what's the difference foil/non foil kingspan

[Ivan]

What's the difference in insulation value between the foiled and non-foiled kingspan? You can buy the non-foil seconds quite cheaply, and as I'm planning to improve my roof insulation this summer, I thought the 'seconds' would be well worth considering (at £14/sheet)

[Amy]

I can ask Joe in the morning if you like?

[Ivan]

I've no idea who Joe is, but if he has the answer, it will be most welcome. I'm particularly interested in the official difference and the real-life difference.

I suppose I could always use spray-adhesive and kitchen foil on the un-foiled insulation

[Eleanor]

Could you ask Joe if Kingspan is better than Celotex? I've always wondered what the difference is

[Ivan]

...and why there's so much available in the way of 'seconds'

[Eleanor]

And, how big is a "minor imperfection that doesn't affect the U Value"?

[Richard Owen]

PU boards need a covering of some kind to constrain the foam during the blowing process. So, they always have a covering of some sort.

Foil covering is claimed to add to the insulation value where the board faces onto an air gap. When the board is covered on both sides the foil adds no value.

Almost all of the boards were perfectly fine for sticking in a roof. Most had cosmetic flaws. Even the ones with physical damage were useful as off-cuts.

In our roof (still available for inspection Ivan if you want to pop down) I used the paper (cheapest) faced boards because they have a vapour barrier and plasterboard on the inside and roofing membrane on the outside: foil would have added no value.

A couple of other tips I found useful in buying insulation:

1) Seconds sometimes sell stuff on ebay and a canny buyer can do well

2) Tapered insulation is a lot less desirable, and therefore cheaper, than regular boards. I needed 150mm of insulation for the roof and bought 25mm-45mm boards and 105mm-125mm boards and laid them counter to each other. Worked well.

How well did I do?

 The quote from seconds for plain faced boards (I think it was 100mm and 50mm boards) for our roof was £1,200 delivered. I bought the tapered boards off ebay for a total of £210. It came in three lots and Seconds even consolidated the orders and only charged me for one (£30) delivery.

[breezy]

Celotex PU boards and Kingspan PU boards are effectively the same thing (albeit from different manufacturers), although they do offer a different range of thicknesses. A few years ago the Kingpan boards achieved (claimed??) a slightly lower R value, but their current literature shows like-for-like.

I used Kingspan TP10 on my current project. The foil facing was important to me, as it provides a vapour barrier, and makes airtightness easier to achieve (but if, and only if, you are totally obsessive about sealing the board joins with foil tape).

I've never managed to get a good deal from Seconds and Co., but that's no reflection on them - it's a hit-and-miss business as to what they have in stock at any one time. The most recent quote from them (about 12 months ago) was on a par with the price that I got for new, shrink-wrapped bales from bmdinsulation.com (brokerage based in Swindon).

The only disadvantage of the foil faced board is that it makes a fairly effective Faraday cage (if properly taped up) so mobile phone signals are attenuated noticeably 

I can see how using tapered boards back-to-back could be useful on large flat areas, but I think they would drive me nuts anywhere that boards need to be trimmed to fit. Also, unless the board faces are in intimate contact, circulating air currents (in the voids between the boards) would have a significant impact on the overall R value, I think.

[Richard Owen]

I can see how using tapered boards back-to-back could be useful on large flat areas, but I think they would drive me nuts anywhere that boards need to be trimmed to fit. Also, unless the board faces are in intimate contact, circulating air currents (in the voids between the boards) would have a significant impact on the overall R value, I think.

Trimming to fit is a pain. Doesn't last forever though.

As for intimate contact, that's what spray foam is for. We foamed between wall plate and bottom of insulation board, between edges of boards as we butted them together and between the top of the boards and the ridge board.

And then we taped everything.

[Amy]

Ive asked if there is any u value difference between foil and paper faced urethane board.

Answer is:-

"There is a marginal difference but it realy depends on the application, .........see you next week sweetheart!!" xxx

[Rooster]

I think the foil is more about creating a vapour barrier than anything else.

Its tempting to think it must reflect the heat back from the surface but if that was significantly true then why would your foil wrapped chicken ever cook in the oven?

[desperate]

Radiant energy in the roof would tend to be reflected slightly, but conducted energy in the oven would pass ok in the oven. I think you are right it.s more about vapour check.

Desperate

[Ivan]

Richard,

Yes, I still want to pop over to have a look. Just trying to find a spare day......

[KLD]

Where is that outcry from the multi-foil fraction? Surely the foil does something? 

[wookey]

My understanding from reading last week is that the foil is important to keeping the pentane in. A large part of the reason why the U-value is low on PUR/PIR boards is that the gas used to blow the foam is much more insulating that air. They used to used CFCs, but stopped that a long time ago and now everyone uses pentane, (or CO2). However there will be slow diffusion of the pentane out and air in, which reduces the U-value somewhat. The foil keeps diffusion rates very low so air exchange only really occurs round the edges.

I did see a graph of how the U-value decreases to a steady state over the first 5-8 years or so. Now let's see if I can find it again...
This is a different doc but still full of good info. Relevant graph is pages 30/31: http://www.insulation.kingspan.com/uk/ifs_full_version.pdf