Database of thermal and optical properties of building envelope materials

(for building and urban energy simulation)


Construction materials vary consistently county by county (not just country by country). Factory manufactured products (e.g., glazings, steel, etc.) have quite constant properties and are available on broader areas, whilst products realised in the construction yard, offer higher variability (e.g., plasters). Generally speaking, we may isolate three classes of variation of material properties:

– Small variability, once the specific product has been identified: steel; aluminum; roofing membranes;

– Average variability: tiles; masonry; paints (paint are prepared in the factory, but their final reflectance depends on the thickness, influenced by application, and on the substrate);

– Large variability: concrete; mortars; plasters.

However, all built surfaces might offer large variations in their optical properties, regardless the intrinsic standard deviation of their product category, because of:

– Ageing, especially (but not limited to) soot, dust and dirt deposition, mould growth, etc.;

– Deposition of snow, water, etc.

– Influence of angle of incidence on total value;

– Rate between beam and diffuse radiation, and air mass (all available for building products reflectance data are generally calculated for AM1.5, with reference to the ASTM G 173 solar irradiance spectral distribution).


Weathering and soiling of building envelope materials and components

Green procurement will yield to deploy cool roofs everywhere… but how long will they stay cool? In the US, this issue has been addressed and state regulations (e.g., California Title 24) and environmental rating schemes (e.g., LEED) already require ‘aged’ values, as not all products and materials perform the same over time.

This is to avoid to compute the energy needs of a building considering the initial albedo = 0.80, while after 1.5-2 years it gets to 0.56, because of weathering, soiling, and, at times, biological growth. This is what, in average, happens in Milano, which increases peak exterior surface temperatures by 19°C, for highly insulated roofs.

If you don’t have data for a specific site, a robust approximation can be granted by an accelerated weathering and soiling protocol, devised by the Lawrence Berkeley National Laboratory. It has been recently accepted as ASTM standard D 7897-15, and its repeatability and reproducibility assessed with an international laboratory study, joined by Polimi too.

An extension of the protocol to mimic the weathering & soiling in EU urban areas is coming, likely to be used by the EU-CRC. It will extend the method to façade materials too, including photocatalytic ones.



Polimi database on aged solar spectral reflectance and thermal emittance of building envelope materials

Under construction, for the moment. We exposed to the urban environments of Milano and Roma roofing and façade materials, and we measured their optical-radiative performance over time. Measurements include UV-Vis-NIR reflectance (from 300 to 2500 nm @ 5nm, with a Perkin Elmer Lambda 950, equipped with an integrating sphere), and thermal emittance.

At the present time, we exposed [within brackets start and end date of the exposure campaign]:
– 16 roofing materials including single-ply membranes, field applied coatings on modified bitumen, roofing felts, clay tiles. These are exposed low sloped, in Milano and Roma, and tilted by 45° facing south, in Milano only [Apr 2012 – ongoing].;

– 3 fabrics for tensile structures [Apr 2012 – Apr 2014]. Something is here:;

– 4 types of glazing [Apr 2013 – Apr 2014]. Unpublished;

– 6 types of façade finish [Oct 2011-Oct 2013; Apr 2012 – ongoing]. Something is here:;

– 8 types of shading devices and glazing [Nov 2014 – ongoing]. Unpublished.

For scientific purposes only: if you need data please contact: riccardo . paolini (at) polimi . it

Please note that if the dataset is unpublished we may decide not to release it until the related paper is out there.



Other databases on the topic

Reading’s Spectral Library of Urban Materials:

Glazing International Glazing Database (managed by Windows Group – LBNL)

Cool Colors Project Pigment Database [Project funded by California Energy Commission and developed by Heat Island Group – LBNL: Cool Colors Project]

Contents: spectral library of 88 pigments used for paints adopted in the construction sector. Plots of spectral reflectance (300 nm – 2500 nm), transmittance and absorbance are available; spectral data with password, to be required. A method is described for calculating the spectral reflectance of a coating film over a given substrate, known the spectral data of the film (over void) and of the substrate.

Cool Roofs Cool Roofing Material Database [Developer: Heat Island Group – LBNL]

Contents: solar reflectance (300 nm – 2500 nm) , emissivity and SRI (solar reflectance index) for: asphalt shingles; coatings (white, tinted, and aluminum); roofing membranes; metal roofings; and tiles

Note: these products are used in the US market. They might not be widespread (or even not available in EU, particularly asphalt shingles). 


US Cool Roofs Council [Developer: CRRC – Cool Roofs Rating Council, i.e. network of US National labs, manufacturers, ASTM representatives, etc.]

Contents: solar reflectance (300 nm – 2500 nm) , thermal emittance for all kind of roofing products used in the US market. Initial values and, for some products, after 3 years of natural exposure.

Rated products directory 
EU Cool Roofs Council (ongoing) [Developers: EU project, project partners]

Cool roof database and COOL ROOFS_database_report


Contents of the first release (2009): more than 100 products, including tiles, paints, membranes, and coatings.

All downloads from the project


Nasa Spectral Library [Developers: NASA, California Institute of Technology]

Contents: spectral library including 84 materials (under Man-Made) adopted in the construction sector [not specified where, supposed USA]. Spectral reflectance (420 nm – 14000 nm) plots and spectral data available.


Select a class of materials to search from the list below:
Minerals (1748) Lunar (17) Vegetation(4)
Rocks(473) Meteorites (60) Water/Snow/Ice(9)
Soils (69) Man-Made (84)


USGS Spectral Library (current version) 2017

Data access

Original measurements made using lab, field and imaging spectrometers

Kokaly, R.F., Clark, R.N., Swayze, G.A., Livo, K.E., Hoefen, T.M., Pearson, N.C., Wise, R.A., Benzel, W.M., Lowers, H.A., Driscoll, R.L., and Klein, A.J., 2017, USGS Spectral Library Version 7: U.S. Geological Survey Data Series 1035, 61 p.,


Spectroscopy of Rocks and Minerals, and Principles of Spectroscopy

by Roger N. Clark U.S. Geological Survey. Federal Center – Denver, CO 80225-0046

Non-free databases




Weather data and solar position

Weather data currently used for building energy simulations:

Extraterrestrial total and spectral irradiance data (since 2003):

Spectral irradiance distribution calculator: (to compute the solar spectrum as a function of atmosphere composition, DOY, etc.)

Solar position calculator NREL

Solar position calculator (+MAP)

[Algorithm for uncertainties of ±0.0003°: Reda, I.; Andreas, A. (2003). Solar Position Algorithm for Solar Radiation Applications. 55 pp.; NREL Report No. TP-560-34302, Revised January 2008. (1.9 MB PDF Document)]

Day of the Year

NOAA Interpolated Outgoing Longwave Radiation (OLR)

NREL Measurement and Instrumentation Data Center




Software for Urban Micromet simulation:





Other (general) useful refs

General reference: heat transfer textbook (for Mechanical Engineering), useful if you want to check a formula. You can download it for free from

View factors

IBPSA (the International Building Performance Simulation Association)

Building Physics, Building Energy Simulation and much more.. 





This page is meant for students who attend our courses. Therefore it is not necessarily complete. Neither Politecnico di Milano nor its employees take any responsibility for the accuracy and correctness of the data herein reported.