Foil bubblewrap insulation

[everlastuk]

Hi,
In the summer we had the loft floor boarded and foil bubble wrapped the rafters.

last week I went up in the loft and I noticed there was condensation all over the foil insulation. The work that went into putting to up the foil and boarding the floor wasn't easy, and now that the loft is full of storage boxes etc I'm really dreading that someone is going to say rip off all the bubblewrap.

However I was wondering would fitting a condensation ventilation unit help?

The bubble wrap is from B&q, B&q also have a video on YouTube doing the exact same thing I've done.

I've attached a few images, can someone please confirm a condensation ventilation unit would solve the problem.

Thank you very much

 

[freddiemercurystwin]

What kind of membrane is under the tiles, a modern breathable one or traditional felt? How was the roof vented before? Does your foil go down to meet the insulation at floor level? Kind of looks like it does in the first photo?

Some of the videos that B&Q publish should not be allowed!

 

[everlastuk]

Thanks for the reply,

Traditional felt under the tiles, I'm
not sure how the roof was vented sorry,
and yes the insulation goes down to floor level.

 

[JohnD]

Any of these apply?

//www.diynot.com/diy/threads/condensation-in-loft-answers.160032/

 

[freddiemercurystwin]

Are there soffit vents or eaves vents? You need to find out.

The warm is that is getting through the ceiling insulation is condensing on the underside of your foil insulation. This will continue to happen until you open up a vent path at the eaves which you have likely blocked with foil insulation.

Furthermore, without eaves and ridge ventilation any air that may get through the foil insulation that has any vapour in it will condense against the underside of the felt underlay causing condensation to occur between the foil and the felt causing the timber to decay long term.

 

[everlastuk]

As far as I can remember doesn't notice any soffit or eaves vents, would a condensation
Unit be efficient?

 

[freddiemercurystwin]

Do you mean positive ventilation from Passivent or similar? Maybe - not really designed for putting bodges right really though.

 

[everlastuk]

Ok, so what would you suggest? I was looking at one of these:

http://www.amazon.co.uk/gp/aw/d/B00..._UL115_SR115,115_&refRID=0VZZYXER2TD8PGZRXV2G

 

[freddiemercurystwin]

Remove the insulation that was incorrectly specified and fitted.

 

[everlastuk]

Ok, but once removed what would be the correct procedure to reapply the insulation to the rafters?

 

[mointainwalker]

Bubble insulation sounds like absolute nonsense because in fact there will be significant areas where there there is nothing but one thickness of plastic film which offers no insulation worth mentioning and will create condensation.

Put bluntly , you need an impermeable membrane (plastc sheet ) over the full area of the joists aand whatever insulation you choose on top of that *.


* hi , Freddy !

My post only replies to your question about insulating the ceiling and nothing to do with with the roof which is completey separate.

 

[AronSearle]

The multi-foil (bubble wrap?) insulation in this case is simply inadequate, it is getting cold enough to allow condensation.

Originally this stuff was designed to have a vapour control layer (plastic sheet), 25mm *airtight* airspace / multi-foil / 25mm airspace. The sealed airspace in front of the multi-foil was part of the insulation system, in that it became a part of the insulation layer. Frankly can't understand how B&Q advise this (not looked at the link mind you), if this is what B&Q advise then I am surprised some lawsuits/insurance claims are not coming their way.

Without a vapour control layer or the 25mm airspace, it is not working thus the condensation, (and this is all before we get into any arguments about the actual performance of multi-foil insulation).

In theory the rafters and felt behind should not be getting any condensation as it is all happening in your loft, the bubble wrap is acting as a VCL, but Freddy is right to raise it as a risk, I would not be putting the theory to the test.

You have three options.

* Ensure that there is through ventilation behind the multi-foil to the felt and rafters from eaves to ridge, batten out to create a 25mm sealed airspace with a VCL, and add additional rigid insulation (the multi-foil on its own cannot meet thermal regs, multi-foil is used in addition with further insulation to meet regs for a comparatively thinner wall thickness).

* Rip it out, its a roof!, insulate the ceiling joists as is normal.

* Rip it out, ensure through ventilation rafters to ridge, face the rafters with rigid insulation, or put insulation between rafters NOT to their full depth and with ventilation behind the felt.

As you can see, doing it properly requires a lot more work and thought. Rigid insulation is not necessary, just easier.