stuff, the gap is about 9mm (a corrugated-like style within the gap). Would I still need a barrier?

 

[RedHerring2]

Can I suggest that the evaporation from the water, therefore moisture in the air, is reduced if the air is kept warmer than the water, rather than vice-versa, which should happen anyway if you are relying on the air and structure warming the water.
Also, if the water is kept covered as much as possible. I appreciate that with fish there is a relationship with the surface of the water and oxygen and the amount of fish kept.

Be aware of condensation in any extractor fans or ducting.
And don't underestimate the damage done to structures long term by moisture laden air. It has a habit of finding the weak spots in the buildings.

 

[Manhattan63]

Thanks guys. part of the fish room has a tropical pond, a 2.5m square area that does not have a cover, so there will be a lot of moisture in the air. Most of the tanks have covers, but it's still a very moist environment. I was thinking a timber structure is easier to repair/replace than a blockwork structure. The air is heated rather than the water, so the air will be warm (and wet), hence why I want to keep it insulated and cladded.