loft insulation - thermal insulation foil or normal loft roll?

[bongoboy]

We have one layer of the normal yellow loft insulation roll in our loft at the moment.
Due to our roof construction (coated aluminium) it gets very hot in the bedrooms in the summer and cold in the winter.

I was wondering which one to add to the layer of insulation roll in the loft at the moment, thermal insulation foil or second layer of the normal loft roll.

I looked up some reviews for the aluminimum foil which were all positive and it states - Keeps cool in the summer and warm in the winter, but my husband said a second layer of the normal roll will probably do the same.

Any thoughts would be appreciated

many thanks

[KARL]

Additional insulation alone will (no surprise) correspondingly increase heat retention. The foil will have two effects, the first of which is to reflect parts of the electro-magnetic wave spectrum back from whence it came (heat is radiated in the form of such ways) - from both sides if it is shiny on both sides (i.e. into the house and out back toward the roof). The effect of this in your case will not be very large (my assessment) although it may just be measurable. The other effect will be to act as a vapour barrier. Moisture that passes from your house out through the ceiling and insulation above it will stop at the foil. If the ceiling is impervious (say, lined with vinyl wallcovering) then effectively there will no moisture transfer. This may or may not be what you want to achieve - if the foil is at the very top and the ceiling is pervious then in cold conditions within the loft you may get condensation within the insulation (not necessarily anything to be concerned about) so it might then be better to have the foil at the bottom of the new layer, i.e in the middle of a sandwich. The best approach would be to have a vapour barrier nearest the inside of the house (such as on top of or on the inside of the ceiling) then all the insulation on top of it, with the foil at the very top/outside. This would ensure no vapour transfer through the insulation and best use of any foil.

[bongoboy]

thanks very much for your reply.

I will do exactly what you said, in the winter we do hear a little condensation dripping on the loft hatch, i don't want to cause anymore condensation up there.

thanks again

[buildersmate]

A pretty good assessment by Karl.
These multi-foil products have become popular because they purport to give good insulatative properties in a very narrow width of material and are thus most useful in places like loft conversions where the width is little (without impingeing on the headheight available for the conversion).
If you have no constraint on space (width of material), I'd be inclined to use fibreglass because it will be far cheaper for the same level of insulation effect.
As Karl points out, the more insulation you put in the better the effect - and it works both ways - better at keeping the heat inside in the winter and conversely better at keeping the heat out during the hot summar.

[The Builder]

I've managed to get extremely low U-values using TLX Silver combined with glassfibre roll.
You can guess from what Karl has said, that Vapour Check, and its positioning, is VERY important.

http://www.just-insulation.com/multifoil.html

[bongoboy]

KARL, buildersmate and the builder, thank you for your answers and for the link, we are going to do as you say and it will hopefully make alot of difference this winter.