Underfloor Insulation

[osprey]

I have been thinking about insulating under suspended wooden floors, but I have not found an answer to the following:

 

I think U-values are calculated with the material in a verticle orientation,  but the orientation must have some affect? (I have seen examples where a double glazed window U-Value drops from 0.29 to 0.4, when going from verticle to 45⁰).

 

With underfloor insulation, the heat source is above, the sink below, so heat transfer by convention should be almost non-existent. Should not e.g. Rockwool have a higher U-Value for this use?

[Nickfromwales]

Have you browsed yet? 
 

 

[osprey]

Yes, but I dont think it answers my question.

[Nickfromwales]

8 minutes ago, osprey said:

Yes, but I dont think it answers my question.

Ah, gotcha. I just recall it discussed in quite fine detail the values of the different insulation types, and included mineral wool in one example, wood fibre in another, and PIR at the outset.

 

One would assume all types are ‘useful’ but the option to fit PIR snugly vs compressing mineral wool in had good arguments for them either way, with the conclusion that convection airflow through any material (including ill fitting PIR) would virtually obliterate any gains from thickness / type.

 

Seems methodology reigns supreme here, so great results come from finite detailing and meticulous execution of the membrane installation methinks.

 

I just thought that thread covered this more comprehensively.   

[ADLIan]

Conductivity of insulation materials are measured in horizontal plane, it’s how the test kit works. In the overall u-value the orientation and direction of heat flow is accounted for in the surface and airspace resistance.

[osprey]

Horizontal? Do you mean the insulation layer is horizontal, or the heat flow? If the former, the in nearly all cases the U value of insulation that uses a gas as it main insulation material is worse when installed other than horizontal?

 

If that latter, then they are nor considering convection within the insulator would change with orientation.

 

it may (or may not) be a small effect. However, I used PIR under my floor, suspended using membrane. It got me thinking: even if  the PIR was not cut perfectly, the gaps would be fully protected from drafts by the membrane and would therefor be a static column/pocket of air: probably a better insulator than the PIR! 

 

Therefore, would not a loose layer of Rockwool  withn the protective membrane be even better? A static gas being better than any solid for conductive transmission. 

 

How good would bubble wrap be in the horizontal orienation!

Edited February 11 by osprey

[JohnMo]

Bunch of info in here 

 

conventions-for-u-value-calculations.pdf

 

You basically have two surface resistants, floor and void below floor to add in. Plus you need to include the P/A ratio into the calculation.

 

Other than that, I think your trying to hard. Are you thinking this hard for you roof insulation? Which is no different. The only difference is UFH temperature is the mean flow temperature a roof is inside building temperature. Flow direction is either up or down.

[ADLIan]

Test sample is horizontal so heat flow is vertical. You’re really overthinking this, the insulation will perform the same irrespective of orientation. There are many other things, workmanship included, that have a bigger impact.

[saveasteading]

The only difference might be that mineral wool could sag if horizontal in a free space. 

All the figures that are published are from lab testing and some iteration, and the workmanship will be immaculate.

Convection may affect room heat loss because of renewal of heat and higher temperature at the ceiling, but not the actual conductivity of the barrier.

[osprey]

If the rockwool sags, then you will have an unvented air space over it. A sheet of foil covering would give that air space an R-value of 0.5 m²K/W, according to the .pdf. Pretty good.

[Nickfromwales]

20 hours ago, saveasteading said:

The only difference might be that mineral wool could sag if horizontal in a free space.

Wouldn't matter if a membrane is detailed properly below it?

[saveasteading]

2 hours ago, Nickfromwales said:

Wouldn't matter if a membrane is detailed properly below it?

agreed. I'm just meaning that the reality might be different from the lab figures if it is allowed to sag. If built tight then no difference.

[Nickfromwales]

1 hour ago, saveasteading said:

agreed. I'm just meaning that the reality might be different from the lab figures if it is allowed to sag. If built tight then no difference.

Yup, that kind of minute detail will get you in the ground a lot sooner lol.