Air Space R-values

HEAT TRANSMISSION THROUGH BUILDING STRUCTURE ELEMENTS AND AIR SPACES RESISTANCE VALUES

Heat 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.

The tables below are;

Thermal Resistance of Parallel Un-ventilated Airspaces
Thermal Resistance of Air Films
Thermal Resistance of Pitched Roof Spaces

Table 1 | Go to Table 2 | Other Tables |

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.

Table 3 | Go to Table 4 | Other Tables |

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.

Table 8 | Back to Table 7 | Other Tables |

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.

Table 5 | Go to Table 6 | Other Tables |

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.

Table 7 | Go to Table 8 | Other Tables |

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.

Table 9 | Other Tables |

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
	Horizontal	Down	0.16	0.80
	22.5°-slope	Up	0.11	0.24
	22.5°-slope	Down	0.15	0.6
	45°-slope	Up	0.11	0.24
	45°-slope	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

Table 2 | Back to Table 1 | Other Tables |

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.

Table 4 | Back to Table 3 | Other Tables |

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.

Table 6 | Back to Table 5 | Other Tables |

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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Air Space R-values

HEAT TRANSMISSION THROUGH BUILDING STRUCTURE ELEMENTS AND AIR SPACES RESISTANCE VALUES

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