Products: Multifoil Insulation

391 to 420 of 966

- CommentAuthorMike George
- CommentTimeNov 25th 2008
Presumably you have had no problems with condensation? You would surely know about it by now if you did. Nice to see a real life opinion- thanks.

I wonder why we have not had a lot of people screaming about their bad experience with multifoil?
- CommentAuthorMike George
- CommentTimeNov 25th 2008
I know - it must work
- CommentAuthorfostertom
- CommentTimeNov 25th 2008
Honestly Mike, you should know better than to trust common experience - how unscientific!
- CommentAuthorMike George
- CommentTimeNov 25th 2008
lol
- CommentAuthordimengineer
- CommentTimeNov 26th 2008
I don't think I've had any problems - I can get into the eaves,so next very cold day I will take a look. I assume that it would be on the inside, and fairly obvious.

Tim
- CommentAuthorMatt
- CommentTimeNov 26th 2008
I think my point was COMPARED to other systems multifoil it was not performing as well. It does do something, but I have stayed in attics that I personally converted, and the rockwool / foam backed plasterboard is much,much better from many points than our own home.

For me the issue of acoustic performance is a big one - when ever we stay elsewhere, I makes us realise how noisy our room is (being in a city centre doesn't help...)

I am also disappointed by the short time it has taken for the tape to come off - its causing a real draft at points - bu this is maybe a separate issue....
- CommentAuthordimengineer
- CommentTimeNov 26th 2008
Matt,
Tape is a seperate issue I think. Between the Architect & Myself we got the builders to do an awful lot of taping and stapling. You do need a heavy duty stapler (14mm minimum) and lots & lots of staples. If you read the Actis guidance notes very carefully (cos its not obvious) you have to staple almost everywhere. The devil truly is in the detail.

I spent a jolly weekend stapling

Tim
- CommentAuthorfostertom
- CommentTimeNov 26th 2008
As I understand it, tape is no good at all - starts leaking within a year or two and gets worse. Only continuous mechanical clamping. And staples only where covered by a full-compression crossbatten. That could be your problem, Matt. Except, no point in any sealing if the multifoil is the through-stitched variety - is yours? As 90% of multifoils are the through-stitched type, it's ridiculous to think that their performance is due to better airtightness.
- CommentAuthorMike George
- CommentTimeNov 26th 2008
Posted By: fostertomAs 90% of multifoils are the through-stitched type, it's ridiculous to think that their performance is due to better airtightness.

Hmm, so you think air tightness is not a factor at all then? I think that it depends on what it is being compared to. The TRADA test for example compares MF to mineral wool. Air tightness must therefore be a factor surely?

Obviously those which are welded are more airtight - at least until you put all of those luvly staples in them
- CommentAuthorMatt
- CommentTimeNov 26th 2008
Mine are stitched through....

Tape was not supplied by foil supplier - they claimed I should use 'duck tape' - I sourced some other tape (can't remember brand now - could go and find out, the receipt is in a file upstairs)- and it is all held back by battens on nail-gun fired fixings - and all fixed by me and my old labourer. I would lay a bet that the duck tape would hold for longer. It all should be held back by the battens, but if the tape has peeled off up above where I cannot see, the edges could be drooping and touching back of plasterboard rather than leaving a gap.

Shame we never took pictures - but we put it all on in one long day, and had it plasterboarded next day as the plasterers were on site (5 of us working on one room...)
- CommentAuthorfostertom
- CommentTimeNov 26th 2008
We're constantly being told that 90% airtightness isn't airtight at all, 99% is getting there, and really it's down to pinholes and hairlines. It's really challenging, to be airtight so it's significantly above the inadequate norm.

Posted By: Mike GeorgeThe TRADA test for example compares MF to mineral wool. Air tightness must therefore be a factor surely?
How d'you mean, Mike - why does comparing MF to min wool make airtightness a factor? Everybody uses that excuse, but if you just put a bit of perforated MF to you mouth it's easy to suck air through it. I'd be confident of being able to breathe through a mask of perforated MF. Don't know what pa my powerful lungs can generate, but spread over a whole loft area, I'm sure perforated MF wd allow many ac/hr even at gentle breeze pressure. Uncovered staples in imperforate MF not quite so bad but still poor. I think airtightness probably works on a logarithmic scale, i.e. all the worthwhile action's in the 99% to 100% perfection part of the scale. That's why Passivhaus and other strategies focussing principally on extreme heat-demand-reduction are doomed as a national standard, in UK at least, tho maybe viable in the hands of German/Scandinavian housebuilders/workforce.
- CommentAuthorMike George
- CommentTimeNov 26th 2008 edited
Posted By: fostertomWe're constantly being told that 90% airtightness isn't airtight at all, 99% is getting there, and really it's down to pinholes and hairlines.

Says who? 90% seems pretty good to me. Thermal modelling indicates massive savings to be made by reducing airleakage from say 1ach- 0.5ach [the latter being close to the breg requirement of 10m3/hr/m2.

Posted By: fostertom

Posted By: Mike GeorgeThe TRADA test for example compares MF to mineral wool. Air tightness must therefore be a factor surely?
How d'you mean, Mike - why does comparing MF to min wool make airtightness a factor?

Just that the TRADA tests were relied upon for years. I believe one of the reasons the results are as they are is down to the relative airtightness or the comparative materials.

Posted By: fostertomDon't know what pa my powerful lungs can generate, but spread over a whole loft area, I'm sure perforated MF wd allow many ac/hr even at gentle breeze pressure.

Just tested my sample of a market leading brand. It is possible to blow through where it is stiched - though not easilly - impossible to blow through where not stitched, which would be a large proportion of the surface area. Good question about lung Pa? anyone have a stab at it?
- CommentAuthorfostertom
- CommentTimeNov 27th 2008
Posted By: Mike Georgemassive savings to be made by reducing airleakage from say 1ach- 0.5ach
True, but you don't halve the leakage by just stopping up half the holes and cracks area - that wd give minimal improvement - you have to stop up 95-99% of the holes and cracks area.
Posted By: Mike Georgethe TRADA tests were relied upon for years. I believe one of the reasons the results are as they are is down to the relative airtightness
I'm saying that was always transparent bollocks - not building-airtightness, but maybe convection into the naked surface texture of the min wool.
Posted By: Mike GeorgeIt is possible to blow through where it is stiched - though not easilly
Tri-Iso Super 9 and YBS - both dead easy! You Welshmen ruin your lungs with too much singing.
Posted By: Mike Georgeimpossible to blow through where not stitched
Of course
Posted By: Mike Georgewhich would be a large proportion of the surface area
I think that's a red herring.
- CommentAuthordimengineer
- CommentTimeNov 27th 2008
Lung capacity - somewhere about 50 - 100cm Water column. 10m water column (1 bar) is 100,000Pa. So Lungs can develop about 5000 - 10000 Pa. Someone may be able to equate/relate this to wind pressure levels?

In terms of air leakage, the builders who did mine commented that they felt it was better than the slab/foam insulation, as it was impossible to fit the blocks tightly without "cabinet making" standards of cutting/fitting. So there are always significant - up to 10mm - gaps around the blocks letting the wind whistle past.

Anecdotal evidence I know

Tim
- CommentAuthorEd Davies
- CommentTimeNov 27th 2008 edited
Just measured the pressures I could get blowing into and sucking out of a plastic bag containing the predecessor to one of these: http://www.ewuk.co.uk/

Ambient pressure in my office today corresponds to a pressure altitude of 160 metres (above the standard "sea-level" 1013.25 hPa (or millibars as they used to call them) pressure level used in aviation). (Wycombe Air Park which is a just over a km away and pretty much level from me is at 520 feet above sea level so the actual atmosphere is pretty close to the standard one, today.)

160 m pressure altitude corresponds to a pressure of 99.4 kPa. Blowing into the bag I got the indicated altitude down to -140 metres corresponding to a pressure of 103.0 kPa. Sucking I got it up to a pressure altitude of 420 metres, 96.4 kPa. Therefore, without really trying too hard and at a slightly awkward angle as I was reading the display of the barograph as I was testing I could suck 3000 Pa and blow 3600 Pa. Somewhat less than Dimengineer's numbers but those a probably for fit divers or something.

Dynamic pressure from airflow is Â½ÏvÂ² where Ï is the density (in kgÂ·mâ»Â³, about 1.3 kgÂ·mâ»Â³ for the atmosphere near the surface) and v is the velocity (in mÂ·sâ»Â¹). So for 10 mÂ·sâ»Â¹ wind (22 mph) the pressure would be 0.5 Ã— 1.3 Ã— 100 = 65 Pa.

(Sanity check: a gliding textbook says the airspeed calibration pressure for 20 knots (i.e., about 23 mph) is 0.26 inches of water gauge. 10 metres of water gauge is about 100 000 Pa so 0.26" would be 66.04 Pa which is close enough.)

Conclusion: I suck about about 46 times worse than the wind.

[Edited to change "Static pressure from airflow..." to "Dynamic pressure....". Doh. ]
- CommentAuthorPaul in Montreal
- CommentTimeNov 27th 2008
Posted By: fostertomTrue, but you don't halve the leakage by just stopping up half the holes and cracks area - that wd give minimal improvement - you have to stop up 95-99% of the holes and cracks area.

Actually, Tom, you do halve the leakage if you stop up half the holes and cracks. When we had our blower door test done, the figures are also reported in "equivalent leakage area". We halved our ACH figure and the leakage area was about half. Makes sense if you think of a pipe - for a given pressure the flow rate is purely determined by the cross-sectional area. If you have two pipes of the same area, then you can pass twice as much fluid. Since air leakage is driven by pressure, it works the same way. Half as many holes, half as much leakage.

Paul in Montreal.
- CommentAuthorfostertom
- CommentTimeNov 27th 2008
If so, then why all the doubts about whether worthwhile airtightness is possible given feasible UK workmanship (which is conditioned by housebuilders' typical UK drive for speed/productivity/cheapness). It's not difficult to halve the lazy crack area of a typical post-war house, and halve that and halve that again, I'd have thought. That should then be down from say 5 ac/hr to 1.25 - good enough to get brownie points - but it surely isn't that easy, by a long chalk.
- CommentAuthorfostertom
- CommentTimeDec 16th 2008
Now Ed's brought it up http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3135&page=1#Item_15, I'd still like an answer to my last question above.
Posted By: Paul in MontrealWe halved our ACH figure and the leakage area was about half
doesn't say anything about open area.
Posted By: Paul in MontrealIf you have two pipes of the same area, then you can pass twice as much fluid
If you have one pipe twice the area, or two thousand pipes one thousandth the area, what then?
- CommentAuthorPaul in Montreal
- CommentTimeDec 16th 2008
Posted By: fostertomdoesn't say anything about open area.

The "equivalent leakage area" is the open area, by definition.

Posted By: fostertomIf you have one pipe twice the area, or two thousand pipes one thousandth the area, what then?

They should be the same thing. I guess you're hinting at that bizarre multifoil you guys in Europe have that's full of holes. I don't think we have anything like that over here - but, then, we don't have multifoils, just "double-bubble" type material - which is both an air and a vapour barrier (if properly taped).

Paul in Montreal.
- CommentAuthorEd Davies
- CommentTimeDec 16th 2008
I seem to remember from school physics that the flow rate through a pipe (for a given pressure) is proportional to râ´. That's why the gas main into a town doesn't have to have the same cross section as the sum of the gas pipes into all of the houses.

If you have two pipes of the same area you can pass twice as much fluid as with one. However, if you have one pipe of twice the area (root 2 times the radius) you can pass four times the amount of fluid.

If you have one thousand pipes of one thousandth the area you can pass one millionth of the flow rate.

If you have two thousand pipes of one thousandth of the area you can pass 1/500 000th of the flow rate.

Is that right?
- CommentAuthorfostertom
- CommentTimeDec 16th 2008
Posted By: fostertom
We halved our ACH figure and the leakage area was about half
doesn't say anything about open area.
Posted By: Paul in MontrealThe "equivalent leakage area" is the open area, by definition.
Sorry, misread you Paul, thought you said 'the leakage was about half'.
- CommentAuthorPaul in Montreal
- CommentTimeDec 16th 2008
Ed, flow through pipes is indeed more complicated than the simple cross sectional area. The pressure in the pipe also has an effect - the gas mains are at a much higher pressure than the pipes into homes. Another complicating factor is the Reynolds number of the fluid in the pipe and whether the flow is laminar or turbulent. This is why a lot of small pipes are not necessarily equal to one large pipe as their surface effects will be much greater than that of the single large pipe. From the point of view of air leakage testing, the "equivalent leakage area" is just a convenient number to compare leakage rates - it's sort of the sum of all the small holes as the actual air flow is measured at certain pressures. One would reasonably expect that if you plugged half of the small holes (assuming they're all the same size) you'd also reduce the equivalent leakage area by a factor of two as well - and thus the heat loss as well for a given pressure. In the reports I have on my old house, the measured air leakage figures are actually converted into an annual heat loss in mega Joules, taking into account a year's worth of average weather data. This figure is far more interesting than the ELA, though it was fun visualizing the pre-renovation house having a hole large enough to put a bicycle through!

Paul in Montreal.
- CommentAuthorfostertom
- CommentTimeDec 16th 2008
I think that's right Ed - mass flow can't be directly got from total open area - lots of small holes are far more resistive than one hole of same total area. 'Equivalent leakage area' seems a confusing concept - surely can't be same as 'total of actual leakage areas'.

So why is it that in air-tighting a building, if you seal up 'half' the holes (i.e. the obvious, easier ones) you've probably not cut leakage by half? You have to do a great deal better than that, to get worthwhile leakage reduction.
- CommentAuthorfostertom
- CommentTimeDec 16th 2008
Posted By: Paul in Montrealthat bizarre multifoil you guys in Europe have that's full of holes
What would you expect the airtightness of that to be, Paul? See http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3135&page=1#Item_18:
Posted By: fostertomThat's 20,000mm of stitching per m2, 1mm2 holes 3mm apart, gives 6,667mm2 of hole per m2 of multifoil, equivalent to a single hole 82x82mm
- CommentAuthorPaul in Montreal
- CommentTimeDec 16th 2008
Posted By: fostertomSo why is it that in air-tighting a building, if you seal up 'half' the holes (i.e. the obvious, easier ones) you've probably not cut leakage by half? You have to do a great deal better than that, to get worthwhile leakage reduction.

Actually, based on what you posted and Ed posted, the bigger holes will have more airflow and so sealing these up will be very worthwhile. The equivalent leakage area is just a figure of merit that helps one visualize how much a building looks like a piece of gorgonzola. The air leakage test measures actual leakage volume and from this the heatloss is easily calculated. If you half the airflow, you half the heatloss - no matter how you visualize the holes.

Paul in Montreal.

p.s. the only way to know for sure is to have the blower door test done pre- and post-renovation
- CommentAuthorfostertom
- CommentTimeDec 16th 2008
Posted By: Paul in Montrealbased on what you posted and Ed posted, the bigger holes will have more airflow and so sealing these up will be very worthwhile
Yes, so you'd think, but that doesn't seem to be the case, hence the worries about whether the UK housebuilders/workforce are capable of the incredibly demanding Passivhaus-inspired mainstream approach that's coming into UK Building Regs. Are we saying that airtightness is a lot less demanding than has been supposed? Blower tests seem to say no, it really does need 99% perfection to get 90% towards the 'ideal'.
- CommentAuthorMike George
- CommentTimeDec 16th 2008 edited
EDITED

Tom, I've not looked at this in a huge way but do have some data from Tas on the effects of reducing air losses. Savings are tremendous when reducing the air losses from 1ach to 0.25 ach [Approx 20m3/hr/m2 @ 50 Pa and 5m3/hr/m2 @50 Pa respectively]
- CommentAuthorfostertom
- CommentTimeDec 16th 2008
Looks like quartering the airchange rate halves the fuel use - sounds about right.
But that says nothing about what it takes to reduce airchange by three quarters - a lot more than stopping up three quarters of the total crack and pinhole area, I'd say, and certainly more than stopping up only say one quarter of the leakage area, the bigger holes, which is what theory, and Paul, would suggest.
- CommentAuthorMike George
- CommentTimeDec 16th 2008 edited
OOPS- wrong chart. will ammend comentary.

Edited now
- CommentAuthorMike George
- CommentTimeDec 16th 2008
Posted By: fostertomLooks like quartering the airchange rate halves the fuel use - sounds about right.
But that says nothing about what it takes to reduce airchange by three quarters - a lot more than stopping up three quarters of the total crack and pinhole area, I'd say, and certainly more than stopping up only say one quarter of the leakage area, the bigger holes, which is what theory, and Paul, would suggest.

Fair point. Beyond me- will ask a colleague who will know

391 to 420 of 966



	Site Map \| Home \| View Cart \| Pressroom \| Business \| Links	Contact Us
Logout
© Green Building Press

Green Building Forum

Categories

Feeds

Products: Multifoil Insulation