underfloor insulation

[tweak'e]

yeah this again
a bit of a follow on from an old thread http://pressf1.pcworld.co.nz/showthr...r-installation
looking at it for a winter project.

netsearching around i see a bit of conflicting info.
nz seams to be promoting underfloor insulation but lots of info from overseas about removing flooring insulation and insulating the crawl space walls instead.
this is with a house on piles above dirt.

it seams insulating the floors can cause the floor joists to be reduced to outside temp which then can have moisture condense on it. in our typical high humidity and warm temps (muggy old northland)
that could be a long term problem.
the alternative method is seal the dirt (moisture barrier ie polythene sheet), insulate the crawl space wall and block off ventilation. the idea being to stop humid air coming in and the lack of floor insulation means the joist are now heated by room above and the insulated crawl space walls is to trap the heat into the crawl space.
anyone one heard of that being done in nz?

i think moisture barrier on the dirt is going to be done regardless. can't see the point of evaporating moisture under there. evaporating water does a huge amount of cooling and that moisture is driven up through the floor.

[gary67]

Pir chch house had ground polythene and no insulation can't say it was any better because polythene sweats.

[pctek]

Insulate ceiling and walls.
Hot air rises, why seal your floor.

[gary67]

Draughts

[tweak'e]

Pir chch house had ground polythene and no insulation can't say it was any better because polythene sweats.

did that get water on top of the polythene?
if no what did you mean by sweats?

Insulate ceiling and walls.
Hot air rises, why seal your floor.

heat travels from hot to cold. even tho hot air rises, the heat will also go down through the floor.
as your walking on the floor, floor temp makes a big difference to comfort.

[plod]

We have noticed a difference since we did ours. We asked about the ground cover,which all the insulation place were doing,But all the people giving us quotes said our house did warrant it as it wasn't damp underneath. Plumber mater also commented how dry it was.

[tweak'e]

We have noticed a difference since we did ours. We asked about the ground cover,which all the insulation place were doing,But all the people giving us quotes said our house did warrant it as it wasn't damp underneath. Plumber mater also commented how dry it was.

i was thinking along the same lines but then i thought, its only dry because its evaporating the water off. evaporating water = lower temp and that moisture has to go somewhere.
hence why i think ground cover is the first thing to do.

[dugimodo]

I don't think blocking ventilation is a good Idea, it might stop humid air getting in but it will also trap any moisture that does find it's way in. House that are raised off the ground are ventilated beneath the floor to prevent moisture build up among other things.
https://www.consumer.org.nz/articles/under-the-floor suggests sealing the ground to prevent evaporation but mentions mentions nothing about blocking ventilation and in fact states that moisture issues are often a result of poor ventilation.

I was going to get my floor insulated, even signed up and made a deposit, but the unusual construction of my house baffled that company and they never went ahead. Oh well. I do have 38mm triboard and foil on my floors which is better than tongue and groove or particle board floors at least. I'd definately do it myself if I had a conventional floor. One frugal person I know (but won't name ) spend months collecting polystyrene packing material and stapling up under his floor. It was slow, possibly a fire hazard, but almost free and effective in terms of insulation.

The way I see it you are always going to have to compromise, a house needs to be well insulated and well ventilated and the two are a bit counter productive.

[tweak'e]

.........

The way I see it you are always going to have to compromise, a house needs to be well insulated and well ventilated and the two are a bit counter productive.

exactly. that seams to be what i'm finding.
its a balance between heat, moisture and ventilation.

old homes had no insulation and overkill ventilation but where dry. then they added insulation so they became warm but wet.

what is the unusual construction in your house?

[notechyet]

Insulate ceiling and walls.
Hot air rises, why seal your floor.

The bigger the temperature drop from ceiling down to floor the more it rises up. Plus Gary67's post #4.
Where do you want to have the warm temperature?
I would suggest cover the ground( weigh it down), plus subfloor should be ventilated and be made vermin proof(rats, mice) and insulate the floor(and do not be to tight). Of course you want to insulate walls(r2.8 at least) and ceiling(r 6- r7). You will feel a magic difference!