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  1. #1
    tweakedgeek tweak'e's Avatar
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    Default underfloor insulation part 2

    expanding from previous threads on underfloor insulation, i finally did mine.

    i really need to write this to correct a post i did early saying it wasn't really needed, i was a bit wrong.
    with the recent few cold morning (down to -2 overnight) the lino floor was still ok to walk on, a nice improvement. before your first few steps on it would be " o crap thats cold!"
    room temps is hard to judge. it feels better, little bet less drafty and less smells coming up from under neath.
    i have a temp gauge but no real data to compare it to and give a definitive answer. temps are highly related to heat input over the day. as thats highly variable its hard to tell if the temp drop is normal or not.

    first thing, last year i fitted moisture barrier on the dirt. ground was already dry so drainage is ok so no work needed on that. put down polythene plastic, pinned down to the dirt. holes in the low spots for drainage. wrapped the piles and came up the sides a bit.
    this made it so much easier when i put the insulation in. clean and easy to slide around on.

    for insulation i chose polyester.
    batts is horrible for anything close to moisture and becomes a nightmare when it gets wet. also it would have been a major pain to install as your working underneath it.
    polystyrene is ok for moisture but very hard to install well, especially trying to cut straight and get well fitting joins or fitting snugly against timber. any gaps looses its insulation value.
    polyester is easy to work with, easy to do good joins and fit well even when roughly cut. easy to staple up.

    i did both blanket and between joist style.
    bulk of the floor is done blanket style, with the ends being tucked up against the rim joist area and an overlap over the top of the main beams (that hold the joists up).
    this gives an insulated tunnel of air between the joists from the hot side of the house to the cold side. should help with heat distributing through the floor. technically it lowers R value as your moving heat from one room to another, however i don't see that as a bad thing. where the rooms are even in heat it actually raises the R value.
    it also covers all the joists so now the joists are on the warm side of the insulation and become thermal mass.
    the blanket is R1.8 which is meant to give R2.6 when used in blanket form across the joists.

    the lino parts of the house is the kitchen, bathroom etc, which all has plumbing under neath. so blanket was not suitable as you have to leave bare areas around pipes in case of leaks. so i used R2.6 between the joists. r2.6 is 140mm thick and joists are 140mm, so filled rather nicely.

    mistakes.
    i probably should have used the R2.6 around the rim joist area, ie at the end of the joists rather than fold the ends of the blanket up. this would have given a much thicker insulation at the ends and could be easily overlapped by the blanket. also would mean less cutting of the blanket.
    one catch with polyester insulation is that you can tear across it easy enough but its a major pain to cut length wise.

    over all, i rate it as being worth it even in northland temps. i think the comfort value trumps the technical insulation value due to the fact that your standing on the floor so you notice small temp changes.
    i could have gone with lower R value insulation (cheaper) but i kinda like overkill and only doing it once. the clips on tv showing them very quickly installing a rather thin (R1 ?) product is a joke. its not a big increase in cost to go from crap to good.
    Last edited by tweak'e; 03-07-2016 at 04:58 PM.
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  2. #2
    amateur expert dugimodo's Avatar
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    Default Re: underfloor insulation part 2

    I'd be interested in how you find it after a few weeks, unfortunately with the colder weather only just starting it'll be hard to compare but even so.

    I'm wishing I had it today, started at -2 outside and didn't quite get to 7 before starting too cool off again. Inside my house was about 11 degrees this morning and it's taken the heat pump all day to get it up to a comfortable level. For the first time I wished I'd left it on overnight, normally it's a lot warmer inside.

    My floors are 36mm tri-board with silver paper underneath. I did sign up for underfloor insulation to be installed once but when they came to do it the construction of the floor made them backtrack and say they couldn't do it. Maybe I should revisit it, I'm pretty sure they could have just stapled directly into the floor but they didn't want to. I'm not doing it myself though, I barely fit under there as it's quite low to the ground. One problem is most mounting methods are designed around the same standard wooden construction and I don't have that, my floor is just tri-board sitting directly on thin folded metal beams that sit on the piles and are spaced at approx 1200mm so there is no timber to attach anything to.
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  3. #3
    tweakedgeek tweak'e's Avatar
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    Default Re: underfloor insulation part 2

    interestingly enough silver paper is on the way out. partly cause its fairly useless for insulation but mainly electrical issues.

    height off the ground is another interesting thing. people talking about a lot of the older homes. a lot of their problems is due to being built almost on the ground.
    i'm guessing you probably have the standard beam height but no joist on top of that.
    the blanket insulation i was using is 1200mm wide so might fit straight in. staple directly to the floor. tho that does reduce the insulation value a bit. the beams themselves i have no idea. the metal will conduct a lot of heat so would be best to wrap that in insulation, but my concern would be moisture control. last thing you want is for it to sweat.
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  4. #4
    Retired old codger kenj's Avatar
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    Default Re: underfloor insulation part 2

    We redid our roof with the thick blanket just laid on top of the ceiling beams. House is 20 years old and has a concrete floor with pebble dash exterior which was insulated during construction. I normally get up at 6am to around 12-14 degrees. Had our second (for this year) fire last night so it was around 17 inside this morning. No other heating except for an 2400W oil heater which has not been used so far this year. By the time I got home from a walk this morning the sun was streaming into our family room/kitchen. SWMBO had just risen and it was lovely and warm after Napier having a frost this morning.

    Our problem, both in our seventies and think we should downsize our house. The thing is to find a similar setup but smaller. We feel we are spoilt with what we have got. Our previous house we built in 1970 and it was cold in the winter and needed heating every night, especially when the kids were little.

    I have great sympathy with anyone with a cold damp house. My chippie mate once told me that old houses needed to breathe and I saw something about that fact in the paper a day or two ago. If it is not done properly it is just a waste of money.
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  5. #5
    tweakedgeek tweak'e's Avatar
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    Default Re: underfloor insulation part 2

    all houses need to breathe. the catch is old homes don't have modern moisture control systems in place so you can't just shove insulation in without putting some form of moisture control in.
    i cringe at those drill holes in your wall and pump insulation in crowds. no thought into moisture control plus the insulation settles and is crap.
    how long before some of these homes that have had insulation poorly installed, are going to start mold/rotting due to water build up in the insulation.
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  6. #6
    Senior Member pctek's Avatar
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    Default Re: underfloor insulation part 2

    Quote Originally Posted by tweak'e View Post
    all houses need to breathe. the catch is old homes don't have modern moisture control systems in place so you can't just shove insulation in without putting some form of moisture control in.
    .
    +1

    Also, hot air rises, cold air falls.
    Batts in the ceiling, the walls too perhaps, the rest, you're making your house a sealed plastic bag.

    Try a rug instead.
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  7. #7
    tweakedgeek tweak'e's Avatar
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    Default Re: underfloor insulation part 2

    Quote Originally Posted by pctek View Post
    Batts in the ceiling, the walls too perhaps, the rest, you're making your house a sealed plastic bag.
    .
    yes and no
    insulation does help stop drafts but water vapor still goes through it (except polystyrene).
    putting insulation into an old home won't stop it "breathing". a lot of the air leaks are around windows, doors and timber floors.
    they are no where near air tight as new homes and nothing close to the new ones with air barriers installed. those new ones are literally a house wrapped in a plastic bag.
    all you need to do is open some windows for a house the 'breathe'. thats far better than having it breathe stinking wet air from under the house.

    need to remember that stack effect pulls air up through the floor and up through the ceiling.
    Last edited by tweak'e; 04-07-2016 at 09:59 AM.
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  8. #8
    tweakedgeek tweak'e's Avatar
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    Default Re: underfloor insulation part 2

    i left a bit out of my original post

    i don't recommend blanket insulation (ie over the top of the joists creating a tunnel) with T&G or plank flooring. to many air gaps which lets warm air raise up through it and pull cold air past the insulation, making the insulation perform poorly. its best used with sheet flooring ie chipboard or plywood.
    you would need to put a layer of insulation against the T&G floor first, then put 2nd layer as blanket over the joists. you can use two thin layers eg two layers of R1 = single layer of R2.
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