Foil or non foil backed insulation

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Planning on insulating the ceiling of my cold draughty basement and garage as the house floors seem pretty cold and cool down quickly overnight.

I aim to use rigid insulation boards. Question is, is there any real benefit in using a board with a foil backing? As no heat will be rising from the basement I'm not looking to reflect anything back. Would polystyrene boards be more than sufficient?

Basement is a little damp but ventilated so assume condensation isn't a concern so no need for any form of membrane between the plasterboard ceiling and the insulation board.

Thanks.
 
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It depends if you want insulation twice as thick as other insulation to do the same job.

Why are you insulating if you are not looking to reflect anything back?
 
Space isn't really an issue so if cheaper thicker insulation did the same job as thinner more expensive then fine.

I am assuming insulating would make some difference as my entire living space is above a large cold open space. Surely insulating between the 2 would make a difference. However as there's no heat in the basement to lose I'm assuming foil backed isn't needed. Please correct me if I'm wrong :)
 
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That was my other consideration SNM. I'm not really sure what best to do the more I think about it. The loft is well insulated and the windows are double glazed. It is a detached brick house and I'm used to a stone victorian terrace which I know held its heat well. This one seems to cool very quickly and I'm wondering if it is the fact that there's a cold basement below and only a standard floor between me and it.
 
Ah, so your basement is ventilated, so every time the wind blows, a little puff of cold air tries to get into your living space. If you want it to remain "cold", then a good air tight VCL is all thats required. So the little puffs don't go into your living space. The problem is now inverted, little puffs of hot air will percolate your flooring and cause condensation ABOVE the VCL and rot (eventually)your joists. You pays yer money. . .
Frank
 
Cold air is not rising to make the room cold. Rather, heat is escaping through the floor. Really you should insulate the warm side of the floor under the floor deck and not the ceiling of the cold side. There will be air leakage within the floor void which will negate any benefit of insulation on the ceiling of the cold garage.
 
Ok, so something to maybe consider if/when we decide to change the floor covering. Currently laminate which is in good nick and great for the kids.

Ah well. Slippers it is this winter.
 
No, woody said to insulate under the deck. Your floor deck is an appreciable thickness.. The top of the deck is the floorboards you walk on. The bottom of the deck is the ceiling of the basement. He's saying to attach your insulation to the underside of the boards that comprise the top of the floor deck, not rest it on top of the boards that form the ceiling that comprises the bottom of the deck. Top to bottom, slicing like a cake, it's:

floorboards
insulation
void
ceiling

not

floorboards
void
insulation
ceiling
 
Further, reflective surfaces only work if there is an air void next to them. A reflective surface has a lower emissivity, meaning a hot mirror polished silver object will warm you less when you sit next to it than a matte black one will. If you are the source of heat then a silver shiny object will bounce back more heat than a matte black one will. The gap between you and the object is vital for the reflection to work. If you're using insulated plasterboard (ca't see why you would) then you need a void behind the silver part to get the benefit, but the plasterboard insulation is geared towards providing the benefit to the room which the plasterboard faces, which is why you wouldn't use it if you were insulating the underside of floorboards. Save money on the insulated plasterboard and buy thicker rigid board. Also bear in mind that heat rises, and your floor is not your heat emitter, so insulating the underside of the boards isn't appreciably going to make your floor feel warmer because nothing is warming the floorboards up (heat in the room.. it rises, and floorboards are at the bottom).
You'll have to stand for quite a while before the heat from your feet warms the boards to the point where you can appreciate the fact that the underside of them is insulated. Thus arises the earlier comment about installing a membrane to stop draughts, which your feet will feel and perceive directly as the floor being cold
 
Interesting comment about the air-gap next to the reflective surface ... it makes sense really.

Although makes me wonder why rigid insulation that's used going under a screed nearly always has a reflective surface.

Perhaps it's not necessary.
 
Ok, this is all sounding a bit complicated. If I understand correctly there is little point in putting insulation boards on the ceiling of the basement?

I appreciate all the comments but maybe this is beyond me and my budget if it involves membranes to stop draughts.
 
Although makes me wonder why rigid insulation that's used going under a screed nearly always has a reflective surface.

It's so rare to find non-foiled insulation (due to lack of demand/numbers) that buying in foiled is pretty much the only realistic option unless you opt for seconds quality boards - which are great to use under screed and pads because the screed takes out any unevenness, warp, misshapenness etc that makes them second quality in the first place

The foiling doesn't contribute significantly to the cost of the board in the volumes with which it is used, added to the fact that it's one of the most abundant elements in the earth's crust (just a pig to extract)

Heat is transmitted in one of 3 ways: convection, conduction or radiation. Ignoring convection, radiant heat crosses space/void/gases but upon reaching a solid object transfers through it via conduction (the surface is warmed, then the heat spreads through the solid by making molecules vibrate, knocking into each other more and transferring the heat energy like balls on a snooker table cause each other to move when striking). As the heat reaches the other side of the solid and again encounters a void it converts back to radiant heat to cross the space. Transfer by radiation is rather ineffective and this is how insulations work; foams that inhibit air movement - reducing convection, having bubbles with thin membranes - inhibiting conduction and providing lots of tiny voids that (ineffective) radiation must traverse

If a foiled board has an air gap, the radiant heat is reflected back. If it has no void then it's just part of the solid - the concrete molecules vibrate the aluminium molecules directly by conduction

As noted earlier, radiation is rather ineffective. Those radiant halogen heaters heat you and make you feel warm rather than heat the room. Because radiant heat is ineffective if someone offered me 25mm foiled kingspan or 50mm nonfoiled kingspan for the same price I'd go for the 50 because there's no way the foil would compensate for the loss of half the insulating material. It's also why those space foil insulations were a jar of snake oil
 
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If I understand correctly there is little point in putting insulation boards on the ceiling of the basement?

Pretty much, in the same way that buying a big stack of kingspan and leaving it in the garden is going to do little to insulate your house. Even leaning it up against the house wall isn't going to help if the draft can get behind it

I appreciate all the comments but maybe this is beyond me and my budget if it involves membranes to stop draughts.
It's like wallpapering, really. You buy a roll of something like tyvek airguard for about 100 quid (50 metres, 1.5m wide) and tubes of glue like stickslikesh**t. You rip the ceiling down in the basement, bash flat anything that could puncture the membrane like stray nails in the timbers etc then using a staple gun and few staples as possible, attach the membrane to the underside of the joists, where membranes join there is an overlap and it's glued together. It's also glued to the walls either side etc, then you might go back with something like gutter sealant (permanently gooey) and run lines of it over every timber, then mount your plasterboards for new ceiling. The goo will seal up any screw holes that puncture the membrane and presto, your ceiling is now airtight. If youre not bothered about boarding the ceiling you don't have to. Can alternatively treat the top in the same way by taking up the floorboards. You might find it easier to have the basement ceiling ripped down and spray the underside of the floorboards with a foaming insulation like icynene https://www.youtube.com/results?search_query=icynene or DIY it with something like touchnfoam https://www.youtube.com/user/touchnfoam
 

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