Air Space R-values
HEAT TRANSMISSION THROUGH BUILDING STRUCTURE ELEMENTS AND AIR SPACES RESISTANCE VALUESHeat transfer across an air space is the result of the combined effects of conduction, convection and radiation. The thermal resistance of an air space is also dependant on the position or orientation of the air space and the direction of the heat flow, ie: up, down or horizontal. Since still air is an insulator, the thermal resistance of the air space will be dominated by the level of both convection and radiation. Other effects that influence the thermal resistance of an air space are the emittance values of the bounding surfaces of the air space, the mean indoor and outdoor temperatures and the temperature difference across the air space itself.
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Thermal Resistance of Parallel Un-ventilated Airspace m².K/W | ||||||||
Width of Airspace 13mm | ||||||||
Facing Surfaces and Emissivities | ||||||||
Orientation of Airspace & Direction of Heatflow | Airspace Temperature Difference | Mean Temp | foil x 2 | foil x 1 | foil x 1 | foil x 1 | foil x 1 | no foil |
dT K | deg C | 0.03/0.03 | 0.03/0.9 | 0.05/0.9 | 0.1/0.9 | 0.2/0.9 | 0.9/0.9 | |
Horiz – up |
3 deg |
23 | 0.4361 | 0.4202 | 0.4004 | 0.3586 | 0.29760 | 0.142 |
5 deg |
23 | 0.3960 | 0.3828 | 0.3664 | 0.3311 | 0.2784 | 0.1375 | |
7 deg |
23 | 0.3628 | 0.3517 | 0.3378 | 0.3075 | 0.2615 | 0.1332 | |
45° – up |
3 deg |
23 | 0.4959 | 0.4754 | 0.4503 | 0.3982 | 0.3243 | 0.1478 |
5 deg |
23 | 0.4605 | 0.4428 | 0.4209 | 0.375 | 0.3088 | 0.1445 | |
7 deg |
23 | 0.4321 | 0.4165 | 0.3971 | 0.356 | 0.2957 | 0.1416 | |
Vert – Horiz |
3 deg |
23 | 0.4907 | 0.4707 | 0.4461 | 0.3948 | 0.3221 | 0.1473 |
5 deg |
23 | 0.4879 | 0.4681 | 0.4437 | 0.393 | 0.3208 | 0.1471 | |
7 deg |
23 | 0.4840 | 0.4645 | 0.4405 | 0.3904 | 0.3191 | 0.1467 | |
45° – down |
3 deg |
23 | 0.4748 | 0.456 | 0.4329 | 0.3845 | 0.3151 | 0.1459 |
5 deg |
23 | 0.4786 | 0.4596 | 0.4361 | 0.387 | 0.3168 | 0.1462 | |
7 deg |
23 | 0.4809 | 0.4617 | 0.438 | 0.3885 | 0.3178 | 0.1464 | |
Horiz – down |
3 deg |
23 | 0.4823 | 0.4629 | 0.439 | 0.3893 | 0.3184 | 0.1466 |
5 deg |
23 | 0.4810 | 0.4617 | 0.438 | 0.3885 | 0.3178 | 0.1464 | |
7 deg |
23 | 0.4798 | 0.4606 | 0.437 | 0.3877 | 0.3173 | 0.1463 | |
Notes:1: The thermal resistance airspace values shown in the above tables are based on Robinson and Powlitch data validated by Oak Ridge National Laboratory.2: If the above table values are to be used for assesement of in-situ performance, then the values should be treated as indicative since they will be dependant on prevailing environmental conditions.3: The deltaT values shown in the above tables are relative to the temperature difference across parallel reflective airspaces that correspond to overall inside / outside temperature differences, 6K, 12K and 18K as shown in AS/NZS4859.1:2002. |
Thermal Resistance of Parallel Un-ventilated Airspace m².K/W | ||||||||
Width of Airspace 20mm | ||||||||
Facing Surfaces and Emissivities | ||||||||
Orientation of Airspace & Direction of Heatflow | Airspace Temperature Difference | Mean Temp | foil x 2 | foil x 1 | foil x 1 | foil x 1 | foil x 1 | no foil |
dT K | deg C | 0.03/0.03 | 0.03/0.9 | 0.05/0.9 | 0.1/0.9 | 0.2/0.9 | 0.9/0.9 | |
Horiz – up |
3 deg |
23 | 0.4705 | 0.452 | 0.4293 | 0.3816 | 0.3132 | 0.1455 |
5 deg |
23 | 0.4215 | 0.4066 | 0.3881 | 0.3488 | 0.2907 | 0.1404 | |
7 deg |
23 | 0.3863 | 0.3737 | 0.358 | 0.3243 | 0.2735 | 0.1363 | |
45° – up |
3 deg |
23 | 0.5859 | 0.5576 | 0.5233 | 0.4542 | 0.3605 | 0.1549 |
5 deg |
23 | 0.5232 | 0.5005 | 0.4727 | 0.4156 | 0.3357 | 0.1501 | |
7 deg |
23 | 0.4769 | 0.4580 | 0.4346 | 0.3858 | 0.3161 | 0.1461 | |
Vert – Horiz |
3 deg |
23 | 0.7259 | 0.6829 | 0.6322 | 0.534 | 0.409 | 0.1632 |
5 deg |
23 | 0.6789 | 0.6411 | 0.5963 | 0.5082 | 0.3937 | 0.1607 | |
7 deg |
23 | 0.6491 | 0.6145 | 0.5732 | 0.4913 | 0.3835 | 0.159 | |
45° – down |
3 deg |
23 | 0.7207 | 0.6783 | 0.6283 | 0.5312 | 0.4074 | 0.1629 |
5 deg |
23 | 0.7062 | 0.6654 | 0.6172 | 0.5233 | 0.4027 | 0.1622 | |
7 deg |
23 | 0.6916 | 0.6525 | 0.6061 | 0.5153 | 0.3979 | 0.1614 | |
Horiz – down |
3 deg |
23 | 0.7144 | 0.6727 | 0.6235 | 0.5278 | 0.4054 | 0.1626 |
5 deg |
23 | 0.7114 | 0.67 | 0.6212 | 0.5261 | 0.4044 | 0.1625 | |
7 deg |
23 | 0.7084 | 0.6674 | 0.6189 | 0.5245 | 0.4034 | 0.1623 | |
Notes:1: The thermal resistance airspace values shown in the above tables are based on Robinson and Powlitch data validated by Oak Ridge National Laboratory.2: If the above table values are to be used for assesement of in-situ performance, then the values should be treated as indicative since they will be dependant on prevailing environmental conditions.3: The deltaT values shown in the above tables are relative to the temperature difference across parallel reflective airspaces that correspond to overall inside / outside temperature differences, 6K, 12K and 18K as shown in AS/NZS4859.1:2002. |
Thermal Resistance of Parallel Un-ventilated Airspace m².K/W | ||||||||
Width of Airspace 90mm | ||||||||
Facing Surfaces and Emissivities | ||||||||
Orientation of Airspace & Direction of Heatflow | Airspace Temperature Difference | Mean Temp | foil x2 | foil x 1 | foil x 1 | foil x 1 | foil x 1 | no foil |
dT K | deg C | 0.03/0.03 | 0.03/0.9 | 0.05/0.9 | 0.1/0.9 | 0.2/0.9 | 0.9/0.9 | |
18° – up |
3 deg |
23 | 0.5889 | 0.5601 | 0.5255 | 0.4557 | 0.3613 | 0.155 |
5 deg |
23 | 0.5327 | 0.5091 | 0.4803 | 0.4213 | 0.3394 | 0.1508 | |
7 deg |
23 | 0.4904 | 0.4704 | 0.4457 | 0.3945 | 0.3217 | 0.1472 | |
22.5° – up |
3 deg |
23 | 0.5958 | 0.5664 | 0.531 | 0.4598 | 0.3639 | 0.1555 |
5 deg |
23 | 0.5386 | 0.5145 | 0.4851 | 0.425 | 0.3418 | 0.1513 | |
7 deg |
23 | 0.4956 | 0.4751 | 0.45 | 0.3978 | 0.324 | 0.1477 | |
22.5° – down |
3 deg |
23 | 1.6444 | 1.4157 | 1.1966 | 0.8723 | 0.5752 | 0.1835 |
5 deg |
23 | 1.5489 | 1.3408 | 1.1397 | 0.8386 | 0.5586 | 0.1815 | |
7 deg |
23 | 1.4719 | 1.2802 | 1.0933 | 0.8107 | 0.5447 | 0.1798 | |
18° – down |
3 deg |
23 | 1.7709 | 1.5128 | 1.2682 | 0.912 | 0.5929 | 0.1853 |
5 deg |
23 | 1.6771 | 1.4407 | 1.2145 | 0.8811 | 0.5781 | 0.1836 | |
7 deg |
23 | 1.6002 | 1.3813 | 1.17 | 0.8551 | 0.5656 | 0.1821 | |
Notes:1: The thermal resistance airspace values shown in the above tables are based on interpolated data.2: If the above table values are to be used for assessment of in-situ performance, then the values should be treated as indicative since they will be dependant on prevailing environmental conditions.3: The delta T values shown in the above tables are relative to the temperature difference across parallel reflective airspaces that correspond to overall inside / outside temperature difference, 6K, 12K and 18K as shown in AS/NZS4859.1:2002. |
Thermal Resistance of Parallel Un-ventilated Airspace m².K/W | ||||||||
Width of Airspace 40mm | ||||||||
Facing Surfaces and Emissivities | ||||||||
Orientation of Airspace & Direction of Heatflow | Airspace Temperature Difference | Mean Temp | foil x 2 | foil x 1 | foil x 1 | foil x 1 | foil x 1 | no foil |
dT K | deg C | 0.03/0.03 | 0.03/0.9 | 0.05/0.9 | 0.1/0.9 | 0.2/0.9 | 0.9/0.9 | |
Horiz – up |
3 deg |
23 | 0.5112 | 0.4894 | 0.4629 | 0.408 | 0.3307 | 0.1491 |
5 deg |
23 | 0.4613 | 0.4436 | 0.4216 | 0.3756 | 0.3091 | 0.1446 | |
7 deg |
23 | 0.4245 | 0.4094 | 0.3907 | 0.3508 | 0.2922 | 0.1407 | |
45° – up |
3 deg |
23 | 0.5947 | 0.5655 | 0.5303 | 0.4595 | 0.3638 | 0.1555 |
5 deg |
23 | 0.5317 | 0.5083 | 0.4797 | 0.4209 | 0.3392 | 0.1508 | |
7 deg |
23 | 0.4866 | 0.4669 | 0.4426 | 0.3921 | 0.3203 | 0.147 | |
Vert – Horiz |
3 deg |
23 | 0.8264 | 0.7711 | 0.7072 | 0.5865 | 0.4391 | 0.1678 |
5 deg |
23 | 0.7161 | 0.6742 | 0.6248 | 0.5287 | 0.4059 | 0.1627 | |
7 deg |
23 | 0.6390 | 0.6054 | 0.5653 | 0.4854 | 0.3799 | 0.1584 | |
45° – down |
3 deg |
23 | 1.1046 | 1.008 | 0.9014 | 0.7142 | 0.507 | 0.1768 |
5 deg |
23 | 0.9791 | 0.9024 | 0.8161 | 0.6595 | 0.4788 | 0.1733 | |
7 deg |
23 | 0.8859 | 0.8227 | 0.7503 | 0.6159 | 0.4554 | 0.1701 | |
Horiz – down |
3 deg |
23 | 1.2749 | 1.1479 | 1.0117 | 0.7817 | 0.5401 | 0.1807 |
5 deg |
23 | 1.2565 | 1.1329 | 1.0001 | 0.7747 | 0.5367 | 0.1803 | |
7 deg |
23 | 1.2394 | 1.119 | 0.9892 | 0.7682 | 0.5336 | 0.18 | |
Notes:1: The thermal resistance airspace values shown in the above tables are based on Robinson and Powlitch data validated by Oak Ridge National Laboratory.2: If the above table values are to be used for assesement of in-situ performance, then the values should be treated as indicative since they will be dependant on prevailing environmental conditions.3: The deltaT values shown in the above tables are relative to the temperature difference across parallel reflective airspaces that correspond to overall inside / outside temperature differences, 6K, 12K and 18K as shown in AS/NZS4859.1:2002. |
Thermal Resistance of Parallel Un-ventilated Airspace m².K/W | ||||||||
Width of Airspace 90mm | ||||||||
Facing Surfaces and Emissivities | ||||||||
Orientation of Airspace & Direction of Heatflow | Airspace Temperature Difference | Mean Temp | foil x2 | foil x 1 | foil x 1 | foil x 1 | foil x 1 | no foil |
dT K | deg C | 0.03/0.03 | 0.03/0.9 | 0.05/0.9 | 0.1/0.9 | 0.2/0.9 | 0.9/0.9 | |
Horiz – up |
3 deg |
23 | 0.5614 | 0.5353 | 0.5037 | 0.4393 | 0.3511 | 0.1531 |
5 deg |
23 | 0.5091 | 0.4876 | 0.4612 | 0.4066 | 0.3299 | 0.1489 | |
7 deg |
23 | 0.4698 | 0.4514 | 0.4287 | 0.3812 | 0.3129 | 0.1454 | |
45° – up |
3 deg |
23 | 0.6301 | 0.5974 | 0.5583 | 0.4803 | 0.3767 | 0.1578 |
5 deg |
23 | 0.568 | 0.5413 | 0.509 | 0.4434 | 0.3536 | 0.1536 | |
7 deg |
23 | 0.5214 | 0.4988 | 0.4712 | 0.4144 | 0.335 | 0.15 | |
Vert – Horiz |
3 deg |
23 | 0.7902 | 0.7395 | 0.6805 | 0.5681 | 0.4287 | 0.1663 |
5 deg |
23 | 0.6846 | 0.6462 | 0.6007 | 0.5114 | 0.3956 | 0.161 | |
7 deg |
23 | 0.6137 | 0.5827 | 0.5454 | 0.4707 | 0.3708 | 0.1568 | |
45° – down |
3 deg |
23 | 1.0114 | 0.9298 | 0.8384 | 0.674 | 0.4864 | 0.1743 |
5 deg |
23 | 0.9077 | 0.8414 | 0.7658 | 0.6263 | 0.461 | 0.1709 | |
7 deg |
23 | 0.8303 | 0.7745 | 0.71 | 0.5885 | 0.4402 | 0.168 | |
Horiz – down |
3 deg |
23 | 2.2773 | 1.9015 | 1.5548 | 1.0706 | 0.6639 | 0.1927 |
5 deg |
23 | 2.19 | 1.8402 | 1.5136 | 1.0509 | 0.6562 | 0.1921 | |
7 deg |
23 | 2.1134 | 1.7858 | 1.4766 | 1.0329 | 0.6492 | 0.1915 | |
Notes:1: The thermal resistance airspace values shown in the above tables are based on Robinson and Powlitch data validated by Oak Ridge National Laboratory.2: If the above table values are to be used for assesement of in-situ performance, then the values should be treated as indicative since they will be dependant on prevailing environmental conditions.3: The deltaT values shown in the above tables are relative to the temperature difference across parallel reflective airspaces that correspond to overall inside / outside temperature differences, 6K, 12K and 18K as shown in AS/NZS4859.1:2002. |
Thermal Resistance of Air Films | ||||
Resistance (m².K/W) | ||||
Wind speed (m/s) | Surface position | Direction of heat flow | High emittance surface | Low emittance surface |
Still air | Horizontal | Up | 0.11 | 0.23 |
Down | 0.16 | 0.80 | ||
22.5°-slope | Up | 0.11 | 0.24 | |
Down | 0.15 | 0.6 | ||
45°-slope | Up | 0.11 | 0.24 | |
Down | 0.13 | 0.39 | ||
Verticle | Horizontal | 0.12 | 0.30 | |
6.00 m/s (winter) | Any position | Any direction | 0.03 | |
3.00 m/s (summer) | Any position | Any direction | 0.04 | |
0.50 m/s (internal air movement) | Any position | Any direction | 0.08 |
Thermal Resistance of Parallel Un-ventilated Airspace m².K/W | ||||||||
Width of Airspace 13mm | ||||||||
Facing Surfaces and Emissivities | ||||||||
Orientation of Airspace & Direction of Heatflow | Airspace Temperature Difference | Mean Temp | foil x2 | foil x 1 | foil x 1 | foil x 1 | foil x 1 | no foil |
dT K | deg C | 0.03/0.03 | 0.03/0.9 | 0.05/0.9 | 0.1/0.9 | 0.2/0.9 | 0.9/0.9 | |
18° – up |
3 deg |
23 | 0.46 | 0.4423 | 0.4204 | 0.3744 | 0.3083 | 0.1443 |
5 deg |
23 | 0.4218 | 0.4068 | 0.3882 | 0.3487 | 0.2906 | 0.1403 | |
7 deg |
23 | 0.3905 | 0.3776 | 0.3615 | 0.3269 | 0.2752 | 0.1366 | |
22.5° – up |
3 deg |
23 | 0.466 | 0.4478 | 0.4254 | 0.3784 | 0.311 | 0.1449 |
5 deg |
23 | 0.4283 | 0.4128 | 0.3937 | 0.3531 | 0.2936 | 0.141 | |
7 deg |
23 | 0.3975 | 0.3841 | 0.3675 | 0.3318 | 0.2786 | 0.1374 | |
22.5° – down |
3 deg |
23 | 0.4786 | 0.4595 | 0.436 | 0.3869 | 0.3168 | 0.1463 |
5 deg |
23 | 0.4798 | 0.4607 | 0.4371 | 0.3878 | 0.3173 | 0.1463 | |
7 deg |
23 | 0.4804 | 0.4812 | 0.4375 | 0.3881 | 0.3176 | 0.1464 | |
18° – down |
3 deg |
23 | 0.4793 | 0.4601 | 0.4366 | 0.3874 | 0.3171 | 0.1463 |
5 deg |
23 | 0.48 | 0.4609 | 0.4372 | 0.3879 | 0.3174 | 0.1463 | |
7 deg |
23 | 0.4802 | 0.461 | 0.4374 | 0.388 | 0.3175 | 0.1463 | |
Notes:1: The thermal resistance airspace values shown in the above tables are based on interpolated data.2: If the above table values are to be used for assessment of in-situ performance, then the values should be treated as indicative since they will be dependant on prevailing environmental conditions.3: The delta T values shown in the above tables are relative to the temperature difference across parallel reflective airspaces that correspond to overall inside / outside temperature difference, 6K, 12K and 18K as shown in AS/NZS4859.1:2002. |
Thermal Resistance of Parallel Un-ventilated Airspace m².K/W | ||||||||
Width of Airspace 20mm | ||||||||
Facing Surfaces and Emissivities | ||||||||
Orientation of Airspace & Direction of Heatflow | Airspace Temperature Difference | Mean Temp | foil x2 | foil x 1 | foil x 1 | foil x 1 | foil x 1 | no foil |
dT K | deg C | 0.03/0.03 | 0.03/0.9 | 0.05/0.9 | 0.1/0.9 | 0.2/0.9 | 0.9/0.9 | |
18° – up |
3 deg |
23 | 0.5167 | 0.4942 | 0.4669 | 0.4106 | 0.1493 | 0.1493 |
5 deg |
23 | 0.4622 | 0.4442 | 0.4219 | 0.3755 | 0.1443 | 0.1443 | |
7 deg |
23 | 0.4225 | 0.4074 | 0.3886 | 0.3489 | 0.1402 | 0.1402 | |
22.5° – up |
3 deg |
23 | 0.5282 | 0.5048 | 0.4763 | 0.4179 | 0.1502 | 0.1502 |
5 deg |
23 | 0.4724 | 0.4536 | 0.4304 | 0.3822 | 0.1453 | 0.1453 | |
7 deg |
23 | 0.4316 | 0.4159 | 0.3963 | 0.3551 | 0.1412 | 0.1412 | |
22.5° – down |
3 deg |
23 | 0.7176 | 0.6755 | 0.6259 | 0.5295 | 0.1628 | 0.1628 |
5 deg |
23 | 0.7088 | 0.6677 | 0.6192 | 0.5247 | 0.1624 | 0.1624 | |
7 deg |
23 | 0.7 | 0.66 | 0.6125 | 0.5199 | 0.1619 | 0.1619 | |
18° – down |
3 deg |
23 | 0.7169 | 0.6749 | 0.6254 | 0.5292 | 0.1627 | 0.1627 |
5 deg |
23 | 0.7093 | 0.6682 | 0.6196 | 0.525 | 0.1624 | 0.1624 | |
7 deg |
23 | 0.7017 | 0.6614 | 0.6138 | 0.5208 | 0.1619 | 0.1619 | |
Notes:1: The thermal resistance airspace values shown in the above tables are based on interpolated data.2: If the above table values are to be used for assessment of in-situ performance, then the values should be treated as indicative since they will be dependant on prevailing environmental conditions.3: The delta T values shown in the above tables are relative to the temperature difference across parallel reflective airspaces that correspond to overall inside / outside temperature difference, 6K, 12K and 18K as shown in AS/NZS4859.1:2002. |
Thermal Resistance of Parallel Un-ventilated Airspace m².K/W | ||||||||
Width of Airspace 40mm | ||||||||
Facing Surfaces and Emissivities | ||||||||
Orientation of Airspace & Direction of Heatflow | Airspace Temperature Difference | Mean Temp | foil x2 | foil x 1 | foil x 1 | foil x 1 | foil x 1 | no foil |
dT K | deg C | 0.03/0.03 | 0.03/0.9 | 0.05/0.9 | 0.1/0.9 | 0.2/0.9 | 0.9/0.9 | |
18° – up |
3 deg |
23 | 0.5446 | 0.5198 | 0.4899 | 0.4286 | 0.3439 | 0.1517 |
5 deg |
23 | 0.4895 | 0.4695 | 0.4448 | 0.3937 | 0.3211 | 0.1471 | |
7 deg |
23 | 0.4493 | 0.4324 | 0.4115 | 0.3673 | 0.3034 | 0.1432 | |
22.5° – up |
3 deg |
23 | 0.553 | 0.5275 | 0.4966 | 0.4338 | 0.3473 | 0.1523 |
5 deg |
23 | 0.4965 | 0.476 | 0.4507 | 0.3983 | 0.3242 | 0.1477 | |
7 deg |
23 | 0.4556 | 0.4382 | 0.4167 | 0.3715 | 0.3063 | 0.1439 | |
22.5° – down |
3 deg |
23 | 1.1898 | 1.078 | 0.9566 | 0.748 | 0.5236 | 0.1788 |
5 deg |
23 | 1.1178 | 1.0177 | 0.9081 | 0.7171 | 0.5078 | 0.1768 | |
7 deg |
23 | 1.0627 | 0.9709 | 0.8698 | 0.6921 | 0.4945 | 0.1751 | |
18° – down |
3 deg |
23 | 1.2068 | 1.0919 | 0.9676 | 0.7547 | 0.5269 | 0.1791 |
5 deg |
23 | 1.1455 | 1.0407 | 0.9265 | 0.7286 | 0.5135 | 0.1775 | |
7 deg |
23 | 1.098 | 1.0005 | 0.8936 | 0.7073 | 0.5023 | 0.176 | |
Notes:1: The thermal resistance airspace values shown in the above tables are based on interpolated data.2: If the above table values are to be used for assessment of in-situ performance, then the values should be treated as indicative since they will be dependant on prevailing environmental conditions.3: The delta T values shown in the above tables are relative to the temperature difference across parallel reflective airspaces that correspond to overall inside / outside temperature difference, 6K, 12K and 18K as shown in AS/NZS4859.1:2002. |
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