R value of insulation

[Ihavenojob]

If a roll of insulation which is 100mm thick has an R value of "X", would that R value stay the same if it was compressed to 75mm ? I'm thinking the air pockets may contribute to insulation property of the roll, so compressing would reduce it.

 

[Notch7]

Yes you are correct, compressing would compromise insulation value

 

[Swwils]

Yes and some insulation products can be rendered totally ineffective if the correct compression or clearance is not maintained.

A common example is reflective foil types that people then omit the air gap each side of... Which most likely makes the thermal performance worse!

 

[^woody^]

Yes you are correct, compressing would compromise insulation value

With that logic expanding the quilt will increase the insulation value.

 

[Swwils]

With that logic expanding the quilt will increase the insulation value.

Yes at the sacrifice of space and probably practically.

Also, the R value if insulation is not constant. It changes depending on temperature. Polyiso loses 25% of its R value below 10C...

 

[Ihavenojob]

Yes at the sacrifice of space and probably practically.

Also, the R value if insulation is not constant. It changes depending on temperature. Polyiso loses 25% of its R value below 10C...

What would you suggest for insulating a sectional concrete shed with corrugated concrete roof ? I have some sheets of 50mm kingspan for the walls, just deciding what to put between the rafters, rockwool,polystyrene or kingspan (or similar) ? Was thinking of keeping some fish tanks in it, it has double glazed doors and window and seems fairly constant temperature (ie quite cool in summer and not to cold in winter) as it is.

 

[tony1851]

Polyiso loses 25% of its R value below 10C...

Genuine question - is that a fact? Is there any published information/research on this?

 

[Swwils]

Genuine question - is that a fact? Is there any published information/research on this?

Yes mostly from BRC and NRCA etc - R value entirely dependant on age, temperature and application. Generally recommendations are shifted between warm climates and cold climates which covers some of this effect.

https://www.professionalroofing.net/Articles/An-analysis-in-progress--01-01-2020/4604
https://www.buildingscience.com/documents/information-sheets/info-502-temperature-dependent-r-value

 

[Swwils]

What would you suggest for insulating a sectional concrete shed with corrugated concrete roof ? I have some sheets of 50mm kingspan for the walls, just deciding what to put between the rafters, rockwool,polystyrene or kingspan (or similar) ? Was thinking of keeping some fish tanks in it, it has double glazed doors and window and seems fairly constant temperature (ie quite cool in summer and not to cold in winter) as it is.

Depends on your budget and what space you have available, the simplest is probably to do a cold roof with a ventilated void before your insulation. But it will vary. A low occupancy area is not too much of a concern.