1950s home. Want to insulate house under floors. What are the considerations please? Any recommendations. Thinking I dont want Batts though.Thank you in advance.
trade4us2,
Jul 24, 10:35pm
I don't think flexible insulation is good enough to stay there, so not Batts or anything like that. Certainly not metal foil of any kind as that can kill people at any time from electrocution and I believe it is banned. That's two reasons. Polystyrene foam is cheap. It could be fireproof. Mine is fireproof and I have tested it. It must not touch the wiring. Rockwool is the best for many reasons, if it can be held up there.
tweake,
Jul 26, 3:48pm
i prefer polyester. its light, its easy to install. fits in odd spaces well, its larger size means better side coverage. its highly permeable.
polystyrene is low permeable which means it can cause moisture problems. its thin which means side coverage is poor. often does not fit well on old timber.
rockwool would be great but its heavy and hard to fit.
batts is just meh
sossie1,
Jul 26, 4:17pm
ive just had Mammoth blankets put in the ceiling and underfloor, does the job. 24 hours and no condensation anymore
trade4us2,
Jul 26, 11:05pm
I don't think any of that is correct. Do you know what polystyrene is?
tweake,
Jul 27, 9:54am
i suggest you read the specs. polystyrene is classed as permeable, but its actual permeability is actually quite low, especially when compared to most others. you can run into issues if you use it under a sealed floor (lino etc). you effectively end up with a floor sealed on both sides and no way for it to dry. even with normal floor your risking it not be able to dry as it cannot dry through the polystyrene very well. add in very cold temps (most people use bare minimum floor insulation) and you can end up with condensation on the top side of the insulation.
because polystyrene is a "good" insulator, its quite thin for its R rating. which makes it good for areas where you have space constraints. however with underfloor it means it doesn't cover much of the joists. so the joists are left open to the air to act as radiator fins. insulation like polyester, which is thicker for its R rating, covers more of the joists which reduces the heat loss through via the joist. (polyester also tends to be 'fluffy' and hang down the joist more as well).
if you have a look at an expol install you will see tons of wood not insulated.
of course the other way around all that is to blanket insulate across the bottom of the joists. i've done that with polyester but i have heard of that done with expol sheets.
ang_ck,
Jul 27, 3:21pm
@tweake, I agree what you said about running into issues with lino. It is for that reason, that i was worried about putting expol under my kitchen floor.
As per your suggestion of polyester being "fuffy", I have to disagree as I have seen some of the installers basically stapling the polyester onto the joist, thereby compressing the ployester. Instead, imo, they could have put straps on the joist to "hold" the polyester.
martin11,
Jul 27, 3:28pm
Expol Solid Wood itself is a good insulator it will be the joist you still see exposed . Doubt wether you would get condesation on top of the poly under floor boards .,Any proof of that statement ?
tweake,
Jul 27, 4:03pm
stapling is fine, it really doesn't compress that much. the point about being "fluffy" is compared to polystyrene and that "fluffy" edges tend to fit up against edges better and it droops down. polyester is a bit wider than the joist width, you tuck it into the corner and staple. the side of it comes down the joist a bit. that helps seal the corner. tho depends on size, i used 150mm thick polyester inbetween 150mm joists. so just stapled the edges .
tweake,
Jul 27, 4:31pm
i would not call wood a good insulator. in most walls etc wood degrades the R value. ideally you want less wood so you can use more insulation to get a better installed R value. where people claim 'wood is a great insulator" is they are typically referring to very thick timber that has a lot of thermal mass, which gives it the appearance of being a good insulator.
someone on here mentioned they actually found water sitting on top of the polystyrene. however any time you part of the house where you are stopping it drying in any direction you run the risk of moisture problem (which is why we don't use vapor barriers in walls etc). its not great if it can't dry down through the floor, but even worse if the floor cannot dry up or down. of course condensation depends on quite a few factors.
edit: to add, the more timber you insulate, the more it becomes usable thermal mass that works for the house.
dinx,
Jul 27, 8:51pm
We have polyester rolls stapled up, they only staple edge and its not really compressed as not stapled full thickness. Added moisture barrier at same time as it was included in funding grant we got and im surprised how much drier it is even thou we thought it was already very dry. Unfortunately it turns out rodents bloody love it and we are having trouble keeping thsm out even with rodent proofing the under floor space. They are getting in thd space between floor and polyester and given the urine stains and smell i am pretty sure they are rats. I would have paid extra for glass wool in hindsight. They may staple the edge of batts too to make sure they dont move as they slump over time.
marte,
Jul 27, 11:57pm
Would polyester insulation fitted in, then polystyrene slabs fitted inbetween the bottom ( flat with ) the joists, then some sort of sheeting under that, stapled to the bottom of the joists. Be the best idea? It's a 1910 villa & will probably sand/vacuum out the cracks in the floor & seal them too. It gets cold in Southland. I have the polyester fill in 1/2 the house & would have to dig out the dirt where I can't get to & redo the piles as they get exposed.
tweake,
Jul 28, 1:40pm
i'm told rats love getting into all flooring insulation. even polystyrene which surprised me. glass wool is the cheapest so not sure why you would pay extra for it. however its harder to install, can't be stapled in place.
tweake,
Jul 28, 1:46pm
i would not use polystyrene especially if you plan to seal the floors. if its low to the ground i would just fit insulation between the joists so you don't risk anything hanging down and hitting the ground. you could put plywood or wire mesh across the bottom if you want to vermin proof it. with plywood you could air seal it, tho i would be more inclined to use one of the membranes "house wrap" as that would be easier to install. those old floors tend to open up when they dry and you get tons of air flow up through the floor.
frankly the best thing you can do is to put vapour barrier (plastic sheet) down on the ground under the house and reduce the moisture coming up.
dinx,
Jul 29, 6:24pm
If you install anything, permit or not it must still be to code, not sure wire mesh or wrap would be acceptable? Foil can no longer be used I thought due to potential electrical conductivity and I dunno if a non permeable layer would be ok? We have concrete block into soil with very fine vent mesh so should have been vermin proof, but they have got in somewhere, only need a space the size of thumb for a rat.
Glass wool (pink Batts or Bradford gold etc) was def not cheaper than polyester. We have underfloor Nova blanket R1.8 (now branded mammoth), not rigid polyester batts, materials only it was def cheaper for m2 cost and as our underfloor is only under kitchen, dining & laundry it made sense. Rest of the house is two levels and concrete on lower floor.
tweake,
Jul 29, 7:59pm
i'm not aware of anything stopping a "building wrap" being used. a permeable wrap would work well.
those are two of the expensive brands of batts. there are much cheaper brands. when i looked up prices a few years back, polyester was certainly dearer.
edit: a quick look now shows batts cheaper.
suie1,
Oct 11, 2:02am
Have you got black polythene on the ground? If you do that first properly ie taped around the piles & plenty of overlap on the joins & weighted down around the outside edges that is your best line of defence in terms of protecting the timber joists, bearers and flooring from damp rot. You can get up to 40lt of moisture coming off the ground & through the floor boards per day, add to that 1-2lt given off by each person then cooking as well, it can be huge & damp causes cold, mould, dust mites etc. It is cheap to do as well especially if you do it yourself or pay a lad to do it, my son does it.
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