Chel1978
|
| posted on 27/1/16 at 09:33 AM |
|
|
Bubblewrap foil insulation condensation in loft
Hi guys,
In the summer we had the loft floor boarded and we had foil bubble wrap insulation put across 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.
Thank you very much
|
|
|
|
|
nick205
|
| posted on 27/1/16 at 09:45 AM |
|
|
When insulating a loft it's important that air can still move around. Typically by leaving gaps at the eaves so air can pass through the roof
space. I'd imagine fitting high level vents would help to allow warm damp air to exit the building rather than create condensation on the
insulation.
I spent some time fitting another 150mm of rockwool type insulation in my loft at low level being very careful to leave air space at the eaves.
It's improved the heat retention of the house dramatically and there is no condensation in the roof space. It's not boarded out and I
don't store stuff in there though.
ETA...you can get vented ridge tiles, but that may require disturbing cemented in tiles to fit them - could alleviate the issue though.
[Edited on 27/1/16 by nick205]
|
|
|
cliftyhanger
|
| posted on 27/1/16 at 09:48 AM |
|
|
(this is a kitcar forum BTW!)
Anyway, a fair amount of moisture will pass though plasterboard ceilings and into the loft. What you have done is created a trap, and that moisture
will just condense on the impermeable insulation. That is why rockwool is normally used.
To stop the condensation, you need to ventilate the space. And that means the insulation will no longer do its job as well as intended.
**EDIT**
Re read you original post. I originally though you had laid foil insulation under the boarding. However, the answer is still ventilation....
[Edited on 27/1/16 by cliftyhanger]
|
|
|
nick205
|
| posted on 27/1/16 at 09:55 AM |
|
|
This image shows some ways of venting the roof space (as above doing so may reduce the effectiveness of the insulation, but damp roof space is worse
IMHO)...
|
|
|
v8kid
|
| posted on 27/1/16 at 10:04 AM |
|
|
Condensation is fairly inevitable under certain conditions and quite often it evaporates and no harm is done. i.e. warm muggy weather after a cold
snap leaves chilly surfaces which the increased RH dumps the water on.
You only need to be concerned if the condensation is persistent so keep an eye on it before spending a lot of effort. I had something similar and it
was due to a combination of poorly sealed cold water tank cover and no ventilation. In this case I used a 117mm core drill to put vents in the
opposing gable walls and bought a close fitting cover for the tank to reduce evaporation.
If you do this make sure any pipes in the loft are well lagged.
Cheers!
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
|
|
|
MP3C
|
| posted on 27/1/16 at 10:36 AM |
|
|
Just to confirm. When you boarded the loft floor, did you add any insualtion below the boards or was there any existing? If not then you have just
created another warm room in the loft as the heat will travel up through the floor from your house. By adding the foil insulation to the rafters you
have eliminated the veintailtion. This air will now be traveling up the back of the foil backed insulation and not ventilating the room and not
removing the warm moist air. The U-value (how well the insulation conducts heat) of the foil backed insulation will not be great and it will be cold
due to the air traveling up the back of it, which means the warm moist air from your house will be condensating on the inulsation you have installed.
You would need to install something with a better U-value to stop the cold transfering to make the surface temperature higher to stop the moisture
condensing which will be tricky and you will need to remove all the cold spots to stop condensation and will need to be done crorrectly. Or remove the
foil insulation from the rafters and install insualtion in the floor (usually 250 - 270mm rockwool) which will keep the heat in your house and your
loft area will be cool and dry. Although 270mm rockwool does present a problem for storage due to its thickness... you could use something simlar to
Cellotex either 60mm between rafters and 60mm over or 100mm over the rafters and put some MDF loft boards down and this will achieve a simlar if not
better u-value.
However if you wanted to keep the foil insulation you just need to allow ventialtion back into the room to remove the air. If you remove some small
areas at intervals in the insulation on both sides of the house to allow the air in the loft area this will allow ventilation, removing the wam moist
air. However putting insualtion on the floor will be the best solution and save you a fortune on your heating bill.
Matt
[Edited on 27/1/16 by MP3C]
|
|
|
Chel1978
|
| posted on 27/1/16 at 11:36 AM |
|
|
quote:
Originally posted by v8kid
Condensation is fairly inevitable under certain conditions and quite often it evaporates and no harm is done. i.e. warm muggy weather after a cold
snap leaves chilly surfaces which the increased RH dumps the water on.
You only need to be concerned if the condensation is persistent so keep an eye on it before spending a lot of effort. I had something similar and it
was due to a combination of poorly sealed cold water tank cover and no ventilation. In this case I used a 117mm core drill to put vents in the
opposing gable walls and bought a close fitting cover for the tank to reduce evaporation.
If you do this make sure any pipes in the loft are well lagged.
Cheers!
Thank you for your reply, well I regularly go up and down the loft and I didn't notice any condensation, even through Xmas when we bought down
the decorations etc the loft was bone dry, it was only until recently when we started getting this really bad weather I noticed the condensation, I
will definately get my partner to keep a close eye, fingers crossed it is only a temporary thing, it would be an absolute nightmare if we would have
to rip off the insulation, so many storage boxes with the kids old clothes and toys up there,grr
|
|
|
Chel1978
|
| posted on 27/1/16 at 11:40 AM |
|
|
quote:
Originally posted by MP3C
Just to confirm. When you boarded the loft floor, did you add any insualtion below the boards or was there any existing? If not then you have just
created another warm room in the loft as the heat will travel up through the floor from your house. By adding the foil insulation to the rafters you
have eliminated the veintailtion. This air will now be traveling up the back of the foil backed insulation and not ventilating the room and not
removing the warm moist air. The U-value (how well the insulation conducts heat) of the foil backed insulation will not be great and it will be cold
due to the air traveling up the back of it, which means the warm moist air from your house will be condensating on the inulsation you have installed.
You would need to install something with a better U-value to stop the cold transfering to make the surface temperature higher to stop the moisture
condensing which will be tricky and you will need to remove all the cold spots to stop condensation and will need to be done crorrectly. Or remove the
foil insulation from the rafters and install insualtion in the floor (usually 250 - 270mm rockwool) which will keep the heat in your house and your
loft area will be cool and dry. Although 270mm rockwool does present a problem for storage due to its thickness... you could use something simlar to
Cellotex either 60mm between rafters and 60mm over or 100mm over the rafters and put some MDF loft boards down and this will achieve a simlar if not
better u-value.
However if you wanted to keep the foil insulation you just need to allow ventialtion back into the room to remove the air. If you remove some small
areas at intervals in the insulation on both sides of the house to allow the air in the loft area this will allow ventilation, removing the wam moist
air. However putting insualtion on the floor will be the best solution and save you a fortune on your heating bill.
Matt
[Edited on 27/1/16 by MP3C]
Thank you for your reply,
Yes before boarding there was insulation already down, about the small areas at intervals, how do we do that? Do we have to rip of the foil
unnaturally?
[Edited on 27/1/16 by Chel1978]
|
|
|
MP3C
|
| posted on 27/1/16 at 12:15 PM |
|
|
The condensation problem will be present when it's colder outside. If it is frosty outside then there will be a lager amount of condensation on
the insulation due to the differances in temperature and the insualtion getting colder from the ventilation behind it due to the external air
temperature. The sections would only need to be small. simlar to what v8kid said, "117mm core drill to put vents in the opposing gable
walls" so a knife to cut the holes in the inulation to allow air to pass through to remove the moist air only need to be small you could start
off with 2 (one on each side of the loft) to see how you get on.
Might be worth monitering before you do anything though aslong as its not constantly wet and is able to dry like v8kid said then it will be ok. I am
assuming the condensation was due to the cold wether we had with the frosty mornings. Now the temperature has gone back up I would imagian you
wouldent be having the problems anymore.
Matt
|
|
|
nick205
|
| posted on 27/1/16 at 12:21 PM |
|
|
Might be worth reading up on cold and warm roofs as there is a marked difference between the two methods.
|
|
|
Chel1978
|
| posted on 27/1/16 at 12:42 PM |
|
|
quote:
Originally posted by MP3C
"117mm core drill to put vents in the opposing gable walls" so a knife to cut the holes in the inulation to allow air to pass through to
remove the moist air only need to be small you could start off with 2 (one on each side of the loft) to see how you get on.
Matt
Just to confirm, you're saying drill a hole either side of the walls, and then a few tiny holes above into the foil insulation?
|
|
|
MP3C
|
| posted on 27/1/16 at 12:53 PM |
|
|
quote:
Originally posted by Chel1978
quote:
Originally posted by MP3C
"117mm core drill to put vents in the opposing gable walls" so a knife to cut the holes in the inulation to allow air to pass through to
remove the moist air only need to be small you could start off with 2 (one on each side of the loft) to see how you get on.
Matt
Just to confirm, you're saying drill a hole either side of the walls, and then a few tiny holes above into the foil insulation?
You shouldent have to drill anything sorry for the confusion. You already have ventilation but you have stopped it by using the foil insulation, as
the air flow is now trapped behind it between the rafters and not able to ventilate the room. You just have to either remove some small sections of
the foil insulation or cut some small holes in it to allow the air to move through.
Like I said though, monitor it first. It sounds as if the condensation was due to the cold weather we had recently and now it has warmed up I suspect
it won't be there anymore. However if there are prolonged periods of cold weather then you will have to ventilate so the condensation doesnt
build up and start to run off onto the timber in the loft which over time will start to cause a whole host of other issues.
Matt
[Edited on 27/1/16 by MP3C]
|
|
|
Chel1978
|
| posted on 27/1/16 at 07:23 PM |
|
|
quote:
Originally posted by MP3C
quote:
Originally posted by Chel1978
quote:
Originally posted by MP3C
"117mm core drill to put vents in the opposing gable walls" so a knife to cut the holes in the inulation to allow air to pass through to
remove the moist air only need to be small you could start off with 2 (one on each side of the loft) to see how you get on.
Matt
Just to confirm, you're saying drill a hole either side of the walls, and then a few tiny holes above into the foil insulation?
You shouldent have to drill anything sorry for the confusion. You already have ventilation but you have stopped it by using the foil insulation, as
the air flow is now trapped behind it between the rafters and not able to ventilate the room. You just have to either remove some small sections of
the foil insulation or cut some small holes in it to allow the air to move through.
Like I said though, monitor it first. It sounds as if the condensation was due to the cold weather we had recently and now it has warmed up I suspect
it won't be there anymore. However if there are prolonged periods of cold weather then you will have to ventilate so the condensation doesnt
build up and start to run off onto the timber in the loft which over time will start to cause a whole host of other issues.
Matt
[Edited on 27/1/16 by MP3C]
OK thank you for your help, we will definately monitor it. While looking online at other similar problems people have in the loft I came across a
condensation Unit, would that be something worth investing in?
|
|
|
dirth
|
| posted on 27/1/16 at 09:02 PM |
|
|
https://en.wikipedia.org/wiki/Vapor_barrier
however it is more likely the problem is
https://en.wikipedia.org/wiki/Interstitial_condensation
If it had been me
I would have used 60 or better 80kg density Rockwool slabs 50mm thick foiled one side stuck to the roof inside and since you've done the floor
, sheet over with ply if you leave a air space between the foil and the ply all the better
You could use a phenolic type slab but the rockwool has better sound absorbing qualities
both are far superior to fibreglass
based on insulating serious stuff for what felt like forever
I apologies if that comes across as a touch arrogant, it's not meant to be
|
|
|
Sam_68
|
| posted on 27/1/16 at 10:27 PM |
|
|
quote:
Originally posted by v8kid
Condensation is fairly inevitable under certain conditions and quite often it evaporates and no harm is done...
This.
In fact your bubble wrap may be doing you a big favour.
quote:
Originally posted by cliftyhanger
To stop the condensation, you need to ventilate the space.
This was true in the old days, and remains true for older properties (hence is probably perfectly correct for the OP), but for what it's worth,
the situation can be 180 degrees opposite for modern properties (post-millenium), or those that have had fibreglass insulation upgraded to fully
modern standards.
WARNING: Long-winded rant ahead!
Bit of a fixation of mine, loft condensation, and it's quite technical, so skip the following soapbox speech if you like...
...But I can tell you that the major housing developers now have a very serious problem with loft condensation, which in most cases they are
failing to acknowledge.
In the 'old days', the problem used to be that the warm, moist air from inside the house (with moisture added from cooking and occupant
respiration) would leak into the loft, and there condense. That's where the traditional advice to keep your loft well ventilated comes from.
It's called interstitial condensation, and the solution is to disperse it with ventilation.
By and large, airtightness is now massively better on modern houses than it used to be, so vapour leakage from inside the house is much less
prevalent, and unless you've got a defect that is causing major leakage, interstitial condensation shouldn't be a problem any more.
What has happened, though, is that the Building Regulations have hugely increased the thickness of loft insulation required. So instead of a certain
amount of heat leaking up into the loft space and keeping it a few degrees above ambient external temperature in winter, the loft space is now so well
insulated that it becomes cold enough for a dew fall to happen each night. If you use an impermeable insulation, like your bubble wrap or
Celotex/Kingspan-type polyisocyanurate rigid foam, this isn't a big deal, because the moisture sits on top of the insulation, then evaporates
off again when it warms up the following morning.
With the traditional fibreglass quilt insulation, however, the effect is cumulative, 'cos it soaks into the quilt and no amount of passing air
over the top of it will dry it off. What you end up with is a foot-and-a-half of very soggy fibreglass, to the point where it has been known to bring
ceilings down. It's typically at its worst in late autumn, due to the cycle of cool, damp nights but days warm enough to increase the air
humidity.
Now the even worse news for new home owners: increasing loft ventilation won't work and may even make the situation worse: if you
had and unventilated loft, the nightly 'dew fall' would be limited to the volume of air within the loft space. With a ventilated loft, the
felted underside of the roof (even with permeable roofing membrane) acts as a very effective condensing surface, and the more air you pass over it,
the more it will condense out to drip onto the fibreglass below.
There are a couple of other factors that make the situation even worse:
- The pitch of the roof slopes acts like a very crude aerofoil, creating a low pressure bubble on the downwind slope of the roof, which further cools
the roof and increases its potential to condense moisture out. I've actually witnessed the effects of this, where you can go up into a loft
space on a night and see that the underside of the roof on the downwind side is noticeably wetter with condensation.
- V8Kid may be able to explain this better than me, 'cos it goes against my limited understanding of physics, but I'm told by the
boffins at the BRE that roof tiles continue to emit heat radiation as they cool down, even when they have cooled below ambient air temperature, so the
roof tiles will actually be slightly colder than the air that surrounds them, at night, further increasing the effectiveness of the upper roof
structure.
The modern solutions, are:
- Use impermeable insulation, such Polyisocyanurate rigid foam, instead of fibreglass quilt, so that the condensed moisture sits on top and has a
chance to 'flash off' the following day. The major developers are unwilling to do this, because the cost of this type of insulation is
much higher.
- Use an unventilated 'warm roof' construction, where the loft space is itself insulated (ie. insulation layer at the outer surface of
the roof, instead of at upper floor ceiling level). That way, you don't have a large volume of cold air in which the 'dew fall'
condensation can occurs each night. This only makes sense if you use the loft space as living space, however., otherwise you're heating the
volume of air within the loft space for no purpose.
|
|
|
Chel1978
|
| posted on 28/1/16 at 09:37 AM |
|
|
Is there a way I can attach images? So it gives you guys an idea of how we insulated the rafter and also show you the condensation on the foil.
Thank you
|
|
|
nick205
|
| posted on 28/1/16 at 09:41 AM |
|
|
quote:
Originally posted by Chel1978
Is there a way I can attach images? So it gives you guys an idea of how we insulated the rafter and also show you the condensation on the foil.
Thank you
Yes, you can upload photos to your photo archive and the forum then gives you a chunk of code to copy and paste into your post to show the photo(s).
Can be fiddly the first time, but easy and fast thereafter.
|
|
|
nick205
|
| posted on 28/1/16 at 09:46 AM |
|
|
There's a website here covering warm and cold roof types and insulation of them...
http://buildingdesignexpert.com/warm-roof-or-cold-roof-which-would
-you-choose/
|
|
|
dav555
|
| posted on 29/11/16 at 04:59 PM |
|
|
Sorry to jump in on this thread but I am just going through something similar and am concerned about condensation and wanted to see what people
thought about my installation.
I am looking to improve the storage in my loft and make an area in the middle of my loft a little nicer and cleaner for storing nice things - like
children toys etc.
My loft is about 9m x 9m at its widest point (around the edges).
Its got 4 equal sides and goes to a pitch in the middle.
I am mounting bubble foil on 1.5" batons that I've put parallel across the top half of my rafters. This is to allow airflow parallel
across my joists as well as up and down.
I am running the foil from the top of the roof down each of the 4 sides to a large parallel joist that sits 1.2m off the floor. There is 1 of these
joists on each of the 4 sides of the roof.
At the point it meets the parallel joists I am simply letting the foil drop down to the boarded floor.
This will create a box area measuring about 3.5m sq.
The outer (cold) edges will be left as is and have boxes stored behind the foil curtains.
There won't be any heat up there, only if I am sorting boxes out for a couple of hours I may bring up the fan or element heater to keep me warm
whilst up there. If needed I could always raise up the curtains when not up there to create better air flow through the nicer area?
My loft is usually breezy on a windy day and doesn't currently suffer from condensation.
How does this setup sound?
If its a problem I could always have a couple of tile vents fitted but wanted to avoid having to do that once the foil is fitted incase anything falls
in and damages it.
Let me know your thoughts..
Thanks
D
|
|
|
