Advice Required Please About Use of SuperFoil Multi Purpose Wrap for Loft Heat Insulation

[webbythewebster]

Hello

I am not a builder but I am seeking some advice please from people who know better than me on behalf of my father who is looking to insulate the loft to reduce heat loss so improving the heat retention in the house so saving money on heating costs. He has seen rolls of "SuperFoil Multi Purpose Wrap" on sale in Aldi for £9.99 a roll. It says on the aldi site that it is 3-in-1 bubble foil provides insulation and Reduce heat loss in your home. He wants to add it to the loft roof to stop the heat loss through the roof so making the loft warmer meaning the house is warmer.

 

I have done some research on this and I have read that not only the "SuperFoil Multi Purpose Wrap" do very little to reduce heatloss through the roof (basically bubble wrap with foil on it) but it can cause more problems with damp and condensation build up. My personal opinion is that this product is more suited to outdoor heat insulation usage in garden sheds, garages, outdoor summer houses etc and not in the home especially for roof insulation but my father seems keen to use it in the loft which I personally think is a bad idea following my research online.

 

If my father wanted to reduce heat loss in the house through the loft area would it be advised and better to leave the loft as a open, cold and well ventilated area, allowing air flow around the whole loft and the house cavity and keeping the roof open and not covered with insulation to reduce damp and condensation in the roof and house cavity. Instead focus on adding more rockwool type material to the floor/ceiling section of the loft to increase the insulation of the ceiling area upstairs so reducing heat loss in the house. The loft space is only used as a storage area and gets cold in winter hence my fathers concern about heat loss in the house through the roof during the winter months.

 

Thank you in advance

webbythewebster

Edited Friday at 13:13 by webbythewebster
Spelling

[JohnMo]

A normal loft needs a draft to stop the roof structure getting damp and rotting. The roof structure should be left well alone. He needs to ensure the eaves are left open to provide this air flow.

 

To insulate use normal loft roll ideally insulated to a thickness of about 300 to 400mm in alternating layers. If he needs a floor above the insulation B&Q etc sell brackets that extend through the insulation so as not to compress it.

 

Bubble wrap isn't going to do much - ok in the green house, but that's about it.

[saveasteading]

3 hours ago, webbythewebster said:

people who know better than me 

You have understood and explained beautifully. As has

@JohnMo

 

It is highly marketed, stopping just short of untruth.

Bubble wrap for sheds or greenhouses.

 

In case he needs further convincing... reflective surfaces need to reflect back to an air space to perform. Squeezing lots together doesn’t work.

And condensation could cause problems.

 

Interesting that it has dropped in hype from 'the most amazing development,' to the Aldi aisles....

 

For more insulation, add more fibreglass to the loft floor, perhaps the opposite direction to what is there.

[SteamyTea]

Pythagoras has something to say about this (from beyond the grave, it is All Hallows Eve after all).

A pitched roof area would be greater than the ceiling below it, so a lower U-Value is needed.

As others have said, better to add to the ceiling insulation.

Good luck convincing your Father, tried to talk mine out if buying a Fiat Regatta, instead of a Ford Fiesta as a family run about 35 years ago. The Fiat was dreadful, was worth a few hundred quid after 3 years.

[webbythewebster]

Thank you @JohnMo @saveasteading and @SteamyTea for your replies and advice it is most appreciated.

 

Webbythewebster

[saveasteading]

@webbythewebsterI'm seriously impressed with your research. You must have come across lots of promotional material, with the criticism difficult to find. Is science or research your skill?

 

@SteamyTea if I recall, superfoil had their own way of assesssing insulation properties, thus getting improved numbers.  Something to do with heat escaping from a box..  I'm wondering if your example of the greater area of slope may explain their trick.

 

 

 

 

 

[Gus Potter]

On 31/10/2025 at 13:13, webbythewebster said:

I have done some research on this and I have read that not only the "SuperFoil Multi Purpose Wrap" do very little to reduce heatloss through the roof (basically bubble wrap with foil on it) but it can cause more problems with damp and condensation build up.

Hello webby. Thanks for a good post and the work you have put in. 

 

I've attached a document from the RICS which is to do with spray foam insulation. This might seem a bit odd as at first glance it has got nothing to do with your post. But read the last paragraph of page 4. Then look at the diagram on page 5, then read around.

 

For all on BH, it's also a good guide to help you understand some of the basics about roof insulation.

 

@webbythewebster. Here is a bit of a lay persons guide to insulating an old loft.

 

Let's say your Dad's ceiling is just plasterboard, painted but with no vapour barrier and it's got say 100mm of glass wool at the moment.

 

I'm going to call simplistically water vapour a gas. When the gas gets cold enough the water gas turns into water drops and at that point the problem starts. Gas molecules are farther apart and move more freely than liquid molecules so they can get out the roof more easily. 

 

The paint (may have some gloss paint) acts as a bit of a vapour barrier. The loft space may have some ventilation but not that much. When the weather is cold some moist air will penetrate the ceiling and now and again, depending on the temperature in the void above you will hit what is called the dew point. This is where the water vapour turns from a gas into a liquid.

 

Now when the insulation is only 100mm thick this won't happen very often. The water gas will keep migrating into the roof void and escape more easily. The insulation will get a bit wet from time to time but it often dries out in an old roof. 

 

The techy bit is called the dew point. This is where the water gas turns to a liquid. Like when the gas in the clouds turns to water and it rains. In the thinner insulation the dew point will occur less frequently and the gas will just exit the roof more often without causing any harm.

 

But to bring a roof up to modern standards we are looking at (350 - 400 mm in Scotland) and a say 300mm in England, this insulation comes in standard thickness. Here you can see that the loft will be much colder as you have added insulation. As the insulation is thicker the dew point will occur more often within the depth of the insulation and the insulation will become wet more often. Wet insulation against a timber roof don't make good bed fellows. 

 

To solve this we need to make the roof void much more drafty.. by installing more roof vents so it dries out the thicker insulation and reduces the time that the roof timbers are exposed to moisture. 

On 31/10/2025 at 13:13, webbythewebster said:

"SuperFoil Multi Purpose Wrap"

The big problem with this is that the foil is impermeable. We know that at some point we will get the water gas turning to water drops. The foil stops this water from venting out into the loft and then out the roof so it is trapped and will rot the timbers. 

 

@webbythewebster To upgrade the loft insulation, it sounds counter intuitive, you need about 300 to 400 mm of glass wool and then increase the ventilation to the void. The loft will become much colder, but the house will be warmer. 

 

Here is a link to a free calculator that you can play with. It also chucks out a basic condensation analysis. 

 

https://tools.knaufinsulation.com/en-GB/tools/u-value-insulation-calculator

 

But why is this product to be treated with extreme caution!

 

Basically, because if it is laid on top of insulation is stops the water that has condensed within the insulation and then turned back to a gas when the weather warms up (evapourated say) from getting into the loft void and out the roof.

 

For all, and the teckies. At some point many buildings will, depending on the weather get condensation happening in the depth of the structure. If we try and avoid all cases we end up over designing and that costs you money.

 

For the really tecky we have what I would call a reverse condensation effect.. few if any condensation models take this into account. Your house outer pane of glazing is cool, a warm weather front moves in from the west, it's misty, you can see the mist with the eye. This mist / humid air penetrates the wall and condenses from the outside in! 

 

@webbythewebster

To save money the easiest target is the loft. But you need to ventilate more. 

 

Have you explored whether your Dad can get a grant for this work?

 

 

 

 

RICS Spray foam insulation downloaded 31-10-2025.pdf

[webbythewebster]

@saveasteading  My main trade is Horticulture but I like to research things and learn new ideas.

 

@Gus Potter Thank you for your detailed post it is most appreciated. I have read about spray foams for the loft and grants from the government and they have had some bad news recently. I would not advise my father using spray foams in the loft because there are risks as noted in your attatchment and the links bellow:-

 

https://www.citizensadvice.org.uk/policy/publications/a-foamidable-challenge-tackling-the-impact-of-the-mis-selling-of-spray-foam/

 

https://www.bbc.co.uk/news/articles/cqjrpv218r0o

 

https://www.theguardian.com/money/article/2024/aug/12/they-encouraged-us-to-insulate-our-home-now-its-unmortgageable

 

Again thank you  Gus Porter for your detailed information and post. If my father wants to increase the insulation then it would be best and safer to use normal loft roll as advised by @saveasteading and @JohnMo

Edited Monday at 22:19 by webbythewebster

[Temp]

On 31/10/2025 at 13:13, webbythewebster said:

If my father wanted to reduce heat loss in the house through the loft area would it be advised and better to leave the loft as a open, cold and well ventilated area, allowing air flow around the whole loft and the house cavity and keeping the roof open and not covered with insulation to reduce damp and condensation in the roof and house cavity. Instead focus on adding more rockwool type material to the floor/ceiling section of the loft to increase the insulation of the ceiling area upstairs so reducing heat loss in the house. The loft space is only used as a storage area and gets cold in winter hence my fathers concern about heat loss in the house through the roof during the winter months.

 

+1 Add more wool type on top of the existing.

 

If he currently has insulation on the floor of the loft then the loft space itself is/should be ventilated at the eaves. Typically air enters at the eaves on one side, goes across the loft above the insulation and out at the other side. The idea is to remove any water vapour that gets through the plasterboard and insulation and prevents it condensing on the rafters. This is sometimes called a cold loft. If he adds more insulation on top he should try and preserve a gap at the eaves. There are eaves tunnels available to maintain this gap allowing you to stuff insulation down in there without blocking the ventilation.

 

If he wants to convert the loft from the above cold loft to a warm/heated loft then its not as simple as adding foil insulation at rafter level. You normally have to redesign the ventilation scheme. How you do that depends on the type of roof membrane. In many cases you must create a 50mm deep ventilated void between the rafters and replace the ridge tiles with a ventilated ridge. eg so air can enter at the eaves, go up this 50mm void and exit at the ridge. The amount of insulation needed between and/or below the rafters is considerable and needs to be calculated. A single layer of a foil type insulation won't meet Building Regulations. You at least need a layer of rigid foam insulation as well. 

 

A random combination of insulation some at rafter level and some at floor level would be ineffective, and potentially damaging in the long term.

 

Avoid spray foam in the loft at all costs. Sadly too many cowboys about and many mortgage companies won't lend on houses with it installed. The main issue is it messes with proven ventilation strategies mentioned above. There are ways it could be installed without issue but mortgage companies don't seem to appreciate the subtle differences. Some people have had to get it removed just to sell the house.  

Edited Monday at 23:16 by Temp

[webbythewebster]

Thank you for your post @Temp No my father does not want to convert the loft space into a living area. It is just used for storage. The best way forward is for my father if he wants to increase insulation is just to add more layers of rockwool to the base of the loft and leave the loft void open to breath. Adding more rockwool insulation to the base of the loft would be like getting a thicker tog duvet to keep you warmer at night in bed 🙂

Edited Monday at 23:33 by webbythewebster

[saveasteading]

8 hours ago, webbythewebster said:

thicker tog duvet

One difference. If your feet stick out from the duvet it can be uncomfortable however high the tog.

But if the attic insulation is improved over say 90%of the area, the benefit will be there.

ie you don't need to get technical close to the eaves, just stop a bit short.

[Nickfromwales]

23 minutes ago, saveasteading said:

One difference. If your feet stick out from the duvet it can be uncomfortable however high the tog.

But if the attic insulation is improved over say 90%of the area, the benefit will be there.

ie you don't need to get technical close to the eaves, just stop a bit short.

Running one 400mm wide layer of say 50mm along the wall plate will give a nice controllable ‘straight edge’, then butt the next 100mm against that and roll that out, and there’s you pitched layers of insulation managed in the eave where it’s a git to get in to and detail.

 

Then overlay as you wish to get to the minimum 300mm stated. 
 

After 300mm it’s assumed that the weight of any further layers will start to compress the bottom (first) layer and then that layer becomes far less effective.

 

Wool needs to remain as decompressed as possible to function best, so those stilts from the sheds to raise the attic flooring up and over will defo be needed if you intend to store anything up there (which requires a deck and walk/crawl areas).