Anyone know how how to compare insulation values?

[gwebstech]

Hi all

 

Im juat wondering if anybody knows of a tool or calculator where i can compare ie  50mm foil insulation to 100mm rockwool

 

im thinking of insulating a loft and it will need 400mm of rockwool but i know how horrible that is to use, even with masks etc and was considering spending more and using foil boards for example but i dont know what to compare. id imagine 250mm foil boards is as warm as 400mm rockwool but i need to work it out

 

thanks

[phatboy]

Use earthwool, which is sold in B&Q.  It's very low itch, I did it in shorts and a t-shirt!

 

The proper glass fibre is usually yellow or pink, where as the earthwool is brown

[Conor]

The reason you use glass fibre or mineral wool in a loft is because it's breathable. In most houses you have a fair bit of warm, most air entering the loft space. It has to get out or you'll have damp problems. Squeezing rigid insulation between joists will trap air and cause water to condense on the surface, eventually causing rot and mould problems.

 

Mineral wool is ok, I recommend a full set of overalls and tape up the gloves to the sleeves. And it'll only take a couple hours to get the job done.

Edited June 5, 2019 by Conor

[Jeremy Harris]

23 minutes ago, gwebstech said:

Hi all

 

Im juat wondering if anybody knows of a tool or calculator where i can compare ie  50mm foil insulation to 100mm rockwool

 

im thinking of insulating a loft and it will need 400mm of rockwool but i know how horrible that is to use, even with masks etc and was considering spending more and using foil boards for example but i dont know what to compare. id imagine 250mm foil boards is as warm as 400mm rockwool but i need to work it out

 

thanks

 

 

You can use the U value for the thickness to compare different insulation types, or the lambda value.

 

For example, the lambda for rockwool/glasswool is typically around 0.035 W/m.K, the lambda for PIR foam is typically around 0.022 W/m.K, so for the same U value (insulation effectiveness, in effect) then the thickness of rockwool needed would be ~1.6 x the thickness of PIR.  In other words, 160mm of rockwool would be about the same as 100mm of PIR foam like Celotex.

[SteamyTea]

1 minute ago, JSHarris said:

00.22 W/m.K

Needs a correction to 0.022 W/m.K

This foil board, is that similar to multifoil?

[Alexphd1]

Been working with rockwoll a few days ago above head in jeans and a tshirt. It was a bit cooler and as soon as I started to sweat I stopped for a rest. I didnt itch once..... I was in a panic to get a small bit done today it was warm and I didnt have time to have a rest..... just about killed myself itching. 

 

Edited June 5, 2019 by Alexphd1

[andyscotland]

You could also look at sheep's wool insulation - I've used thermafleece before but there are other brands. It's totally non-itchy and really nice to work with. Much less messy than cutting PIR too.

 

Not only is it breathable but unlike a lot of synthetic insulation, it doesn't lose insulating value when damp. In fact as the temperature falls it absorbs moisture from the air and releases heat, then as the temperature rises again the wool releases the moisture which has a cooling effect. So it helps to balance out moisture and temperature changes over the seasons, and sucks any condensation away from the timbers (up to a point, obviously). As I understand it, the heat-release properties aren't accounted for in the u-value so it actually performs a bit better than the figures suggest (where a lot of man-made actually perform a bit worse than the lab-conditions tests). It's also fire-retardant and very eco-friendly - low embodied energy to produce and a lot of it is made in the UK.

[Ed Davies]

For simple layers you don't really need a special tool or calculator - an ordinary calculator will do as you're just doing multiplication or division. Ultimately you want to be comparing the U-value (conductance, W/m²·K) or R-value (resistance, m²·K/W) for the two layers. These are inverses of each other: if a layer has a conductivity of 0.1 W/m²·K then it has an R-value of 10 m²·K/W. Lower U-value or higher R-value is better.

 

If you know the conductivity of the material (often written k or λ (lambda), W/m·K) and the thickness of the layer you can work out the U-value as the conductivity / divided by the thickness (in metres). E.g., if you have 400 mm of rockwool, λ= 0.035 then U = λ/t = 0.035 W/m·K / 0.4 m = 0.0875 W/m²·K.

 

In general, if you have any two of these numbers and want to work out another then you can do so by multiplying or dividing the numbers you have. It's pretty obvious how each contributes to the result: if the material has a high conductivity then the resulting conductance will be higher so the λ value goes on top, if the layer is thicker then it will have a lower conductance so the thickness goes underneath. So long as you use the correct units (e.g., metres rather than millimetres) it should all come out right. If you use American units you're firkined.

 

For example, if you want to work out the thickness of PUR (λ = 0.022 W/m·K) needed to have the same U-value as the 400 mm of rockwool then the higher the conductivity of the material the thicker the result will be and the higher the U-value you're willing to accept the lower the thickness needed so t = λ/U = 0.022 W/m·K / 0.0875 W/m²·K = 0.2514… m ~= 250 mm.

 

A useful check is to write the units out and make sure they cancel properly: W/m·K / W/m²·K = 1 / (1/m) = m which is nice.

[Ferdinand]

There is an online calculator here which you can use to get the u value of one or more layers, and that can be used to compare approximately.

 

https://www.vesma.com/tutorial/uvalue01/uvalue01.htm

 

The bloke likes detail so PIR is isanocyanurate is Celotex or Kingspan. 

 

Ferdinand

Edited June 6, 2019 by Ferdinand

[gwebstech]

wow very helpful guys thank you

[scottishjohn]

Is there a complete list somewhere of the U values of all the different types of insulation available

So  you can  do a thickness over cost comparison  

and a simple calulator  to get to a target value for the insulation alone at the chosen thickness

Edited June 27, 2019 by scottishjohn

[Ian]

28 minutes ago, scottishjohn said:

Is there a complete list somewhere of the U values of all the different types of insulation available

So  you can  do a thickness over cost comparison  

and a simple calulator  to get to a target value for the insulation alone at the chosen thickness

You could try this website which is very good although it is German so a lot of the branded materials are German rather than UK. Nevertheless, it does have options for standard generic insulation materials such as mineral fibre, EPS, PIR etc.

https://www.ubakus.de/u-wert-rechner/index.php?#