Indoor air quality recently entered legislation in Portugal. Several parameters must beevaluated and kept within limits in order to obtain a certification for air quality and energyconsumption. Certification parameters were analyzed in two Portuguese archives in order toassess indoor air quality both for people attending or working on these premises and for maintenanceof a written heritage that must be retained for future generations. Carbon monoxide(CO) and carbon dioxide (CO2), formaldehyde, and fungal counts were kept within stipulatedlimits. Relative humidity (RH), volatile organic compounds (VOC), particulate matter (PM10),and ozone (O3) showed values above legislated levels and justified the implementation ofcorrective measures. In terms of conservation, studies on the limit values are still needed,but according to the available international guidelines, some of the analyzed parameters suchas PM10, O3, and RH were also above desirable values. Corrective measures were proposedto these institutions. Although this study was only of a short duration, it proved valuable inassessing potential eventual problems and constitutes the first Portuguese indoor air qualityassessment taking into consideration both aspects of an archive such as human health andheritage safekeeping.