floor insulation

[wreckless]

I am in the uk and have just looked at a double unit in places the floor is soft
so i looked under and it seems there is very little or no insulation.
i am an engineer and would plan to do the work myself should i purchase the home
my question is
i plan to replace the floor with builders exterior ply fareastern but am not sure where to put the insulation at present it looks like it is on top of the beams and under the flooring is this for air flow to the beams.
or can i buy a loft insulation with silver outer coating you staple the silver coating to the beame and the insulation is glued to the coating and would sit between the beams. if i do this will it stop the air getting to the beams and make them rot earlier.

here is what i was thinking of using
any advice would be greatfull

[JD]

I don't know how the older mobile homes are built in the UK, but here in the US the R-13 (or less) insulation will go between the floor joists in some homes and other manufacturers will use blanket insulation that droops down low to allow more ventilation. In both cases, the insulation is primarily held in place with the underbelly material. The underbelly material is similar to the common blue nylon tarps, but is black and designed to allow some air flow while holding back moisture, like goretex. Some homes with the insulation up between the joists will use a thick buffalo board or a heavy cardboard style sheeting. Both are made to be bug and water resistant.

Basically, if you are in an area with winter freeze, you will want the insulation to cover the plumbing and have some room for air flow to distribute warm air from the sides of the hvac ducting.

[wreckless]

the ones i have seen here built in 1980s/90s seem to have 2 types of insulation
1, the beams/ floor joists have nothing between them on top is a black paper similar to that used in house roofing then on top of that is insulation and on top of that is the ply floor.
2, the floor joists have nothing in between but on top there is a grey plastic with the insulation on top and then the ply floor.
our temperature here does not drop below -5 that often and we have a lot of rain and damp most of the year.
i will lag the pies separate to the insulation, in the videos i have seen online they put fiberglass insulation in between the floor joists and hold it in place with a breathable material underneath and put the floor on top, i just would like to know what is the best way to go to give best insulation and protect the wood joists
once i have been friday i will try to post some pictures of what i have

[DaveyB]

As an ex-Brit, I'm all too familiar with the weather in the UK - it's one of the reasons I moved some place warmer

For those that haven't experienced it, Britain is an island, so temperatures are very much moderated by the surrounding seas. In summer, highs of 60-70 are common, over 70 and they declare a heat wave, anything over 80 is very rare indeed. A typical winter may see rain on Christmas Day, a white Christmas is not guaranteed by any means! Typical winter temperatures are in the mid 30's, with night time drops into the high 20's. In a really bitter winter, it is possible that the temperatures could drop to single digits, and on northern exposed coastlines, wind chill could take that to negative figures, but again this is pretty rare.

One thing that Britain gets in quantity is rain. Total annual rainfall is nothing to brag about, but it comes as light showers, you know, that gentle sprinkling that soaks through your clothes and chills you to the bone. Not a lot of rain, but it takes so long coming down that it seems like the UK gets around 250 days of rain (or more) each year. Now you know why the weather is a favourite topic in British conversation!

In light of this, I would suggest going with the rolls of fiberglass insulation with underbelly material to protect it from below. Given the lower summer temperatures, air conditioning is rarely used in the UK, so condensation is not a problem (other than the cold water lines, which should be lagged in any case), but humidity is. Using the rolled fiberglass, it is easy to strip a section to replace some rotting wood, and then reinstall the original insulation. Also, the fiberglass will not retain moisture, gravity will take care of any that does get in, if the heating ducts and hot water pipes don't take care of it first. This means there is no wet material nestling alongside the wooden joists and slowly soaking the timber to rotting point.

Hope that is of some help to the OP, and also some help to those that may wish to comment

DaveyB