How to install under-floor insulation?

[lukec]

Hi all, 

I'm in the process of planning some underfloor insulation for part of my house. My house is a 90's build house in Brisbane where the upstairs area hangs out over the built in downstairs by about 40sqm. This area is partially open aired, and partially built in by the laundry which is essentially the temperature as the outside given the door is always open and its not insulated itself. Unsurprisingly on a hot day, the floor is noticably warmer in this area of the house and is a huge source of heat into the house. 

I plan to use earthwool underfloor insulation but I would like to know if I need any form of moisture barrier between the underside of the floor and the insulation, and do I need some other sort of barrier between the insulation and the open air. 

This area is not exposed directly to the elements, but is open aired and prone to filling up with spiders etc, and being Brisbane it can get humid at different parts of the year. 

Thanks in advance

[EricL]

Hello @lukec 

There might be an Ametalin product that will work with the Earthwool. Please allow us to double check with our supplier to find out. Once we have more information, we'll get back to you.

Thank you for your patience.

Eric

[MitchellMc]

Hi @lukec,

The use of a moisture barrier isn’t generally necessary in your situation. Do you have any existing moisture issues under that section of flooring? Adding insulation alone won’t normally create moisture problems, but if there’s already some dampness or humidity you’d like to isolate from the floor, you could certainly install a vapour barrier.

Another option would be something like Ametalin SilverSark stretched across the underside of the floor joists over your Earthwool. That would stop moisture from passing through the insulation and into the floor above. There are also other vapour barrier products typically used on walls that would do a similar job; they allow the area to breathe while still protecting the insulation from humidity.

That said, it’s not essential unless you have a moisture concern. Another approach, if you’re enclosing the area, is to clad the ceiling with plasterboard once the insulation is in. It’ll give you a clean, finished look and keep pests out, which sounds like a good idea given your description. 

Let me tag @Nailbag to see if he has any thoughts.

Please let me know if you have any questions.

Mitchell

[Nailbag]

Hi @lukec 

I came really add anything to all the great advice and comments by @MitchellMc A few houses ago I needed to insulate my floor as the living area was all tiled and was freezing in winter under foot. I used Earthwool with I held in with stapled plastic straps. It worked very well, but highly recommend getting a helper. One to hold the batt while the other straps it in.

If you were to use silver marking and was concerned about moisture, you could simply pop holes into it. But as @MitchellMc mentioned I would be concerned either unless there is an existing issue.

Nailbag