What size width under floor insulation would I need to get, I would go and measure but it is 4 hours drive away
tegretol,
Mar 31, 12:07pm
Depends how far apart they are.
toyboy3,
Mar 31, 1:23pm
I thought a government built house everything was a set measurement and standard
stevo2,
Mar 31, 3:01pm
At a guess I would say 16".
tweake,
Mar 31, 5:39pm
you need to measure and plan it. you have no idea whats been altered over the years or if it was even done to spec to start with. also you will have a few different spacing used. so you need to know how much of each size to get. quite common to find they are not all that straight. i would not use polystyrene because its a pain to fit older homes and you can get moisture issues with it. i recommend polyester as its really easy to install on wonky timber. tho its a pain to cut.
the other way is to use blanket insulation. this goes under the joists which gets around joist spacing issues. but you need to insulate the rim joist.
tygertung,
Apr 1, 8:14am
I found out with polyester you don't need to cut it (which is difficult), you can just rip it / tear it apart, quite easily.
tegretol,
Apr 1, 11:45am
Wouldn't that create a huge cavity with resultant moisture/vermin issues?
pauldw,
Apr 1, 11:58am
Typical joist spacing in 50s was max 18" centre giving spaces around 16" 400mm. That would be covered by 450mm width insulation.
tweake,
Apr 1, 4:32pm
in one direction yes, but its really tough to cut or tear in the other. i'm a bit rusty but i think its fine if you tearing off the end that you have fitted between joists. the hard bit is tearing it length wise.
tweake,
Aug 6, 8:15am
vermin issues, quite possibly so. any under floor insulation thats not super firmly placed has that issues. have heard of mice getting between polystyrene and the floor before. keep on top of your pest control.
moisture issues, no. a gap will not cause moisture issues. its polystyrene that can cause issues due to it being low permeability. what the cavity will do is allow heat to move down the length of the joist. so one room may heat another room via the floor. that may be a good or poor thing depending on what your trying to do. if you heat the whole house its a good thing. if you only heat one room it may be a bad thing (tho only heating one room is a bad thing anyway).
the upside to it is that the joists are now on the conditioned side, ie they are now inside the house. so they become thermal mass and increases moisture holding capacity. both good things.
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